FLUID MACHINE AND METHOD FOR MANUFACTURING COMPONENTS OF FLUID MACHINE THAT GUIDE A FLUID MEDIUM

Abstract

The present invention relates to a fluid machine, in particular a turbomachine, preferably a fan, having a component for guiding a fluid medium, such as an impeller blade, guide vane, hub ring, cover ring, base disk, nozzle or housing part / element, wherein the component for guiding the fluid medium is manufactured from a synthetic material by casting, preferably by injection molding, and wherein riblets are formed at least partially on and / or on and / or in the surface of the component in the area around which the flow occurs. The invention also relates to a method for manufacturing a component for guiding a fluid medium.

Description

[Technical Field]

[0001] The present invention relates to a fluid machine, in particular a turbomachine, preferably a fan, having at least one component for guiding a fluid medium, such as an impeller blade, guide vane, hub ring, cover ring, base plate, nozzle or housing part / element.

[0002] Furthermore, the invention relates to a method for manufacturing a component of a fluid machine for guiding a fluid medium. [Background technology]

[0003] Fluid machines of the type discussed herein are well known in practice. The fan and its components are just one example. In such fluid machinery, wall friction is a problem not only from the viewpoint of operational noise but also from the viewpoint of power consumption and efficiency. Therefore, measures must be taken to reduce wall friction.

[0004] In practice, it is already known that riblets on the flow surface reduce wall friction and thus reduce friction losses and additional load torque. This is true for fluid machinery such as turbomachinery and fans. It may be interesting to provide such riblets on components that are stationary or that are rotating or moving in operation.

[0005] Riblets are elongated structures raised above the flow surface with their lengths oriented generally along the direction of relative flow velocity in the surface area. To achieve the wall friction reduction effect, the cross section of the riblets must meet special requirements depending on the relative flow velocity. In particular, the cross-sectional dimensions of the riblets are relatively small, for example, the width, the distance between adjacent riblets, and the height of the riblets are in the range of 1 μm to 100 μm.

[0006] Generally, a large number of riblets need to be placed adjacent to each other to cover the surface on which the flow occurs. For this reason, no large scale manufacturing process suitable for producing large quantities per unit of time is known in the prior art. Known manufacturing methods include incorporating riblets into pre-manufactured components, for example by gluing a film in the shape of riblets or by surface modification by laser processing, machining or other post-treatments. manufacturing The following methods are listed. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a cost-effective method for fabricating wall friction reducing riblets. manufacturing The object is to identify a fluid machine, in particular a turbomachine, preferably a fan and its components, which can be implemented with the method. The use of riblets in fluid machinery must be cost-effective. In particular, it is possible to easily and cost-effectively select components suitable for fluid machinery depending on the relative flow speeds. manufacturing It must be possible to manufacture it by a method. Furthermore, the fluid machinery according to the present invention must be different from competing products. [Means for solving the problem]

[0008] The object of the fluid machine according to the invention is achieved by the features of claim 1. The components which guide the fluid medium and which are in any case essential are therefore manufactured from synthetic materials by casting, preferably by injection moulding. At least a number of riblets are formed on and / or in the surface of the component, in each case in critical areas around which flow occurs, and these riblets can be easily incorporated into the component using casting techniques.

[0009] Advantageously, riblets are formed in areas of each component where flow losses, wall friction losses and / or noise generation are high. This reduces wall friction in that region.

[0010] The riblets are designed as elongated, preferably raised structures extending substantially parallel to the direction of flow over the riblets. The riblets may be straight or curved. Furthermore, multiple riblets may be positioned adjacent to one another in an arrangement suitable for the particular component, and where appropriate, multiple such riblet arrangements may be arranged so that they are at least largely parallel to one another. When riblets are arranged adjacent to each other in multiple rows in this manner, the riblets may be spaced equidistant from each other.

[0011] The riblets may also be arranged in the form of a circular arc or an involute curve. Alternatively, the riblets may be arranged in a curved line, with the individual riblets adjacent to each other. Advantageously, two or more such arrangements are formed substantially parallel to one another, if desired.

