Square grid plasma exciter for turbulence drag reduction

Abstract

The square grid plasma exciter for turbulence drag reduction comprises high-voltage electrode (11), dielectric layer (13), low-voltage electrode (12) and insulating substrate (14) from top to bottom, the high-voltage electrode (11) is staggered grid, the low-voltage electrode (12) is arrayed square, and the center position of each square corresponds to the center position of each grid hole of the high-voltage electrode (11). The square grid plasma exciter solves the problems of traditional flow control technology, such as high processing difficulty, high cost, complex structure and limited effective drag reduction wind speed range of ordinary plasma exciter. The excitation strength and working mode of the invented plasma exciter are controlled by electric signal, which is beneficial to realize adaptive adjustment of different environmental parameters and intelligentization. The invented plasma exciter has friction drag reduction and flow separation control, which can greatly improve the performance of military low-speed unmanned aerial vehicle, including stall prevention under high attack angle, flight safety boundary expansion, flight range improvement and the like.

Description

Technical Field

[0001] This invention relates to the field of plasma flow control technology, and in particular to a novel plasma actuator configuration for reducing frictional drag in turbulent boundary layers. Background Technology

[0002] Lift increase and drag reduction have always been the goals of aircraft aerodynamic design. In the cruise phase of large transport aircraft and high-aspect-ratio UAVs, frictional drag accounts for nearly 50% of the total drag. Therefore, reducing frictional drag, especially turbulent frictional drag, can improve the aircraft's cruise lift-to-drag ratio, thereby reducing engine fuel consumption, increasing flight range and time, and saving energy. Boundary layer flow drag reduction control technology is mainly divided into passive control and active control methods. Typical flow control methods include ribs, grooves, and micro-blowing arrays. Ribs and grooves, as passive control technologies, have achieved certain drag reduction effects, but their operating range is limited. In high-speed, high Reynolds number flows, the size of groove structures needs to be developed to the micrometer scale, making the manufacturing process increasingly complex and increasing costs. Existing research has shown that micro-blowing arrays can achieve frictional drag reduction in turbulent boundary layers, but problems exist such as complex air supply systems and difficulties in maintaining porous media. Plasma aerodynamic excitation, as a novel active flow control technology, has advantages such as simple structure, rapid response, and wide bandwidth compared to other methods.

[0003] Existing plasma actuators used for turbulent drag reduction can be broadly categorized into three types: flow-direction jets, spanwise jets (CN111465162A, Turbulent Boundary Layer Plasma Drag Reduction System and Method, Huang Zhiwei, Zhou Yucheng, Xiao Qi, Ouyang Teng), and spanwise oscillations (CN115023017A, An Oscillating Discharge Plasma Actuator for Turbulent Boundary Layer Drag Reduction Control, Wu Bin, Gao Chao, Yan Rihua, Zheng Haibo, Wang Yuling). Their basic idea is to induce parallel jets along the wall to interact with the near-wall flow structure of the boundary layer. Although all three types of plasma actuators have achieved certain drag reduction effects, the effective incoming flow velocities are mostly below 15 m / s. To further improve the drag reduction effect of flow control, it is necessary to break away from the traditional paradigm of flow-direction / spanwise plasma jet drag reduction and design a novel plasma actuator to solve the aforementioned technical problems.

[0004] Plasma actuator configurations can be formed by combining different electrode patterns. Most configurations used for turbulence drag reduction, as described in patents CN113068294A, CN115023017A, and CN109587920A, have comb-shaped, strip-shaped, or filament-shaped high-voltage electrodes and elongated rectangular low-voltage electrodes. Other configurations, such as those described in patents CN112399694A, CN107914865A, CN101511146A, CN111225486A, and CN112607032A, have annular, square, mesh-shaped, or loop-shaped high-voltage electrodes and annular or rectangular low-voltage electrodes. Conventional electrode configurations cannot achieve the effect of generating vertical jet disturbance on the wall, while lattice-shaped plasma actuators can meet the requirements. Plasma actuators with a grid-like configuration are mentioned in patents CN111432543A, CN111298974A, CN111328955A, CN203554775U, and CN108016622A. However, patents CN111432543A, CN111298974A, CN111328955A, and CN108016622A primarily focus on biomedical plasma treatment, plasma sterilization, and aircraft de-icing, and are not suitable for turbulent friction reduction. In the configuration designed in patent CN203554775U, the upper and lower surface electrodes overlap, resulting in a large parasitic capacitance of the actuator and a significant portion of the power supply being consumed as reactive power during operation, leading to low efficiency. The application of the grid-like structure in patent CN108016622A is mainly to increase the plasma length per unit area, thereby improving the heat generation and anti-icing effect of the actuator. However, it is not suitable for turbulent friction drag reduction, and its intended function needs to be verified. Table 1 lists the characteristics and applicable scenarios of the prior art.

