Method for applying a fluid-dynamically functional film to complex airfoils

Abstract

The invention relates to a method for providing a complex airfoil (1), in particular a commercial aircraft, with a fluid-dynamically effective film (20) having a micro-structured surface. The airfoil (1) has at least one identifiable alignment line (11). The method comprises the following steps: – identifying an optimized surface structure for a continuous surface region (10) of the complex airfoil (1), over which surface region a complex flow passes and which surface region directly adjoins at least one alignment line (11); – producing a fluid-dynamically effective film (20) having at least one edge (21) which is provided for alignment along the at least one alignment line (11) and has a micro-structured surface which corresponds to the identified surface structure when the film (20) is arranged as intended; and – applying the produced film (20) to the complex airfoil (1) in such a way that the edge(s) (21) provided for alignment is / are aligned along the alignment line(s) (11) provided therefor and cover(s) the continuous surface region (10). The invention also relates to a complex airfoil (1) which is accordingly provided with a fluid-dynamically effective film (20), and to a film (20) produced for this purpose.

Description

Method for the application of fluid-dynamic functional film on complex flow bodies

[0001] The invention relates to a method for providing a body subjected to complex flow, in particular a commercial aircraft, with a fluid-dynamically effective film having a microstructured surface. The invention also relates to a body subjected to complex flow, to which a fluid-dynamically effective film is applied, and to a film designed for application to a body subjected to complex flow.

[0002] Fluid-dynamically, particularly aerodynamically functional films are known in various forms and applications from the state of the art and are regularly used to reduce the wall shear stress on the surfaces of bodies subject to flow. For this purpose, the fluid-dynamically functional films generally have a microstructured surface with one or more preferred directions. A preferred direction refers to a preferred overflow direction (i.e., the direction of the local flow on the surface) in which the reduction in wall shear stress is particularly high or even maximum.

[0003] A common microstructure is the so-called riblet structure, with very small ribs that run essentially along the preferred direction. The ribs or riblets can be aligned parallel to one another and run parallel over long distances and with the same geometry in terms of spacing, height, and angle. The ribs can also exhibit periodically changing patterns (so-called 3D riblets). Riblet structures can be found, for example, on the outer surfaces of aircraft, but also on the rotor blades of wind turbines, on the outer skin of ships, or on the outer surfaces of high-speed trains.

[0004] In order to achieve the greatest possible reduction in wall shear stress through riblet structures, it is necessary that the foil is aligned with its preferred direction as precisely as possible or with only minor deviations from the local flow direction - i.e. the direction in which the flow over the surface in the area of ​​the foil is mainly to be expected.

[0005] Riblet structures can be quite easily applied to surfaces of a body with a flow pattern that is relatively uncomplicated and generally nearly uniform, for which the flow direction and thus also the preferred direction are practically inevitable. Examples of such surfaces are the outer skin of high-speed trains, with a flow direction that corresponds to the direction of travel, or the upper surface of aircraft wings or wind turbine blades, where the flow direction generally runs in the profile direction.

[0006] In order to reduce the flow resistance of a body subject to flow as much as possible, it is generally desirable to provide aerodynamically functional foils that reduce wall shear stress even on those surfaces of the body where a more complex flow pattern exists. In commercial aircraft of known configurations, such an area is found, for example, on at least parts of the outer skin of the aircraft fuselage.

[0007] The complex flow pattern in corresponding areas can be easily determined, for example, using suitable simulation. On this basis, a favorable arrangement of riblet foils in this area can then be determined, whereby a large number of smaller areas are regularly identified, in each of which a riblet foil with a predetermined orientation for their preferred direction. This results in a pattern of different riblet foils or areas of riblet foil, each with a different orientation of the preferred direction.

[0008] Although fundamentally possible and advantageous overall in terms of reducing wall shear stress, it has been shown that the application of fluid-dynamically functional films, which have a preferred direction and must be aligned accordingly, is very complex and time-consuming in areas with more complex flow patterns. The fluid-dynamically functional film must be individually cut for each area with its own specified orientation and applied with its preferred direction precisely according to the specified orientation.

