High-efficiency riblet structure, and method for producing such structure.

Abstract

The present invention relates to a riblet structure (1) comprising longitudinal channels (2) oriented in a principal direction (H). Each longitudinal channel (2) has a substructure (3) having structural elements (4) specifically arranged periodically and continuously for fluid flow within the longitudinal channel (2) in the principal direction (H), wherein the ratio of the average spacing (d) of the structural elements (4) in the principal direction (H) to the average spacing of the channel edges of the longitudinal channel (2) is less than 1, specifically between 0.09 and 0.33. The present invention further relates to a method for producing a surface having such a riblet structure (1), and a method for computer simulation of its implementation.

Description

[Technical Field]

[0001] The present invention relates to a riblet structure having longitudinal channels oriented in the principal direction.

[0002] The present invention further relates to a method for producing such riblet structures.

[0003] Furthermore, the present invention relates to a method for computer implementation simulation of a surface having a riblet structure, wherein the riblet structure comprises longitudinal channels oriented in the principal direction. [Background technology]

[0004] Riblet structures are known from the prior art. These riblet structures are surface structures, typically in the sub-millimeter range, designed to reduce surface frictional resistance to fluids flowing along a surface, such as air or water. Riblet structures are used, for example, on the fuselage or wings of aircraft to reduce the aircraft's frictional resistance to airflow along the aircraft.

[0005] The riblet structure is typically formed using longitudinal ribs positioned on the bottom horizontal plane, extending along the main direction corresponding to the main flow direction of the fluid in use, and spaced apart from each other, so that each pair of adjacent longitudinal ribs forms a longitudinal channel.

[0006] For example, document EP 3 170 743 A1 discloses a riblet structure having multiple ribs thus embodied. The bottom surface positioned between the ribs may be embodied as flat or curved.

[0007] Scientific studies have shown that when a surface is fitted with riblets, the frictional resistance of the surface can be reduced by up to approximately 8%. This is considered the theoretical maximum; in practice, smaller values ​​are usually obtained. Higher efficiency, combined with the ease of production and / or installation of riblets, should be desired. [Overview of the project]

[0008] This is the starting point of the present invention. The object of the present invention is to define the first type of riblet structure that has high efficiency and, preferably, high implementability.

[0009] Furthermore, another objective is to define methods for producing these riblet structures.

[0010] Furthermore, another objective is to define methods for simulating such booklet structures.

[0011] According to the present invention, the objective is achieved in the case of the first type of riblet structure, such that each of the longitudinal channels has a substructure comprising structural elements specifically arranged periodically and continuously for the fluid flow within the longitudinal channel in the principal direction, wherein the ratio of the average spacing of the structural elements in the principal direction to the average spacing of the channel edges of the longitudinal channel is less than 1, specifically between 0.09 and 0.33.

[0012] Typically, a riblet structure, or longitudinal channel, is formed using multiple longitudinal ribs that protrude from the base, are oriented in the principal direction, and are spaced apart from one another. Each longitudinal channel is usually formed by two adjacent longitudinal ribs. The longitudinal ribs are usually oriented in the principal direction. Specifically, the portion of the base of each longitudinal channel located between two longitudinal ribs is usually called the base section. The longitudinal channel walls of each longitudinal channel, specifically the multiple longitudinal channel walls, are usually formed using the sides of each longitudinal rib and the base section located between the longitudinal ribs. The sides of each longitudinal rib that are usually adjacent in a second direction and that form a longitudinal channel are also called the longitudinal rib sides of the longitudinal channel. The base is usually embodied as a bottom horizontal plane, and the base section is embodied as a bottom horizontal section. The longitudinal ribs are usually oriented in the principal direction, and specifically, they are arranged adjacent to each other and spaced apart in a direction perpendicular to the principal direction, which is called the second direction. The longitudinal ribs of each longitudinal channel may be oriented in a corrugated or, preferably, linear manner in a plan view of the riblet structure. The height direction of the riblet structure is usually perpendicular to the principal direction and perpendicular to the second direction.

[0013] The basis of this invention is the discovery that, in the case of a conventional riblet structure without substructures, formed using longitudinal channels oriented in the main direction, it is possible to influence the flow behavior of a fluid flowing along the riblet structure in close proximity to the riblet structure, specifically in the viscous sublayer of the hydrodynamic boundary layer of the fluid flow, without causing significant influence or disturbance on the boundary layer profile of the fluid flow some distance from the riblet structure, specifically in what is called the turbulent sublayer of the fluid flow's hydrodynamic boundary layer. Therefore, it is possible to improve the flow behavior in close proximity to the riblet structure by using structural improvements to the substructures of each longitudinal channel.

[0014] A conventional riblet structure without substructures, typically having flat bottom sections between the longitudinal ribs of each longitudinal channel, generates turbulent viscous drag, primarily caused by the interaction zones of the longitudinal channel walls in each bottom section positioned between the ribs. It has been shown that viscous drag can be reduced by providing substructures within the longitudinal channel walls, specifically in the bottom sections of the longitudinal channels and / or the sides of the longitudinal ribs. The substructures can be realized using structural elements arranged continuously in the principal direction, preferably formed by ridges and / or depressions arranged continuously in the principal direction within each longitudinal channel. Preferably, the structural elements within each longitudinal channel are arranged periodically and continuously in the principal direction. Typically, each longitudinal channel forms substructures such that the fluid flow flowing through the longitudinal channel in the principal direction continuously strikes the structural elements. The reduction in viscous drag can be explained by the reduction of the interaction zones of the longitudinal channel walls. As a result of introducing substructures, which are usually in the form of raised and / or recessed sections, the area of ​​the longitudinal channel wall exposed to the flow along the longitudinal channel wall can be reduced, or a portion of the longitudinal channel wall can be lowered by the recess, and therefore contribute less to viscous resistance. This is particularly applicable in the plan view of the riblet structure. For example, the area of ​​the bottom section located at the same height can be reduced, or the bottom or a portion of the bottom section can be lowered by the recess, in which case it may contribute less to viscous resistance. However, in this case, it has been shown that the substructure, specifically the recess, generates additional pressure resistance. In a riblet structure with substructures, specifically in each longitudinal channel, the total resistance used for comparison is obtained from the sum of viscous resistance and pressure resistance, compared to the simple viscous resistance in the case of a riblet structure without substructures, specifically in each longitudinal channel.Therefore, in the case of a riblet structure with substructures, the advantageous reduction in total resistance or frictional resistance can be achieved when, as a result of the substructures, the reduction in viscous resistance is as significant as possible, and the resulting pressure resistance is kept as small as possible. The region of the longitudinal channel wall, specifically the bottom surface of each longitudinal channel and / or the longitudinal rib side surface, which is not part of the structural elements, is also called the bottom interaction zone or reference zone, or more specifically, similarly the bottom horizontal interaction plane or reference plane. The reference zone usually represents the bottom surface without substructures. It is preferable that the structural elements are specifically embodied as recesses.

[0015] The study has shown that, in each longitudinal channel, specifically when structural elements are formed by recesses, the reduction in total resistance or frictional resistance, specifically viscous resistance and the degree of pressure resistance, can be altered by setting the average spacing of structural elements in the principal direction relative to the average spacing of channel edges in the longitudinal channel. Advantageously low total resistance can be obtained when the ratio of the average spacing of structural elements in the principal direction to the average spacing of channel edges in the longitudinal channel is less than 1.0, specifically at most 0.8, preferably at most 0.5, particularly preferably at most 0.33, and especially preferably at most 0.22. The ratio is usually greater than 0.05, specifically at least 0.09, and preferably at least 0.13. The occurrence of rotation in the flow field in the region of structural elements is assumed to be a physical cause. Simulations of flow behavior have shown that, in the case of flows flowing in the principal direction, the structural elements cause or enhance the partial lateral guidance or diversion of the flow portion outward from each longitudinal channel, specifically accompanied by rotation of the flow portion, thereby reducing resistance in the principal direction. This is sometimes called the "cross-channel effect." Typically, the rotation of the flow portion is generated laterally with respect to the principal direction, specifically orthogonally. Therefore, it is advantageous if the ratio of the average spacing of structural elements in the principal direction to the average spacing of the channel edges of the longitudinal channels is 0.05 to 0.8, specifically 0.09 to 0.5, particularly preferably 0.09 to 0.33, and especially preferably 0.13 to 0.22.

[0016] In this way, an advantageous riblet structure for surfaces can be obtained for the purpose of reducing frictional resistance related to the fluid flowing along the surface in the principal direction. Typically, the longitudinal channels are oriented in the principal direction and are arranged adjacent to each other in a second direction oriented perpendicular to the principal direction. The fluid may be formed using a gas, such as air, and / or a liquid, such as water.

[0017] It is advantageous for each longitudinal channel to have structural elements arranged continuously in the principal direction. In a plan view of the riblet structure, the structural elements may be arranged continuously in a second direction oriented perpendicular to the principal direction. The average spacing of structural elements in the principal direction usually refers to the spacing in the principal direction, regardless of whether the continuously arranged structural elements are arranged continuously in the second direction. Thus, structural elements arranged continuously in the principal direction may completely overlap, partially overlap, or not overlap at all in the principal direction. The riblet structure can be seen in a plan view. A fluid or fluid flow flowing in the principal direction within a longitudinal channel may, specifically as described above, strike and be affected by the continuous structural elements, and specifically be guided or diverted laterally, at least partially. The foregoing applies specifically to each longitudinal channel. Typically, multiple, specifically the majority, and preferably essentially all, longitudinal channels of a riblet structure are realized specifically using this type of substructure. Preferably, the longitudinal channels are separated by longitudinal ribs, and each adjacent longitudinal channel is formed using the sides of the longitudinal ribs that face each other in each longitudinal rib.