[0012] As a further advantage, the riblets are entirely or at least largely free of undercuts in the mold release direction. It is also advantageous to have a draft angle of at least 1°, preferably at least 3°.

[0013] In particular, the riblet sidewalls may be designed asymmetrically with respect to the local normal on the riblet-free imaginary base region of each component, thereby facilitating demolding in a specific demolding direction that is tailored to or required by the component shape.

[0014] Each component, including the riblets, can be demolded in one piece due to the specific design of the riblets, and there are no undercuts in the casting mold.

[0015] It is also conceivable to make at least the region of the riblets from a thermoplastic synthetic material, preferably a fiber-reinforced material. This increases stability and reduces wear.

[0016] With regard to the manufacturing method according to the invention, the object stated at the outset is achieved by the features of claim 11, in that the component for guiding the fluid medium has riblets in at least some areas. Here too, the manufacturing method using casting techniques is important, with the components being manufactured using injection molding with forming tools. The concave and convex shapes of the riblets are incorporated into the molding die. Since the manufacturing method according to the invention refers to the fluid machine according to the invention, the relevant features are also incorporated into the manufacturing method according to the invention.

[0017] Advantageously, the mould surface into which the riblet features are incorporated is surface treated before the riblet features are incorporated to have a low roughness and roughness depth, in particular a roughness depth of less than 10 μm, preferably less than 4 μm. In particular, the surface may be polished or honed.

[0018] Riblet features may also be retrofitted to a mold, especially a mold already in production. This allows existing molds to be reworked to fit the riblet shape.

[0019] It is advantageous to design the mold so that the wall temperature of the mold during production is higher in the area where the riblets are to be formed (e.g., at least 5 K higher than in other areas of the mold face). This can be achieved, for example, by providing separate cooling channels with high flow temperatures, or by taking other appropriate measures in relation to the mold cooling system. This improves the formability of the riblets as the synthetic material can more easily flow into the small recesses that form the riblets. Without such a configuration, there is a risk that the riblets will not be sufficiently filled with synthetic material.

[0020] The cross section of the riblets is designed to ensure a wall friction reduction effect while maintaining high stability of the riblets on the component and robustness of the mold against erosion and other wear. It is especially designed to release without undercuts.

[0021] There are various possibilities for developing the invention. On the one hand, reference is made to the claims dependent on claim 1 and, for the manufacturing method thereof, to the claims dependent on claim 11. On the other hand, please refer to the following description of an embodiment of a fan according to the invention, with reference to the drawings. In conjunction with the description of embodiments of the present invention, preferred designs and developments of the present invention are also described. [Brief explanation of the drawings]

[0022] [Figure 1] 1 shows an axial fan impeller in a perspective view from the inlet side, together with a schematic of the path of riblets on the air guide surface. [Figure 2] A prior art schematic of riblets on an air guide surface of a fluid machinery component is shown together with the associated forming die in a detailed cross-sectional view in a plane section that is locally approximately perpendicular to the air guide surface or its base region and approximately perpendicular to the longitudinal path of the riblets. [Figure 3] 3 shows a view comparable to FIG. 2, in which a modified riblet shape is formed for undercut-free demolding in accordance with the present invention. [Figure 4]1 shows a plan view of a radial fan impeller from the inlet side, together with a schematic of the path of the riblets on the air guide surface. [Figure 5] 1 shows a plan view of a radial fan impeller from the outflow side, together with a schematic of the path of the riblets on the air guide surface. [Figure 6] 1 shows a perspective view of an axial fan housing from the inlet side, together with a schematic of the path of riblets on the air guide surface. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 shows a perspective view of an impeller 19 of an axial flow fan as seen from the inlet side. The impeller 19 is a rotating part of a fan (not shown in its entirety), i.e. a fluid machine, in particular a turbofluid machine, the assembled fan being driven by a motor attached to transport a fluid medium. The impeller 19 basically includes a hub ring 21 and blades 22 attached to the hub ring 21 . The impeller 19 is a fluid element 1 of a fluid machine, in particular of a turbomachine, more particularly of a fan with an air guide surface 13 . Here, the air guide surfaces 13 are in particular the surfaces of the suction and pressure sides of the blades 22 and the surfaces of the hub ring 21 .