[0009] Due to the considerable effort involved in applying fluid-dynamically functional films in areas of complex flow, this application results in significant downtime, for example, for aircraft. The application also requires a significant amount of personnel, particularly to determine and maintain the correct alignment and positioning of the films.

[0010] The object of the present invention is to provide a method, a body with a complex flow around it and a film in which the disadvantages of the prior art no longer occur or only occur to a reduced extent.

[0011] This problem is solved by the subject matter of the independent claims. Advantageous further developments are the subject matter of the dependent claims.

[0012] Accordingly, the invention relates to a method for providing a body with complex flow, in particular a Commercial aircraft , with fluid dynamically effective film with a microstructured surface , wherein the body flowed around has at least one identifiable alignment line , with the steps : - Determination of an optimized surface structure for a coherent complex flow-over surface area of ​​the complex flow-around body immediately adjacent to at least one alignment line; - producing a fluid-dynamically effective film with at least one edge intended for alignment with the at least one alignment line and having a microstructured surface which corresponds to the determined surface structure when the film is properly arranged; and - Attaching the produced film to the body around which the air flows in a complex manner in such a way that the edge(s) intended for alignment are aligned with the respective alignment guide(s) provided for this purpose and cover the contiguous surface area.

[0013] Furthermore, the invention relates to a body with a complex flow around it and having at least one identifiable alignment line, wherein at least one surface area adjacent to the alignment line is provided with a fluid-dynamically functional film using the method according to the invention.

[0014] The invention also relates to a fluid dynamic functional film which is produced according to steps ( a ) and ( b ) of the process according to the invention .

[0015] First, some terms used in connection with the invention will be explained.

[0016] A "body with complex flow" is a body in which, due to the shape of the body, at least in parts of the surface of the body, a complex flow pattern occurs along the surface, even if the body is in a parallel flow.

[0017] A "complex flow pattern" is a flow pattern along a surface section that cannot be reasonably approximated by a parallel flow pattern.

[0018] A "complex flow area" is a clearly defined, arbitrarily shaped part of the surface of a body surrounded by a complex flow, in which a complex flow pattern is present, even in the case of parallel flow.

[0019] The "identifiable alignment lines" can be structural features of the surface of the body, for example edges or gaps in the surface of the body. However, a alignment line can also be identified if only two discrete points on the alignment line are clearly identifiable, which can then be marked on the body, for example, using string lines or adhesive strips. Corresponding points of a alignment line can be formed, for example, by structural features of the body's surface, such as holes, screws, rivets, frames, ribs, etc., or can be determined by measuring based on such structural features.

[0020] According to the invention, in a predetermined area on the surface in which a complex overflow is provided, unlike in the prior art, no partial areas are to be identified in which film sections are arranged with a predetermined orientation, but rather at least one alignment line arranged adjacent to the area in question is to be identified and a film is to be produced which is matched to this at least one alignment line and whose surface is microstructured in such a way that, when correctly arranged along the at least one alignment line, it is directly adapted to the complex flow pattern in the area.

[0021] Because the film is adapted according to the invention to at least one alignment line, the final application of the film is significantly simplified and can be carried out quickly: The film only needs to be applied to the surface of the body around which the air flows, aligned with the at least one alignment line. The surface structure, adapted to the complex flow over the surface area covered by the film, is directly provided by the microstructured surface of the film. A complex alignment of individual partial films, as is known from the prior art, is no longer required.

[0022] In order to produce and apply a corresponding film, the first step of the method according to the invention involves determining an optimized surface structure for a generally predetermined surface area. This surface area is a partial surface of the body subjected to complex flow, which is characterized by, or must be selected accordingly, directly bordering at least one alignment line.

[0023] To actually determine the optimized surface structure in the surface area, as a rule, or at least preferably, the complex flow over it is first determined, on the basis of which a suitable surface structure can then be determined. The complex flow around the body in the surface area can be determined, for example, by CFD simulation. Determining the optimized surface structure based on this basically corresponds to what is known from the state of the art. Artificial intelligence can also be used to determine the optimized surface structure, which may do without the intermediate step of determining the flow over the surface area.

