Method for producing an object having grooves on and / or in the surface, and object produced thereby

Abstract

The invention relates to a method for producing an object provided with grooves on and / or in the surface, around which a fluid flows during use. According to the invention, the frictional resistance acting on the surface area in the flow direction during the flow around the object in the fluid is calculated and added to the cumulative frictional resistance over the length of the surface area in the flow direction, for which purpose grooves are provided on and / or in a portion of the surface, the cumulative frictional resistance of which portion has an increase of at least 0.9, in particular greater than 1.0 to 0.9. Furthermore, the invention relates to an object manufactured in a corresponding manner. Furthermore, the invention relates to a method for modifying the surface of an object, such as a wing, around which a fluid flows during use, wherein a structure with grooves is manufactured on and / or in the surface, which structure reduces the flow resistance of the object. Furthermore, an object around which a fluid flows during use is provided.

Description

[0001] The present invention relates to a method for producing an object provided with grooves on and / or in a surface, around which a fluid flows during use.

[0002] The invention also relates to an object produced in a corresponding manner.

[0003] Furthermore, the invention relates to a method for modifying the surface of an object, such as an airfoil, around which a fluid flows during use, wherein a structure with grooves is built on and / or in the surface, which structure reduces the flow resistance of the object.

[0004] Finally, the invention relates to objects around which a fluid flows during use, in particular airfoils, such as airfoils of an aircraft.

[0005] When an object moves in a fluid (i.e. a gas or liquid), laminar or turbulent flow in the near-surface region of the object occurs on the surface of the moving object in contact with the fluid. The same thing applies in reverse when it is not the object but the fluid that moves in or around the object (which is stationary in this case). Simultaneous movement of the object and the fluid is also possible. Laminar flow results in relatively low frictional resistance between the fluid and the object, while turbulent flow in the near-surface region of the object results in increased frictional resistance.

[0006] When an object is moving or being pushed in a fluid, or conversely, when a fluid flows around or through an object, a high degree of frictional drag is generally undesirable, since such drag can lead to increased fuel consumption, for example in the case of aircraft. This applies analogously to other applications, where an object or part of an object is moving in a fluid, or where a fluid flows around an object or part of an object when the object is stationary. This concerns, for example, wind turbines with rotor blades moving in the air, or, as an example of a stationary object, a pipe through which a fluid flows. In each case, a higher frictional drag would appear to be disadvantageous, since more work must be expended to achieve the effect than would be the case if the frictional drag were lower.

[0007] In particular in the field of aviation, attempts have been made in recent years to reduce the frictional drag of aircraft, or at least parts of aircraft, such as wings or fuselage, and thus reduce the need for fuel. For this purpose, observations from nature, which have been known for decades, are used, according to which the surface structure of sharks can reduce the frictional drag when moving in water. The skin of sharks has a structured surface, which includes so-called grooves on the outer skin. In sharks, these grooves are usually short, longitudinally extending profiles with a certain height and a certain width, as well as a certain length and a specific arrangement. These grooves ensure that turbulence in the near-surface area of ​​the shark skin is prevented or at least reduced, so that there is also less turbulence and therefore the frictional drag of the flow in this area is increased to a lesser extent. The corresponding findings from biology are then applied to mechanical systems, such as aircraft, pipelines or other application cases, in which the surfaces around which the flow occurs are equipped with similar grooves.

[0008] At present, the application of grooves in the aviation industry seems to be becoming the most successful application so far, namely because the cost savings in aviation will undoubtedly constitute the greatest benefit from the current point of view. Also from the point of view of environmental protection, the continuous application of grooves in the aviation industry or aircraft will be sustainable, especially because theoretical studies have shown that in the case of corresponding effectiveness of the design of the grooves, the aviation industry or during the operation of the aircraft can save up to 4% of fuel expenditure.

[0009] For example, an aircraft can be provided with grooves by means of a corresponding film which, during use, appears on the outer surface adjacent to the fluid. It is also possible that an object, such as a pipe, is directly embodied with a corresponding structure. In the case of a pipe, the corresponding structure will be located on the inside, since the fluid flows around the inner structure or around the clear diameter of the pipe.

