Electroactive smart material extensionally deformable drag reduction surface and its control method

Abstract

The present invention discloses an electroactive smart material extensionally deformable drag reduction surface, comprising a dielectric elastomer film and a flexible electrode layer, wherein the dielectric elastomer film is processed with straight micro-ribs with cross-sectional geometric dimensions of 2-20 μm in width, 10-100 μm in height and 20-200 μm in spacing in the middle of the upper surface, and flexible electrode arrays are distributed on both sides. According to the electroactive smart material extensionally deformable drag reduction surface of the present invention, the drag reduction surface is deformed in the extension direction by turning on and off the power of the flexible electrode array, which can: (1) change the extensional spacing of the straight ribs, (2) form a sinusoidal structure, and (3) simultaneously change the spacing and form a sinusoidal structure. The beneficial effect achieved is that the flexible electrode layer changes with the flow field environment, turns on and off the power, or changes the size of the received voltage signal, thereby changing the spacing between the ribs, the wavelength and amplitude of the sinusoidal structure alone or simultaneously, so that the turbulent friction resistance near the wall can be significantly reduced under different flow field environments, and a better drag reduction effect can be provided.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft drag reduction design, and in particular to an electroactive intelligent material flow-directional deformable drag reduction surface. Background Art

[0002] A large part of the energy consumed by an aircraft during flight is used to overcome air resistance, of which turbulent friction resistance accounts for a considerable proportion. For civil airliners, under cruising conditions, 50-60% of the total resistance is caused by turbulent friction resistance. This means that turbulent friction drag reduction of aircraft has a series of positive effects: less fuel consumption, less exhaust emissions, and a longer flight range. Therefore, around turbulent friction drag reduction, domestic and foreign scholars have proposed various drag reduction methods, which can be mainly divided into passive drag reduction methods and active drag reduction methods.

[0003] As one of the most widely studied passive drag reduction methods so far, the micro-rib structure has been fully demonstrated by a large number of experimental and numerical calculation results. The straight rib surface along the flow direction was first found to have a drag reduction rate of 2%-8%. The rib height h and the rib spacing s are the main factors affecting the drag reduction. Later, the sinusoidal rib surface along the flow direction was proved to have a drag reduction rate of 10%-12%, which is 40%-50% higher than the straight rib surface. The wave number λ and amplitude A of the rib in the flow direction have also become important factors affecting the drag reduction.

[0004] However, as a passive drag reduction method, the micro-rib structure can only play a drag reduction effect within a given parameter range after it is manufactured, and cannot actively adapt to changes in the flow field environment in a wider flight speed range and more complex flow field flow to play a better drag reduction effect. If a rib structure surface that can be actively deformed can be designed to actively adapt to the changing flow field environment, it will help to further improve the drag reduction effect. For example, a bionic shark skin drag reduction structure disclosed in Chinese patent application CN106585949A involves adapting to the changing flow field through the deformation of a dielectric elastomer, but it can only change the rib height h, and cannot change the rib spacing s, let alone change the spatial shape of the ribs at different positions. For another example, a sandwich-structured intelligent hydrogel material drag reduction surface disclosed in Chinese patent application CN107323602A involves changing the rib h and the rib spacing s through an intelligent hydrogel material, but still cannot change the shape of the ribs in three-dimensional space to adapt to a more complex local flow field environment. And the characteristics of hydrogel materials are more suitable for underwater vehicles, and it is difficult to adapt to the harsh environment of high-altitude flight of aircraft.

[0005] Therefore, there is an urgent need to provide a new drag reduction surface that can change the rib spacing and spatial shape in the span direction. Summary of the invention

[0006] The purpose of the present invention is to address the problem that the existing drag reduction surface with a micro-rib structure cannot more flexibly change the spanwise spacing of the ribs and the spatial shape in the flow direction to adapt to the complex and changeable three-dimensional flow field environment to further improve the turbulent drag reduction rate. A spanwise deformable drag reduction surface of an electroactive intelligent material is disclosed.