[0018] Typically, a longitudinal channel is formed using multiple longitudinal ribs projecting from the bottom surface, oriented in the principal direction, and spaced apart from one another, with the average spacing of the channel edges being the average rib tip spacing of the longitudinal ribs forming the longitudinal channel. Each longitudinal channel is typically formed using two longitudinal ribs, usually immediately adjacent in a second direction, also called a longitudinal rib pair. The longitudinal channel bottom of a longitudinal channel wall may be formed by bottom surfaces or bottom sections of bottom surfaces positioned between the longitudinal ribs, and / or the longitudinal channel sides of a longitudinal channel wall may be formed by the longitudinal rib sides of the longitudinal channel. Structural elements are typically formed using the bottom sections and / or longitudinal rib sides, and are specifically inserted therein. The longitudinal ribs are typically embodied in a wedge shape or a basic triangular or trapezoidal shape in a cross section perpendicular to the longitudinal extension of the longitudinal rib. The side walls or surfaces of the longitudinal ribs may be embodied as flat, concave, or convex. The longitudinal ribs are typically located on or protruding from the bottom surface. The bottom surface, specifically the bottom sections of the bottom surface located between each of the two longitudinal ribs, may be embodied as essentially flat. Structural elements, specifically in the form of raised and / or recessed portions, may be inserted into or formed with the bottom surface and / or surfaces of the longitudinal ribs of the longitudinal channel. In the main direction of the longitudinal channel or in cross-sections perpendicular to the longitudinal direction, the longitudinal channel often essentially forms an inverted trapezoidal or parabolic recess into which a substructure is superimposed. Each bottom section may be embodied as concave, convex, or preferably flat. When the bottom surface is embodied as flat, it is often referred to as the bottom horizontal surface. In the longitudinal direction of a longitudinal rib, each longitudinal rib may have a corrugated or preferably linear course, specifically regardless of its substructure. The longitudinal direction of a longitudinal rib is usually oriented essentially parallel to the principal direction.

[0019] Specifically, a plan view of the riblet structure and / or the longitudinal channels usually refers to a view orthogonal to the main direction and orthogonal to the second direction. The plan view usually occurs along the height direction. Usually, the longitudinal channels are disposed adjacent to each other in the second direction. Ordinarily, specifically, the longitudinal ribs of each longitudinal channel are arranged such that they are spaced apart from each other in the second direction. The second direction is usually oriented orthogonal to the main direction.

[0020] The rib height of the longitudinal channels, or the rib pair, is usually larger than the sub-structure, specifically larger than the topology formed between the ribs using the bottom surface or each bottom surface section. Preferably, the average height of the bottom surface section is lower than the average rib height of the two ribs of the longitudinal channels that define the boundary of the bottom surface section, specifically half of it, preferably one quarter of it. It should be understood that the described height, specifically the rib height, is usually defined in the height direction. The height direction is usually orthogonal to the bottom surface, or specifically orthogonal to the main direction and orthogonal to the second direction.

[0021] Each longitudinal rib side surface of the longitudinal channels is usually oriented essentially parallel to the main direction. This is specifically such that in a cross-section orthogonal to the main direction, the tangent applied to the longitudinal rib side surface has an angle of 15° to 25°, preferably about 20°, with respect to the direction orthogonal to the height direction or the bottom surface, specifically the bottom surface section in contact with the longitudinal rib side surface. This is usually applied to one or both longitudinal rib side surfaces of the longitudinal channels. Conveniently, both side surfaces of each longitudinal rib can be embodied in such a manner. The opening angle of the rib tip of each longitudinal rib can conveniently be 30° to 50°, preferably about 40°.

[0022] An efficient reduction of the total resistance can be achieved when the ratio of the average rib height of the longitudinal ribs forming the longitudinal channels to the average rib tip spacing of the longitudinal ribs is at least 0.1 and / or at most 0.8, specifically at most 0.6. This specifically applies to each longitudinal channel. High feasibility and high efficiency can be achieved when this ratio is from 0.1 to 0.8, specifically from 0.2 to 0.5, preferably from 0.25 to 0.4, particularly preferably from 0.28 to 0.37, and especially preferably from 0.32 to 0.35.

[0023] The substructure, specifically the structural elements, can be arranged at least partly on the bottom surface of each longitudinal channel, specifically on the bottom surface section, and / or at least partly on at least one of the longitudinal rib side surfaces of each longitudinal channel specifically formed using it. A low total resistance can be obtained when the substructure, specifically the structural elements, is formed at least partly using at least one longitudinal rib side surface and at least partly using the bottom surface of the longitudinal channel. The substructure can be formed at least partly using the longitudinal rib side surfaces of both longitudinal ribs of the longitudinal channel. The longitudinal rib side surfaces of the longitudinal channel usually refer to the side surfaces of each longitudinal rib using which the longitudinal channel is formed, and the longitudinal rib side surfaces of the longitudinal channel usually face each other. For example, the structural elements can be arranged on the bottom surface of each longitudinal rib, specifically on the bottom surface section, and preferably on one or both longitudinal rib sides of the longitudinal channel. This specifically applies when the substructure, specifically the structural elements, is formed using a recess or by a recess.

[0024] Each substructure, specifically the structural element, of a longitudinal channel typically has a height of at least 2% and / or up to 60% of the average rib height of the longitudinal rib of the longitudinal channel. The height of the substructure, specifically the structural element, may be 5% to 50%, specifically 10% to 40%, preferably 15% to 30%, of the average rib height of the longitudinal rib of the longitudinal channel. Typically, the average apex region, specifically the peak, of each substructure, specifically the structural element, of a longitudinal channel is located at a height level of at least 2% and / or up to 60% of the average rib height of the rib of the longitudinal channel. The height level may be 5% to 50%, specifically 10% to 40%, preferably 15% to 30%, of the average rib height of the longitudinal rib of the longitudinal channel. The rib height may be the average rib height of the two longitudinal ribs of the longitudinal channel. The rib height of each longitudinal rib may refer to the average rib height of the longitudinal ribs. The foregoing applies specifically to recesses when substructures, specifically structural elements, are formed using or by recesses. In this case, the height may be the depth of each recess.

[0025] Structural elements may be formed using raised and / or recessed portions. Typically, each structural element is formed using, specifically by, raised portions, and / or using, specifically by, recessed portions. To reduce resistance, it is beneficial if structural elements are formed using wall segments that are arranged continuously in the principal direction and extend at least partially laterally, specifically orthogonally, to the principal direction. As a result, it is envisioned that the wall segments can be used to achieve or enhance at least partial guidance or diversion of fluid flow in the longitudinal channel laterally to the principal direction, or to achieve or enhance the generation of rotational motion of fluid flow oriented laterally to the principal direction. Each structural element may be realized using, specifically by, recessed portions.

[0026] To reduce overall resistance, it is particularly beneficial if substructures, specifically structural elements, are formed using, and specifically by, recesses. This is assumed to be due to the entry of at least a portion of the fluid flow into the recess, and specifically to the accompanying reduction of viscous resistance. Thus, specifically, the lateral rotational motion of the flow appears to develop in a particularly stable manner. In this case, the wall segment may be part of the recess wall forming the recess. In particular, the wall segment may be formed by a recess wall section of the recess wall, which faces the main direction. Each structural element is usually realized using, and specifically by, a recess.

[0027] In this case, each longitudinal channel may have substructures having continuously arranged recesses, specifically recess walls or recess wall sections, for fluid flow in the principal direction within the longitudinal channel. Typically, each longitudinal channel may have recesses such that fluid flow in the principal direction within the longitudinal channel strikes the continuous recesses, specifically recess walls or recess wall sections. It is beneficial if the ratio of the average spacing of the recesses, specifically recess walls or recess wall sections in the principal direction, to the average spacing of the channel edges of the longitudinal channel, specifically the average rib tip spacing of the longitudinal ribs, is less than 1, specifically at most 0.8, preferably at most 0.5, particularly preferably at most 0.33, and especially preferably at most 0.22. The ratio is usually greater than 0.05, specifically at least 0.09. Therefore, a ratio of 0.05 to 0.8, specifically 0.09 to 0.5, particularly preferably 0.09 to 0.33, and especially preferably 0.13 to 0.22 is advantageous. The ratio can be advantageously embodied as defined in this document, specifically in relation to structural elements. Each longitudinal channel, specifically its longitudinal channel walls, may then be provided with recesses spaced apart from one another in the principal direction. It is particularly important that the fluid flow in the principal direction strikes a series of recesses, specifically recess walls or recess wall sections, spaced apart from one another according to the aforementioned ratio. This applies specifically to the plan view of the riblet structure, specifically to each longitudinal channel. A recess wall section is typically a region of the recess wall of a recess, whose region faces the principal direction. Recess wall sections are typically oriented laterally, specifically orthogonally, with respect to the principal direction. Specifically, the features described with respect to substructures, and more specifically to structural elements or wall segments, are similarly applied to recesses. Recesses can be embodied such that they are connected to one another or separated from one another, so that they form a recess network.

[0028] It is preferable that each longitudinal channel has structural elements, specifically recesses, on the sides forming the longitudinal channel of at least one, specifically both, longitudinal ribs of the longitudinal channel, and / or within the bottom surface of the longitudinal channel, specifically within the bottom section. Specifically, each structural element, specifically each recess, may be located on both the sides of at least one, specifically both, longitudinal ribs of the longitudinal channel, and on the bottom surface of the longitudinal channel, specifically within the bottom section.

[0029] It is beneficial if the structural elements, specifically the recesses, extend from one of the longitudinal ribs of the longitudinal channel to the other longitudinal rib, and preferably along at least one of the longitudinal rib sides of the longitudinal channel to at least half the rib height of each longitudinal rib. This preferably applies to the sides of both longitudinal ribs that form the longitudinal channel and whose sides are used to form the longitudinal channel. Specifically, the structural elements, specifically the recesses, may essentially extend to the rib tip or the longitudinal channel edge. It is particularly beneficial if each structural element, specifically each recess, is embodied in this manner.

[0030] Structural elements, specifically recesses, can be advantageous for reducing pressure resistance if they are spaced at least partially, preferably completely, from at least one or both of the longitudinal ribs of each longitudinal channel in a direction perpendicular to the principal direction or in a second direction. This can be implemented by clearly separating the structural elements, specifically the recesses, at the bottom surface, or by clearly spacing each structural element, specifically each recess, from the longitudinal ribs, at least partially. This can be advantageously implemented using the bottom surface region in contact with each structural element, specifically between at least one of the longitudinal ribs and the structural element. It is advantageous for reduced viscous resistance if the structural elements are spaced at least partially, preferably completely, from both longitudinal ribs. In this case, it should be understood that the two longitudinal ribs refer to two immediately adjacent longitudinal ribs between which the structural elements are positioned. The structural elements, or each structural element, can be implemented specifically by recesses, or each recess.