[0005] Table 1. Features and Applicable Scenarios of Existing Technologies

[0006]

[0007]

[0008] Therefore, further improvements are needed to the grid exciter to make it more suitable for turbulence drag reduction. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a grid-like plasma actuator for turbulence drag reduction, comprising, from top to bottom, a high-voltage electrode 11, a dielectric layer 13, a low-voltage electrode 12, and an insulating substrate 14, wherein...

[0010] Dielectric layer 13 is a rectangular thin sheet;

[0011] The high-voltage electrode 11 is arranged in an interlaced grid pattern on the upper surface of the dielectric layer 13. The warp and weft of the grid are both long strips. The warp and weft are parallel to the four sides of the dielectric layer 13. The outermost warp and weft maintain a certain distance from the four sides of the dielectric layer 13. Several grid holes are formed between the warp and weft. All grid holes are square.

[0012] The low-voltage electrodes 12 are arranged in an array of square blocks on the lower surface of the dielectric layer 13, located in the interlayer between the dielectric layer 13 and the insulating substrate 14. Except for the wiring points, the low-voltage electrodes 12 are not in contact with the air. The center position of each block corresponds exactly to the center position of each grid hole of the high-voltage electrode 11. The four edges of each block in the low-voltage electrode 12 are aligned with the edges of the strip-shaped warp and weft lines of the high-voltage electrode, and the two do not overlap, that is, the blocks fill the grid holes exactly.

[0013] An insulating substrate 14 is disposed at the bottom of a dielectric layer 13, and its projection on a horizontal plane coincides with the projection of a dielectric layer 13.

[0014] In one embodiment of the present invention, the length and width of the grid-like plasma exciter 1 range from 50 to 500 mm; the width of the warp and weft of the high-voltage electrode 11 ranges from 0.5 to 3 mm; the side length of each square in the low-voltage electrode 12 ranges from 5 to 20 mm; and the thickness of the high-voltage electrode 11 and the low-voltage electrode 12 ranges from 50 to 100 μm.

[0015] In one specific embodiment of the present invention, the warp and weft widths of the high-voltage electrode 11 are 1 mm; the side length of each block in the low-voltage electrode 12 is 10 mm; and the thickness of the high-voltage electrode 11 and the low-voltage electrode 12 is 75 μm.

[0016] In another embodiment of the present invention, the dielectric layer 13 is made of polyimide and is bonded to the high-voltage electrode 11 and the low-voltage electrode 12 by acrylic adhesive; the thickness of the dielectric layer 13 is in the range of 100-250 μm; and the thickness of the insulating substrate 14 is 50-200 μm.

[0017] In another specific embodiment of the present invention, the thickness of the dielectric layer 13 is 200 μm; the thickness of the insulating substrate 14 is 100 μm.

[0018] The aforementioned grid-like plasma exciter for turbulence drag reduction is manufactured using flexible circuit board processing technology.

[0019] A grid-like plasma actuator device for turbulence drag reduction is also provided. Based on the above-mentioned grid-like plasma actuator for turbulence drag reduction, the positive terminal of the plasma power supply 2 is connected to the high-voltage electrode 11, and the negative terminal is grounded together with the low-voltage electrode 12.

