Method for applying an aerodynamic function film

Abstract

The present invention relates to a method for applying an aerodynamic functional membrane to a body in which complex flows occur, such as in a commercial aircraft. The method includes the following steps: - using numerical flow simulation, based on a computer model (1) of the subject, determining streamlines (4) on the surface (7) of the subject in which the flow occurs for a predetermined surrounding flow state; - unfolding at least one surface segment (3) of the computer model (1) to form a two-dimensional surface, wherein the surface segment is provided with streamlines (4); - positioning at least one coherent field (10, 20, 30, 40) in the unfolded surface segment (3) by means of local flow directions, such that the local flow directions that can be read on the streamlines (4) are within a predetermined angular range relative to the main flow directions of the relevant fields (10, 20, 30, 40); and - applying an aerodynamic functional membrane to the subject in which the flow occurs within the field boundaries (10.1-4, 11.1-4, 12.1-4, 13.1-4) of at least one field (10, 20, 30, 40) located in the processed surface segment, and cutting the membrane to a size such that the aerodynamic functional membrane is oriented in the main flow direction of the relevant fields, as needed.

Description

[0001] The present invention relates to a method for applying an aerodynamic functional membrane to a body in which complex flows occur, such as on a commercial aircraft.

[0002] Aerodynamic functional membranes are known in implementations and applications different from existing technologies and are commonly used to reduce wall shear stress on the surface of a host around which flow occurs. Aerodynamic functional membranes typically have microstructured surfaces with one or more preferred orientations for this purpose. Preferred orientations here refer to preferred overflow directions (and thus directions of localized flow on the surface) in which the reduction of wall shear stress is particularly large or even maximum.

[0003] One widely used microstructure is the so-called striped thin film structure, which has very small ribs that extend substantially along a preferred direction. Therefore, striped thin film structures are found, for example, not only on the outer surfaces of aircraft, but also on the rotor blades of wind turbines, the outer skin of ships, or the outer surfaces of high-speed trains.

[0004] In order to achieve the maximum possible reduction in wall shear stress through aerodynamic functional membranes (especially striped thin film structures), the membrane must be aligned as precisely as possible with the local flow direction in its preferred orientation, or with only a small deviation relative to the local flow direction. Therefore, the overflow direction of the surface is mainly expected to be in the region of the membrane.

[0005] To date, aerodynamic functional membranes have been virtually only arranged on the surfaces of the surrounding body where flow occurs. These surfaces have relatively simple (usually almost uniform) flow patterns, for which flow directions are practically and inevitably generated, and therefore, preferred directions are inevitably generated. An example of such a surface is the outer skin of a high-speed train, where the flow direction corresponds to the direction of travel or the upper side of an aircraft wing or wind turbine blade, where the flow direction extends primarily in the profile direction.

[0006] To minimize the flow drag on the surrounding body where flow occurs, it is also desirable to provide an aerodynamic functional membrane to reduce wall shear stress on those surfaces of the body, where more complex flow patterns exist. In commercial aircraft with known constructions, one such region exists, for example, on the outer skin of the fuselage in the region at the wing root.

[0007] However, according to existing technology, aerodynamic functional membranes can only be aligned in the direction of the suspected flow in the corresponding region. However, it has been shown that the corresponding arrangement of aerodynamic functional membranes in regions with more complex flow patterns on the surface of the host body where flow occurs generally does not result in a sufficiently large reduction in wall shear stress, which would justify the effort of applying the aerodynamic functional membrane. Therefore, the application of aerodynamic functional membranes is often practically limited to regions around the host surface where flow occurs with less complex or even nearly uniform flow patterns.

[0008] The purpose of this invention is to provide a method for applying an aerodynamic functional membrane to a body in which complex flows occur, wherein wall shear stress can be effectively reduced even in regions with more complex flow patterns.

[0009] This objective is achieved by the method according to the main claim. The subject matter of the dependent claims is an advantageous improvement.

[0010] Therefore, the present invention relates to a method for applying an aerodynamic functional membrane to a body in which complex flows occur (particularly to a commercial aircraft), the method comprising the following steps:

[0011] - Using numerical flow simulation, based on a computer model of the main body, streamlines on the surface of the main body where the flow is occurring are determined for a given surrounding flow state.