[0031] It is beneficial if each recess is embodied as a lateral groove extending laterally, specifically perpendicular to, the principal direction. It is particularly practical if the substructure is formed using wedge-shaped lateral ribs that are continuously arranged in the principal direction and oriented laterally to the principal direction, and thus recesses are formed between the lateral ribs. The lateral ribs may be oriented perpendicular to the principal direction. In this case, the recesses between the lateral ribs may, in this document, specifically constitute the recesses or structural elements described above. The lateral ribs are usually embodied as being wedge-shaped or having a basic triangular or trapezoidal shape in a cross section perpendicular to the longitudinal extension of the lateral rib. The walls of the recesses or lateral ribs may be embodied as flat, concave, or convex. Specifically, structural elements may be formed by the walls of the lateral ribs, specifically the sides. These walls are usually the walls of the lateral ribs facing the principal direction. Wall surfaces typically extend laterally to the main direction, specifically perpendicular to it.

[0032] Typically, the average depth of the longitudinal channels and / or the average rib height of the longitudinal ribs is less than 250 μm, specifically less than 100 μm, preferably less than 80 μm. It is beneficial if the average depth and / or average rib height is between 250 μm and 1 μm, specifically between 100 μm and 5 μm, preferably between 25 μm and 40 μm, particularly preferably between 30 μm and 37 μm, and especially preferably about 34 μm. Typically, the average spacing of the channel edges and / or the average rib tip spacing of the longitudinal ribs of the longitudinal channels is less than 100 μm, specifically less than 80 μm. It has been found that an effective average depth of the longitudinal channels or average rib tip spacing is between 60 μm and 85 μm, specifically between 70 μm and 80 μm, preferably about 74 μm. Therefore, it has been found that the average rib height of the longitudinal ribs is between 30 μm and 37 μm, preferably about 34 μm, and the average rib tip spacing of the longitudinal ribs is between 70 μm and 80 μm, preferably about 74 μm, which is particularly effective. The rib tip spacing of the longitudinal ribs is usually measured in a cross section perpendicular to the principal direction, between the highest point of the longitudinal rib or the rib tips of the longitudinal rib. The rib tip spacing of the longitudinal ribs is usually the distance between the tips or peaks of the immediately adjacent longitudinal ribs or pairs of longitudinal ribs in each longitudinal channel.

[0033] Typically, in a cross section perpendicular to the principal direction, the bottom section is provided to have a width between 50 μm and 70 μm, specifically about 60 μm, or the rib spacing of the longitudinal ribs in the above cross section is provided to have such a size. The bottom section is typically in contact with the longitudinal ribs or their side walls.

[0034] Specifically, in the principal direction, it is advantageous if the structural elements, preferably wall segments and / or recesses, are embodied using a repeating structural arrangement. This applies specifically to each longitudinal channel. The structural elements are arranged in the principal direction, preferably in a repeating manner. This is particularly applicable in the plan view of the riblet structure. As a result, it becomes possible to achieve resistance reduction characteristics over a wide area in a practical manner. This can be implemented in the principal direction and / or orthogonal to the principal direction, specifically in a second direction. This applies specifically to recesses if the structural elements are formed by recesses. For this purpose, the structural elements, specifically recesses, can form a periodic structure, usually regular and preferably at a constant distance, between the structural elements, specifically recesses, specifically in the principal direction. This applies specifically to each longitudinal channel.

[0035] In particular, there may be multiple structural element classes represented by structural elements or recesses that are embodied in different forms, and structural elements, specifically recesses, from different structural element classes are arranged adjacent to each other according to a predetermined arrangement pattern. Typically, identically embodied structural elements, specifically recesses, are each assigned to the same structural element class. It is advantageous for structural elements from different structural element classes to be arranged adjacent to each other so that they alternate periodically. For this purpose, individual structural elements from a given structural element class, or groups of immediately adjacent structural elements, can be arranged alternately. While it is possible to arrange structural elements irregularly, a regular arrangement, or an arrangement with a structural arrangement or arrangement pattern, is preferred. The foregoing applies specifically in the principal direction and / or perpendicular to the principal direction, specifically in a second direction. This is particularly applicable in the plan view of the riblet structure. Each structural element is preferably a recess. In this case, the structural element class may be called a recess class. Therefore, structural elements from different structural element classes, specifically recess classes, and specifically recesses, may differ in terms of their shape, depth, the spacing between two immediately adjacent structural elements, specifically recesses, or any other features described in this document. Furthermore, the foregoing may be implemented so that it applies to each longitudinal channel.

[0036] It may be advantageous if each longitudinal channel is embodied using the longitudinal ribs of the longitudinal channel, specifically adjacent sides in a second direction, and these sides are directly connected to each other, specifically transitioning directly into each other. In this case, the longitudinal channel walls of the longitudinal channel may be formed by the sides of the longitudinal ribs, or longitudinal rib sides, specifically without a bottom section. In this case, the longitudinal rib sides may comprise substructures, specifically structural elements. Conveniently, the longitudinal rib sides may be connected to each other so as to form an angle.

[0037] Depending on the applicable flow conditions, it may be advantageous for the longitudinal rib sides of each longitudinal channel to be continuously connected to each other or to the bottom section of the longitudinal channel. The bottom section may be implemented to be flat or curved, specifically concave or convex.

[0038] It has been shown that a clear spacing between each structural element from at least one, preferably both, of the longitudinal ribs can be beneficial for low pressure resistance. In a plan view of a riblet structure, it is advantageous if the average spacing in the direction perpendicular to the principal direction between at least one of the two longitudinal ribs and the structural element edge sections of the structural element edges that define the boundaries of each structural element facing the longitudinal rib is greater than 5%, specifically greater than 10%, preferably greater than 20%, and particularly preferably greater than 25%, of the average rib spacing between the longitudinal ribs. The rib spacing of the longitudinal ribs usually refers to the spacing of the longitudinal ribs at the height of the base or its reference area in a cross section perpendicular to the principal direction, or usually corresponds to the width of each base section. The rib spacing of the longitudinal ribs is usually measured perpendicular to the rib height of the longitudinal ribs. As described above, the spacing between structural elements, or between structural element edge sections of each structural element, can be used to optimize the resistance behavior, specifically the degree of viscous resistance or pressure resistance. It is preferable that such spacing exists from both longitudinal ribs, that is, specifically, that both longitudinal ribs each have such spacing from the structural element edge sections that define the boundaries of each structural element and face each longitudinal rib. Therefore, it should be understood that the spacing from each longitudinal rib may be different or equal. The average spacing between at least one of the two longitudinal ribs and the structural element edge sections that define the boundaries of each structural element and face the longitudinal rib is usually less than 90% of the average rib spacing between the longitudinal ribs, specifically less than 80%, preferably less than 65%, particularly preferably less than 50%, and especially preferably less than 45%. It is advantageous if the area centroid of the region formed by the structural element, preferably the edge of the structural element, is located essentially in the center between the two longitudinal ribs, that is, specifically in the center between the two longitudinal ribs in a direction perpendicular to the principal direction.Therefore, the aforementioned spacing between the longitudinal ribs and structural element edge sections is usually determined between the point where each longitudinal rib touches the bottom section and the point of the structural element edge section. This is particularly applicable in the plan view of the riblet structure. Each structural element is preferably a recess. In this case, the structural element edge, or structural element edge section, may be a recess edge, or recess edge section. The foregoing applies specifically to each longitudinal channel.

[0039] It is preferable that the structural elements, specifically the structural element edge segments of the structural elements, are in contact with a bottom region located between the recess and the longitudinal rib, specifically in a direction perpendicular to the principal direction or a second direction. For optimized resistance behavior, it is beneficial that the bottom region is essentially flat. The bottom region may connect to the structural element, or the structural element edge segment, and to at least one longitudinal rib, specifically both sides of that longitudinal rib. Preferably, such bottom regions exist between both longitudinal ribs and each structural element, or each structural element edge segment of the structural element. Feasibly, the structural element edge segment may be a structural element edge section. It is preferable that the structural element or structural element edge is almost, specifically preferably essentially, completely surrounded by such bottom regions. The foregoing applies specifically to each longitudinal channel.

[0040] A particularly significant reduction in frictional resistance can be achieved when, in the bottom surface, specifically in a cross section parallel to its reference area, the structural elements in the main direction, specifically the average longitudinal extension of the recess, are at most 1.5 times, specifically 1.2 times, the size of the structural elements in the direction perpendicular to the main direction or a second direction, specifically the average width extension of the recess. This is particularly applicable in the plan view of the bottom surface. Specifically, it is advantageous if the opening area of ​​the recess, defined by the edge of the recess, is realized in this manner. Therefore, it is beneficial if the average longitudinal extension of the recess in the main direction is at most 0.9 times, specifically 0.5 times, preferably 0.3 times, and particularly preferably 0.2 times, the size of the average width extension of the recess in the direction perpendicular to the main direction or a second direction.

[0041] If the average depth of the recess is less than 75% of the average rib height of the longitudinal ribs of each longitudinal channel, specifically between 5% and 70%, it is advantageous for reducing pressure resistance. It has been shown that greater depths can lead to turbulence, which in turn can increase pressure resistance. Preferably, the average depth of the recess is between 5% and 60% of the average rib height of the longitudinal ribs of the longitudinal channel, specifically between 10% and 45%, preferably between 10% and 30%, and particularly preferably between 10% and 20%.

[0042] For the purpose of setting viscous resistance, it may be advantageous if multiple structural elements, specifically recesses, between the two longitudinal ribs of a longitudinal channel overlap each other in a direction perpendicular to the principal direction, specifically in a second direction. This is particularly applicable in the plan view of a riblet structure.