[0024] During operation, the relative velocity between the conveying medium and the flow surface 13 creates wall shear stresses that can increase the required driving force and / or decrease the conveying flow rate. Therefore, at a comparable operating point, i.e., a comparable relative flow velocity, reducing the wall shear stress reduces the required driving force and / or increases the delivered flow rate, thus improving efficiency. Reducing wall shear stress can also reduce noise generation.

[0025] The cross-sectional design of the riblets will be explained using Figures 2 and 3. In the impeller 19 shown in FIG. 1, riblets 14 are formed on the air guide surface 13 of the blades 22. The longitudinal paths of some of the riblets 14 are shown schematically. In reality, a large number of riblets 14 are formed parallel to each other and at short distances, but for the sake of clarity, only the paths of a small number of riblets 14 are shown in the figure. The riblets 14 extend generally parallel to the relative flow on the flow surface 13 of the vane 22 from the inlet edge 27 to the outlet edge 28 . It is also contemplated that the riblets 14 may extend along only a portion of the length of the blade 22 or cover only a portion of the blade 22, for example, in areas where flow losses and noise generation due to wall shear stress are particularly high. It is also conceivable to form riblets 14 on the flow surface 13 of the hub ring 21, but this is not the case here.

[0026] In order to economically manufacture the impeller 19, which is a component 1 of a fluid machine, the component 1, the impeller 19, including the riblets 14, is produced in one piece according to the invention by a casting process, advantageously by synthetic material injection molding. This allows for mass production. Therefore, the uneven shape of the riblets 14 is incorporated in an appropriate manner into the corresponding molding surface of the casting mold (see also the description of Figures 2 and 3). The impeller 19 of Figure 1 is manufactured using a mold that includes, among other things, two main molded parts.

[0027] During part demolding, one molded part, which in the illustrated example mainly forms the face of the impeller 19 facing the inlet side, moves in the demolding direction 12, i.e., approximately to the left from the component 1. The other molding part of the casting mold, which in the illustrated example mainly forms the face of the impeller 19 (not shown) facing the outlet side, moves in a different demolding direction 12a, i.e., approximately to the right from the component 1, during the demolding process. Since the constituent element 1 has a complex shape with the blades 22 that are twisted three-dimensionally, the direction of release from the mold is largely determined by the basic shape of the constituent element 1.

[0028] In such components, it is either not possible, or can only be done with great difficulty and expense, to adapt the release direction to the undercuts that may be caused by the riblets 14. In particular, the release direction 12, 12a is often not parallel to the local wall normal of the flow surface 13 as well as the inlet and outlet sides of the vanes 22. For this reason, it has been impossible to form such a component 1 in a single casting. In the prior art, riblets 14 can be implemented by applying a special film having the shape of riblets 14 to the component or by laser machining the component. However, these techniques do not allow mass production with reduced manufacturing time and costs.

[0029] To illustrate the problems associated with demolding riblets 14 integrated into cast parts, FIG. 2 shows a prior art schematic of riblets 14a on an air guide surface 13a of a fluid machinery component 1a, together with the associated molding die part 17a, in a detailed cross-sectional view in a plane section generally perpendicular to the air guide surface 13a or its base region 23a and generally perpendicular to the longitudinal path of the riblets 14a. The release direction 12 of the mold part 17a relative to the air guide element 1a is shown. This demolding direction 12 can be seen as a projection onto the plane of the drawing, and the actual demolding direction may also have a three-dimensional component perpendicular to the plane of the drawing.