[0012] - The computer model is unfolded with at least one surface segment having streamlines to form a two-dimensional surface;

[0013] - Position at least one coherent field within the unfolded surface segment such that the local flow direction, which can be read on the streamline, is within a predetermined angular range relative to the main flow direction of the corresponding field; and

[0014] - An aerodynamic functional membrane is applied to the body and may be modified, and flow occurs around the body within the field boundary of at least one field located in the unfolded surface segment, such that the aerodynamic functional membrane is aligned to have a preferred orientation along the main flow direction of the respective field.

[0015] First, we will explain some of the terms used in conjunction with this invention.

[0016] "A subject in which complex flow occurs around it" is a subject in which, due to the shape of the subject, even if the subject is in parallel flow, complex flow patterns are generated along the surface in at least several segments of the subject's surface.

[0017] "Complex flow patterns" are flow patterns along the surface segment that cannot be reasonably approximated by parallel flow patterns.

[0018] The present invention recognizes that even in the surface regions of a body with complex flow patterns and surrounding flow, a suitable arrangement of known aerodynamic functional membranes (particularly those with striped film structures) can generally be determined, resulting in a significant and worthwhile reduction in wall shear stress after the corresponding application of the membrane. The present invention takes into account both the geometrically complex formation of the surrounding flow body in regions with complex flow patterns and the design of the aerodynamic functional membrane to maintain a uniform and regular orientation in the main flow direction above the membrane surface. Thus, for example, striped film membranes have a uniform design and alignment of essentially a single striped film over the entire membrane surface.

[0019] In the first step of the method according to the invention, the flow around the body to which the aerodynamic functional membrane will ultimately be applied is determined by means of arbitrary flow simulations (from "CFD simulations") known from the prior art. For this purpose, a pre-determined flow state is established, for which a reduction in wall shear stress is desired, for example, because the flow state in question occurs most frequently, or because flow drag or wall shear stress is particularly high in the pre-determined flow state. If the body to which the flow occurs is, for example, a commercial aircraft, the flow around it during cruise is typically pre-determined as the flow state.

[0020] The flow simulation is also based on a computer model of the surrounding body in which the flow occurs, which plots the geometry of the body. The corresponding computer model can be obtained directly in many common application areas of this invention (e.g., aviation), or can be directly derived from other available digital design data.

[0021] The flow around a body is simulated by a computer model of the body under predetermined flow conditions, specifically by generating streamlines on the surface of the computer model of the body. These streamlines each represent the local flow direction along the surface of the body, and thus, in particular, the direction that causes wall shear stress. It is known in the art to determine streamlines on the surface of a body where flow occurs using flow simulation.

[0022] In the next step, at least a portion of the surface of the computer model around the subject (i.e., the selected surface segment) is unfolded to form a two-dimensional surface with streamlines. By unfolding the subject surface, known from its representative geometry, almost arbitrarily complex surface geometries are transferred into a plane, where the distance between two points on the unfolded surface corresponds to a measurable length distance between those two points along the surface in a three-dimensional representation. In the case of very complex geometries, unfolding may only be possible if there are overlapping regions in the plane. While various possibilities for handling such overlapping regions are known from the prior art, it is preferable to select surface segments such that their Gaussian curvature is zero everywhere, or surface segments that form surfaces that can be unfolded without problems. In any case, unfolding will be performed without distortion.

[0023] According to the invention, the unfolding is used not only to transfer the geometry of the selected surface segment into a plane, but also to transfer the streamlines arranged thereon into a plane, such that the result is a two-dimensional flow image of the selected surface segment.

[0024] Based on the unfolding of the main surface and streamlines, at least one coherent field is thus positioned, resulting in a continuous region without internal gaps, where the local flow direction at each point in the field is within a predetermined angular range around the main flow direction established for the field. It has been shown that, in the case of aerodynamic functional membranes, even if the overflow flow direction deviates completely from the main flow direction or only slightly in several segments, a satisfactory reduction in wall shear stress is often provided. This permissible deviation can be accounted for by a predetermined angular range corresponding to the properties of the provided aerodynamic functional membrane.