[0043] Structural elements of a longitudinal channel, specifically wall segments and / or recesses, can form arrangement rows of structural elements, specifically wall segments and / or recesses, oriented in the principal direction. It is advantageous if the structural elements of a longitudinal channel, specifically wall segments and / or recesses, form multiple arrangement rows of structural elements, specifically wall segments and / or recesses, oriented in the principal direction. For example, two arrangement rows of structural elements, specifically recesses, extending in the principal direction, may exist within a longitudinal channel. It is advantageous if immediately adjacent arrangement rows are positioned such that they are offset from each other in the principal direction by, preferably, half the distance between two immediately adjacent structural elements in each arrangement row. In this way, flow behavior that is advantageous in relation to total resistance can be achieved. Therefore, structural elements between arrangement rows may overlap each other in a direction perpendicular to the principal direction, specifically in a second direction. This is particularly applicable in plan views of riblet structures. The foregoing applies similarly to wall segments and / or recesses when structural elements are realized by wall segments or recesses.

[0044] It is practical for each recess to have a constant cross-section, primarily, and specifically essentially, along the depth direction of the recess. For example, a recess may be formed using, or by means of, a recess that is essentially cylindrical or prismatic, specifically block-shaped, cubic, or pyramidal. The recess edges of the recess, and / or the base of the prismatic shape, may therefore be polygonal, such as a triangle, quadrilateral, pentagon, or hexagon. It may be beneficial for turbulent flow behavior if the recess has a cross-section that narrows at least partially, specifically mostly, preferably essentially, along the depth direction of the recess. A recess may be formed using, or by means of, an essentially conical or pyramidal recess. The tip of the conical or pyramidal shape usually points away from the riblet structure, specifically the height direction of the longitudinal ribs. The base of the pyramidal shape may therefore be triangular, quadrilateral, pentagon, or hexagonal. In a cross section perpendicular to the principal direction, it is beneficial if the recess wall of the recess has an inclination that corresponds at least partially, specifically essentially, to the inclination of one of the longitudinal rib sides of the longitudinal channel. The longitudinal rib is usually the longitudinal rib closer to the recess wall. The recess wall is usually a side wall of the recess oriented in the principal direction. The recess wall is preferably essentially parallel to the longitudinal rib side of the longitudinal rib. Preferably, opposing recess walls or side walls of the recess are thus embodied. Along the depth direction of the recess, it is advantageous for the recess to comprise a first recess segment having a constant cross section along the depth direction, and a second recess segment having a cross section that narrows along the depth direction, specifically downstream from the first recess segment in the depth direction. Preferably, the second recess segment constitutes the end segment of the recess. The cross-section of the recess is usually oriented perpendicular to the depth direction of the recess. Therefore, the first or second recess segment can be realized in the manner described above.

[0045] Depending on the intended application, various shapes of the recesses, specifically the cross-sections of the recesses, may be particularly beneficial. For example, each recess or recess edge in the cross-section may be formed without corners, specifically elliptical or rounded, or it may be formed as a polygon, such as a triangle, quadrilateral, pentagon, or hexagon.

[0046] It is beneficial to reduce pressure resistance if each recess has a recess wall formed using it, which is at least partially, specifically essentially, embodied as a plane of rotation using an axis of rotation in the depth direction of the recess. Therefore, the recess wall can be formed using a surface segment of a spheroid, specifically a spherical surface, a paraboloid of revolution, or a hyperboloid of revolution. It may be beneficial if the recess wall section is formed using a segment of a conical envelope or a cylindrical envelope. For example, the recess may have a recess wall that is essentially embodied to form a dome shape.

[0047] In the depth direction, each recess is formed using a first recess region and a second recess region located after the first recess region, and it is advantageous if the first recess region has a smaller diameter than the second recess region. Therefore, it is preferable that the diameter of the first recess region, specifically the cross-sectional area, is less than 80% of the diameter of the second recess region, specifically the cross-sectional area. This has been shown to be advantageous for reducing pressure resistance. It is also preferable that the diameter or cross-sectional area of ​​the first recess region is less than 65% of the diameter or cross-sectional area of ​​the second recess region, specifically between 5% and 50%, preferably between 10% and 30%, and particularly preferably less than 20%. The advantageous effect on pressure resistance during use appears to be due to the interaction between the flow or turbulence within the different recess regions. Conveniently, multiple, specifically most, preferably essentially all, recesses within each longitudinal channel can be embodied in this manner. The recessed areas may be shaped differently from each other, or specifically, they may be embodied according to defined characteristics regarding the shape and size of the recesses, so as to be different from each other.

[0048] If multiple recesses are connected to one another using at least one fluid guide connection channel, it may be beneficial to the flow behavior within the recesses. Conveniently, multiple recesses within each longitudinal channel, specifically arranged adjacent to one another in the principal direction and / or perpendicular to the principal direction or in a second direction, can be connected to one another via at least one connection channel. Thus, it has been found that it is effective if these recesses are immediately adjacent to each other. Although it results in a more complex design, if recesses from different longitudinal channels that are preferably immediately adjacent to each other are connected to one another via at least one fluid guide connection channel, it may be beneficial to the flow behavior. Thus, the connection channel preferably extends beneath one or more longitudinal ribs of the longitudinal channel to connect recesses from different longitudinal channels to one another. Feasibly, recesses within multiple, most, preferably essentially all, longitudinal channels can be connected to one another via at least one or more connection channels. Preferably, recesses perpendicular to the principal direction, or specifically immediately adjacent in a second direction, are connected by at least one connecting channel, specifically if these recesses are recesses from different longitudinal channels. It should be understood that it is beneficial to provide multiple connecting channels for connecting the recesses to each other. Therefore, multiple connecting channels may be present between each of the two recesses. The connecting channels may be formed, for example, as holes inside the material forming the bottom surface. It has been found to be effective if the connecting channels connect to each recess, usually laterally, within the lower third of the recess, specifically within the bottom of the recess. This applies specifically in plan views.

[0049] For the purpose of setting pressure resistance, there exist multiple longitudinal channel classes, each representing a longitudinal channel having different embodiments of recesses, and it is advantageous if the longitudinal channels and their respective recesses from different longitudinal channel classes are arranged adjacent to each other, usually in a direction orthogonal to the principal direction, specifically in a second direction, according to a predetermined arrangement pattern. Thus, longitudinal channels having recesses with a first depth and longitudinal channels having recesses with a second depth may be arranged adjacent to each other, for example, in an alternating manner. Different longitudinal channel classes may differ from each other, for example, in the different shapes of the recesses, in the different depths of the recesses, in the different spacing between the recesses, and / or in the different arrangement of the recesses within each longitudinal channel. Typically, identically embodied longitudinal channels are assigned to the same longitudinal channel class. This applies specifically in plan views.

[0050] It is advantageous for the base to have a basic shape that spans multiple longitudinal channels formed with multiple alternating, specifically wave-shaped, height variations in a direction lateral to the main direction, specifically orthogonal to the main direction. This is particularly applicable to a base area or base without substructures. The direction may be a second direction. The average interval, specifically the period, of immediately adjacent height variations may be greater than the average rib tip interval of each longitudinal channel. The average interval, specifically the period, may be at least twice, preferably at least three times, and particularly preferably at least five times, the size of the average rib tip interval of each longitudinal channel. The basic shape is preferably embodied as a wave shape, specifically a sine wave.

[0051] It is advantageous if a surface exists for the component, and that surface specifically has a riblet structure, such as those described in this document. Due to the characteristics and effects of the riblet structure, the surface of the component can be realized with lower frictional resistance with respect to a fluid flowing along the surface, or the corresponding fluid flow. Conveniently, the component may be part of a means of transport, such as an aircraft, ship, or automobile, or a fluid guide element, such as a pipe, or part of a garment, such as a protective suit or athletic suit, which is intended to reduce the frictional resistance of the surface of the part having a riblet structure with respect to a fluid flowing along the surface. The fluid flow may be, for example, a gas flow, specifically an air flow, and / or a liquid flow, specifically a water flow.

[0052] As described above, in a further aspect, the present invention relates to a component having a surface, wherein the surface comprises a riblet structure that reduces the frictional resistance of the fluid by more than 8.5%, preferably more than 9.0%, specifically more than 9.5%, for example more than 10.0%, or more than 10.5%, or more than 11.0%, or more than 11.5%, or more than 12.0%, or more than 12.5% ​​as the fluid flows around the surface. Typically, this reduction is between 8.5% and 13%. This applies specifically in relation to the riblet structure described herein. The component may be the component described above. The riblet structure may be the riblet structure described herein, or it may be implemented to correspond to the features and effects described herein. The riblet structure may be applied to the bottom of the component of the component using a film to form its surface, and / or the surface may be embossed or processed in another manner to form its surface.

[0053] If a method for producing riblet structures is implemented, the other objective can be achieved, and the riblet structure is embodied as described in this document, specifically as described above, and the riblet structure is introduced to the surface by embossing or material removal treatment of the surface. The surface may be the surface of the component described above. Thus, it is advantageous to produce the riblet structure described in this document which has low frictional resistance with respect to fluid flowing along the riblet structure. The riblet structure can be produced with the characteristics and effects corresponding to those described in this document. For production, it is practical to use a negative form of the riblet structure in order to introduce the riblet structure to the surface by pressing the negative form onto the surface.

[0054] Methods for production can be embodied in this document, specifically in accordance with the features and effects described above in relation to the riblet structure or the surface of a component having a riblet structure. The same applies, and vice versa, to methods for production of the riblet structure or the surface of a component having a riblet structure.

[0055] If a method for computer implementation simulation of a surface having a riblet structure is implemented for the purpose of generating a riblet structure, the other objective mentioned first can be achieved, where the riblet structure comprises longitudinal channels oriented in the principal direction, with substructures assigned to each longitudinal channel, thereby reducing the flow resistance with respect to fluid flow along the riblet structure in the principal direction by more than 8.5%, specifically more than 9%, preferably more than 10%, particularly preferably more than 11%, and especially preferably more than 12%. Thus, the form of the riblet structure can be generated specifically by a computer implementation method. As described above, by realizing each longitudinal channel having a substructure, it has been shown that, advantageously, a particularly reduced total resistance or flow resistance with respect to fluid flow in the principal direction can be achieved. The riblet structure or substructure may be the riblet structure or substructure described in this document, and may be specifically realized accordingly. The generated riblet structure, specifically the actual surface of the riblet structure according to the form of the generated riblet structure, can then be realized. This can be specifically implemented according to the method for producing the riblet structure described in this document.

