Aerodynamic surface structure for outer skin regions of an aircraft, corresponding method and use

Abstract

The invention relates to an aerodynamic surface structure for an outer skin region (4) affected by a turbulent air flow, in particular for an outer skin region (4) of an aircraft (100), comprising a microstructured layer (6) which is configured to reduce the frictional resistance of the outer skin region (4) to which the aerodynamic surface structure (2) is attached in a turbulent air flow, wherein the microstructured layer (6) comprises a forward edge (8) facing the direction (dF) of the air flow. According to the invention, a leading edge portion (10) is proposed which is arranged adjacent to the forward edge (8), wherein the leading edge portion (10) comprises a flow guide surface (12) facing the direction (dF) of the air flow, wherein the flow guide surface (12) is configured to guide the air flow over the forward edge (8) and towards the microstructured layer (6). The microstructured layer (6) can comprise a small rib structure (14).

Description

[0001] The present invention relates to an aerodynamic surface structure for an outer skin region affected by turbulent airflow, particularly for an outer skin region of an aircraft, the aerodynamic surface structure comprising a microstructured layer configured to reduce the frictional drag of the outer skin region to which the aerodynamic surface structure is attached in turbulent airflow, wherein the microstructured layer includes a forward edge facing the airflow direction.

[0002] Aerodynamic surface structures can be used in various embodiments and applications. By utilizing microstructured layers, the wall shear stress in the outer skin region around which airflow passes can be reduced. These microstructured layers are inspired, for example, by shark skin, and specifically reduce the frictional drag of turbulent airflow.

[0003] When applied to outer skin regions (such as the outer skin of an aircraft), the microstructured layer typically includes a forward edge facing the airflow direction. This forward edge generates aerodynamic pressure drag and negatively impacts airflow around a specific outer skin region. In particular, the airflow is deflected by this edge. This creates separation bubbles before and after the edge. Along with the deceleration of the flow, the pressure in front of this edge increases, leading to increased aerodynamic pressure drag.

[0004] In the prior art, attempts have been made to improve the airflow around such a forward edge, as described, for example, in EP 3323 514 B1. This document proposes an aircraft structure comprising an edge line with a ramp-shaped cross-section. However, this solution is optimized for laminar flow and is therefore unsuitable for microstructured layers constructed to reduce the frictional drag of aerodynamic surface structures affected by non-laminar turbulent airflow.

[0005] Furthermore, WO 2018 / 184635 A1 proposes a self-adhesive plastic membrane in which at least some sections of the membrane boundary have wavy edges in the plane of the membrane. These wavy edges are intended to prevent erosion of the microstructured layer. The purpose of this structure is not to improve the aerodynamic flow around the forward edge of the microstructured layer.

[0006] WO 2014 / 179405 A1 provides methods and systems for applying aerodynamically functional coatings to surfaces. However, the proposed methods are not particularly suitable for microstructured layers that must remain uncoated to ensure the desired aerodynamic functionality can be provided.

[0007] In the prior art, it is also known to protect technical markings or advertising films on aircraft by using so-called edge sealants (which only protect the edges of such technical markings or advertising films) or by applying a clear varnish to the entire surface of the markings or films. However, it has been found that edge sealants do not provide the durability required for use with microstructured layers. Furthermore, clear varnish cannot be used to completely coat the microstructured layer because the beneficial aerodynamic effects of such a layer will be suppressed.

[0008] Because such microstructured layer structures typically have a much longer lifespan than advertising films or a much larger surface area than technical markers, known solutions cannot be utilized.

[0009] In view of the above, there is still a need for an effective means to reduce the aerodynamic drag associated with the forward edge of the microstructured layer. Therefore, the object of the present invention is to reduce the drag associated with the forward edge of the microstructured layer and improve the aerodynamic characteristics of the aerodynamic surface structure when subjected to turbulent airflow.

[0010] The present invention achieves the above objective by proposing a leading edge portion arranged adjacent to the forward edge, wherein the leading edge portion includes a guide surface facing the airflow direction, wherein the guide surface is configured to guide the airflow above the forward edge and toward the microstructured layer.

[0011] By utilizing the leading edge portion of a guide surface, which includes a guide surface above the leading edge and directs airflow toward the microstructured layer, the aerodynamic characteristics of the aerodynamic surface structure can be improved, and thus the pressure drag associated with the leading edge can be reduced. Furthermore, it has been found that applying a leading edge portion with a guide surface not only improves aerodynamic characteristics but also enhances the durability of the microstructured layer. Additionally, it has been found that the guide surface can also be used to provide UV protection, thereby increasing the lifetime of the microstructured layer and thus the lifetime of the aerodynamic surface structure itself.

[0012] Furthermore, it has been found that leading-edge portions with guide surfaces are beneficial in terms of erosion protection. On one hand, ballistic particles are prevented from impacting the leading edge of the microstructured layer, instead being captured by the leading-edge portion. Additionally, by improving aerodynamic properties, particles contained in the airflow (such as dust or ice) can also be deflected—at least partially—along with the turbulent airflow surrounding the leading-edge portion, preventing them from impacting the leading edge or the microstructured layer itself. As another advantage, it has been found that leading-edge portions including guide surfaces also provide chemical protection for the microstructured layer, such as de-icing fluids and hydraulic fluids that would otherwise directly affect the microstructured layer or the area between the outer skin region of the aircraft and the microstructured layer.

[0013] Compared to solutions based on monolithic coatings of aerodynamic surface structures, the proposed solution has the advantage that the microstructured layer itself is either not covered or only partially covered. Therefore, the proposed solution preserves the beneficial aerodynamic properties of the microstructured layer.

[0014] In this specification, the term aerodynamic surface structure refers to a structure that can be applied to an outer skin region affected by turbulent airflow. For example, the outer skin region may be the outer skin region of an aircraft. Aerodynamic surface structures can have variable dimensions and may comprise only a few square centimeters or 1 square meter or more. Aerodynamic surface structures can be layers, particularly on the outer skin of an aircraft.