[0010] Planar areas or ducts constitute very simple examples of application of grooves, whether or not these grooves are subsequently attached to a film with a corresponding groove structure, for example the grooves can be provided directly, in particular if the object is extruded, stamped or otherwise formed into a corresponding structure in a forming step, as can be provided within the scope of the invention, as will be explained below. However, it is problematic that the cross-section of the external structure of an aircraft varies, as is also the case with natural objects such as sharks. This means that it is extremely difficult to reduce the frictional resistance by attaching a large number of grooves in an economical manner. For aircraft, this is because the production costs of the corresponding films are very high. Therefore, the design and production of the film may exceed the expected benefits during the operation of the aircraft, which naturally makes the design and installation of the corresponding film obsolete.

[0011] The object of the present invention is to create a solution suitable for this purpose which makes it possible to reduce the frictional resistance of an object around which a fluid flows relative to it in practice appropriately and at reasonable cost.

[0012] This object is achieved in a first variant using a method of the type described at the outset, wherein the frictional resistance acting on a surface area along the flow direction during the flow of a fluid around an object is calculated and accumulated as a cumulative frictional resistance over a length of the surface area along the flow direction, and grooves are then arranged on and / or in a partial area of ​​the surface, wherein the cumulative frictional resistance of the partial area has an increase of at least 0.9 (in particular, greater than 1.0 to 0.9).

[0013] In the course of the invention, it was found that for applications with the purpose of reducing frictional resistance, it is also or can be sufficient if the grooves are not designed over the entire area of ​​the object (around which the flow occurs), but only in those areas where the cumulative frictional resistance reaches a certain minimum value. In particular in the case of wing-shaped objects, for example, it has been shown that the provision of grooves on and / or in the surface of the object in specific partial areas is already completely sufficient to achieve a significant reduction in frictional resistance. Of course, other partial areas of the profile that are not covered by the grooves may still be affected by turbulence; however, with appropriate design, these partial areas become less important. Although these partial areas can also be optimized in principle, this is not necessary. In general, such a view has emerged that, in particular for a single groove structure fixed in a suitable area of ​​an object (such as a wing), a percentage reduction in frictional resistance can be fully achieved. As a result, corresponding objects, or films attached to objects or other components to be applied, can be produced in this way. This applies similarly in the case of flow around stationary objects. All in all, the use of the method according to the invention results in a good reduction in frictional resistance which is disproportionate from the point of view of material costs, as well as cost savings, since less material is required.

[0014] For example, partial areas in which the cumulative friction resistance increases by more than 1.0 to 0.9 are preferably arranged in a continuous manner. This means that the groove structure is not present in areas that act outside this value range, but is only present in the indicated partial areas and is present in a full-area or at least substantially full-area manner. If there are a plurality of partial areas with corresponding conditions, it is possible to alternate the areas covered by the grooves with the areas not covered by the grooves, wherein coverage is provided only in those areas that also meet the conditions outlined.

[0015] According to the foregoing, within the scope of the present invention it is not important whether the object moves in a fluid or is pushed in a fluid, or whether the object is at rest and the fluid moves around the object. Thus, the concept according to the present invention can be applied to all cases of relative motion, i.e., cases where the object moves in a fluid, and cases where the object is at rest and the fluid moves in or around the object. The former is the case, for example, when an aircraft or a wing moves in a medium such as air or water; the latter is when a fluid flows around an object, such as a pipe constructed inside.

[0016] The frictional resistance acting along the flow direction can in principle be calculated in any desired manner. In particular, it can be provided that the frictional resistance is calculated at certain points. However, a continuous calculation of the frictional resistance is also possible.

[0017] In the case of profiles such as fins, as well as other profiles, the frictional resistance may exist differently transversely to the flow axis. In this sense, when calculating the minimum value of the frictional resistance of the groove, it may be necessary to proceed so as to use the average value of multiple calculations. In particular, it can be provided that the frictional resistance acting in the flow direction is calculated at a plurality of points in a plane transverse to the flow direction, in particular at points arranged along a straight line in a plane transverse to the flow direction, after which the accumulated frictional resistance is added from the frictional resistance calculated in this way. This means taking an average value at a plurality of points of the profile in order to optimize in this respect. Of course, it is possible to determine the optimization conditions for each individual point of such a cross-section, which would, however, require the production of a plurality of films, or if the grooves are formed directly in the object by stamping or other forming means, which is of course undesirable. Instead, a result with an optimized technical effect will be achieved in a single process.

[0018] For some objects moving in a fluid, it may be appropriate that the surface areas starting downstream are still ignored in the calculation. In particular, this can be derived from the fact that laminar flow exists in these areas anyway.