[0056] The reduction in total resistance, frictional resistance, or flow resistance is usually based on a surface without riblets. A surface without riblets may, for example, be a flat surface. In the case of riblets with longitudinal channels, it is generally assumed that a theoretical reduction in flow resistance of up to 8% can be achieved. Specifically, by implementing each longitudinal channel with its substructure as described in this document, a greater reduction in flow resistance and a higher efficiency of the riblet structure can be achieved.

[0057] It is advantageous if a substructure is simulated, specifically if it is generated, for the fluid flow in the main direction within the longitudinal channel, comprising structural elements that are arranged periodically and continuously. Specifically, as described in this document, high efficiency can be achieved using structural elements arranged continuously within each longitudinal channel. The substructure can be realized as described in this document. Therefore, it is advantageous if the ratio of the average spacing of structural elements in the main direction to the channel edges of the longitudinal channel, specifically the average spacing of the average rib tips of the longitudinal ribs, is less than 1, specifically between 0.09 and 0.33. The ratio may be less than 1, specifically at most 0.8, preferably at most 0.5, particularly preferably at most 0.33, and especially preferably at most 0.22. The ratio is usually greater than 0.05, specifically at least 0.09. A ratio of 0.05 to 0.8, specifically 0.09 to 0.5, particularly preferably 0.09 to 0.33, and especially preferably 0.13 to 0.22, is advantageous.

[0058] It is preferable that the simulation, specifically the generation, of the substructure of each longitudinal channel be performed by iteratively changing, specifically by iterative fitting, the spacing between structural elements within each longitudinal channel.

[0059] Specifically, if the generation of substructures for each longitudinal channel is performed using machine learning, specifically involving the use of computer-implemented neural networks, a high degree of applicability can be achieved.

[0060] Methods for computer implementation simulation can be embodied in this document, specifically in accordance with the features and effects described above in relation to the riblet structure, or the surface of a component having a riblet structure, and methods for producing a riblet structure. The same applies, and vice versa, to methods for computer implementation simulation, regarding the riblet structure, or the surface of a component having a riblet structure, and methods for producing a riblet structure.

[0061] Please understand that the height and depth information provided is usually based on a direction perpendicular to the base or its reference area, while the length and width descriptions are usually based on a direction parallel to the base or its reference area. [Brief explanation of the drawing]

[0062] Additional features, advantages, and effects of the present invention will become apparent from the following description of exemplary embodiments, as shown in the drawings referenced therein:

[0063] [Figure 1] This is a schematic diagram of a conventional riblet structure from the prior art, having longitudinal channels oriented in the main direction with flat bottom sections between longitudinal ribs. [Figure 2] This figure shows a schematic detail of the riblet from Figure 1 in the oblique top view and the plan view. [Figure 3] This figure shows a schematic detail of the riblet from Figure 1 in the oblique top view and the plan view. [Figure 4] This is a schematic profile diagram of the detailed riblet structure from Figure 1. [Figure 5] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure. [Figure 6] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure. [Figure 7] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure. [Figure 8] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure. [Figure 9] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure. [Figure 10]This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure. [Figure 11] This is a schematic diagram of the riblet structure, in which each longitudinal channel has a recessed portion that extends laterally relative to the main direction within the bottom section as a structural element. [Figure 12] This is a schematic diagram of the riblet structure, in which each longitudinal channel has a recessed portion that extends laterally relative to the main direction within the bottom section as a structural element. [Figure 13] This is a schematic diagram of the riblet structure, in which each longitudinal channel, as a structural element, has a recess that extends laterally with respect to the principal direction within the bottom section and on the longitudinal rib side surface of the longitudinal rib. [Figure 14] This graph shows the determined resistance change ΔR for 530 different riblet structures, displayed in percentage units. [Figure 15] These are graphs showing the results of resistance reduction ΔR for the riblet structure, as shown in Figures 1 and 2, 5 and 6. [Figure 16] These are graphs showing the averaged boundary layer profiles for the riblet structures, as shown in Figures 1 and 2, 5 and 6. [Figure 17] These are graphs showing the time-averaged vertical velocity v+ for the riblet structure, as shown in Figures 1 and 2, 5 and 6. [Figure 18] This figure shows the flow pattern corresponding to the time-averaged velocity v+ from Figure 17. [Figure 19] This is a diagram of a riblet structure, in which each longitudinal channel comprises two rows of structural elements extending in the principal direction, which are embodied as recesses. [Figure 20] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 21]This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 22] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 23] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 24] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 25] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 26] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 27] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 28] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 29] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 30] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 31]This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 32] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 33] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 34] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 35] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 36] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 37] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 38] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 39] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 40] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 41]This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 42] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 43] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 44] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 45] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 46] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 47] This is a diagram of a riblet structure having longitudinal channels with substructures having different ratios of the average spacing d of structural elements and the average rib tip spacing RS in the main direction. [Figure 48] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 49] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 50] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 51]Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 52] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 53] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 54] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 55] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 56] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 57] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 58] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 59] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 60] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 61] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 62] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 63] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 64] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 65] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 66] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 67] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 68] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 69] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 70] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 71] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 72]Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 73] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 74] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 75] Specifically, it shows a further riblet structure investigated using computer simulations, and its longitudinal channels contain substructures. [Figure 76] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure formed using transverse ribs. [Figure 77] This shows schematic details of the longitudinal channel of the riblet structure, which comprises a substructure formed using transverse ribs. [Figure 78] This is a diagram of the riblet structure, in which each longitudinal channel has a lateral rib as a structural element, extending laterally with respect to the principal direction within the bottom section. [Figure 79] This is a diagram of the riblet structure, in which each longitudinal channel has a lateral rib as a structural element, extending laterally with respect to the principal direction within the bottom section. [Figure 80] This is a diagram of the riblet structure, in which each longitudinal channel has a lateral rib as a structural element, extending laterally with respect to the principal direction within the bottom section. [Modes for carrying out the invention]

[0064] Figure 1 shows a schematic diagram of a typical riblet structure 1 from the prior art. The riblet structure 1 comprises longitudinal channels 2 oriented in the principal direction H, which are formed by wedge-shaped longitudinal ribs 5 projecting from a base surface 6, extending in the principal direction H, and spaced apart from one another. The base surface 6 forms flat base sections 7 between two immediately adjacent longitudinal ribs 5, or between pairs of longitudinal ribs. Each longitudinal channel 2 is typically formed by two immediately adjacent longitudinal ribs 5 in a second direction N, which is usually perpendicular to the principal direction, and a base section 7 positioned between the longitudinal ribs 5. The longitudinal ribs 5 typically comprise flat longitudinal rib sidewalls, or longitudinal rib sides 8. Figures 2 and 3 show schematic diagrams of the details of the riblet structure 1 from Figure 1 in order to more clearly illustrate the riblet structure 1 from Figure 1. Figure 2 shows an oblique top view of the riblet structure 1 from Figure 1, and Figure 3 shows a plan view.

[0065] Figure 4 shows a schematic profile of the details of the riblet structure 1 from Figure 1, and its details show the longitudinal channel 2. Typically, the rib tip spacing R is used as characteristic data to describe the riblet structure 1. S , rib spacing R D , and rib height R z These are defined and measured in cross-sections perpendicular to the main direction H and perpendicular to the bottom surface 6, specifically to each bottom surface section 7. Rib tip spacing R S This refers to the distance between the longitudinal ribs 5 of the longitudinal channel 2, or the distance between pairs of longitudinal ribs, and the rib spacing R. D R refers to the width of the bottom section 7 between the longitudinal ribs 5 of the longitudinal channel 2, and the rib height R. z This refers to the height of the longitudinal rib 3 measured from the bottom surface 2 or each bottom surface section 4. This applies similarly to other riblet structures 1 as defined herein, specifically below.

[0066] Structures of the type shown in Figures 1 to 4 have been found to be suitable for reducing frictional resistance for fluids flowing in the main direction H along the riblet structure 1. In this type of riblet structure 1, a reduction in frictional or flow resistance of 8% is theoretically achievable.

[0067] During the development of the riblet structure 1 described in this document, investigations and computer simulations were conducted using multiple different riblet structures 1, specifically by varying the extension, shape, and / or expansion of the substructure 3 introduced into the longitudinal channel 2. Figure 14 shows graphs indicating the resistance change ΔR in percentage units for 530 riblet structures 1 with different substructures 3, with each riblet structure 1 represented as a point on the graph. As development progressed, riblet structures 1 with resistance reductions ranging from over 8% to 13% were produced.

[0068] An advantageous riblet structure 1 comprises longitudinal channels 2 oriented in the main direction H, each longitudinal channel 2 comprising a substructure 3 having continuously arranged structural elements 4 for fluid flow within the longitudinal channel 2 in the main direction H, wherein the average spacing d of the structural elements 4 in the main direction H is equal to the average spacing R of the channel edges of the longitudinal channel 2, or the average rib tip spacing R. SThe ratio to is less than 1. Advantageously, this ratio may be from 0.05 to 0.8, specifically from 0.09 to 0.5, particularly preferably from 0.09 to 0.33, and most preferably from 0.13 to 0.22. The design variations described below can be realized using such ratios. Such implementation of the riblet structure 1 enables advantageous reduction of frictional resistance and specifically remarkable implementation feasibility. Specifically, the reduction of resistance can be variably realized by varying the spacing, specifically the average spacing d between the structural elements 4, and usually by varying the arrangement and / or shape of the structural elements 4. In this document, specifically as described above, depending on the specific embodiment, the harmony between the reduction of viscous resistance in the interaction region of each longitudinal channel 2 and the pressure resistance additionally generated by the substructure 3 can be varied.

[0069] In the examples provided in this specification, the average rib height R of the longitudinal rib 5 z may be less than 250 μm, preferably about 34 μm. The average rib tip spacing R of the longitudinal rib 5 of each longitudinal channel 2 S may be between 70 μm and 80 μm, preferably about 74 μm. The opening angle of the rib tip of each longitudinal rib may advantageously be from 30° to 50°, preferably about 40°.