[0015] The term "microstructured layer" refers to a layer comprising microstructures with specific aerodynamic effects, i.e., a microstructured layer configured to reduce the frictional drag of aerodynamic surface structures in turbulent airflow. In this regard, a microstructured layer may include ribs or other surface elements.

[0016] The term "forward edge" refers to the edge facing the direction of airflow. In the case of aircraft, the forward edge typically faces forward of the aircraft.

[0017] The leading edge portion is arranged adjacent to the forward edge. This means that the leading edge portion directly contacts the forward edge, or there may be a gap between the leading edge portion and the forward edge. The leading edge portion, as the first part of the aerodynamic surface structure, interacts with the airflow. In other words, the leading edge portion faces the direction of the airflow. Preferably, the optional gap between the leading edge portion and the forward edge has a width of 10 mm or less. In one embodiment, the gap has a width greater than 10 mm.

[0018] In one embodiment, a gap may exist between the forward edge of the microstructured layer and the guide surface. It has been found that, although such a gap may optionally exist, beneficial aerodynamic properties of the aerodynamic surface structure can be achieved at least partially.

[0019] In one embodiment, the microstructured layer comprises or is composed of a foil layer. By providing a microstructured layer in the form of a foil layer, aerodynamic surface structures can be conveniently applied to the outer skin region of an aircraft or other outer skin regions affected by turbulent airflow. Furthermore, such aerodynamic surface structures can be provided as a retrofit solution for aircraft and other vehicles.

[0020] In one embodiment, the foil layer comprises or consists of hot-embossed foil and extruded foil.

[0021] According to one embodiment, the foil layer may include a functional coating layer, wherein the functional coating layer includes a microstructured surface. This solution has been found to be easy to manufacture and, on the other hand, provides a limited weight per unit surface area, making such foils suitable for use as outer skins of aircraft. The functional coating layer may be a UV-crosslinkable coating layer.

[0022] Preferably, the foil layer includes a backing layer, and wherein the backing layer is attached to the functional paint layer. In one embodiment, the backing layer is made of a thermoplastic material. The thermoplastic material may be selected from the group consisting of: poly(methyl methacrylate), poly(butyl methacrylate), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyvinylidene fluoride, polyvinyl chloride, polyesters (including polycarbonate and polyvinyl acetate, preferably polyesters such as PBT and PET), polyamides, polyolefins (such as polyethylene, polypropylene, polystyrene, and also polybutadiene), polyacrylonitrile, polyacetal, polyacrylonitrile ethylene-propylene-diene-styrene copolymer (A-EPDM), polyimide (PI), polyetherimide (PEI), cellulose triacetate (TAC), phenolic resins, urea resins, melamine resins, alkyd resins, epoxy resins, polyurethanes (including thermoplastic polyurethane (TPU)), polyetherketones, polyphenylene sulfide, polyethers, polyvinyl alcohol, and mixtures thereof. Particularly preferred substrates or layers on their surface are polyolefins, such as PP (polypropylene), which may alternatively be isotactic, syndiotactic, or atactic, and may alternatively be unoriented or oriented by uniaxial or biaxial stretching; SAN (styrene-acrylonitrile copolymer); PC (polycarbonate); PMMA (polymethyl methacrylate); PBT (polybutylene terephthalate); PA (polyamide); ASA (acrylonitrile-styrene-acrylate copolymer); and ABS (acrylonitrile-butadiene-styrene copolymer); and physical mixtures thereof (blends). Particularly preferred are PP, SAN, ABS, ASA, and blends of ABS or ASA with PA, PBT, or PC. Especially preferred are PET, PBT, PP, PE, and polymethyl methacrylate (PMMA) or impact-modified PMMA.

[0023] According to one embodiment, the microstructured surface includes a riblet structure having ribs oriented along the direction of airflow. This riblet structure is inspired by shark skin and consists of ribs oriented along the airflow direction. This structure typically reduces the frictional drag of turbulence by up to 10%. This reduction is primarily achieved by separating eddies (a characteristic feature of turbulence) from the surface. This separation prevents crossflow that generates losses and reduces the interaction between the wall and the flow. For the riblet to function, the flow must be attached to the surface; the separated flow prevents the riblet from functioning. Therefore, the aforementioned separated bubbles behind the step not only generate pressure losses but also reduce the functionality of the microstructured layer of the present invention.

[0024] In one embodiment, the ribs extend across the entire microstructured layer. In an alternative embodiment, the ribs extend only across a portion of the microstructured layer. In particular, regions including ribs may alternate with regions not including ribs. Since small rib structures are known to increase the frictional resistance of laminar flow, such regions are preferably not equipped with small rib structures.

[0025] In one embodiment, an adhesive layer is disposed between the functional paint layer and the backing layer. Preferably, the backing layer is attached to the outer skin region by means of an adhesive. According to an alternative embodiment, the backing layer may include a microstructured layer. In one embodiment, the foil layer includes an adhesive layer configured to attach the foil layer to the outer surface region. Preferably, the adhesive layer is attached to the backing layer.

[0026] According to one embodiment, the foil layer includes a height from the underside of the adhesive layer to the upper side of the functional coating layer, wherein the height is 40-500 micrometers, preferably 45-400 micrometers, more preferably 50-300 micrometers. In one embodiment, the height may be 55-250 micrometers or 60-200 micrometers. It has been found that the aforementioned ranges are advantageous in providing the desired surface properties of the microstructured layer, a durable aerodynamic surface structure, and a favorable weight per unit area, allowing the aerodynamic surface structure to be used, for example, in the outer skin region of an aircraft.