[0024] The optimized surface structure can, for example, comprise two or more regions, each of which contains riblets, although in at least two of the regions the riblets have a direction that differs from one another. Alternatively or additionally, the geometry of the riblets can also differ from one another in at least two of the regions. The geometry of riblets includes, for example, the height of the individual riblets and the distance between two neighboring riblets. A periodically changing pattern of riblets, i.e. a 3D riblet, can also be provided in at least one of the regions. If two regions have 3D riblets, they can have different periodically changing patterns.

[0025] Based on the optimized surface structure, a foil is produced in the next step, the surfaces of which are microstructured in such a way that - if one or more of its edges are properly aligned to one or more alignment lines and are fully applied to the body surrounded by a complex flow - the microstructured surface of the foil has a microstructuring in the area realized which corresponds to the previously determined surface structure .

[0026] The production of the film or its microstructuring can generally be carried out additively or subtractively. The film as a whole or just the microstructuring (e.g. based on a film blank) can be created by 3D printing, printing or applying varnishes, in particular UV-curing varnishes, which are suitably embossed before curing or at least complete curing, or by spraying. Any machining processes, such as milling or grinding, and in particular laser ablation processes, can be considered as subtractive processes. Any combination of different additive and / or subtractive processes is of course also possible. The production processes known from the state of the art for extruding riblet films, for example, are generally not suitable because they only produce films with uniformly oriented riblets.

[0027] The film produced in this way is designed for a specific surface area of ​​the body subjected to complex flow and can be applied to the surface area in question in the final step - particularly in relation to the state-of-the-art processes - easily and quickly.

[0028] For this purpose, the film is to be aligned and fixed with at least one edge provided for this purpose to the alignment guide. It is particularly preferred if the film has two non-parallel edges that are aligned to two corresponding non-parallel alignment guides. If the film is aligned to two non-parallel alignment guides at the same time, their position is clearly defined, which ensures that the Surface structuring on the body with complex flow corresponds to the previously determined optimized surface structure.

[0029] If components or elements are planned in the area to be covered with the film which should or must remain accessible or free of film even after the film has been applied, suitable cutouts or perforations can be provided in the film during production so that sections of the film can be partially severed and removed later. If, for example, windows or flaps are planned in the area in question, the film can have cutouts for these during production which, if the film is correctly arranged on the surface area, will lie directly above them. In particular if cutouts or similar reduce the structural integrity of the film to such an extent that the application of the film is made more difficult, perforations can be provided as an alternative, with which parts of the film can be easily removed again after it has been applied. For example:A circumferential perforation can be provided in the area of ​​a window or flap so that the window or flap is covered by the film immediately upon application, but can be exposed again after it has been removed along the perforation. In this case it is preferred if the film is only firmly connected to the surface of the body around which the complex flow occurs during application in those areas in which it is to remain permanently. Cutouts can also be provided to prepare the two-dimensionally produced film for application to a three-dimensionally curved surface area or area with angles. For example, lateral triangular incisions can be provided in the film, with the sides of the triangles being closed when the film is actually applied to the complexly curved film and basically lying against one another.

[0030] If the surface area to be covered with film is large, applying the entire film in one piece can be complex. In this case, provision can be made for the film to be divided into tiles, at least one tile having an edge for alignment with the at least one alignment line. If two non-parallel alignment lines are provided, it is preferred if one of the tiles is designed for alignment with both alignment lines and has corresponding edges. Once at least one tile has been attached correctly aligned with the at least one alignment line, the other tiles can be aligned with the tile(s) already arranged. The tiles can be shaped such that two adjacent tiles at least partially interlock. This makes it much easier to arrange the other tiles correctly.

[0031] For larger films or tiles, it may also be provided that they are rolled up after production in such a way that the edge intended for alignment with a guide line or another tile is exposed. The film can then be aligned practically in the rolled-up state and, once aligned, applied by unrolling over the entire area to be covered. Application comprising unrolling the film is generally known from the prior art.