[0070] Figures 5 to 10 show schematic diagrams of the details of the longitudinal channels 2 of the riblet structure 1. The longitudinal channels 2, specifically their longitudinal channel walls, are formed using the longitudinal rib sides 8 of the longitudinal ribs 5 and bottom sections 7, usually located between the longitudinal ribs 5. Each longitudinal channel 2 comprises a substructure 3 such that structural elements 4 of the substructure 3 are arranged in a continuous manner, and these structural elements 4 are embodied as recesses for fluid flow within the longitudinal channel 2 in the main direction H. Each recess may be located in the bottom section 7 and / or on the longitudinal rib sides 8 of the longitudinal channel 2. Each detail of the longitudinal channel 2 is usually representative of the substructure 3 within each longitudinal channel 2, or of the longitudinal channel 2 of the riblet structure 1. It is beneficial if each recess is embodied as a lateral channel, also called a lateral groove, extending laterally, specifically perpendicular to, the main direction H. This is illustrated as an example in Figures 5 to 8. The substructure 3 of the longitudinal channel 2 may be arranged in a continuous manner with respect to the principal direction H and may include transverse ribs 9 extending laterally with respect to the principal direction H, so that recesses, specifically transverse grooves, are formed between, specifically by, the transverse ribs 9. The transverse ribs 9 may extend perpendicular to the principal direction H, specifically in a second direction N. The second direction N is usually perpendicular to the principal direction H and perpendicular to the height direction z of the riblet structure 1. Preferably, the recesses or transverse ribs 9 are embodied as wedge shapes, usually having a basic triangular or trapezoidal shape in cross-section. The walls of the recesses or transverse ribs 9 may be embodied as flat, concave, or convex, specifically when the walls are oriented laterally or perpendicular to the principal direction. Different resistance reductions can be obtained depending on whether the recesses or transverse ribs 9 are located within the bottom section 7 and / or on one or both longitudinal rib sides 8 of the longitudinal channel 2. In the longitudinal channel 2 from Figure 5, the recessed portion, specifically the transverse groove, is located within the bottom section 7 and is specifically introduced there, and the longitudinal rib side surface 8 of the longitudinal rib 5 is realized without substructure 3, specifically without structural element 4.The longitudinal rib sides 8 of the longitudinal channel 2 are typically realized to be flat, but can alternatively be realized to be concave or convex. Such embodiments of the longitudinal channel 2 are typically associated with a 11.5% reduction in drag, as an example. Figures 11 and 12 schematically show the riblet structure 1 corresponding to the details from Figure 5. The average spacing d of the structural elements 4 in the main direction H and the average spacing of the channel edges, or the average rib tip spacing R of the longitudinal ribs 5 of each longitudinal channel 2. SThe ratio is greater in the longitudinal channel 2 from Figure 11 than in the longitudinal channel 2 from Figure 12. Figure 11 shows a figure with a ratio between 0.5 and 1. Figure 12 shows a figure with a ratio from 0.09 to 0.5, specifically from 0.09 to 0.33. The resistance reduction can be varied depending on the selected ratio. In the longitudinal channel 2 from Figure 6, the recesses, specifically the lateral grooves, are located within the bottom section 7 and on the longitudinal rib side surface 8 of the longitudinal channel 2, and are specifically introduced therein. Such embodiments of the longitudinal channel 2 are typically associated with a resistance reduction of 11.5%, as an example. Figure 13 schematically shows a riblet structure corresponding to the details from Figure 6. Similar to Figures 5 to 10, schematic diagrams of the details of the longitudinal channel of the riblet structure 1 are depicted in Figures 76 and 77, where Figure 76 shows the details in a perspective view and Figure 77 shows the details in a plan view. In the longitudinal channel 2 from Figures 76 and 77, the substructure 3 is formed using transverse ribs as structural elements 4 located within the bottom section 7, specifically introduced therein, and the longitudinal rib side 8 of the longitudinal rib 5 is embodied, for example, without the substructure 3, specifically without the structural elements 4. As shown, for example, in detail from Figures 76 and 77, each transverse rib extends laterally with respect to the principal direction, specifically orthogonally, and is provided to have an inclination of up to 50° in the principal direction, specifically up to 45°, preferably up to 35°, and particularly preferably up to 25°. The inclination is usually with respect to a flat reference area from which the transverse rib protrudes. The transverse ribs are usually embodied in a wedge shape, preferably symmetrically. The transverse ribs can be embodied as specifically described above with respect to the transverse ribs. Figures 78 to 80 show riblet structures 1 corresponding to the details from Figures 76 and 77. Figure 79 shows the riblet structure 1 from Figure 78 in a cross section perpendicular to the main direction H. Figure 80 shows the height profile of the riblet structure 1 from Figure 78 in a cross section oriented parallel to the main direction H.

[0071] Table 1 shows, as an example, the resistance reduction in the riblet structure 1 shown in Figures 1 and 2, which does not have substructure 3, compared with the resistance reduction in the riblet structure 1 shown in Figures 5 and 6. By introducing structural elements 4, specifically lateral grooves, to each bottom section 7 of the longitudinal channel 2, a significant resistance reduction can be achieved compared to the riblet structure 1 without substructure 3. Furthermore, it can be seen that this resistance reduction can be further increased if the longitudinal rib sides 8 of the longitudinal channel 2 are also realized using structural elements 4, specifically lateral grooves.

[0072] Table 1: Resistance change ΔR in percentage units in the riblet structure 1 in which the longitudinal channel 2 is embodied according to Figures 2, 5, and 6. [Table 1] Figure 15 shows graphs containing measurement and computer simulation results for riblet structure 1 from Figures 1 and 2, riblet structure 1 from Figure 5, and riblet structure 1 from Figure 6, showing the resistance reduction ΔR in percentage units against the local Reynolds number s+. The results for riblet structure 1 from Figure 2 are shown as dashed lines and with circular measurement points. The results for riblet structure 1 from Figure 5 are shown as solid lines and with triangular measurement points. The results for riblet structure 1 from Figure 6 are shown as dashed lines and with square measurement points. The results for riblet structure 1 from Figures 5 and 6 show a greater resistance reduction than the results for the standard riblet from Figure 2.

[0073] Figure 16 shows graphs illustrating the averaged boundary layer profiles for the riblet structures shown in Figures 1 and 2, riblet structure 1 shown in Figure 5, and riblet structure 1 shown in Figure 6. In the graphs, dimensionless wall spacing y+ is shown against dimensionless velocity u+. The results for riblet structure 1 shown in Figure 2 are drawn as dashed and double-dotted lines. The results for riblet structure 1 shown in Figures 5 and 6 are drawn as dashed and solid lines, with the results for riblet structure 1 shown in Figure 5 drawn in gray. The velocity in the valleys of longitudinal channel 2 can be seen in the dashed and double-dotted lines, and the velocity in the tip regions of longitudinal channel 2 or longitudinal rib 5 can be seen in the double-dotted and solid lines. The results show that the riblet structures from Figures 5 and 6 have significantly higher velocities.

[0074] Figure 17 shows graphs of the dimensionless wall spacing y+ against the time-averaged vertical velocity v+ or velocity parallel to the height direction z for the riblet structures 1 according to Figures 1 and 2, Figure 5, and Figure 6. The results for riblet structure 1 according to Figure 2 are shown as dashed and double-dashed lines. The results for the riblet structures according to Figures 5 and 6 are shown as dashed and solid lines, with the results for riblet structure 1 according to Figure 5 shown in gray. It can be seen that the results for riblet structure 1 according to Figures 5 and 6 show a reduced vertical velocity compared to the results for riblet structure 1 according to Figure 2. For illustrative purposes, the corresponding flow patterns are shown in Figure 18, where the flow field has a velocity pointing vertically downward in the valley region of each flow channel and a velocity pointing vertically upward at the tip of the longitudinal rib 5 of each longitudinal channel 2.

[0075] Figures 11 and 12 show schematic diagrams of the riblet structure 1, in which each longitudinal channel 2 is provided with a recess as a structural element 4 within the bottom section 7, extending laterally with respect to the main channel H, specifically in the second direction N. The longitudinal rib side surface 8 of each longitudinal channel 2 does not have a substructure 3 or structural element 4. Each recess extends from one of the longitudinal ribs 5 of the longitudinal channel 2 to the other longitudinal rib. Each recess has an opening area that is essentially band-shaped, specifically rectangular. The recess may have an essentially constant cross-sectional shape along the depth direction T of the recess. The recess may be realized to taper in the depth direction T. In particular, the substructure 3, specifically the structural element 4, may be realized according to the substructure 3 described in relation to Figure 5. The average spacing d of structural elements 4 in the main direction H, the average spacing of channel edges, or the average rib tip spacing R of the longitudinal ribs 5 of each longitudinal channel 2. S The ratio is greater in longitudinal channel 2 from Figure 11 than in longitudinal channel 2 from Figure 12. Figure 11 shows a figure with a ratio between 0.5 and 1. Figure 12 shows a figure with a ratio between 0.09 and 0.5, specifically between 0.09 and 0.33.

[0076] Figure 13 shows a schematic diagram of the riblet structure 1, in which each longitudinal channel 2 comprises substructures 3, specifically structural elements 4, within the bottom section 7 and on the longitudinal rib sides 8. The substructures 3, specifically structural elements 4, may be realized so that they are embodied similarly to those in Figures 11 and / or 12. Each recess may essentially extend along the bottom section 7 and the longitudinal rib sides 8 of the two longitudinal ribs 5 of the longitudinal channel 2. In particular, the substructures 3, specifically structural elements 4, may be realized according to the substructure 3 described in relation to Figure 6.