[0027] According to one embodiment, the leading edge portion includes a coating, and said coating forms a guide surface. It has been unexpectedly found that an aerodynamically effective guide surface can be created by utilizing the coating. This is advantageous because such a coating can be readily applied to the microstructured layer. Furthermore, it has been found that the coating also effectively protects the leading edge of the microstructured layer from erosion and effectively deflects particles along with the turbulent airflow around the leading edge. In addition, the coating provides protection against UV radiation and chemical effects from de-icing fluids or hydraulic fluids.

[0028] Preferably, the coating partially covers the microstructured layer. In this way, improved adhesion can be achieved between the coating and the microstructured layer because the coating flows into the valleys of the microstructured layer. On the other hand, the percentage of the microstructured layer covered by the coating is very limited, so that the aerodynamic properties of the microstructured layer are not significantly affected.

[0029] In one embodiment, the coating has a minimum width corresponding to the height of the forward edge in the direction facing the airflow. In another embodiment, the coating has a maximum width of 250 mm, 200 mm, 150 mm, or 100 mm in the direction of airflow. In this way, durable adhesion is achieved between the coating and the microstructured layer, while the coating has a very limited effect on the aerodynamic properties of the microstructured layer.

[0030] Preferably, the coating is applied by at least one of the following methods: roller coating (especially with an application roller), spraying, application with a coating bar, or application with a barrel.

[0031] According to one embodiment, the coating comprises or consists of a coating composition selected from or composed of the following: radiation-curable coating compositions, physically cured coating compositions, chemically cured coating compositions, melts, and mixtures thereof.

[0032] The coating composition is preferably a liquid or a highly viscous composition. This allows for the effective filling of depressions and protrusions on structured surfaces, thereby reducing unwanted air inclusions.

[0033] If the coating composition is a radiation-curable, physically-curable, or chemically-curable coating composition, then the coating composition preferably has a strength of 1 to 500,000 mPa at 23°C. s, more preferably 25 to 100,000 mPa s, or even more preferably 50 to 50,000 mPa s, especially 80 to 9,000 mPa s. Particularly preferred 90 to 3,000 mPa s, especially 100 to 2,000 mPa The viscosity of s, as determined according to DIN 53019-1:2008-09, DIN 53019-2:2001-02, DIN 53019-3:2008-09 and DIN 53019-4:2016-10.

[0034] If the coating composition is a melt, such as a TPU melt, the coating composition preferably has a glass transition temperature of 20°C to -60°C, more preferably 0°C to -45°C, which is determined by dynamic scanning calorimetry (DSC) at a heating rate of 10 K / min according to DIN EN ISO 11357-2:2014-07.

[0035] In one embodiment, the coating composition comprises aircraft paint. Preferably, aircraft paint already certified for the corresponding aircraft type or series is used. By utilizing paint already certified for aircraft, complex recertification can be avoided. Furthermore, chemical compatibility between the paints is ensured.

[0036] According to one embodiment, the leading edge portion further includes a membrane, particularly wherein the membrane is at least partially attached to the outer skin region, and wherein a coating partially covers the membrane and the microstructured layer. The membrane can be used to provide a guide surface for the leading edge portion. Alternatively, the membrane and coating together can form a guide surface. It has been found that the application of the membrane has beneficial aerodynamic properties by establishing a guide surface to direct airflow above the leading edge and toward the microstructured layer.

[0037] According to one embodiment, the membrane is a first membrane, and the guiding surface includes a second membrane disposed on the first membrane, wherein the first and second membranes are arranged in an alternating manner toward the airflow direction. By providing the membranes in an alternating manner, a guiding surface is established that guides the airflow above the forward edge and toward the microstructured layer.

[0038] Preferably, the first and second films overlap with the microstructured layer. This also allows for the permanent attachment of the films to the microstructured layer. In one embodiment, an adhesion promoter is applied to the overlapping area where the first or second film overlaps with the microstructured layer. In another embodiment, the adhesion promoter penetrates into the valleys between the ribs of the microstructured layer, such as the surface of the small ribs, to improve adhesion to the microstructured layer.

[0039] The flow guide surface and the microstructured layer each have a corresponding height perpendicular to the outer skin region. In particular, the height is measured from the outer skin region and may involve a backing layer or an adhesive layer. In one embodiment, the height of the microstructured layer exceeds the height of the flow guide surface, particularly exceeding 500 micrometers, preferably 200 micrometers, more preferably 150 micrometers, or even more preferably 120 micrometers, 100 micrometers, or 75 micrometers or less.

[0040] According to alternative embodiments, the height of the guiding surface exceeds the height of the microstructured layer, particularly exceeding 300 micrometers, preferably 200 micrometers, more preferably 100 or 75 micrometers or less.

[0041] According to one embodiment, the height of the guide surface can be substantially equal to the height of the microstructured layer. In one embodiment, the height of the guide surface can be less than the height of the microstructured layer, but exceeds the height of the ribbed undercoat, particularly by 10 micrometers, 20 micrometers, 30 micrometers, 40 micrometers, or 60 micrometers. Alternatively, the microstructured layer can exceed the height of the ribbed undercoat by 10%, 25%, 50%, 75%, or 90% of the total height of the ribbed.

[0042] Surprisingly, it has been found that beneficial aerodynamic properties can be achieved even when the height of the guide surface and the height of the microstructured layer differ within the mentioned range. In other words, turbulent airflow can overcome these differences without significantly negatively impacting the flow characteristics.

[0043] The present invention has been described to date with respect to aerodynamic surface structures. In another aspect, the present invention relates to an aircraft comprising an outer skin region and an aerodynamic surface structure attached to the outer skin region. The aircraft achieves the object of the invention in such a manner that the aerodynamic surface structure is constructed according to any of the foregoing embodiments. The aircraft utilizes the same benefits and preferred embodiments as the aerodynamic surface structure, and vice versa. In this regard, to avoid unnecessary repetition, please refer to the above explanation.