[0030] According to the prior art, the riblets 14a in cross section are respectively the air guide surface 13a or its base region 2 3 It is formed almost symmetrically with respect to the virtual local normal of a. base area 2 3 a corresponds to the trajectory of a virtual air guide surface 13a without riblets 14a. Each riblet 14a has a lateral distance (i.e., jump dimension) to an adjacent riblet 14a (measured transversely to the longitudinal direction of the riblet 14a) measured at the center of the cross section, and a height from the base region 23a. It is advantageous if the height from the base region 23a corresponds to 15% to 70% of the jump dimension. In particular, each riblet 14a has two side walls 18a that are not parallel to each other but form a wedge angle with each other, the wedge angle being advantageously between 10° and 50°.

[0031] Here, in the prior art shown, an undercut is formed in the side wall 18a of the riblet 14a (the side wall 18a facing upward in the figure), which can be clearly seen from the hatching of the molding die part 17a extending parallel to the demolding direction 12 defined by the components. The reason for this is that the release direction 12 defined by the component 1a deviates significantly from the local wall normal direction of the flow surface 13a. Such configurations are common in fluid machinery components 1a, such as impellers, inlet nozzles, housings or guides, which are designed in axial or radial flow, and in which the flow is optimized with complex three-dimensional shapes. If the demolding shown here is performed as a forced demolding in the demolding direction 12, the riblets 14a will be destroyed during the demolding process. The reason for this configuration is that the proper flow-related function of the riblets 14a requires that the side walls 18a and base regions 23 of the riblets 14a are properly formed, and in particular, it is important that the ratio of the height of the riblets 14a to the jump dimension between two adjacent riblets 14a be between 15% and 70%.

[0032] Figure 3, comparable to Figure 2, shows an embodiment of a flow surface 13 of a fluid machinery component 1, which is adapted for the manufacturing method or demolding process according to the invention, and in which riblets 14 are provided on the flow surface 13. Figure 3 shows a schematic view of a fluid element 1 of a fluid machine having riblets 14 on its air guide surface 13, together with the associated forming die part 17, in a detailed cross-sectional view in a plane section that is locally approximately perpendicular to the air guide surface 13 or its base region 23 and approximately perpendicular to the longitudinal path of the riblets 14. This figure shows the demolding direction 12 of the mould part 17 relative to the component 1, i.e. the air guide element 1. This demolding direction 12 can be seen as a projection onto the plane of the drawing, and the actual demolding direction may also have a three-dimensional component perpendicular to the plane of the drawing.

[0033] For undercut-free release, a riblet shape is formed, which is modified from the prior art shown in Figure 2, and this riblet shape essentially has the function of reducing wall friction during the operation of the fluid machinery. The riblets 14, and in particular their cross sections, have been redesigned to take into account the demolding direction 12 defined by the component 1. Thus, for example, in a cross section such as that shown in FIG. 3, the riblets 14 are asymmetric with respect to an imaginary local normal to the air guide surface 13 or its base region 23. The two side walls 18 of each riblet 14 are therefore asymmetric with respect to an imaginary local normal to the air guide surface 13 or its base region 23 . In areas where the demolding direction 12 deviates significantly from the imaginary local normal to the base region 23 of the air guide surface 13, for example by 25° or more, the two exterior angles of the two side walls 18 of the riblet 14 relative to the base region 23 differ significantly from each other, for example by 10° or more. The mold part 17 has the concave and convex shape of the component 1 having the riblets 14, i.e., the fluid element 1, so that the aforementioned design features of the riblets 14 are also visible in the mold part 17.

[0034] The cross-sectional path of the side wall 18 is adapted to the demolding direction 12 so that the riblets 14 can be demolded essentially without undercuts in the demolding direction 12, and advantageously has a draft angle of at least 1°, advantageously 3°, relative to the demolding direction 12, as shown in FIG. 3. The possibility of demolding without undercuts can be clearly seen in FIG. 3 by the hatching of the cross section of the mold part 17 parallel to the (projected) demolding direction 12 . In this embodiment, the riblets 14 are not damaged or destroyed during the demolding process.