[0077] Figures 7 and 8 show further design variations of a longitudinal channel 2 having a substructure 3, which may be beneficial depending on the application and / or the resistance reduction to be set. Figure 7 shows details of a longitudinal channel 2 in which the substructure 3, specifically a structural element 4, is positioned on the longitudinal rib side surface 8 of the longitudinal channel 2 and specifically introduced therein, and the bottom section 7 of the longitudinal channel 2 is essentially embodied without the substructure 3, specifically without the structural element 4. In this case, the bottom section 7 is usually embodied as flat, but alternatively, it may have a concave or convex shape. It may be beneficial to embodied each longitudinal channel 2 having longitudinal rib side surfaces 8 of the longitudinal channel 2 that connect directly to each other, specifically transition directly to each other. In this case, the longitudinal channel wall of the longitudinal channel 2 may be formed by the longitudinal rib side surfaces 8 of the longitudinal channel 2, specifically without the bottom section 7. This is shown as an example in Figure 8. In this case, the longitudinal rib sides 8 may comprise structural elements 4, specifically transverse grooves or transverse ribs 9. Conveniently, the longitudinal rib sides 8 of the longitudinal channel 2 may be connected to one another such that they form an angle. Depending on the applicable flow conditions, it may be advantageous in each longitudinal channel 2 for the longitudinal rib sides 8 to be continuously connected to one another or to the bottom section 7 of the longitudinal channel 2. The bottom section 7 may be embodied to be flat or curved, specifically concave or convex. This is shown as an example in Figure 9. It may be advantageous for the structural elements 4 to be at least partially, preferably completely, spaced away from at least one or both of the longitudinal ribs 5 of the longitudinal channel in a second direction N. In this case, the structural elements 4 are usually located within or formed using the bottom section 7 of the longitudinal channel 2. Figure 10 shows an example of a flow channel in which the structural elements 4 are spaced away from both longitudinal ribs 5 of the longitudinal channel 2. Therefore, structural element 4 is embodied, for example, as a rectangular or square recess.

[0078] Depending on the intended application, the features specifically presented above with respect to embodiments of the longitudinal channel 2 or structural element 4 may be freely combined in various ways and are not particularly limited to the exemplary implementations presented as examples, as will be understood by those skilled in the art.

[0079] For the purpose of reducing resistance, it has been shown that multiple different degrees of pronouncement of structural elements 4 are possible, which may differ from one another in terms of shape and / or depth and / or spatial arrangement within the longitudinal channel 2. Structural elements 4 may be recesses and / or protrusions. Each longitudinal channel 2 may comprise multiple arrangement rows of structural elements 4, which extend in the principal direction H. As an example, Figure 19 shows a riblet structure 1 in which each longitudinal channel 2 comprises two arrangement rows of structural elements 4, embodied as recesses, extending in the principal direction H, and the arrangement rows are located within the bottom section 7.

[0080] Figures 20 to 47 show, as an example, different riblet structures, specifically those investigated using computer simulations, in which the longitudinal channel 2 is equipped with a substructure 3. The substructure 3 has an average spacing d of structural elements 4 in the main direction H and an average rib tip spacing R at the channel edge. S or are embodied using different ratios of the tip spacing of the longitudinal ribs 5 of each longitudinal channel 2. Table 2 shows the determined drag reduction ΔR for each.

[0081] Table 2: Resistance change ΔR in percentage units in the riblet structure 1 in which the longitudinal channel 2 is embodied according to Figures 20 to 47, where the substructure 3 of the longitudinal channel 2 is the average spacing d of the structural elements 4 in the main direction H and the average rib tip spacing R of the longitudinal ribs 5 of each longitudinal channel 2. S The ratio d / R S It holds. [Table 2] The riblet structure 1 shown in Figures 20 to 23 has an average spacing d of structural elements 4 in the main direction H, which is 0.67, and an average rib tip spacing R of the longitudinal ribs 5 in each longitudinal channel 2. S It has the ratio of . Figures 20 and 22 show each riblet structure 1 in perspective view; Figures 21 and 23 show each riblet structure 1 in cross section perpendicular to the principal direction H. The grayscale bars in the figures, and specifically also provided in subsequent figures, correspond to the change in grayscale value in the height direction z. The riblet structure 1 shown in Figures 20 and 21 comprises a substructure 3 realized by an arrangement of rectangular recesses as structural elements 4, oriented in the principal direction H, within each longitudinal channel 2. Each recess is realized so that it tapers in the depth direction T of the recess, specifically corresponding to the inclination of the longitudinal rib side surface 8 of the longitudinal channel 2. Figures 22 and 23 show a riblet structure 1 realized similarly to the riblet structure 1 from Figures 20 and 21, where the longitudinal ribs 5 are realized at a smaller height.

[0082] The riblet structure 1 shown in Figures 24 to 31 has an average spacing d of structural elements 4 in the main direction H, which is 0.33, and an average rib tip spacing R of the longitudinal ribs 5 in each longitudinal channel 2. SIt has the ratio of . Figures 24, 26, 28, and 30 show each riblet structure in perspective view; Figures 25, 27, 29, and 31 show each riblet structure 1 in cross section perpendicular to the main direction H. The riblet structure 1 shown in Figures 24 and 25 comprises a substructure 3 realized within each longitudinal channel 2 by arrangement rows of rectangular recesses as structural elements 4, oriented in the main direction H. Each recess is specifically realized so as to taper in the depth direction T of the recess, corresponding to the inclination of the longitudinal rib side surface 8 of the longitudinal channel 2. Figures 26 and 27 show a riblet structure 1 in which the substructure 3 is realized within each longitudinal channel 2 by arrangement rows of rectangular or square recesses as structural elements 4, oriented in the main direction H. Figures 30 and 31 show riblet structures in which substructures 3 are realized by arrangements of rectangular or square recesses as structural elements 4, oriented in the main direction H, within each longitudinal channel 2, and the structural elements 4 are spaced apart from both longitudinal ribs 5 of each longitudinal channel 2.

[0083] The riblet structure 1 shown in Figures 32 to 37 has an average spacing d of structural elements 4 in the main direction H, which is 0.22, and an average rib tip spacing R of the longitudinal ribs 5 in each longitudinal channel 2. SIt has the ratio of . Figures 32, 34, and 36 show the respective riblet structures in perspective views; Figures 33, 35, and 37 show the respective riblet structures in cross-sections perpendicular to the principal direction H. The riblet structures 1 shown in Figures 32 and 33 include a substructure 3 realized within each longitudinal channel 2 by arrangements of rectangular recesses as structural elements 4, oriented in the principal direction H, where each recess extends across both longitudinal rib sides 8 of the longitudinal channel 2 and the bottom section 7 of each longitudinal rib. Figures 34 and 35 show a riblet structure in which the substructure 3 is realized within each longitudinal channel 2 by arrangements of rectangular or square recesses as structural elements 4, oriented in the principal direction H, where the structural elements 4 are spaced apart from both longitudinal ribs 5 of the longitudinal channel 2. Figures 36 and 37 show riblet structures 1 in which substructures 3 are realized by arrangements of rectangular recesses as structural elements 4, oriented in the main direction H, within each longitudinal channel 2. Specifically, each recess is realized so as to taper in the depth direction T of the recess, corresponding to the inclination of the longitudinal rib side surface 8 of the longitudinal channel 2.

[0084] The riblet structure 1 shown in Figures 38 to 43 has an average spacing d of structural elements 4 in the main direction H, which is 0.17, and an average rib tip spacing R of the longitudinal ribs 5 in each longitudinal channel 2. SIt has the ratio of . Figures 38, 40, and 42 show the respective riblet structures in perspective views; Figures 39, 41, and 43 show the respective riblet structures in cross-sections perpendicular to the principal direction H. The riblet structures 1 shown in Figures 38 and 39 include a substructure 3 realized within each longitudinal channel 2 by an arrangement of rectangular recesses as structural elements 4, oriented in the principal direction H, with each recess extending across both longitudinal rib sides 8 and bottom sections 7 of each longitudinal channel 2. Figures 40 and 41 show the riblet structures in which the substructure 3 is realized within each longitudinal channel 2 by an arrangement of rectangular recesses as structural elements 4, oriented in the principal direction H. Each recess is specifically realized so that it tapers in the depth direction T of the recess, corresponding to the inclination of the longitudinal rib side 8 of the longitudinal channel 2. Figures 42 and 43 show riblet structures in which substructures 3 are realized by arrangements of rectangular or square recesses as structural elements 4, oriented in the main direction H, within each longitudinal channel 2, and the structural elements 4 are spaced apart from both longitudinal ribs 5 of each longitudinal channel 2.

[0085] The riblet structure 1 shown in Figures 44 to 47 has an average spacing d of structural elements 4 in the main direction H, which is 0.13, and an average rib tip spacing R of the longitudinal ribs 5 in each longitudinal channel 2. SIt has the ratio of . Figures 44 and 46 show the respective riblet structures in perspective views; Figures 45 and 47 show the respective riblet structures in cross-sections perpendicular to the principal direction H. The riblet structures 1 shown in Figures 44 and 45 include a substructure 3 realized within each longitudinal channel 2 by an arrangement of rectangular recesses as structural elements 4, oriented in the principal direction H, with each recess extending across both longitudinal rib sides 8 of the longitudinal channel 2 and the bottom section 7 of each longitudinal rib. Figures 46 and 47 show the riblet structures in which the substructure 3 is realized within each longitudinal channel 2 by an arrangement of rectangular recesses as structural elements 4, oriented in the principal direction H. Each recess is specifically realized so that it tapers in the depth direction T of the recess, corresponding to the inclination of the longitudinal rib side 8 of the longitudinal channel 2.

[0086] Figures 48 to 75 show, as an example, a further riblet structure in which the longitudinal channel 2 is equipped with a substructure 3, specifically investigated using computer simulations, with the average spacing d of structural elements 4 in the main direction H and the average rib tip spacing R of the longitudinal ribs 5 of each longitudinal channel 2. S Substructure 3 having the aforementioned favorable ratio was investigated. The relevant determined resistance reduction ΔR is shown in Table 3.