[0044] In one embodiment, an aerodynamic surface structure is attached to an outer skin region of an aircraft affected by turbulent airflow. Specifically, the outer skin region may include a surface that widens perpendicular to the airflow direction. In addition to the aerodynamic challenges associated with such an outer skin region, surfaces that widen perpendicular to the airflow direction have been found to be susceptible to erosion, particularly high erosion. By utilizing the aerodynamic surface structure according to the invention, not only can aerodynamic properties be improved, but the impact of erosion on the forward edges of the microstructured surface can also be reduced.

[0045] Preferably, the aerodynamic surface structure is attached to the underside of the aircraft fuselage and / or the forward fuselage and / or the wings and / or the stabilizers and / or the engine nacelles. For example, the aerodynamic surface structure can be attached to the center wing fairing, also known as the belly fairing. Preferably, the aerodynamic surface structure is attached to the outer skin region affected by high wall shear stress. It has been found that even when the aerodynamic surface structure is affected by erosion, high durability of the microstructured layer can be achieved by utilizing the aerodynamic surface structure according to the invention.

[0046] In another aspect, the present invention relates to a method for applying an aerodynamic surface structure according to one of the foregoing embodiments to an outer skin region. The method includes the steps of: attaching a microstructured layer to an outer skin region of an aircraft, the microstructured layer being configured to reduce frictional drag on the outer skin region to which the aerodynamic surface structure is attached in turbulent airflow, wherein the microstructured layer includes a forward edge facing the airflow direction; and attaching a leading edge portion adjacent to the forward edge to the outer skin region, wherein the leading edge portion includes a guide surface facing the airflow direction, wherein the guide surface is configured to guide the airflow above the forward edge and toward the microstructured layer.

[0047] According to one embodiment, the leading edge portion includes a coating, and said coating forms a guide surface. Preferably, the coating is applied by at least one of the following: roller coating (especially with an application roller), spraying, application with a coating bar, or application with a barrel.

[0048] This method utilizes the same benefits and preferred embodiments as the aerodynamic surface structures and aircraft according to the present invention, and vice versa. In this regard, to avoid unnecessary repetition, please refer to the explanation above.

[0049] In another aspect, the present invention relates to the use of the aerodynamic surface structure according to any one of the foregoing embodiments for at least one of the following: aircraft; turbines, such as gas turbines, hydraulic turbines or wind turbines, particularly the rotors of said turbines; land vehicles, particularly automobiles, trucks or trains; marine vehicles, particularly ships or vessels; pipelines, such as water pipelines, natural gas pipelines or oil pipelines.

[0050] The aerodynamic surface structures according to the invention have been found to be advantageous for the stated applications. They share the common feature of including an outer skin region affected by turbulent airflow. Therefore, the aerodynamic surface structures according to the invention can be advantageously used to reduce the frictional drag of the aerodynamic surface structure in turbulent airflow, while on the other hand, the aerodynamic flow conditions around the forward edge of the microstructured layer are also improved.

[0051] The application of this aerodynamic surface structure utilizes the same benefits and preferred embodiments as those of the aerodynamic surface structure, and vice versa. In this regard, to avoid unnecessary repetition, please refer to the explanation above.

[0052] To gain a more complete understanding of the invention, it will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered to be the preferred embodiment of the invention. It should be understood, of course, that various modifications and changes in form and detail can be readily made without departing from the spirit of the invention. Therefore, the invention is not intended to be limited to the exact forms and details shown and described herein, nor to anything in the whole of the invention disclosed herein and claimed below. Furthermore, the features described in the specification, drawings, and claims disclosing the invention may be associated with the invention individually or in combination. In particular, any reference numerals in the claims should not be construed as limiting the scope of the invention. The word "comprising" does not exclude other elements or steps. The word "a / an" does not exclude a plural.

[0053] The invention will now be described with reference to the accompanying drawings, which illustrate, by way of example and not limitation, one of several possible embodiments of the apparatus as presented herein, and in the drawings:

[0054] Figures 1a to 1c An embodiment of the aerodynamic surface structure according to the present invention is shown in a cross-sectional view;

[0055] Figure 2 An alternative embodiment of the aerodynamic surface structure according to the invention is shown in a cross-sectional view;

[0056] Figures 3 to 6 An alternative embodiment of the aerodynamic surface structure according to the invention is shown in a cross-sectional view;

[0057] Figure 7a An embodiment of a microstructured layer including small rib structures is shown in perspective view;

[0058] 7b to 7d show, in perspective view, embodiments of the microstructured layer including small rib structures and the flow-guiding surface;

[0059] Figure 8 An embodiment of an aircraft including an aerodynamic surface structure according to the invention is shown in a side view;

[0060] Figure 9 The streamlines around the forward edge of the stepped shape are shown in the simulation.

[0061] Figure 10 The geometry of a simulated leading edge portion arranged adjacent to the forward edge of an aerodynamic surface structure is shown.

[0062] Figures 11 to 17 Simulation results for pressure drag with different leading-edge geometries and heights are shown;

[0063] Figure 18 An aerodynamic surface structure including a microstructured layer without a leading edge portion is shown;

[0064] Figure 19 , Figure 20 An aerodynamic surface structure according to the invention, including a leading edge portion with a guide surface, is shown.

[0065] Figures 1a to 1c Each example of an aerodynamic surface structure 2 is shown. The aerodynamic surface structure 2 is attached to an outer skin region 4 affected by turbulent airflow. The outer skin region 4 can be the outer skin of an aircraft 100, such as... Figure 8 As shown. The aerodynamic surface structure 2 includes a microstructured layer 6, which is configured to reduce the frictional drag of the aerodynamic surface structure 2 in turbulent airflow. The microstructured layer 6 includes a direction d facing the airflow. F Forward edge 8.