[0025] Positioning at least one field, according to the specification, is particularly easy to achieve and can be performed with acceptable effort because the process is supported on a surface segment including streamlines unfolded in a two-dimensional plane.

[0026] Then, an aerodynamic functional membrane is applied to the surrounding body where the flow occurs using at least one field positioned based on a two-dimensional unfolding. For this purpose, an aerodynamic functional membrane is applied within the field boundary on the surrounding body where the flow occurs, according to the main flow direction of the field in question. This aerodynamic functional membrane, in principle, has a preferred direction relative to the plane with respect to the overflow (in the case of a striped film membrane, for example, the longitudinal direction of the striped film).

[0027] In this case, the application of the aerodynamic functional membrane naturally occurs on a three-dimensional substrate with arbitrary geometry. Since the field boundary and the main flow direction are generated based on two-dimensional unfolding, this ultimately equates to the formation of the aerodynamic functional structure of the membrane. Therefore, when the field boundary and the main flow direction are transferred back to the actual substrate where the flow occurs and the aerodynamic functional membrane is applied to it in a preferred orientation, it is ensured that the local flow direction deviates from the preferred orientation of the aerodynamic functional membrane at each point of the membrane by no more than a predetermined angular range. This essentially two-dimensionally formed membrane adapts when applied to the three-dimensional surface of the substrate, ensuring that even in the formation of more complex surfaces of the substrate, the local flow direction deviates from the preferred orientation of the aerodynamic functional membrane by no more than a predetermined angular range throughout the field or on the membrane applied therein.

[0028] In order to facilitate the final application and possible adjustment of the aerodynamic functional membrane to the body based on the field boundary and main flow direction determined in the two-dimensional unfolding, it is preferable to select the field boundary and main flow direction based on the identifiable alignment line on the body.

[0029] A “recognizable alignment line” can be a structural feature of the surface of the subject, such as an edge or gap in the surface of the subject. However, an alignment line is also identifiable if two discrete points on the alignment line are uniquely identifiable, and can then be marked on the subject, for example, by means of a guide or adhesive tape. For example, the corresponding points of the alignment line can be formed by structural features of the subject surface such as drill holes, screws, rivets, etc.

[0030] In order to select the field boundary and main flow direction based on the alignment lines that can be identified on the body based on the structural features of the body surface, it is obviously preferred that the corresponding alignment lines and / or discrete points used to form the alignment lines are included in the computer model of the body, so that they can be taken into account according to specifications when locating the field in the surface segment.

[0031] As an alternative or addition to identifiable alignment lines based on structural features of the subject surface, at least a portion of the alignment lines can also be identified based on a geometric calibration pattern projected onto the subject. In a corresponding geometric calibration projection, the alignment lines can be projected onto the surface of the subject, for example, by means of a projector, precisely determining or pre-determining the position and alignment of the projector relative to the subject surface, wherein the precise path of the alignment lines is determined based on a computer model of the subject and a two-dimensional unfolding of the projection. Alternatively, a repeating pattern, such as a rectangular pattern, can be projected onto the surface of the subject based on the unfolded surface segment, taking into account the geometry of the subject. The final alignment lines can then be identified based on the projected pattern.

[0032] Furthermore, it is preferable if the main flow direction of the field is chosen to be parallel to the alignment line used for the field boundary. In this case, the aerodynamic functional membrane can be applied to the body with correct alignment starting only from this field boundary, without having to determine and / or consider a separate alignment line for the main flow direction as well.

[0033] To simplify the application and possible trimming of the aerodynamic functional membrane, it is preferable that the field boundary of at least one field on the unfolded surface segment is a straight line and preferably forms a closed lateral region with up to eight, preferably up to six, and more preferably four sides. This limits the number of alignment lines to be positioned for the final application of the aerodynamic functional membrane on the body to a manageable amount. If the field boundary on the two-dimensional surface is a straight line, as described above, the field boundary can be located without problems via only two identifiable discrete points on the body.