[0035] Important design features of the riblets 14 are considered to maintain their ability to reduce wall shear stress. The riblets 14 have a lateral distance (the so-called jump dimension) between adjacent riblets 14 (measured transversely to the longitudinal direction of the riblets 14) as measured at the center of the cross section, and a height from the base region 23. The height from the base region 23 is preferably 15% to 70% of the jump dimension. In particular, each riblet 14 has two side walls 18 that are not parallel to each other but form a wedge angle with each other, the wedge angle advantageously being between 10° and 50°. In this embodiment, the riblets 14 are formed with upper end faces 24, which is advantageous in terms of the stability and durability of the riblets 14. The width of the upper end face 24 of the riblet 14 is advantageously in the range of about 30 to 200% of the height of the riblet 14 when viewed in cross section. Embodiments without upper end surface 24 are also contemplated, for example, where the riblets or their side walls merge into one another at their outer ends in a pointed or rounded manner. In this embodiment, the transition from the side wall 18 to the upper end face 24 is provided with a pronounced outer edge 20 . Again, in other embodiments, it may be advantageous to round these outer edges 20 with a small transition radius.

[0036] Similarly, in this embodiment, a pronounced inner edge 29 is provided at the transition from the side wall 18 to the base region 23 . Again, in other embodiments it may be advantageous to round these inner edges 29 with a small transition radius. In both cases, the rounding improves the stability of the component 1 or the riblets 14 thereon, and of the molding die part 17, reducing wear during manufacture and during operation of fluid machinery equipped with an air guide element 1 having riblets 14. The radius of curvature of the rounding that can be applied to the outer edge 20 or the inner edge 29 is advantageously in the range of up to 30% of the height of the respective riblet 14 .

[0037] It is particularly advantageous if the region of the inner edge 29 is rounded with a variable radius of curvature, similar to the trunk of the tree. The radius of curvature at the transition to the base region 23 is smaller than the radius of curvature at the transition to the side wall 18, advantageously by a factor of at least 1.4.

[0038] In the illustrated embodiment, the fluid element 1 including the riblets 14 is one-piece demoldable and has no undercuts to the casting mold. The riblets 14 are not damaged or destroyed during the demolding process. Component 1 can be manufactured in large quantities at low cost. In order to successfully fill the riblet shape of the mold part 17 with the casting material, suitable process parameters and materials must be selected for injection molding of thermoplastic composite materials, which may also be composed of reinforcing fibers. It is advantageous to use a material with good flow properties and to heat the mold surface well in the area of ​​the riblets 14. The pressure holding time needs to be relatively long and the holding pressure needs to be relatively high. In particular, it is advantageous if the mold areas forming the riblets 14 can be at least partially tempered to a temperature at least 10 K higher than other mold areas not forming the riblets 14 .

[0039] The demolding direction 12 shown in FIG. 3 is understood as a projection onto the plane shown. Therefore, the actual three-dimensional release direction may also have a component perpendicular to the illustrated plane. However, this component perpendicular to the plane of the drawing is parallel to the longitudinal direction of the riblets 14. In this regard, this directional component of the demolding direction perpendicular to the illustrated plane is irrelevant to the occurrence of undercuts. A special configuration of the riblet 14, in particular the asymmetrical design of the two side walls 18 of the riblet 14, which ensures undercut-free release, is particularly necessary in the region of the riblet 14 on the flow surface 13 of the fluid element 1 when the angle between the release direction 12 projected onto the plane shown in Figure 3 and the local wall perpendicular to the base surface 23 exceeds 20°, in particular when it exceeds 45°, in other words when the projected release direction is not parallel to the local wall perpendicular to the base region 23. This is the case when a large portion of the flow guiding surface 13 of the fluid element 1 is provided with riblets 14, for example more than 25% or even more than 50% of the flow surface 13.

[0040] FIG. 4 shows a plan view of the radial fan impeller 19 as seen from the inlet side, together with a schematic of the path of the riblets 14 on the air guide surface 13. The impeller 19 in this embodiment is of radial design and includes, among other things, a hub ring 21 (also called a base plate in the case of radial impellers), a cover ring 16, and blades 22 extending therebetween.