[0066] The aerodynamic surface structure 2 also includes a leading edge portion 10. The leading edge portion 10 is arranged adjacent to the leading edge 8. The leading edge portion 10 includes a guide surface 12. The guide surface 12 faces the direction d of the airflow. F The guide surface 12 is configured to guide airflow above the forward edge 8 and toward the microstructured layer 6. The microstructured layer 6 includes a microstructured surface 14 in the form of a small rib structure 14 having a d-shape along the airflow direction. F The directional rib 16 is also shown in Figure 7.

[0067] Ribs 16 can extend over the entire microstructured layer 6, such as Figures 1a to 1c As shown. Alternatively, the ribs may extend only on a portion of the microstructured layer 6.

[0068] The microstructured layer 6 includes or is composed of a foil layer 18. The foil layer 18 includes a functional coating layer 38, and wherein the functional coating layer 38 includes a microstructured surface 14. The microstructured surface 14 includes a small rib structure 14 having a rib structure d along the airflow direction. F Directional ribs 16.

[0069] In addition, the foil layer 18 includes a backing layer 30. The backing layer 30 is attached to the functional coating layer 38. An adhesive layer 34 is attached to the backing layer 30, and the foil layer 18 includes a height H from the underside of the adhesive layer 34 to the upper side of the functional coating layer 38.

[0070] like Figures 1a to 1c As shown, the leading edge portion 10 includes a coating 20. The coating 20 forms a guide surface 12. The coating 20 partially covers the microstructured layer 6. In this respect, the coating is positioned in the direction of airflow d... FThe coating 20 has a maximum width w. It can be applied by roller coating (especially with an application roller), spraying, application with a coating bar, or by a barrel application. In the embodiment of Figure 1, the guide surface 12 is provided solely by the coating 20.

[0071] The guide surface 12 and therefore the coating 20 include a corresponding height H f .exist Figure 1a In the embodiment, height H f The height H exceeds the foil layer by 18. Figure 1b In the embodiment, the height H of the guide surface 12 f It is equal to or substantially equal to the height H of the foil layer 18. Figure 1c In the embodiment, the height H of the guide surface 12 f The height H is less than that of the foil layer 18, but exceeds the height of the adhesive layer 34, the backing layer 30, and the small rib paint underlayer 32.

[0072] exist Figure 2 In one embodiment, the leading edge portion 10 further includes a membrane 22. The membrane 22 provides a guiding surface 12. The membrane is at least partially attached to the outer skin region 4. Figure 2 In this embodiment, membrane 22 is attached adjacent to the forward edge 8. Aside from these differences, Figure 2 The aerodynamic surface structure 2 shown is similar to Figures 1a to 1c The aerodynamic surface structure shown.

[0073] exist Figure 3 In one embodiment, the leading edge portion 10 includes a membrane 22. The membrane 22, together with the coating 20, provides a guiding surface 12. The membrane is at least partially attached to the outer skin region 4. Figure 3 In this embodiment, the membrane 22 is attached adjacent to the forward edge 8. The transition region between the membrane 22 and the forward edge 8 is covered by the coating 20. Apart from these differences, Figure 3 The aerodynamic surface structure 2 shown is similar to Figures 1a to 1c The aerodynamic surface structure is shown. The membrane 22 may include a coating (not shown) on its leading edge.

[0074] Figure 4 An alternative embodiment of aerodynamic surface structure 2 is shown. Figure 4 In this embodiment, no coating is provided. Instead, membrane 22 is a first membrane 22, and the flow guiding surface 12 includes a second membrane 24. The second membrane 24 is disposed on the first membrane 22. The first membrane 22 and the second membrane 24 are arranged in an alternating manner 26 toward the airflow direction, thereby providing the flow guiding surface 12. Figure 4 As can be seen, the guide surface 12 includes the corresponding height H f The microstructured layer 6 includes a height H that begins perpendicular to the outer skin region 4. These two heights H...f Both H are measured from the outer skin region 4 to the upper limit of the corresponding structure.

[0075] Figure 5 Another embodiment of the aerodynamic surface structure 2 is shown. In this embodiment, only a membrane 22 is provided. The membrane 22 overlaps with the microstructured layer 6. Further, an adhesion promoter 28 is applied to the overlap region 36 where the membrane 22 and the microstructured layer 6 overlap. A coating 20 may be provided near the forward edge and below the membrane 22.

[0076] like Figure 6 As shown, a first membrane 22 and a second membrane 24 can be used, wherein these membranes are at least partially disposed on each other. In this embodiment, the second membrane 24 overlaps with the microstructured layer 6. An adhesion promoter 28 is applied to the overlap region 36 where the second membrane 24 overlaps with the microstructured layer 6. A coating 20 may be provided near the forward edge and between the first membrane 22 and the second membrane 24.

[0077] Figure 7a An embodiment of the microstructured layer 6 is shown. The microstructured layer 6 includes a microstructured surface 14 in the form of a small rib structure 14. The small rib structure 14 includes a rib structure along the airflow direction d. F Oriented ribs 16. Furthermore, it can be seen that the microstructured layer 6 includes airflow-oriented d... F Forward edge 8.

[0078] Figure 7b An alternative embodiment of the microstructured layer 6 is shown. The microstructured layer 6 includes a microstructured surface 14 in the form of a small rib structure 14. The small rib structure 14 includes a rib along the flow direction d. F Oriented ribs 16. Ribs 16 are arranged on the paint base layer 32. Furthermore, it can be seen that the microstructured layer 6 includes flow-oriented d... F The leading edge 8. Further, a leading edge portion 10 is shown. The leading edge portion 10 is arranged adjacent to the leading edge 8. The leading edge portion 10 includes a guide surface 12. The guide surface 12 faces the flow direction d. F The flow guide surface 12 is configured to guide flow above the leading edge 8 and toward the microstructured layer 6. The leading edge portion 10 includes a coating 20. The coating 20 forms the flow guide surface 12. The flow guide surface 12 and therefore the coating 20 include a corresponding height H. f .exist Figure 7b In the embodiment, the height H of the guide surface 12 f The height H exceeds the rib by 16.