[0020] In one embodiment of the present invention, in addition to outputting a steady sine wave, the plasma power supply 2 can also modulate the output sine voltage waveform to change its discharge voltage, discharge frequency, pulse frequency, duty cycle and other parameters, so as to achieve excitation of different intensities or vertical jet pulse excitation of different frequencies.

[0021] Furthermore, a working process for a grid-like plasma exciter device for turbulence drag reduction is also provided. Based on the aforementioned grid-like plasma exciter device for turbulence drag reduction, when using an AC sinusoidal plasma power supply, after connecting the grid-like plasma exciter 1 to the plasma power supply 2, a strong electric field is formed near the edges of the grid-like high-voltage electrodes 11. A small number of free electrons in the air are accelerated in this electric field and collide at high speed with neutral particles, ionizing gas molecules and generating more positive and negative ions, thereby creating a non-equilibrium discharge plasma region between the two electrodes. Charged particles undergo directional acceleration under the action of the electric field, which is plasma aerodynamic excitation. The excitation first... The process induces a starting vortex, which then evolves into a near-wall jet. Since high-pressure electrodes 11 are arranged around the square low-pressure electrode 12, an airflow that accelerates from the periphery to the center is induced inside each grid hole. From the perspective of the cross-section view, the two airflows on the left and right collide and merge in the middle, and then arch to generate a vertical jet along the normal direction. The wall normal jets inside hundreds of grid holes are combined to form a plasma jet array. When this plasma wall normal jet array is used in a turbulent boundary layer, it can produce an effect similar to micro-blowing: the jet array will disturb the boundary layer flow field, lift the fluid, destroy the near-wall vortex structure, and thus suppress the generation of near-wall turbulence, thereby reducing frictional resistance.

[0022] This invention proposes a grid-like plasma actuator, which solves the problems of high processing difficulty, high cost, complex structure, and limited effective drag reduction wind speed range of traditional flow control technologies. Since the excitation intensity and operating mode of the invented plasma actuator are controlled by electrical signals, it facilitates adaptive adjustment of different environmental parameters (e.g., incoming flow velocity and turbulence intensity), achieving intelligent operation. Furthermore, it combines friction drag reduction and flow separation control, which can greatly improve the performance of low-speed military unmanned aerial vehicles (UAVs), including preventing stall at high angles of attack, widening flight safety boundaries, and increasing flight range. Attached Figure Description

[0023] Figure 1 Schematic diagram of the overall structure of the grid-like plasma exciter;

[0024] Figure 2 Planar geometry of the high-voltage electrode and the low-voltage electrode;

[0025] Figure 3 Partial cross-sectional view of a grid-like plasma actuator;

[0026] Figure 4 Schematic diagram of a grid-like plasma actuator jet array;

[0027] Figure 5 Experimental layout diagram of the airfoil for the grid-like plasma actuator;

[0028] Figure 6 Figure showing the wind tunnel test results of the grid-like plasma exciter.

[0029] Attached image annotations:

[0030] 1. Grid-like plasma exciter; 11. High-voltage electrode; 12. Low-voltage electrode; 13. Dielectric layer; 14. Insulating substrate; 2. Plasma power supply; 3. Airfoil; 4. Flat plate model; 5. Aerodynamic measurement device. Detailed Implementation