[0007] The technical solution adopted by the present invention to solve the above problems is: an electroactive smart material extensionally deformable drag reduction surface, including a dielectric elastomer film and a flexible electrode layer;

[0008] The dielectric elastomer film is processed with a straight micro-rib array in the middle of the upper surface, and the cross-sectional geometric dimensions are preferably: a width range of 2-20 μm, a height range of 10-100 μm, and a spacing range of 20-200 μm;

[0009] Rectangular grooves for attaching flexible electrode layers are distributed on both sides of the dielectric elastomer film, wherein the flexible electrode layers are distributed in the form of an array on the upper and lower surfaces of both sides of the dielectric elastomer film.

[0010] The two sides of the electroactive intelligent material spanwise deformable drag reduction surface are pre-stretched and then fixed, so that the entire drag reduction surface is in a tensioned state in the spanwise direction.

[0011] The dielectric elastomer film is a silicone rubber composite material and an acrylic elastomer.

[0012] The flexible electrode layer is a pair of upper and lower flexible electrode layers on one side, the upper flexible electrode layer receives a high voltage DC signal, and the lower flexible electrode layer is grounded. When the upper flexible electrode layer is powered, the upper and lower flexible electrode layers generate Maxwell stress to squeeze the dielectric elastomer film sandwich in the middle, so that the dielectric elastomer film sandwich drives the middle part of the film to deform in the extension direction under the Maxwell stress and the elastic restoring force in the film surface.

[0013] The control method of the electroactive smart material stretching deformable drag reduction surface, the flexible electrode layer is based on a pair, the left and right pairs in the same stretching direction are a group, when the left and right pairs of upper surface flexible electrode layers include the following three situations:

[0014] (1) The same high-voltage direct current V1 is passed through the upper surface flexible electrode layers of each group of left and right pairs, and the dielectric elastomer film shrinks toward the middle. If the voltage is further increased, the shrinkage toward the middle will intensify, and if the voltage is reduced, the middle will expand to both sides, thereby changing the spanwise spacing of the ribs;

[0015] (2) On the left and right pairs of upper surface flexible electrode layers of the i-th group, one side is energized V2i and the other side is de-energized, and the dielectric elastomer film is deformed toward the de-energized side, so that the ribs form the required sinusoidal structure;

[0016] (3) The voltage signals of (1) and (2) are superimposed, that is, each group of two pairs of upper surface flexible electrode layers on the left and right sides are passed through a high voltage direct current V1 of the same magnitude to change the spanwise spacing of the ribs. Then, on the i-th group of two pairs of upper surface flexible electrode layers on the left and right sides, one side continues to increase the voltage V2i based on V1, while the other side maintains the voltage V1, so that the dielectric elastomer film deforms toward the power-off side while shrinking or expanding.

[0017] The technical effects achieved by the present invention are as follows:

[0018] 1. When the flow field changes in the whole or part, each group of flexible electrode layers deforms the surface of the tiny ribs in the spanwise position of the group by turning on or off the power or changing the voltage, thereby: (1) changing the spanwise spacing of the straight ribs, (2) forming a sinusoidal structure, (3) changing the spacing and forming a sinusoidal structure at the same time. The vortex structure near the wall is further attenuated, the high wall shear stress area of ​​the channel wall is limited, and the wetted area becomes smaller. The spacing, wavelength and amplitude of the ribs are changed at any time to approach the optimal parameters, thereby further improving the drag reduction rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of the three-dimensional structure of the electroactive smart material flow-distribution deformable drag reduction surface when not driven in Examples 1, 2, and 3;

[0020] Figure 2 yes Figure 1 A front view of

[0021] Figure 3 yes Figure 2 The enlarged view of the size mark of the part indicated by a in the figure;

[0022] Figure 4 yes Figure 1 Schematic diagram of the combination arrangement of the flexible electrode layer array;

[0023] Figure 5 yes Figure 1 A top view of

[0024] Figure 6 is a top view of the deformation effect of Example 1 after voltage is applied;