[0079] Figure 7c and Figure 7d The illustrated embodiments are similar to Figure 7b The illustrated embodiment. However, in Figure 7cIn the embodiment, the height H of the guide surface 12 f The height H is less than rib 16, but exceeds the height of the paint base layer 32. In Figure 7d In the embodiment, the height H of the guide surface 12 f It is basically equal to the height of the base coat of paint (32).

[0080] Figure 8 An example of an aircraft 100 is shown. The aircraft 100 includes an outer skin region 4 and an aerodynamic surface structure 2 attached to the outer skin region 4. The aerodynamic surface structure 2 can be as shown with respect to Figures 1 to 100. Figure 5 Constructed as described. Specifically, the aerodynamic surface structure 2 is attached to the outer skin region 4, which is affected by turbulent airflow. The outer skin region 4 may further include a direction d perpendicular to the airflow. F A widened surface 102. The aerodynamic surface structure 2 can be attached to the outer skin region 4, which is subject to erosion, particularly high erosion. Preferably, the aerodynamic surface structure 2 is attached to the underside of the fuselage of the aircraft 100, such as the center wing fairing. Preferably, the aerodynamic surface structure 2 can also be attached to the outer skin region 4, which is subject to high wall shear stress.

[0081] The following will describe the initial simulations and test results that have been conducted to provide a proof of concept.

[0082] Figures 9 to 17 The simulation parameters and results presented are shown to analyze the effect of the leading edge portion according to the invention on the microstructured layer including the forward edge. For the simulation, the microstructured layer including the forward edge has been simplified to a so-called forward step. This step is well known in fluid mechanics, and the flow around such a step has been well studied.

[0083] like Figure 9 (As shown in the diagram, the streamlines around this step or forward edge 8) deflect the flow. This creates two so-called separation bubbles before and after the step. With the flow slowing down, the pressure in front of the edge increases. This leads to increased pressure on the forward edge, which is the reason for the increased pressure drag at the forward edge. This increased pressure drag, in turn, leads to increased fuel consumption of the aircraft.

[0084] To reduce pressure on the leading edge, the present invention proposes a leading edge portion 10 arranged adjacent to the leading edge 8, wherein the leading edge portion 10 includes, as shown in the figure below. Figure 10 The guide surface 12 is shown. During the simulation, different geometries of the guide surface 12 were simulated, namely S-curves, exponential curves, and bumps. These different shapes may occur depending on how the guide surface 12 is implemented, such as the application method used, the amount of coating material used, and the viscosity of the coating material. Figure 10In the example, the height of the forward edge 8, which is 200 micrometers, is used for simulation. The step width in the direction perpendicular to the flow, df, is 0.01 m.

[0085] For all simulations, ANSYS CFX, version 2022 R2, was used. A block-structured mesh was employed, with quasi-2D flow conditions, a simulation depth of 0.01 m, and symmetric boundary conditions. Furthermore, steady-state calculations were performed. The absolute values ​​of the 0.01 m step depth were obtained in the simulations. While these absolute values ​​may vary depending on the exact depth simulated, the relative values ​​comparing aerodynamic surface structures with and without leading-edge portions including guide vanes remain quasi-constant and independent of the simulation parameter, step depth.

[0086] Group 1 Simulation

[0087] The first set of simulations utilized the altitude of the forward edge 8 at 200 micrometers. Further, under standard conditions provided by the International Standard Atmosphere (ISA), an altitude of 30,000 feet and a flow velocity of Mach 0.5 (151.6 m / s) were used. These boundary conditions represent the local flow conditions in the boundary layer of the aircraft during typical cruise flight.

[0088] exist Figure 11 In the middle, it is shown that for such Figure 10 The four different pressure drag structures shown represent pressure drag cases for steps without a leading edge, S-curve leading edge, exponential leading edge, and bulging leading edge.

[0089] It can be seen that, compared to a stepped geometry, the leading edge portion according to the present invention significantly reduces pressure drag. This reduction is... Figure 12 As shown in the figure, the S-curve leading edge reduces pressure drag by almost 98% compared to a step. For the exponential form of the leading edge, a 97.5% reduction in pressure drag compared to a step was achieved. As a result of simulations, for the bulging form of the leading edge, a pressure drag reduction in the range of 98.5% was obtained.

[0090] In the simulation, it was assumed that the S-curve leading edge and the exponential leading edge were 10 mm wide, meaning they began to extend 10 mm before the step. The raised leading edge was 20 mm wide. It began 10 mm before the step in the direction of flow and ended 10 mm after the step in the direction of flow.

[0091] exist Figure 13 The simulation results for a scenario named "First Membrane" have been added. This scenario is similar to... Figure 2The embodiment of the invention is shown below. For this simulation, it is assumed that the first membrane has a height of 75 micrometers and a width of 10 mm. It has been found that the "first membrane" case results in a reduction in differential drag of approximately 25% compared to the step case. The reduction in differential drag is even greater for the "S-curve," "exponential," and "bulge" cases.

[0092] Second group simulation

[0093] In the second simulation scenario, a larger width of the leading edge portion was analyzed. The height of the leading edge 8 (and therefore the step) was 200 micrometers. Furthermore, an ISA elevation of 30,000 ft was simulated, considering a flow velocity of Mach 0.5.

[0094] The result is that a reduction, or even a greater reduction, in differential pressure drag has been observed, such as... Figure 14 As shown. Compared to the step case, the differential pressure drag is reduced by up to 99% for the case including an exponentially shaped leading edge portion with a width of 250 mm that begins 250 mm before the step.

[0095] Third group simulation

[0096] In the third case, a lower height of the leading edge, 40 micrometers, was simulated. Furthermore, it was assumed that the exponential form of the leading edge portion had a total width of 10 mm and began 10 mm before the leading edge. All other simulation parameters remained unchanged. The results of this simulation run are as follows... Figure 15 As shown, comparing the exponential case with the step case yielded a reduction in pressure drag over a 98% range. This even increased the reduction in pressure drag compared to a 200-micron step, indicating that the effect is also effective for finer steps.