[0031] like Figure 1-3 As shown, the invented grid-like plasma actuator 1 consists of a high-voltage electrode 11, a low-voltage electrode 12, a dielectric layer 13, and an insulating substrate 14. The length and width of the grid-like plasma actuator 1 need to be adaptively designed according to the specific application, typically ranging from 50 to 500 mm. Figure 1 In the implementation example, the exciter 1 has a total width of 100mm and a total length of 300mm. These dimensions are determined by the airfoil model used in the verification experiment described later. The high-voltage electrodes 11 are arranged in an interlaced grid pattern on the upper surface of the dielectric layer 13. The warp and weft lines of the grid are long strips, with widths ranging from 0.5-3mm (preferably 1mm). The low-voltage electrodes 12 are arranged in an array of square blocks on the lower surface of the dielectric layer 13, sandwiched between the dielectric layer 13 and the insulating substrate 14. The center of each block corresponds perfectly to the center of each grid aperture of the high-voltage electrode 11. To facilitate observation of the correspondence between the high-voltage electrode 11 and the low-voltage electrode 12, [the following is a description of the process]. Figure 1 The medium layer 13 in the drawing is drawn as semi-transparent. Figure 2 The diagram shows the planar geometry of each electrode. The high-voltage electrode 11 and low-voltage electrode 12 can be made of thin copper foil or other conductive metal coatings (such as silver, tungsten, etc.), with an electrode layer thickness ranging from 50-100 μm. From the perspective of reducing disturbance to the incoming flow, 75 μm is preferred. The side length of each square in the low-voltage electrode 12 ranges from 5-20 mm (preferably 10 mm). The four edges of the square are aligned with the edges of the strip-shaped warp and weft lines of the high-voltage electrode, and the two do not overlap. That is, the square exactly fills the grid holes. Preferably, the spacing error is less than 0.1 mm (the square is located in the grid, and its size is consistent with the grid holes; ideally, the square and the grid hole boundaries are aligned, i.e., the spacing is 0 mm). This non-overlapping arrangement is mainly to reduce the parasitic capacitance of the exciter and reduce reactive power consumption during power supply. Figure 1 In this implementation, the high-voltage electrode 11 and the low-voltage electrode 12 are composed of 8 rows and 25 columns, containing 200 square meshes. The dielectric layer 13 is made of, for example, polyimide (Kapton), and is bonded to the high-voltage electrode 11 and the low-voltage electrode 12, for example, using acrylic adhesive. The thickness of the dielectric layer 13 ranges from 100 to 250 μm, preferably 200 μm. To prevent the low-voltage electrode 12 from contacting air, an insulating substrate 14, made of, for example, polyimide, is placed at the bottom of the dielectric layer 13. The insulating substrate 14 and the dielectric layer 13 are first bonded together, for example, with acrylic adhesive, and then further air bubbles that may exist between the adhesive layers are eliminated through a vacuum hot pressing process. The thickness of the insulating substrate 14 is typically 50-200 μm, but a thin insulating substrate layer with a thickness of 100 μm is preferred due to the need for flexible bonding of the actuator.

[0032] The positive terminal of the plasma power supply 2 is connected to the high-voltage electrode 11, and the negative terminal is grounded together with the low-voltage electrode 12, forming a complete discharge circuit. The plasma power supply 2 can be classified into sinusoidal AC, microsecond pulse, and nanosecond pulse dielectric barrier discharge plasma excitation types according to the different driving voltage waveforms. This invention does not limit the frequency and voltage range of the driving waveform, as long as it can break down the air to generate plasma discharge.

[0033] Taking a plasma power supply employing an alternating sinusoidal wave as an example, after connecting the grid-shaped plasma exciter 1 to the plasma power supply 2, a strong electric field is formed near the edges of the grid-shaped high-voltage electrodes 11. A small number of free electrons in the air are accelerated in this electric field and collide at high speed with neutral particles, ionizing gas molecules and generating more positive and negative ions, thus creating a non-equilibrium discharge plasma region between the two electrodes. Charged particles undergo directional acceleration under the influence of the electric field, which is plasma aerodynamic excitation. The excitation first induces a starting vortex, which then evolves into a near-wall jet. Because the present invention arranges high-voltage electrodes 11 around the square low-voltage electrodes 12, an airflow accelerating from the periphery to the center is induced within each grid hole. Figure 3 Taking the cross-sectional view as an example, the two airflows on the left and right collide and merge in the middle, thus arching up to generate a vertical jet along the normal direction. The highest instantaneous velocity of this jet can reach 3 m / s. The combination of the wall normal jets inside hundreds of grid holes forms... Figure 4The plasma jet array is described. Applying this plasma wall-normal jet array to a turbulent boundary layer can produce an effect similar to micro-blowing: the jet array disturbs the boundary layer flow field, lifts the fluid, disrupts near-wall vortex structures, and thus suppresses near-wall turbulence generation, thereby reducing frictional resistance. Furthermore, in addition to outputting a steady sine wave, the plasma power source 2 can modulate the output sine voltage waveform, changing parameters such as discharge voltage, discharge frequency, pulse frequency, and duty cycle to achieve excitation of different intensities or vertical jet pulse excitation of different frequencies.