[0041] During operation of the radial fan, the impeller 19 rotates about its central axis of symmetry, thereby transporting the transport medium in a transport direction from the inlet edge 27 to the outlet edge 28 of the blades 22 (FIG. 5). The conveying medium enters the impeller 19 through a central opening in the cover ring 16 and is conveyed radially outward. In either case, the impeller 19 is the fluid element 1 of the fluid machine (in this case, a fan). The reduction in wall shear stress due to the riblets 14 on the flow surface 13 reduces the required driving torque and / or increases the delivered flow rate, thus improving efficiency. This also reduces noise during operation. In the exemplary embodiment, riblets 14 are shown schematically on the various flow guide surfaces 13 by way of example.

[0042] figure 4 , only the directional paths of a few riblets 14 are shown. In reality, a number of riblets 14 extend on the flow surface 13 at short intervals from each other. The flow surface 13 is shown here as an example being the visible outer surface of the cover ring 16 . On this outer surface, the relative flow velocity is generally circumferential, so the riblets 14 also extend circumferentially. The relative release direction of the mold parts that releases the outer side of the cover ring 16 from the mold is typically approximately perpendicular to the plane of the drawing. Due to the three-dimensional shape of the covering 16, the release direction is not always perpendicular to the outer base area of ​​the covering 16. Also, as shown in FIG. 4, in the present invention, the riblets 14 are designed to avoid undercuts if necessary. The inner surface of the hub ring 21 seen in Figure 4 is also provided with riblets 14, this surface also being a flow surface 13, the riblets 14 being oriented in the relative flow direction expected there.

[0043] The hub ring 21 or its base region is also usually not flat and not parallel to the plane shown, but is designed, for example, as a conical body of revolution. Therefore, again, the expected demold direction of the mold parts is often neither perpendicular to the flow base region nor parallel to the path of the riblets 14. Therefore, the geometric design of the riblets 14 is adjusted according to the description of FIG. 4 to avoid undercuts. The situation is almost similar when riblets 14 are designed on the flow surface 13 of the vane 22 .

[0044] It is not necessary to provide riblets 14 on all air guide surfaces 13 of the component 1 . Depending on the effect of local wall friction, some air guide surfaces 13 may be provided with riblets 14 only partially, or may not be provided with riblets 14 at all. The design of the riblets 14 depends on the release direction of the mold parts relative to the flow surface 13 of the component 1 and the longitudinal direction of the placement of the riblets 14. If there is no need to locally redesign the riblets 14 for undercut-free demolding, it is of course advantageous to omit this.

[0045] For the sake of completeness, it should be mentioned here that embodiments of the axial fan impeller with a circumferential covering are also conceivable. In this case, the cover ring connects the radially outer blade tips together in the circumferential direction. It is also advantageous to attach riblets to such a covering.

[0046] FIG. 5 shows a plan view, seen from the downstream side, of an impeller 19 as a fluid element 1 of a radial fan similar to the radial fan shown in FIG. The outflow edge 28 of the blade 22 can be seen, which is located in the area near the flow outlet during fan operation. Riblets 14 are attached to the outside of the visible hub ring 21, i.e., to the flow face 13. It is advantageous if the hub ring 21 or its base region is not planar. The riblets 14 extend in a substantially circumferential direction on the outer surface of the hub ring 21 . The riblets 14 are designed to avoid undercutting during the demolding process, as shown in FIG. 4 (the demolding direction of the mold parts relative to the flow surface 13 formed by the outer surface of the hub ring 21 is approximately perpendicular to the plane of the illustration towards the viewer).

[0047] The impeller 19 is the component that rotates and transmits power during operation. By reducing the wall shear stress in the circumferential direction of the impeller 19, torque loss can be reduced. In a fluid machine that transmits power from an impeller to a fluid, the required drive torque, and therefore the required drive force, can be reduced. Furthermore, in a fluid machine that transmits power from a fluid to an impeller, if torque loss is reduced, the effective driving torque transmitted to the impeller and the transmitted driving force can be increased.