[0097] Group 4 simulation

[0098] In the fourth scenario, a larger height (500 μm) of the leading edge was simulated for both the exponential and bulging scenarios. For the bulging scenario, it was assumed that its height exceeded the leading edge by 500 μm, with a width of 20 mm, starting 10 mm before the step. In the exponential scenario, the leading edge portion had a width of 10 mm, with the leading edge portion starting 10 mm before the step. The results of this simulation run are... Figure 16 As shown in the figure. It can be seen that, for the same situation, a reduction in pressure drag can be obtained compared to the step situation, which is about 95% for the exponential case and 84% for the convex case.

[0099] Group 5 simulation

[0100] In the fifth simulation run, the height of the leading edge was assumed to be 200 micrometers. However, the flow conditions were adjusted to represent takeoff or landing conditions. Therefore, the elevation was lowered to sea level. This means that the elevation according to the international standard atmosphere was 0 feet. Furthermore, a flow velocity of Mach 0.2 (68.1 m / s) was assumed. The step height was 200 micrometers, and it was assumed that the exponential form of the leading edge portion had a width of 10 mm and began 10 mm before the step.

[0101] Simulation results in Figure 17 As shown in the figure, for the sea level case, a reduction in pressure drag was achieved in 97.8% of the range compared to the step case.

[0102] In summary, simulations demonstrate that by utilizing the leading edge portion arranged adjacent to the leading edge according to the invention, significant reductions in pressure drag can be achieved for different forms and variations of the guide surface, as well as for different heights of the leading edge portion and the guide surface. This applies to different heights of the leading edge and under typical aircraft cruise conditions, as well as during approach and departure phases at low altitudes.

[0103] Flight test

[0104] Figure 19 and Figure 20 This demonstrates another beneficial effect that can be achieved through the aerodynamic surface structure according to the invention: protecting the forward edge of the microstructured layer from damage caused by erosion.

[0105] As practical proof of the effectiveness of this type of guide surface, aerodynamic surface structures were studied in areas of aircraft where such aerodynamic effects are severe, as described above. One practical effect of a successful guide surface is a significant reduction in damage to the leading edge in areas with high erosion potential.

[0106] In this regard, the aerodynamic surface structure was tested in flight tests. The aerodynamic surface structure used in all instances was the commercially available Aeroshark small rib film patch, which was obtained from Lufthansa Technik AG and manufactured by BASF SE.

[0107] Aerodynamic surface structures are attached to different areas of the aircraft fuselage and engines. Each aerodynamic surface structure has a size of 20 × 20 cm and a total thickness of 180 micrometers. This results in a leading edge height of approximately 180 micrometers. A coating is used for the leading edge portion. The results of these measures are... Figure 19 and Figure 20 As shown in the image. For Figure 18 In this case, this leading edge portion was not used.

[0108] exist Figure 20 In one example shown, such as Figure 3 The protective film 22 shown is cut from a commercially available graphic foil typically used in aviation, having a full product thickness of approximately 80 micrometers and dimensions of 10 × 20 cm. This means that the height of the front-facing edge of the film is approximately 80 micrometers.

[0109] The coating on components used as air deflectors consists of typical commercially available clear or topcoat coatings approved for use on the exterior of aircraft, as detailed in the Official Aircraft Maintenance Manual (AMM). During testing, the exact same coating material present on the aircraft surface is used to avoid any adhesion or compatibility issues.

[0110] To apply the test patch to the aircraft, the following procedure is followed. First, an aerodynamic surface structure in the form of an Aeroshark ribbed film patch is applied to several locations on the clean surface of the aircraft using the standard foil application method. Subsequently, a protective film patch is applied again using the standard foil application method, as mentioned.

[0111] As a final step, the coating is applied in a liquid state using typical coating application methods. In this example, a coating roller is used. The coating material is then processed and cured as described in the technical data sheet provided with the manufacturer.

[0112] The test patch was observed for 980 flight hours. At the end of the test duration, the percentage of damaged forward edges was calculated by dividing the number of damaged forward edges in cm by the sum of the forward edges (20 cm) and multiplying by 100. The table below shows the results for three different settings (i.e., foil setting 1, setting 2, and setting 3) based on three test areas on the aircraft.

[0113] In setting 2, the test was conducted based on... Figure 1a The aerodynamic surface structure. Tested according to setting 3. Figure 3 An embodiment is described. The protective film has a width of 100 mm. Furthermore, the contact area between the forward edge of the aerodynamic surface structure and the protective film is covered by a coating. The forward edge of the protective film is unprotected. According to comparative example "Foil-Setting 1," an aerodynamic surface structure with a forward edge that does not have the leading edge portion according to the invention is used.

[0114]

[0115] Based on the results shown in the table, for foil without a guide surface - Setting 1, the structure suffers significant erosion in the range of 94%-100%. This means that this aerodynamic surface structure can no longer provide beneficial aerodynamic properties because after 980 hours of flight, a large area of ​​the surface is eroded and damaged.

[0116] For configurations 2 and 3, which include the leading edge portion according to the invention, a significant reduction in erosion effects has been observed. In particular, it has been found that the leading edge of the microstructured layer remained completely undamaged after 980 hours of flight.

[0117] Therefore, it can be concluded that the guide surface according to the invention is also highly effective in protecting the forward edge from erosion, thereby significantly increasing the replacement interval of such components. This is most likely because the guide surface avoids / reduces the frequency of particle impact and because the suction peak (negative pressure) at the edge of the aerodynamic surface structure is reduced, which reduces damage propagation when damage is present.