[0032] The film is preferably self-adhesive. Suitable adhesives and the production of an adhesive layer on the film are known from the prior art. If the film comprises perforated areas that are to be removed again after the film has been applied to the body subjected to complex flow, it is preferable not to provide the film with self-adhesive properties in these areas.

[0033] For an explanation of the body according to the invention which is subjected to a complex flow, which is preferably an aircraft or commercial aircraft, as well as the fluid-dynamic film according to the invention, reference is made to the above explanations.

[0034] The invention will now be described by way of example using advantageous embodiments with reference to the accompanying drawings. They show: Figure 1: a schematic external view of a part of a body with complex flow; Figure 2: schematic representation of a film produced according to the invention for the complex flow-around body of Figure 1; Figure 3: the foil from Figure 2 in relation to the body from Figure 1, which is subjected to complex flow; and Figure 4: schematic representation of an alternative embodiment of the film from Figure 2.

[0035] Figure 1 schematically shows a part of a body 1 subject to complex flow, namely a part of the tail section of a commercial aircraft.

[0036] On the body 1, which is surrounded by a complex flow, there is a clearly visible longitudinal groove 2, which can be used as an alignment line 11. Furthermore, there is a rivet field 3, from which a further alignment line 11 can be derived, namely a line through two given rivets of the rivet field 3. The further alignment line 11, which is indicated in Figure 1 by a dashed line, can be clearly indicated for a time, for example, by means of a guideline or suitable line laser projection. visible. The two alignment lines 11 are perpendicular to each other, as shown in Figure 1.

[0037] Adjacent to both alignment lines 11, a surface area 10 is defined, which is to be provided with a fluid-dynamically effective film 20 (see Figure 2). The surface area 10 comprises a window opening 4 and extends into a tapered region 5 of the body 1, which is subject to complex flow.

[0038] Starting from the situation in Figure 1, an optimized surface structure is first determined for the entire surface area 10. For example, known tools such as a CFD simulation of the flow over the body 1 with complex flow or at least the surface area 10, followed by surface structure optimization for the surface area 10, can be used for this purpose.

[0039] Based on the determined optimized surface structure, a film 20 is then produced as shown in Figure 2.

[0040] The film 20 is designed to cover the entire surface area 10 when applied to the body 1 subjected to complex flow (see Figure 3). For easy and proper application, the film 20 has two edges 21 that are intended for alignment with the alignment lines 11: If the film 20 is applied with these two edges 21 aligned with the alignment lines 11 provided for this purpose, it is ensured that the entire surface area 10 is not covered, but also receives a surface structuring according to the determined, optimized surface structure.

[0041] The film 20 has a microstructured surface which is already present during the production of the film 20 is adapted to the surface structure optimized for the surface area 10. In the illustrated embodiment, the film 20 is produced by 3D printing on a film blank. However, any other additive and / or subtractive manufacturing processes are possible.

[0042] In the example shown, the microstructuring of the surface of the film 20 is designed as a riblet structure 2 , wherein - as can be seen directly in Figure 2 - several regions 22 are provided within the film 20 in which the riblets 23 have different orientations, whereby in the applied state (cf. Figure 3 ) the previously determined optimized surface structure in the surface region 10 can actually be produced.

[0043] A perforation 24 is provided all around the area which, when attached, corresponds to the window opening 4 (see Figure 1), so that the inner part 24' can be easily removed at a later time - namely after attachment - to expose the window opening 4. Unlike in the remaining area, the film 20 is not self-adhesive within the perforation 24.

[0044] In the part which, in the attached state, coincides with the tapered region 5 of the body 1 subject to complex flow, the film 20 has recesses 25 which enable, or at least simplify, the full-surface attachment of the film 20. The recesses 25 are triangular in shape, with the two legs 26 of the triangular recess 25 being brought together and directly abutting one another in the attached state (cf. Figure 3).