[0048] FIG. 6 is a perspective view of the housing 2 of the axial flow fan, seen from the inlet side, together with an outline of the paths of the riblets 14 on the air guide surface 13. The housing 2 is a fixed, non-driven component and wall shear stresses do not contribute to the driving torque or force. However, reduced wall shear stress can contribute to increased transport flow rate, thus improving efficiency and even acoustic performance. In either case, the housing 2 is the fluid element 1 of the fluid machine.

[0049] The housing 2 contains an integral inlet nozzle 9, an outer ring 4 including an impeller extension region (not shown) and a diameter expansion region, within which an integral guide device 15 is located. The guiding device 15 comprises an outer support element 3 a , a circumferential intermediate ring 5 , an inner guiding element 3 and a hub ring 10 . A motor (not shown) with a fan impeller 19 connected thereto can be mounted on the hub ring 10, and a guide device 15 connects the outer ring 4 of the housing 2 to the hub ring 10, thereby holding the motor with its connected impeller 19 against the outer ring 4 which allows the housing 2 to be mounted to a higher-level system.

[0050] In the entire assembled fan (not shown in its entirety), the impeller 19 operates within the housing 2 or within its outer ring 4 on the inlet side of the guide device 15 and is motor-driven to transport the transport medium in the transport direction (generally from left to right). The conveying medium enters the housing 2 at the inlet nozzle 9 and leaves the housing 2 downstream of the guide device 15 . In either case, as shown, there are multiple flow surfaces 13 in the housing 2 . These flow surfaces 13 include the inner surface of the inlet nozzle 9 , the surfaces of the outer support element 3 a , the inner guide element 3 , the intermediate ring 5 and the hub ring 10 . By fitting all of these surfaces with riblets 14 of appropriate geometric shape, wall friction and therefore fluid losses can be minimized, contributing to improved efficiency and reduced noise.

[0051] The riblets 14 are designed as shown in FIG. 4, where their cross sections are adjusted as required to ensure undercut-free demolding. Although the diagram of FIG. 6 illustrates several riblet 14 paths, the longitudinal path of the riblets 14 is advantageously always selected to be approximately parallel to the local relative flow velocity with respect to the flow surface 13. In this example for fluid elements 1, 2, which correspond to the components shown in Figure 1, the relative demolding direction of the mould parts is oriented mainly parallel to the central axis of the components.

[0052] For the sake of completeness, it should be mentioned that the riblets 14 on the inner contour of the inlet nozzle 9 do not have any circumferential component in the longitudinal direction corresponding to the expected flow direction on the corresponding flow surface 13. Therefore, when the housing 2 is demolded in a demolding direction parallel to the housing axis, it is possible and advantageous to form a riblet cross-section that is symmetrical with respect to the local wall normal without causing undercuts. This is because, as shown in Figure 4, in a cross section in a plane perpendicular to the longitudinal direction of the riblet 14 and perpendicular to the local base region of the flow surface 13, no undercut occurs between the (projected) release direction and the riblet 14.

[0053] It is advantageous for component 1, in other words fluid element 1, to have a symmetrical riblet cross section with respect to the local wall normal as viewed in cross section to the extent possible when the demolding direction is one in which no local undercuts occur, while having an asymmetrical riblet cross section while maintaining an effective riblet cross section when the demolding direction requires an asymmetrical riblet cross section to ensure demolding without undercuts.

[0054] Various other configurations are conceivable for the fluid element 1 of the fluid machine, and it is advantageous to provide these components with riblets in the above-described manner. In particular, the spiral housing of a radial or mixed-flow fan can be provided with riblets in its flow-guiding inner shape, which in cross section have the aforementioned geometric shape, and which are advantageously oriented approximately in the circumferential direction of the impeller. The riblets are incorporated into the component during manufacturing in a single casting operation, allowing the component to be produced cost-effectively in mass production.

[0055] For further advantageous designs of the fluid machine according to the invention, reference is made to the general part of the description and the appended claims, in order to avoid repetition.