[0019] If so specified, the surface area starting from downstream and ignored should account for a maximum of 20%, preferably a maximum of 15%, in particular a maximum of 10% of the total surface area. Similar percentages apply if the corresponding neglect does not concern parts of the surface but rather the longitudinal extension of the object in the flow direction.

[0020] The grooves fixed, bonded, formed or provided in any other way according to the method of the invention can be provided in the flow direction in the range of 20% to 90%, preferably 25% to 85%, in particular 30% to 80% of the longitudinal extension of the surface. Particularly preferably, the grooves are arranged in the flow direction in the range of 20% to 90%, preferably 25% to 85%, in particular 30% to 80%, for example 25% to 65% of the longitudinal extension of the surface. The less area that has to be provided with grooves, the less material is required.

[0021] In light of the above statements, it is preferably provided within the scope of the invention that the grooves are provided or applied only in partial regions of the surface.

[0022] Application means that the grooves are provided directly on the surface, for example by stamping, extrusion or in other ways, or are subsequently fixed to the surface indirectly, in particular by means of a film with grooves or in which the grooves have been formed. In principle, embodiments of grooves of any desired type of structure formed directly or indirectly are suitable, wherein the formation can also first be carried out in a separate step, after which the component constructed in this way is attached to the surface to be applied. The surface can have any desired properties, but in principle the properties are selected so that the desired effect can be achieved. The corresponding structures relate in particular to partial areas of objects moving in a fluid, such as the wings or fuselage of an aircraft; rotor blades, in particular blades of a wind turbine; pipes; or all other objects that are in contact with a fluid and involve a relative movement between the object and the fluid and in which it is desired to reduce the frictional resistance on the surface of the object. This can also include, for example, cars or sports equipment, such as surfboards, bicycles or snowboards, but also professional sportswear and the like.

[0023] As mentioned, the shaping of the grooves can take place directly on the object or in a partial region of the surface of the object. However, it is particularly preferred that the object is a correspondingly used, in particular flexible film. If a corresponding film is produced, existing objects, such as aircraft, can be retrofitted. In the case of aircraft, this is particularly advantageous when the object has a particularly long service life. Thus, with the concept according to the invention, existing objects, such as aircraft, can be adapted at a later point in time while achieving the desired effect, in this case the desired effect being fuel reduction.

[0024] If a film is provided, numerical calculations can be used to appropriately design the film, in particular according to finite volume methods (computational fluid dynamics, CFD). The actual production of the film can be achieved, for example, by stamping, extrusion, welding or in a different way. Preferably, the film is thus supplied by the yard, so that the film can be cut to a length suitable for use, which enables rapid attachment or rapid refitting.

[0025] In accordance with the above-mentioned advantages and preferred applications, provision can in particular be made to use a wing as the object.

[0026] In another aspect, the present invention provides an object obtainable by a method according to the present invention.

[0027] An advantage obtained with the corresponding body is the optimization of the desired effect by simultaneously minimizing the necessary modification of the body. Thus, the body collision, which must be paid very high costs in order to effectively reduce the friction resistance, is thus satisfactorily resolved.

[0028] In another aspect, the present invention relates to a method for modifying the surface of an object, such as a fin, around which a fluid flows during use, wherein a structure having grooves is formed on and / or in the surface, which structure reduces the flow resistance of the object in the fluid. According to the invention, during the formation of the structure having grooves on and / or in the surface, when there is flow around the profile, areas on the profile with higher wall shear stress are provided with grooves, and areas on the profile with lower wall shear stress are not provided with grooves.

[0029] In this aspect of the invention, it can be seen that according to the method, only those areas of the object where a high wall shear stress is present on the contour when there is a flow around the contour in the fluid need to be provided with grooves while the remaining areas are ignored. In this case, it can be provided in particular that the wall shear stress is related to the frictional resistance, in particular the cumulative frictional resistance, as already explained above.

[0030] During use, only those parts of the object are provided with grooves which are also effective for reducing frictional resistance. It is consciously accepted that the remaining parts of the object, where grooves are omitted or not applied, can also be minimized in terms of frictional resistance. Although this may produce a greater effect, the technical effort and cost expenditure will increase dramatically.

[0031] In those areas where the grooves are applied, the grooves can be designed appropriately according to the wall shear stress at the determined points. However, it is also possible to effectively take an average value for the groove structure, as disclosed in EP2261117A2, the subject matter of which is explicitly included here. The corresponding calculation of the groove structure according to this document can be applied to all methods according to the invention.

[0032] In particular, the structure with grooves can be formed on the upper side of an object, in particular the suction side of a wing for an aircraft.