[0025] Figure 7 is a top view of the deformation effect of Example 2 after voltage is applied;

[0026] Figure 8 is a top view of the deformation effect of Example 3 after voltage is applied; DETAILED DESCRIPTION

[0027] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0028] The present invention and its implementation methods are described below, which are not restrictive and the actual implementation methods are not limited thereto. In short, if ordinary technicians in the field are inspired by it and design structural methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

[0029] like Figure 1 As shown, this embodiment discloses an electroactive smart material extensionally deformable drag reduction surface, including: a dielectric elastomer film 1 and a flexible electrode layer 2.

[0030] The upper surface of the dielectric elastomer film 1 has tiny ribs 3 with rectangular cross sections along the flow direction 4, and the geometric dimensions of the cross sections are width t = 2-20 μm and height h = 10-100 μm, and the interval between adjacent rectangles is s = 20-200 μm, such as Figure 3 As shown. The flexible electrode layer 2 is distributed in the form of an array on the upper and lower surfaces of both sides of the dielectric elastomer film 1, with the upper and lower pieces on one side as a pair b, the upper surface flexible electrode layer 2 receives the high voltage DC signal, and the lower surface flexible electrode layer 2 is grounded. The left and right pairs in the same span direction 5 are a group c, and several groups are arranged along the flow direction 4 to control the deformation at different positions.

[0031] Embodiment 1:

[0032] The working method of this embodiment is as follows:

[0033] Pre-stretch and fix both sides of the drag reduction surface along the span direction 5 to make the entire surface in a tensioned state. When the flight speed increases, that is, the Reynolds number increases, the same 2kv high-voltage DC voltage is passed through each group of upper surface flexible electrode layers, and the lower surface flexible electrode layer is grounded. The upper and lower flexible electrode layers generate Maxwell stress to squeeze the dielectric elastomer film sandwich in the middle, so that the dielectric elastomer film sandwich drives the film to shrink toward the middle (arrow direction) under the Maxwell stress and the elastic recovery force within the film surface, as shown in FIG. Figure 6 As shown, the interval s of the ribs 3 is reduced, and the drag reduction rate is improved. The given high voltage DC voltage is different, and the degree of contraction of the middle part is different, so as to adapt to the changing Reynolds number and improve the drag reduction rate.

[0034] Embodiment 2:

[0035] The working method of this embodiment is as follows:

[0036] Pre-stretch and fix both sides of the drag reduction surface along the span direction 5 to make the entire surface in a tensioned state. From top to bottom, the flexible electrode layer 2 on the upper surface of the right side of the array of groups 1, 2, and 3 of flexible electrode layer 2 is respectively connected to 1kv, 3kv, and 1kv high-voltage DC voltages, and the flexible electrode layer 2 on the upper surface of the left side is all powered off; the flexible electrode layer 2 on the upper surface of the left side of the array of groups 4, 5, and 6 is respectively connected to 1kv, 3kv, and 1kv high-voltage DC voltages, and the flexible electrode layer 2 on the upper surface of the right side is all powered off; all the flexible electrode layers 2 on the lower surface are grounded. The upper and lower flexible electrode layers 2 on the powered side generate Maxwell stress to squeeze the dielectric elastomer film 1 interlayer in the middle, so that the dielectric elastomer film 1 interlayer drives the dielectric elastomer film 1 to deform toward the power-off side under the Maxwell stress and the elastic restoring force within the surface of the dielectric elastomer film 1; thereby, the drag reduction surface is deformed along the power-off side in the span direction 5 at different positions in the flow direction 4, so that the drag reduction surface, especially the ribs 3, are formed as follows. Figure 7 The energized flexible electrode layer 2 changes the magnitude of the received high voltage DC voltage as the flow field environment changes, thereby changing the wavelength λ and amplitude A of the sine structure, making the drag reduction surface as close to the optimal state of drag reduction as possible.