[0118] List of reference numerals

[0119] 2 Aerodynamic Surface Layer

[0120] 4. Outer skin area

[0121] 6 microstructured layers

[0122] 8 Forward Edge

[0123] 10 Leading edge section

[0124] 12 guide surfaces

[0125] 14 Microstructured Surface / Small Rib Structure

[0126] 16 ribs

[0127] 18 foil layers

[0128] 20 coatings

[0129] 22 First Membrane

[0130] 24 Second membrane

[0131] 26 staggered membrane arrangement

[0132] 28 Adhesion promoters

[0133] 30 backing

[0134] 32 small rib paint base layer

[0135] 34 Adhesive Layers

[0136] 36 overlapping regions

[0137] 38 Functional Coatings

[0138] 100 aircraft

[0139] Surface that widens in the direction of flow 102

[0140] d F direction of airflow

[0141] Height of H foil layer

[0142] H f Height of the guide surface

[0143] w is the coating width.

Claims

1. An aerodynamic surface structure (2) for an outer skin region (4) affected by turbulent airflow, particularly for an outer skin region (4) of an aircraft (100), the aerodynamic surface structure (2) comprising: - A microstructured layer (6) configured to reduce the frictional drag of the outer skin region (4) to which the aerodynamic surface structure (2) is attached in turbulent airflow, wherein the microstructured layer (6) includes a direction facing the airflow (d F The leading edge (8) of the airflow is characterized by a leading edge portion (10) arranged adjacent to the leading edge (8), wherein the leading edge portion (10) includes a direction facing the airflow (d). F The guide surface (12) is configured to guide the airflow above the forward edge (8) and toward the microstructured layer (6).

2. The aerodynamic surface structure (2) according to claim 1. The microstructured layer (6) includes or is composed of a foil layer (18).

3. The aerodynamic surface structure (2) according to claim 2. The foil layer (18) includes a functional coating layer (38), and the functional coating layer (38) includes a microstructured surface (14).

4. The aerodynamic surface structure (2) according to claim 3. The microstructured surface (14) includes small rib structures (14) having a direction (d) along the airflow. F ) directional ribs (16).

5. The aerodynamic surface structure (2) according to claim 3 or 4. The foil layer (18) includes a backing layer (30), and the backing layer (30) is attached to the functional paint layer (38).

6. The aerodynamic surface structure (2) according to claim 5, wherein the adhesive layer (34) is attached to the backing layer (30), and wherein the foil layer (18) includes a height (H) from the lower side of the adhesive layer (34) to the upper side of the functional paint layer (38), wherein the height (H) is 40-500 micrometers, preferably 45-400 micrometers, more preferably 50-300 micrometers.

7. The aerodynamic surface structure (2) according to any one of the preceding claims. The leading edge portion (10) includes a coating (20), and the coating (20) forms the guide surface (12), wherein the coating (20) only partially covers the microstructured layer (6).

8. The aerodynamic surface structure (2) according to claim 7. The coating (20) comprises or consists of a coating composition selected from or composed of the following: Radiation-curable coating compositions, physically cured coating compositions, chemically cured coating compositions, melts and mixtures thereof.

9. The aerodynamic surface structure (2) according to any one of claims 7 or 8. The leading edge portion (10) further includes a membrane (22), wherein the membrane (22) is at least partially attached to the outer skin region (4), and wherein the coating (20) partially covers the membrane (22) and the microstructured layer (6).

10. The aerodynamic surface structure (2) according to claim 9. Wherein the membrane (22) is a first membrane (22), and wherein the guide surface (12) includes a second membrane (24) disposed on the first membrane (22), and wherein the first membrane (22) and the second membrane (24) are aligned in a direction toward the airflow (d F Arranged in an alternating manner (26), Specifically, the first membrane (22) or the second membrane (24) overlaps with the microstructured layer (6).

11. The aerodynamic surface structure (2) according to any one of the preceding claims. The guide surface (12) and the microstructured layer (6) each contain a corresponding height (H) perpendicular to the outer skin region (4). f H). The height (H) of the microstructured layer (6) exceeds the height (H) of the guide surface (12). f (in particular, exceeding 200 micrometers, preferably 150 micrometers, more preferably 120 micrometers, 100 micrometers, or 75 micrometers, or The height (H) of the guide surface (12) f The height (H) of the microstructured layer (6) is greater than 500 micrometers, preferably 300 micrometers, more preferably 200 micrometers, and even more preferably 100 or 75 micrometers.

12. An aircraft (100) comprising an outer skin region (4) and an aerodynamic surface structure (2) attached to the outer skin region (4), wherein the aerodynamic surface structure (2) is constructed according to any one of the preceding claims.

13. The aircraft (100) according to claim 12. The aerodynamic surface structure (2) is attached to the outer skin region (4) affected by turbulent airflow, and in particular, the outer skin region (4) further includes a direction perpendicular to the airflow (d). F ) Widened surface (102).

14. A method for applying an aerodynamic surface structure (2) according to any one of the preceding claims to an outer skin region (4), the method comprising: - A microstructured layer (6) is attached to the outer skin region (4) of the aircraft (100). The microstructured layer is configured to reduce the frictional drag of the outer skin region (4) to which the aerodynamic surface structure (2) is attached in turbulent airflow, wherein the microstructured layer (6) includes a direction facing the airflow (d). F Forward edge (8), - Attach the leading edge portion (10) adjacent to the forward edge (8) to the outer skin region (4). The leading edge portion (10) includes the direction facing the airflow (d) F The guide surface (12) is configured to guide the airflow above the forward edge (8) and toward the microstructured layer (6).

15. The aerodynamic surface structure (2) according to any one of the preceding claims is used for at least one of the following: - Aircraft (100). - Turbines, such as gas turbines, hydro turbines, or wind turbines, especially the rotor of said turbines, -Land transportation, especially cars, trucks, or trains -Maritime vehicles, especially ships or vessels Pipelines, such as water pipelines, natural gas pipelines, and oil pipelines.

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