[0045] The manufactured film 20 shown in Figure 2 is then applied to the body 1 subjected to complex flow. The film 20 is aligned with its edges 21 to the corresponding alignment lines 10 on the body 1 subjected to complex flow, and the triangular recesses 25 are closed during application, as described and shown in Figure 3. The film 20 is—as already explained—self-adhesive, so that known methods can be used to apply the film 20 to the body 1 subjected to complex flow.

[0046] To facilitate application, the film 20 can be rolled up. Starting from Figure 2, the film 20 is to be rolled up from bottom to top, so that the edges 21 are exposed at least after the film 20 has been partially unrolled and are thus available for alignment with the alignment guides 11. Suitable methods for applying rolled-up self-adhesive film are also known from the prior art and can be used.

[0047] As an alternative to rolling up the film, it can be divided into individual tiles 27, as shown in Figure 4, wherein the division is not carried out along the areas with different riblet orientations, but rather has the aim of achieving an easily manageable tile size. It is important that a tile 27' still has both edges 21 provided for alignment. The tile 27' can then be applied to the body 21 around which the complex flow occurs, aligned with the corresponding alignment lines 11. Once the first tile 27' has been correctly arranged, the further tiles 27 can be attached to it or to tiles 27 that have already been applied.

Claims

Patent claims 1. Method for providing a body with complex flow (1), in particular of a commercial aircraft, with a fluid-dynamically effective film (20) with a microstructured surface, wherein the body (1) around which the air flows has at least one identifiable guideline (11), with the steps: - determining an optimized surface structure for a coherent complex flow-over surface area (10) of the complex flow-around body (1) immediately adjacent to at least one alignment line (11); - producing a fluid-dynamically effective film (20) with at least one edge (21) provided for alignment with the at least one alignment line (11) and having a microstructured surface which corresponds to the determined surface structure when the film (20) is properly arranged; and - Applying the produced film (20) to the body (1) around which the flow is complex in such a way that the edge(s) (21) provided for alignment are aligned with the respective alignment guide(s) (11) provided for this purpose and covers the continuous surface area (10).

2. Method according to claim 1, characterized in that the complex flow around the body (1) in the surface area (10) is determined, preferably by CFD simulation, and on the basis of this flow around an optimized surface structure for this surface area (10) is determined.

3. Method according to one of the preceding claims, characterized in that the optimized surface structure comprises at least two areas (22) with riblet structures, wherein at least the orientation and / or geometric factors of the riblets (23) differ from one another in at least two of the regions (22).

4. Method according to one of the preceding claims, characterized in that the production of the fluid-dynamically effective film (20) is carried out by one or more additive methods and / or by one or more subtractive methods.

5. Method according to one of the preceding claims, characterized in that the fluid-dynamically effective film (20) has two non-parallel edges (21) for alignment with two corresponding non-parallel alignment lines (11).

6. Method according to one of the preceding claims, characterized in that during production of the film (20) recesses (25) and / or perforations (24) are provided for later partial separation and removal of film sections.

7. Method according to one of the preceding claims, characterized in that the film (20) is divided into tiles, wherein at least one tile has an edge for alignment with the at least one alignment line.

8. Method according to one of the preceding claims, characterized in that the film (2) is rolled up after production in such a way that the edge (21) intended for alignment with a guideline (11) or another tile (27) is exposed.

9. Method according to one of the preceding claims, characterized in that the film (20) is self-adhesive.

10. A body (1) with a complex flow around it, having at least one identifiable alignment line (11), characterized in that at least one surface area (10) adjacent to the alignment line (11) is provided with a fluid-dynamically functional film (20) using a method according to one of the preceding claims.

11. Body surrounded by complex flow according to claim 10, characterized in that the body surrounded by complex flow (1) is an aircraft, preferably a commercial aircraft.

12. Fluid dynamic functional film, characterized in that the film (20) is produced according to steps (a) and (b) of the method according to claim 1.

13. Fluid dynamic functional film according to claim 12, characterized in that the film (20) is produced analogously to one of claims 2 to 9.

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