[0037] Embodiment 3:

[0038] The working method of this embodiment is as follows:

[0039] Pre-stretch and fix both sides of the drag reduction surface along the span direction 5 to make the entire surface in a tensioned state. The working mode of Example 1 and Example 2, that is, the DC high-voltage signals of each group of upper surface flexible electrode layers 2 are superimposed, that is, from top to bottom, the 1st, 2nd, and 3rd groups of flexible electrode layer 2 arrays have 3kv, 5kv, and 3kv high-voltage DC voltages on the right upper surface flexible electrode layers 2 respectively, and the left upper surface flexible electrode layers 2 are all connected to 2kv high-voltage DC voltage; the 4th, 5th, and 6th groups of flexible electrode layer 2 arrays have 3kv, 5kv, and 3kv high-voltage DC voltages on the left upper surface flexible electrode layers 2 respectively, and the right upper surface flexible electrode layers 2 are all connected to 2kv high-voltage DC voltage; all lower surface flexible electrode layers 2 are grounded. The drag reduction surface, especially the ribs, shrink toward the middle at the same time and form a structure as shown in the figure. Figure 8 The energized flexible electrode layer 2 changes the magnitude of the received high voltage DC voltage as the flow field environment changes, thereby simultaneously changing the interval s of the ribs 3, the wavelength λ and the amplitude A of the sine structure, so that the drag reduction surface is as close as possible to the optimal state of drag reduction.

Claims

1. An electroactive smart material extensionally deformable drag reducing surface, characterized in that: Mainly includes dielectric elastomer film and flexible electrode layer; The dielectric elastomer film is processed with a straight micro-rib array in the middle of the upper surface; Rectangular grooves for attaching flexible electrode layers are distributed on both sides of the dielectric elastomer film; the flexible electrode layers are distributed in the form of an array on the upper and lower surfaces of both sides of the dielectric elastomer film; The two sides of the electroactive smart material spanwise deformable drag reduction surface are pre-stretched and then fixed, so that the entire drag reduction surface is in a tensioned state in the spanwise direction; The flexible electrode layer is a pair of upper and lower flexible electrode layers on one side. The upper flexible electrode layer receives a high-voltage direct current signal, and the lower flexible electrode layer is grounded.

2. The electroactive smart material extensionally deformable drag reducing surface as claimed in claim 1, characterized in that: The straight micro-rib array processed in the middle of the upper surface of the dielectric elastomer film has a cross-sectional geometrical dimension of 2-20 μm in width, 10-100 μm in height, and 20-200 μm in spacing.

3. The electroactive smart material extensionally deformable drag reducing surface as claimed in claim 1, characterized in that: The dielectric elastomer film is a silicone rubber composite material or an acrylic elastomer.

4. A method for controlling the electroactive smart material to extend toward a deformable drag reducing surface as claimed in claim 1, characterized in that: In the control method, the flexible electrode layer is defined as a pair, and the left and right pairs in the same span direction are a group, and the control is divided into the following three situations: (1) The same high-voltage direct current V1 is passed through the upper surface flexible electrode layers of each group of left and right pairs, and the dielectric elastomer film shrinks toward the middle. If the voltage is further increased, the shrinkage toward the middle will intensify, and if the voltage is reduced, the middle will expand to both sides, thereby changing the spanwise spacing of the ribs; (2) On the i-th group of left and right pairs of upper surface flexible electrode layers, one side is energized V2i and the other side is de-energized, and the dielectric elastomer film is deformed toward the de-energized side, so that the ribs form the required sinusoidal structure; (3) The voltage signals of (1) and (2) are superimposed, that is, each group of two pairs of upper surface flexible electrode layers on the left and right sides are passed through a high voltage direct current V1 of the same magnitude to change the spanwise spacing of the ribs. Then, on the i-th group of two pairs of upper surface flexible electrode layers on the left and right sides, one side continues to increase the voltage V2i based on V1, while the other side maintains the voltage V1, so that the dielectric elastomer film deforms toward the power-off side while shrinking or expanding.

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