[0034] While not explicitly necessary, linearly forming the field boundary in two-dimensional unfolding can also be advantageous for providing one or more knifeless tapes along alignment lines at least one field boundary before the final application of the aerodynamic functional membrane. These knifeless tapes are typically narrow adhesive tapes with integrated tension lines. The adhesive tape is applied along the desired cut edge on the surface before the membrane is adhesively bonded to it. By pulling the tension lines perpendicular to the surface, both the adhesive tape and the membrane resting thereon are precisely cut along the desired cut edge. Unwanted portions of the membrane and the remaining adhesive tape can then be removed, leaving only the membrane located in the desired region with the desired cut edge on the surface. Using corresponding knifeless tapes along alignment lines of the field boundary, the aerodynamic functional membrane can be precisely trimmed to the desired field.

[0035] The latter may be particularly important, especially if the aerodynamic functional membrane is preferably applied in the form of membrane segments (e.g., paving tiles) in at least one field. Aerodynamic functional membranes are typically designed to be manufactured to a workable size, but can be (significantly) smaller than the positioning field where the membrane is to be placed. In this case, multiple membrane segments can be applied adjacent to and abutting each other in the positioning field, thus, like paving tiles, where the individual membrane segments can be correctly aligned because the second membrane segment is aligned when applied to an adjacent and already applied first membrane segment. For example, the final trimming of portions of the individual membrane segments that may extend beyond the field boundary can be done via trimming tape (see above) along the alignment line of the field boundary.

[0036] Preferably, the predetermined angle range is ±7° or less, more preferably ±5° or less, and even more preferably ±3° or less. The corresponding angle range typically provides a good trade-off between the size of the locatable field and the effectiveness of the membrane (and thus, in particular, the reduction of wall stress) in most possible aerodynamically functional membranes.

[0037] In the method according to the invention, preferably, at least two adjacent fields are preferably located in the surface segment. Furthermore, preferably, if a sufficient number of fields are located, the predetermined surface segment is completely filled with fields.

[0038] The aerodynamic functional membrane preferably has a striped film structure. In other words, the aerodynamic functional membrane is preferably a striped film membrane, which preferably extends parallel to the longitudinal extension direction of the ribs.

[0039] As already mentioned, the method according to the invention is particularly suitable for applying aerodynamic functional membranes to commercial aircraft, such as the fuselage area of ​​the aircraft.

[0040] The invention will be explained by way of example with reference to the accompanying drawings and preferred embodiments. In the drawings:

[0041] Figures 1 to 5 Several schematic diagrams are shown illustrating intermediate steps of performing the method according to the invention.

[0042] In the exemplary embodiments explained below, the application of an aerodynamic functional membrane with a microstructured surface in the form of a striped thin film to the fuselage section of a commercial aircraft above the wing root is illustrated by way of example using the method according to the invention.

[0043] At the outset of this method, the region on a real commercial aircraft in which the aerodynamic functional membrane is to be applied is determined. Then, a surface segment 3 is selected based on a computer model 1 of the commercial aircraft in question, which corresponds to or at least includes the region 2 in question.

[0044] In computer model 1, streamlines 4 are used to supplement surface segment 3 based on a previously performed flow simulation. In the flow simulation, the surrounding flow of the aircraft in computer model 1 is determined under predetermined surrounding flow conditions (here, during cruise flight at the common cruising altitude of a commercial aircraft). From these surrounding flow conditions, streamlines 4 on the surface of the main body around which the flow occurs can be derived, reflecting the local flow direction ultimately associated with wall shear stress. Of course, it is also possible to utilize the results of a flow simulation performed significantly earlier than the application of the method according to the invention, for other reasons. It is also possible to perform the flow simulation only after surface segment 3 has been selected, wherein the determination of streamlines can be limited, at least to surface segment 3, to conserve computational power as much as possible.

[0045] exist Figure 1 The results of these steps are shown in the figure.