[0033] The structure with grooves can be attached to the surface of the object as a film. As mentioned above, the grooves can also be formed directly on the object, or the object can already be structured with grooves by forming. If a film is provided, the film can be glued to the surface. The information explained above about the attachment grooves, in particular their percentage-based distribution over the longitudinal extension of the object, applies analogously to this method variant.

[0034] Finally, the present invention relates to an object around which a fluid flows during use, in particular a wing, such as an aircraft wing, wherein it is provided that, when there is a fluid flow around the object, areas of the surface of the object with higher wall shear stress are provided with grooves, while areas of lower wall shear stress are not provided with grooves.

[0035] Furthermore, the invention is explained in more detail below with the aid of exemplary embodiments. In the cited drawings:

[0036] Figure 1a A schematic cross-sectional view of an airfoil is shown;

[0037] Figure 1b Schematic diagram showing a cross section of an airfoil with a natural transition of the flowing air or without measures;

[0038] Figure 2 Shown according to Figure 1a Schematic diagram of the flow condition of the wing with the wire attached;

[0039] Figure 3 shows that when the rough surface is attached according to Figure 1a Schematic diagram of the flow condition when the front side of the wing is

[0040] Figure 4 Shown according to Figure 1a Simulation results of the wall friction (left) and velocity distribution (right) of an airfoil with an angle of attack of 8°.

[0041] Figures 5 to 8 Shown according to Figure 1a Simulation results of the smooth surface of the airfoil with different angles of attack;

[0042] Fig. 9 Shown according to Figure 1a The wall friction distribution of the airfoil on the suction side at different attack angles;

[0043] Fig.10 Shows when attached according to Figure 2 Graph of wind tunnel results for different groove structures when using wire;

[0044] Fig.11 Shown according to Fig.10 Figure Attachment of the grooves in different areas;

[0045] Fig.12 It shows that when Figure 3 Graph of wind tunnel results for different groove configurations when attached to a rough surface;

[0046] Fig.13 Shown according to Fig.12 Figure Attachment of grooves in different areas;

[0047] Fig.14 Shows the Figure 1b Graph of wind tunnel results for the natural transition;

[0048] Fig.15 Shown according to Fig.14 Figure Attachment of the grooves in different areas;

[0049] Fig.16 Shows about Figure 1a Graph of the total frictional drag over the length of the airfoil.

[0050] exist Figure 1a In FIG, the winglet is shown in cross section. The winglet has an asymmetric profile. Figure 1a The upper suction side and the lower pressure side of the wing can be seen in the figure. The corresponding wing is used in wind tunnel tests. In practice, the transition from laminar to turbulent flow occurs on the suction side in the range between approximately 0.4 and 0.6 on the X axis. For the lower side or pressure side, the corresponding area is approximately in the range from 0.7 to 0.9 on the X axis. This is Figure 1b This is explained in the form of examples.

[0051] exist Figure 2 and Figure 3 In FIG. 1 , it is shown that when a disturbance point is intentionally installed to generate turbulence on the wing, according to Figure 1a For example, Figure 2 The situation in this example simulates the real conditions or transition of the boundary layer from laminar to turbulent flow (see Figure 1a ).exist Figure 2 In the wind tunnel tests, so-called tripwires are fixed to the wing. The tripwires are indicated by arrows. In wind tunnel tests, these tripwires lead to turbulence on the wing in the region behind the tripwires. As shown in the figure, tripwires can thus be arranged both on the suction side and on the pressure side. In both cases, the flow behind the tripwires (i.e. when there is flow entering the wing from the front in the flow direction) is found to be turbulent. Before the tripwires, there is laminar flow, such as Figure 2 shown.

[0052] exist Figure 3In the example above, the disturbance point is also fixed on the wing. However, in this case, it is not a linear disturbance point like a tripwire, but a frontal area with a certain roughness. This results in the disturbance point being fixed on the wing when there is a disturbance from the front (i.e. Figure 3 In the case of an inflow of a wing (left side in FIG), there is turbulence on the wing in the flow direction after the disturbance region with increased roughness, which is again indicated by the arrow. For example, the corresponding roughness can be achieved by an adhesive tape having a certain roughness on the surface.

[0053] The tests were carried out in a wind tunnel with the corresponding winglets, which had been modified with grooves as described below. The test line was 2000 mm wide, 1460 mm high and 3200 mm long. The measuring table was located 1500 mm from the leading edge.