[0056] Finally, the above-described embodiments of fluid machinery according to the present invention are intended only to illustrate the claimed teachings and are not intended to limit the claimed teachings to the embodiments. [Explanation of symbols]

[0057] 1, 1a...fluid element 2. Housing 3 Guide elements, guide vanes 3a...Support element 4. Outer ring of housing 5. Intermediate ring of guide device 6...outer flow area 7...Inner flow area 8. Receptive area within the hub ring 9. Inlet nozzle 10. Hub ring of guide device 11. Inner shape of housing 12, 12a....Release direction of mold part relative to component 13, 13a: Air guide surface, flow surface 14, 14a Libretto 15 Guiding device 16 Circumferential covering of impeller 17, 17a...Molding die parts 18, 18a: Riblet side wall 19 Impeller 20, 20a: Outer edge of riblet 21 Impeller hub ring 22 Impeller blades 23 Base region of air guide surface 24, 24a Head of the libretto 25 Outlet rim of housing 26 Fan shaft 27 ...Inflow side edge 28 Outflow side edge 29 Inner edge of the transition between the riblet and the base region

Claims

1. A fluid machine, in particular a turbomachine, preferably a fan, having a component for guiding a fluid medium, such as an impeller blade, guide vane, hub ring, cover ring, base plate, nozzle or housing part / element, 1. A fluid machine, wherein the component that guides the fluid medium is manufactured by casting, preferably by injection molding, from a synthetic material, with riblets formed on and / or in the surface of the component in the area around which the flow occurs.

2. 2. The fluid machinery according to claim 1, wherein the riblets are formed in an area of ​​each of the components where flow loss and / or noise generation is large.

3. 2. A fluid machinery according to claim 1, characterized in that the riblets are formed as elongated, preferably raised structures, substantially parallel to the direction of flow over the riblets.

4. 2. The fluid machinery according to claim 1, wherein the riblets are formed in a straight or curved shape.

5. a plurality of riblets arranged linearly adjacent to one another in a manner appropriate for the particular component; 2. A fluid machine according to claim 1, characterized in that the arrangement of at least two riblets is arranged at least for the most part parallel to one another, preferably equidistant from one another.

6. 6. The fluid machinery according to claim 5, wherein the riblets are formed in the shape of a circular arc, an involute curve or other curve in a manner suitable for the particular component, and are arranged adjacent to and parallel to one another.

7. 2. A fluid machine according to claim 1, characterized in that the riblets are designed in such a way that they are entirely or at least largely free of undercuts in the direction of mold release and advantageously have a draft angle of at least 1°, advantageously at least 3°.

8. A fluid machinery as described in claim 7, characterized in that the riblets, viewed locally in cross section, particularly with respect to the side walls, are asymmetric with respect to a local normal on the face of the component that is not parallel to the demolding direction.

9. The component including the riblets is releasable in one piece; 2. A fluid machinery according to claim 1, characterized in that there is no undercut in the casting mold.

10. 2. A fluid machinery according to claim 1, characterized in that the riblet area is made of a fiber-reinforced thermoplastic synthetic material.

11. 11. A method for manufacturing a component for guiding a fluid medium, at least partially having riblets, for a fluid machine according to claim 1, characterized in that the method uses a casting technique, in particular an injection molding technique, using a molding die in which the concave and convex shapes of the riblets are formed.

12. 12. A method according to claim 11, characterized in that the surface of the forming tool on which the concave and convex curves of the riblets are formed is surface treated, in particular polished or honed, to have a low roughness and roughness depth, in particular a roughness depth of less than 10 μm, preferably less than 4 μm.

13. 12. A manufacturing method according to claim 11, characterized in that the relief shape of the riblets is introduced into the forming tool, in particular into a forming tool that is already in operation, afterwards.

14. 12. A method according to claim 11, characterized in that individual areas on the surface of the mould which form the riblets are tempered to a higher temperature, preferably at least 10 K higher, than other areas which do not form the riblets during production.

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