[0046] Subsequently, as Figure 2 In summary, surface segment 3 unfolds together with streamlines 4 to form a two-dimensional surface 5, such that the unfolded streamlines 4 are also included in the two-dimensional surface 5. Direct points that are directly identifiable on a real aircraft are also included on the two-dimensional surface 5. In this case, the two-dimensional surface 5 includes the locations 6 of rivets that are identifiable on the outer skin of a real aircraft (see...). Figure 3 If position 6 is already included in computer model 1, it can also be deployed in accordance with streamline 4 during the deployment of surface segment 3. Alternatively, position 6 may be subsequently added to the deployed two-dimensional surface 5 based on the aircraft's design drawings.

[0047] Figure 3 The cross-section of the surface segment 3, which unfolds together with the streamline 4, and the location of the rivet 6 are shown, including the region 2 where the aerodynamic functional membrane will be provided.

[0048] For this region 2, fields 10, 20, 30, and 40 are defined. In each field, the local flow direction that can be read at streamline 4 deviates from the predetermined main flow direction for each field 10, 20, 30, and 40 by less than ±5°.

[0049] The number of fields 10, 20, 30, and 40 is chosen such that region 2 is completely covered by fields 10, 20, 30, and 40 that are directly adjacent to each other (wherein, it is also possible to use an appropriate number of fields 10, 20, 30, and 40, ... to cover the entire surface segment 3). Each field is defined by field boundaries 11, 21, 31, and 41 in the form of closed transverse regions, and each field boundary has four edges 11.1-4, 21.1-4, 31.1-4, and 41.1-4. The corner points of field boundaries 11, 21, 31, and 41 coincide with the uniquely identifiable locations 6 of rivets visible on a real aircraft. Furthermore, fields 10, 20, 30, and 40 are chosen such that in each case, one edge 11.1, 21.1, 31.1, and 41.1 of field boundaries 10, 20, 30, and 40 extends parallel to the corresponding main flow direction of the associated field 10, 20, 30, and 40.

[0050] By using methods known about them, such as those that can also be implemented by computers, it may be easy to locate fields 10, 20, 30, and 40 such that all the mentioned conditions are satisfied and the properties are realized.

[0051] Based on these positioned fields 10, 20, 30, and 40, an aerodynamic functional membrane can then be applied to a real aircraft. This ensures that when the aerodynamic functional membrane is aligned with the main flow direction of the corresponding fields 10, 20, 30, and 40, the wall shear stress is effectively reduced across the entire fields 10, 20, 30, and 40 due to the local flow direction, which deviates from the main flow direction by a maximum of ±5° at each point in fields 10, 20, 30, and 40.

[0052] based on Figure 4 and Figure 5 The application and trimming of the aerodynamic functional membrane are described using an example for field 10, in which... Figure 4 The following process is illustrated: Surface 7 of the aircraft is unfolded to form a shape similar to... Figure 3 A fairly two-dimensional plane, and Figure 5 The three-dimensional surface 7 is shown to have an accompanying distortion in the top view.

[0053] First, the rivets on surface 7 are identified, corresponding to positions 6 of the field boundary 11 that defines the positioning field 10. Then, each point is marked using adhesive tape that can be attached to surface 7. Since the field boundary 11 is linear in two-dimensional unfolding, it is also possible to easily locate the associated alignment lines on the three-dimensional surface 7. This is because the alignment lines extend along the shortest path on surface 7 between every two positions 6, even though the alignment lines found may not appear linear in the top view depending on the perspective.

[0054] Along the field boundary 10.1, which extends parallel to the main flow direction of field 10, it is sufficient to provide only adhesive tape for marking alignment lines, while cutting tape is provided along the other field boundaries 10.2, 10.3, and 10.4.

[0055] Subsequently, starting from the field boundary 10.1, a segment 8 of an aerodynamic functional membrane with a microstructured surface in the form of a striped film is applied to the surface 7 in the form of a tile, wherein the preferred direction 9 of the segment 8 or the direction in which the striped film extends is aligned parallel to the field boundary 10.1, which is possible and without problem if the striped film extends parallel to the edge of the segment 8.