[0087] Table 3: Resistance change ΔR in % units in the riblet structure in which the longitudinal channel 2 is embodied according to Figures 50 to 76, where the longitudinal channel 2 comprises different substructures 3. [Table 3] The riblet structure 1 shown in Figure 48 comprises a substructure 3 formed within each longitudinal channel 2 using two arrangement rows, specifically trapezoidal recesses, oriented in the main direction H, where the recesses are connected to each other by longitudinal recesses extending in the main direction H. The riblet structure 1 shown in Figure 49 comprises a substructure 3 formed within each longitudinal channel 2 using two arrangement rows, of raised structural elements 4, oriented in the main direction H, where these arrangement rows are specifically offset from each other by half the distance between two immediately consecutive raised elements in one of the arrangement rows. The riblet structure 1 shown in Figure 50 comprises a substructure 3 formed within each longitudinal channel 2 using two arrangement rows, specifically rectangular or square recesses, oriented in the main direction, where these arrangement rows are specifically offset from each other by half the distance between two immediately consecutive recesses in one of the arrangement rows. The riblet structure 1 shown in Figure 51 comprises a substructure 3 formed within each longitudinal channel 2 using two arrangement rows of rectangular or square recesses, specifically structural elements 4, oriented in the main direction H, where the recesses, which are immediately adjacent to each other, are arranged within their respective arrangement rows such that they are offset from each other in a second direction N. The riblet structure 1 shown in Figure 52 comprises a substructure 3 formed within each longitudinal channel 2 using two arrangement rows of rectangular or square recesses, specifically structural elements 4, oriented in the main direction H, where the arrangement rows are specifically arranged such that they are offset from each other by half the distance between two immediately adjacent recesses, and the recesses of the arrangement rows partially overlap each other in the main direction H.The riblet structure 1 shown in Figures 53 and 54 comprises a substructure 3 formed within each longitudinal channel 2 using a series of rectangular or square recesses, specifically structural elements 4, oriented in the main direction H, wherein the recesses have a tapered recess cross-section in the depth direction T, and this recess cross-section narrows in both the main direction H and the second direction N as the depth direction T increases. Specifically, the recesses may have a recess cross-section that tapers in the depth direction T, specifically in a pyramidal manner with the pyramidal tip oriented opposite to the height direction z. The riblet structure 1 shown in Figure 55 is similarly embodied in Figure 50 using deeper recesses. The riblet structure 1 shown in Figure 56 comprises a substructure 3 formed within each longitudinal channel 2 using three arrangement rows of rectangular or square recesses, specifically structural elements 4, oriented in the main direction H; the recesses of the arrangement rows are arranged continuously in the second direction N, and within each arrangement row, the recesses are arranged so as to be offset from one another in the second direction N in an alternating manner. The riblet structure 1 shown in Figures 57 and 58 comprises a substructure 3 formed within each longitudinal channel 2 using arrangement rows of recesses, specifically structural elements 4, oriented in the main direction H, where the recesses extend diagonally in the bottom section 7 from one longitudinal rib 5 to the other longitudinal rib. Preferably, the riblet structure 1 may comprise a longitudinal channel 2 having recesses extending diagonally in the second direction N and diagonally opposite to the second direction N. The riblet structure 1 shown in Figure 59 comprises a substructure 3 realized by an arrangement of triangular recesses, specifically structural elements 4, oriented in the main direction H, within each longitudinal channel 2. Specifically, the bottom surface of the recesses may have a depth that changes periodically along the multiple longitudinal channels 2, specifically in the second direction N.The riblet structure 1 shown in Figure 61 comprises a substructure 3 formed within each longitudinal channel 2 using arrangement rows of recesses as structural elements 4, oriented in the main direction H, where each recess is realized by a plurality of triangular recesses, which are specifically arranged to form a rectangle. The riblet structure 1 shown in Figure 62 comprises a substructure 3 formed within each longitudinal channel 2 using a plurality of arrangement rows of spherical, specifically circular or elliptical, recesses as structural elements 4, oriented in the main direction H. Specifically, one or more arrangement rows may comprise recesses having recess volumes cut by the longitudinal rib side surface 8 or the extension of the longitudinal side surface 8. Conveniently, one of the arrangement rows may be positioned so as to be in contact with each of the longitudinal ribs 5, so that the recess volume of the recesses of each arrangement row is cut by the respective longitudinal rib or longitudinal rib surface 8, as described above. The riblet structures shown in Figures 63 and 64 include substructures 3 formed within each longitudinal channel 2 using arrangement rows of spherical, specifically circular or elliptical, ridges as structural elements 4, oriented in the main direction H. Specifically, the base surface 6 may have a height that changes periodically along a second direction N, specifically along the multiple longitudinal channels 2. In particular, the ridges of the substructures 3 may be formed such that a virtual spherical ridge is positioned on an imaginary arrangement plane, where a portion of this virtual spherical ridge protruding beyond the base surface 6 forms the ridge of the substructure 3. This is shown in Figure 64. The riblet structure 1 shown in Figure 65 includes substructures 3 formed within each longitudinal channel 2 using arrangement rows of arrow-shaped ridges pointing in the main direction H, specifically, the arrowheads of the arrow-shaped ridges are connected to each other by longitudinal ridges extending in the main direction H. The longitudinal ridges and the two consecutive arrow-shaped ridges may each form a recess between them. As shown in Figure 66, each recess may be embodied such that it increases in depth in the direction of the longitudinal rib closest to the recess.The riblet structure 1 shown in Figure 67 comprises a substructure 3 formed within a longitudinal channel 2 using a series of arrow-shaped recesses, specifically oriented in the principal direction H. The recesses may be spaced apart from both longitudinal ribs 5 of the longitudinal channel 2. The recesses may have a certain depth, specifically in a second direction N. The riblet structure 1 shown in Figure 68 comprises a substructure 3 implemented similarly to the riblet structure 1 from Figure 67, and compared to the riblet structure 1 from Figure 67, these recesses have a smaller average spacing from each other in the principal direction H. The riblet structures shown in Figures 69 and 70 comprise a substructure 3 implemented similarly to the riblet structure 1 from Figure 67, and compared to the riblet structure 1 from Figure 67, these recesses have a larger average spacing in the principal direction H. The riblet structure 1 shown in Figures 71 and 72 comprises a substructure 3 formed within each longitudinal channel 2 using a grid configuration of recesses, which extends in the principal direction H. Each grid configuration may have recesses with opening areas of different sizes. The recesses of each grid configuration may have equal or different depths. It is beneficial if recesses located closer to the center have a greater depth than recesses located further from the center. The riblet structure shown in Figures 74 and 75 comprises a substructure 3 formed within each longitudinal channel 2 using one or more rows of recesses oriented in the principal direction H, where each recess has a width that expands in the principal direction H. The width of the recess is usually measured in a second direction N. The width is usually based on the opening area of ​​the recess. Specifically, the generation of the substructure 3 of the riblet structure in each longitudinal channel 2 may be performed using machine learning. For example, substructure 3 from Figures 71, 72, and 73 was determined using this method.

[0088] The defined shape of structural element 4, specifically the raised or recessed portion, is usually based on the shape of the cross section of the recess and / or the opening area of ​​the recess, usually oriented perpendicular to the height direction z or the depth direction T. The recess may be realized using a normally tapered cross section, which is constant or varies in the depth direction T of the recess.

Claims

1. A riblet structure comprising longitudinal channels oriented in a principal direction, wherein each longitudinal channel has a substructure comprising structural elements specifically arranged periodically and continuously for a fluid flow within the longitudinal channel in the principal direction, and the ratio of the average spacing of the structural elements in the principal direction to the average spacing of the channel edges of the longitudinal channel is less than 1, specifically between 0.09 and 0.

33.

2. The riblet structure according to claim 1, wherein the longitudinal channel is formed using a plurality of longitudinal ribs that protrude from the bottom surface, are oriented in the main direction, and are spaced apart from one another, and the average spacing of the channel edges is the average rib tip spacing of the longitudinal ribs that form the longitudinal channel.

3. The riblet structure according to claim 2, wherein the ratio of the average rib height of the longitudinal ribs forming the longitudinal channel to the average rib tip spacing of the longitudinal ribs is at most 0.8, preferably 0.25 to 0.

4.

4. The riblet structure according to claim 2 or 3, wherein the substructure, specifically the structural element, is at least partially arranged on the bottom surface of each of the longitudinal channels and / or at least partially on the side surface of at least one of the longitudinal ribs of each of the longitudinal channels.

5. The riblet structure according to any one of claims 1 to 3, wherein the structural element is formed using raised portions and / or recessed portions.

6. The riblet structure according to claim 2 or 3, wherein the structural elements of the substructure extend from one of the longitudinal ribs of the longitudinal channel to the other longitudinal rib, and preferably the structural elements extend along at least one of the longitudinal rib sides of each longitudinal channel to half the rib height of each longitudinal rib.

7. The riblet structure according to claim 2 or 3, wherein the structural elements of the substructure are at least partially, preferably completely, spaced apart from at least one or both of the longitudinal ribs in a direction perpendicular to the main direction.

8. The riblet structure according to any one of claims 1 to 3, wherein the substructure is formed using wedge-shaped lateral ribs that are arranged continuously in the main direction and oriented laterally with respect to the main direction, and thus recesses are formed between the lateral ribs.

9. Specifically, the riblet structure according to any one of claims 1 to 3, wherein in the main direction, the structural elements are embodied using a repeating structural arrangement.

10. The riblet structure according to any one of claims 1 to 3, wherein within the longitudinal channel, the structural elements form a plurality of arrangement rows of structural elements, and these arrangement rows are oriented in the principal direction.

11. The riblet structure according to claim 10, wherein immediately adjacent rows of elements are arranged such that they are offset from each other in the principal direction, preferably by half the distance between one or two immediately adjacent structural elements in the row of elements.

12. A surface of a component, wherein the surface comprises the riblet structure described in any one of claims 1 to 3.

13. A method for producing a riblet structure, wherein the riblet structure according to any one of claims 1 to 3 is introduced onto the surface by embossing or material removal treatment.

14. A method for computer implementation simulation of a riblet structure, specifically a surface having a riblet structure according to any one of claims 1 to 3, for the purpose of generating the aforementioned riblet structure, wherein the riblet structure includes longitudinal channels oriented in the principal direction, and substructures are assigned to each of the longitudinal channels, thereby reducing the flow resistance for a fluid flow along the riblet structure in the principal direction by more than 8.5%, preferably more than 10%.

15. The method according to claim 14, wherein the substructure is simulated using structural elements specifically arranged periodically and continuously for a fluid flow within the longitudinal channel in the principal direction.

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