[0054] The ambient pressure of the wind tunnel test is 97000Pa. The ambient temperature is 28℃. The use density is 1.122kg / m 3 The dynamic viscosity is 18.62·10 -6 Pas.

[0055] Figure 4 Shows the Figure 1a and Figure 1b Simulation results for the smooth surface (no grooves) of the wing. Figure 4 The velocity distribution is shown on the left. In the suction side area and the initial area of ​​the wing, the velocity is the highest, reaching about 60m / s. Figure 4 On the right, the wall friction is plotted and the wall shear stress on the suction side is illustrated. The corresponding simulation involves an airfoil angle of attack of 8°.

[0056] exist Figures 5 to 8 The simulation results for the smooth surface of the same airfoil are also plotted in . Again, the wall shear stress is shown to depend on the angle of attack. By increasing the reference angle of attack by 2° increments from 6° ( Figure 5 ) to 12°( Figure 8 ), it can also be seen that areas with particularly high wall shear stress always appear inherently, in which the grooves may have the greatest effect. Figures 5 to 8 These areas correspond to the areas indicated by arrows in the black and white figures and appear red in the color illustrations which use a blue to red scale to represent low to high wall shear stresses. The corresponding points are indicated by arrows.

[0057] exist Fig. 9 In the figure, the wall friction distribution is described, that is, according to Figure 1a The wall friction distribution on the suction side of the wing and the Figures 5 to 8The wall friction distribution of the individual simulations. It can be seen that in all cases there are regions with relatively high wall shear stress or regions with high wall friction. With increasing angle of attack, the starting point of the turbulent region moves forward or towards a smaller longitudinal extension. Therefore, a higher angle of attack leads to a higher wall friction.

[0058] If a tripwire is attached, such as Figure 2 As shown, the attached grooves lead to an improvement in flow in the sense of reduced turbulence.

[0059] Based on these simulations, the Figure 2 The disturbance point or Figure 3 The contour of the disturbed area is actually tested. Fig.10 In the figure, it is shown that according to Figure 2 The corresponding measurement results of the adjusted surface. Fig.10 It can be seen that compared with the smooth surface, Figure 1a The efficiency of the suction side of the wing and therefore the lift to drag ratio is improved (due to the installation of the grooves). If the grooves are Fig.11 The attachment shown, that is, the attachment to the different lengths of the wing, obviously depends on Fig.10 The effect of the groove V_s2 is almost as good as that of the groove V_s3. In other words: even if the groove V_s3 is only fixed in a much smaller local area, i.e. in the range of about 0.2 to 0.6 of the total longitudinal extension of the wing (20% to 60%), it produces almost as good an effect. V_r1, an arrangement with tripwire but without grooves, is used as a reference; according to the relevant calculations (c eff = lift / drag and Δc eff =-100+100·c eff_沟纹 / ceff_光滑 ), the result of this reference is the zero line.

[0060] exist Fig.12 and Fig.13 In the Figure 3 Similar test results are obtained for an arrangement (i.e. the case where a predetermined roughness is subsequently added to the front side of the wing), where flow occurs on this front side during use and this side is located in the frontmost position in the downstream direction. In this case, it is also obvious that the drag can be reduced by means of the grooves, where the grooves V_r3 are sufficient to achieve the necessary reduction in frictional drag over a sufficient area. Overall, the grooves V_r2 are slightly better, but they also require a larger proportion of the wing surface coverage, and therefore the material cost is significantly increased. Although the grooves V_r3 are only arranged in a partial area of ​​approximately 50% (relative to the longitudinal extension), the grooves V_r2 are arranged over nearly 90% of the chord length. V_r1 (for example Fig.10V_r1) in the reference, i.e. the neutral line, in this case, is based on Figure 1a The wing blade is equipped with a test-based roughness but without grooves.

[0061] exist Fig.14 and Fig.15 In the figure, the corresponding results for a natural transition, i.e. a practical situation, are shown. It can be seen that even in practical situations, the efficiency is significantly improved when the grooves are arranged only in certain spaces or areas. Only at very small angles of attack there is a slight loss; however, the advantage of the grooves becomes apparent as soon as practically relevant angles of attack are used, where the coverage of certain areas is already sufficient to achieve a substantial increase in efficiency.