[0034] Furthermore, compared to traditional wall micro-blowing or rib-based drag reduction methods, the exciter of this invention can be easily manufactured using flexible circuit board processing technology, with a single-piece processing cost in the tens to hundreds of yuan range, far lower than the processing cost of micro-orifice jets or wall ribs. Compared to mechanical vibration drag reduction methods, this method has no mechanical devices, responds rapidly, and the exciter, being made of flexible material, makes it easier to install on complex walls.

[0035] Practical experimental verification:

[0036] like Figure 5 As shown, the grid-like plasma exciter 1 provided by this invention is attached to the airfoil 3 and fixed in a flat plate model 4 in a low-speed wind tunnel at the Air Force Engineering University for testing. The wind tunnel test section is 3m long, 1.2m wide, and 1m high. The flat plate model 4 is made of plexiglass and has the following dimensions: length 1.7m × width 1.2m × thickness 0.02m. The airfoil 3 is 3D printed from ABS photosensitive resin 9400. The NACA0012 airfoil is selected, with a chord length c = 0.4m and a span l = 0.44m. A straight strip of transition material made of 30-grit sandpaper, 1cm wide, is arranged 2cm from the leading edge to force transition and ensure that the downstream boundary layer of the airfoil 3 is in a turbulent state. M6 threaded holes are left on the chord line 10cm from the leading edge at both ends of the airfoil 3 as positioning holes to facilitate the fixation of the airfoil 3 on the flat plate model 4. A grid-like plasma actuator 1 is attached to the center of airfoil 3, with its edges aligned with the trailing edge. Airfoil 3 is vertically mounted at the center of the upper surface of flat plate model 4, with the positioning hole 1.235m away from the leading edge of the plate. The high-voltage electrode 11 and low-voltage electrode 12 of the actuator are connected to the plasma power supply 2 via copper foil tape and wires. To obtain the drag reduction effect of the grid-like plasma actuator 1 on airfoil 3, an aerodynamic measurement device 5 is arranged 320mm from the trailing edge of airfoil 3 to collect flow field data. The drag results are then calculated by computer, and the drag reduction rate is defined as follows:

[0037] DR=(C d，baseline -C d，plasma ) / C d，baseline (1) Among them, Cd，baseline With C d，plasma These represent the drag coefficients under the reference and excitation states, respectively. DR is the drag reduction ratio. A positive value indicates a decrease in airfoil friction drag, while a negative value indicates an increase in airfoil friction drag.

[0038] When the operating parameters of the grid plasma exciter are discharge voltage 8kV, pulse power 100Hz and duty cycle 50%, the drag reduction effect under different incoming flow velocities is tested. Figure 6 The trend of drag reduction rate with incoming flow velocity is shown. It can be seen that as the incoming flow velocity increases, the drag reduction rate first increases and then approaches zero. When the incoming flow velocity is less than 10 m / s, the excitation produces a drag-increasing effect; while when the incoming flow velocity is greater than 12 m / s, the excitation achieves a drag-reducing effect, and achieves a maximum drag reduction of 2.8% at 15 m / s.

[0039] From the above description of the working method and structure, it is easy to see that the advantages and effects of this invention are mainly as follows:

[0040] 1. Simple structure and low cost. According to... Figure 1-3 The invented grid-like plasma actuator mainly consists of high and low voltage electrodes, a dielectric layer, and an insulating substrate. It has a simple structure, is very lightweight and thin, has minimal impact on the aerodynamic characteristics of the structure after installation, and is easy to replace. Compared to other flow control technologies, it has advantages such as simple structure, low cost, easy processing, and no moving parts.

[0041] 2. Rapid response. The excitation intensity and operating mode of this invention are controlled by electrical signals. Compared with other active control devices such as micro-blowing, it can generate an induced jet within milliseconds, achieving a rapid response to the flow field.