[0056] The membrane segments 8 are applied continuously to the surface 7 within the field 10 like tiles. It is not critical if each membrane segment 8 extends beyond the field boundaries 10.2, 10.3, 10.4: if the field 10 is completely covered by the membrane segments 8, any protrusions can be removed without any problem by means of the membrane-cutting tape along the field boundaries 10.2, 10.3, 10.4.

[0057] Subsequently, for the remaining fields 20, 30, and 40 (see...) Figure 3 ), execution based on Figure 4 and Figure 5 The application of the aerodynamic functional membrane as explained.

Claims

1. A method for applying an aerodynamic functional membrane to a body around which complex flows occur, the method comprising the following steps: - By means of numerical flow simulation, based on the computer model (1) of the main body, streamlines (4) on the surface (7) of the main body in which the flow occurs are determined for a predetermined surrounding flow state. - Expand at least one surface segment (3) of the computer model (1) with streamlines (4) to form a two-dimensional surface; - Position at least one coherent field (10, 20, 30, 40) within the unfolded surface segment (3) such that the local flow direction that can be read at the streamline (4) is within a predetermined angular range relative to the main flow direction of the corresponding field (10, 20, 30, 40); and - An aerodynamic functional membrane is applied to the body and adjusted as needed, and flows around the body within the field boundaries (10.1-4, 11.1-4, 12.1-4, 13.1-4) of at least one of the fields (10, 20, 30, 40) in the unfolded surface segment, such that the aerodynamic functional membrane is aligned along the main flow direction of the respective field.

2. The method according to claim 1, wherein, The alignment of the field boundaries (10.1-4, 11.1-4, 12.1-4, 13.1-4) and the main flow direction is selected based on the alignment lines identifiable on the body, such that the alignment and on-demand trimming of the aerodynamic functional membrane in the fields (10, 20, 30, 40) are performed based on the alignment lines correspondingly identified on the body.

3. The method according to claim 2, characterized in that, The alignment line is identified based on the structural features of the surface of the subject and / or based on a geometric calibration pattern projected onto the subject, wherein the structural features are mapped in the computer model (1).

4. The method according to claim 2, wherein, The main flow direction of the field (10, 20, 30, 40) is selected such that the main flow direction is parallel to the alignment line of the field boundary (10.1-4, 11.1-4, 12.1-4, 13.1-4) for the field (10, 20, 30, 40).

5. The method according to claim 2, characterized in that, The field boundaries (10.1-4, 11.1-4, 12.1-4, 13.1-4) of at least one field (10, 20, 30, 40) on the unfolded surface segment are straight lines and form a closed transverse region with up to 8 sides.

6. The method according to claim 5, characterized in that, The enclosed transverse region has a maximum of 6 sides.

7. The method according to claim 6, characterized in that, The enclosed transverse region has at most four sides.

8. The method according to any one of claims 2-7, characterized in that, In order to trim the aerodynamic functional membrane, one or more trimming tapes are applied along the alignment lines (10.1-4, 11.1-4, 12.1-4, 13.1-4) of at least one field boundary (10.1-4, 11.1-4, 12.1-4, 13.1-4) of the field (10, 20, 30, 40) on the body before applying the aerodynamic functional membrane.

9. The method according to any one of claims 1-7, characterized in that, The aerodynamic functional membrane is applied in at least one field (10, 20, 30, 40) in the form of membrane segments (8) like tiling.

10. The method according to any one of claims 1-7, characterized in that, The predetermined angle range is ±7° or less.

11. The method according to claim 10, characterized in that, The predetermined angle range is ±5° or less.

12. The method according to claim 11, characterized in that, The predetermined angle range is ±3° or less.

13. The method according to any one of claims 1-7, wherein, At least two fields (10, 20, 30, 40) are located in the surface segment (3).

14. The method according to claim 13, wherein, The at least two fields (10, 20, 30, 40) are adjacent.

15. The method according to any one of claims 1-7, wherein, Position enough fields (10, 20, 30, 40) so that the predetermined surface segment (3) is completely filled with fields (10, 20, 30, 40).

16. The method according to any one of claims 1-7, wherein, The aerodynamic functional membrane has a striped thin film structure.

17. The method according to any one of claims 1-7, wherein, The subject is a commercial aircraft.

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