[0062] The corresponding results can be described very clearly, especially in Fig.16 Based on. Fig.16 As shown, the total frictional resistance along the longitudinal axis of the wing finally adds up to 100%. In those areas where the frictional resistance is particularly large, the slope of the corresponding curve of cumulative frictional resistance is >1. It is in these areas that it is necessary to install grooves to achieve the greatest possible same effect. This can preferably be done in successive areas until the slope reaches 0.9. Below this slope (i.e. the curve of cumulative frictional resistance is flat), it is no longer necessary to provide grooves.

[0063] Although the installation of grooves in certain areas or spaces does not necessarily need to be continuous, it is preferred that a partial area of ​​a wing or another object is continuously covered with grooves. In the remaining areas (where there are no grooves for high efficiency), there are omissions, or grooves are not provided. Figure 1a In the wing of the present invention, in practice, it can occur that the front area and the rear area are implemented as without grooves, and the grooves are arranged in the middle area, that is, in a continuous manner. In this case, continuous does not refer to the actual structure of the grooves, but refers to the planar area covered by the grooves.

[0064] The method according to the invention and the correspondingly manufactured object are characterized by the greatest possible increase in efficiency at a minimum outlay. Even greater increases in efficiency can be achieved by full-area coverage of the grooves, but this is counteracted by considerable production outlay, in particular a significantly greater number of grooves or groove structures and their necessary production.

Claims

1. A method for producing an object having grooves on and / or in its surface, around which a fluid flows during use, characterised in that The frictional resistance acting on the surface area along the flow direction during the flow of the fluid around the object is calculated and accumulated as the cumulative frictional resistance over a length of the surface area along the flow direction, and then grooves are set on and / or in a partial area of ​​the surface, wherein the increase in the cumulative frictional resistance in the partial area is at least 0.9, wherein the cumulative frictional resistance is expressed as a percentage relative to 100% of the total frictional resistance, and the length is expressed as a percentage relative to the total length.

2. The method according to claim 1, characterized in that The frictional resistance acting in the flow direction is calculated at a defined point.

3. The method according to claim 1, characterized in that The frictional resistance acting in the flow direction is calculated at a plurality of points in a plane transverse to the flow direction, after which the cumulative frictional resistance is added from the frictional resistance calculated in this way.

4. The method according to claim 1, characterized in that: The frictional resistance acting in the flow direction is calculated at points arranged along a straight line in a plane transverse to the flow direction, after which the cumulative frictional resistance is added from the frictional resistance calculated in this way.

5. The method according to any one of claims 1 to 4, characterized in that The surface area starting downstream remains ignored in the calculation.

6. The method according to claim 5, characterized in that The surface area starting from the downstream accounts for a maximum of 20% of the total surface area.

7. The method according to claim 1, characterized in that The grooves are arranged in the flow direction in the range of 20% to 90% of the longitudinal extension of the surface.

8. The method according to claim 1, characterized in that The grooves are arranged only in partial regions of the surface.

9. The method according to claim 1, characterized in that: Use the film as an object.

10. The method according to claim 1, characterized in that A flexible film is used as the object.

11. The method according to claim 1, characterized in that: Use the wing as the object.

12. The method according to claim 11, characterized in that The grooves are provided directly or indirectly on the wing.

13. An object obtained using a method according to any one of claims 1 to 12 and provided with grooves only in partial areas of the surface.

14. A method for modifying the surface of an object around which a fluid flows during use, wherein a structure having grooves is formed on and / or in the surface, said structure reducing the flow resistance of the object, characterized in that During construction of a structure with grooves on and / or in a surface, when there is a flow around the contour, areas of the contour with higher wall shear stress are provided with grooves and areas with lower wall shear stress are not provided with grooves, wherein the wall shear stress is related to the cumulative frictional resistance, and wherein the grooves are provided on and / or in a partial area of ​​the surface where the cumulative frictional resistance increases by at least 0.9, wherein the frictional resistance acting on the surface area in the flow direction during the flow of fluid around the object is calculated and added to the cumulative frictional resistance over the length of the surface area in the flow direction, wherein the cumulative frictional resistance is expressed as a percentage relative to 100% of the total frictional resistance, and the length is expressed as a percentage relative to the total length.

15. The method according to claim 14, characterized in that A structure with grooves is formed on the upper side of the profile.

16. The method according to claim 14, characterized in that The object is a wing for an aircraft.

17. The method according to claim 16, characterized in that A structure having grooves is formed on the suction side of a wing for an aircraft.

18. The method according to any one of claims 14 to 17, characterized in that The structure having grooves is attached to the surface of the object as a film.

19. The method according to claim 18, characterized in that The film is bonded to the surface.

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