[0042] 3. Excellent jet disturbance capability. Most plasma actuators are applied to flat plate boundary layers at low speeds. However, according to the above experimental tests, the grid-like plasma actuator of this invention can achieve a certain drag reduction effect on airfoils at higher wind speeds, and has good prospects for engineering applications.

Claims

1. A grid-like plasma actuator for turbulence drag reduction, comprising, from top to bottom, a high-voltage electrode (11), a dielectric layer (13), a low-voltage electrode (12), and an insulating substrate (14), characterized in that, The dielectric layer (13) is a rectangular thin sheet; The high-voltage electrode (11) is arranged in an interlaced grid on the upper surface of the dielectric layer (13). The warp and weft of the grid are long strips. The warp and weft are parallel to the four sides of the dielectric layer (13). The outermost warp and weft maintain a certain distance from the four sides of the dielectric layer (13). Several grid holes are formed between the warp and weft. All grid holes are square. The low-voltage electrodes (12) are arranged in an array of square blocks on the lower surface of the dielectric layer (13), in the sandwich between the dielectric layer (13) and the insulating substrate (14). Except for the wiring points, the low-voltage electrodes (12) are not in contact with the air. The center of each block corresponds exactly to the center of each grid hole of the high-voltage electrode (11). The four edges of each block in the low-voltage electrode (12) are aligned with the edges of the strip-shaped warp and weft lines of the high-voltage electrode, and the two do not overlap. That is, the blocks fill the grid holes exactly. An insulating substrate (14) is arranged at the bottom of the dielectric layer (13), and its projection on the horizontal plane coincides with the projection of the dielectric layer (13).

2. The grid-like plasma actuator for turbulence drag reduction as described in claim 1, characterized in that, The length and width of the grid-like plasma exciter (1) range from 50 to 500 mm; the width of the meridians and parallels of the high-voltage electrode (11) ranges from 0.5 to 3 mm; the side length of each square in the low-voltage electrode (12) ranges from 5 to 20 mm; and the thickness of the high-voltage electrode (11) and the low-voltage electrode (12) ranges from 50 to 100 μm.

3. The grid-like plasma actuator for turbulence drag reduction as described in claim 2, characterized in that, The width of the meridian and parallel of the high-voltage electrode (11) of the plasma exciter (1) is 1 mm; the side length of each block in the low-voltage electrode (12) is 10 mm; and the thickness of the high-voltage electrode (11) and the low-voltage electrode (12) is 75 μm.

4. The grid-like plasma actuator for turbulence drag reduction as described in claim 1, characterized in that, The dielectric layer (13) is made of polyimide and is bonded to the high voltage electrode (11) and the low voltage electrode (12) by acrylic adhesive; the thickness of the dielectric layer (13) ranges from 100 to 250 μm; the thickness of the insulating substrate (14) is 50 to 200 μm.

5. The grid-like plasma actuator for turbulence drag reduction as described in claim 1, characterized in that, The dielectric layer (13) has a thickness of 200 μm; the insulating substrate (14) has a thickness of 100 μm.

6. The grid-like plasma exciter for turbulence drag reduction as described in claim 1 is manufactured using a flexible circuit board processing technology.

7. A grid-like plasma actuator device for turbulence drag reduction, based on the grid-like plasma actuator for turbulence drag reduction according to any one of claims 1 to 5, characterized in that, The positive terminal of the plasma power supply (2) is connected to the high-voltage electrode (11), and the negative terminal is grounded together with the low-voltage electrode (12).

8. The grid-like plasma actuator device for turbulence drag reduction as described in claim 7, characterized in that, In addition to outputting a steady sine wave, the plasma power supply (2) can also modulate the output sine voltage waveform, change its discharge voltage, discharge frequency, pulse frequency, duty cycle and other parameters, so as to achieve excitation of different intensities or vertical jet pulse excitation of different frequencies.

9. The working process of a grid-like plasma actuator device for turbulence drag reduction, based on the grid-like plasma actuator device for turbulence drag reduction as described in claim 7, characterized in that, When using an AC sinusoidal plasma power supply, after connecting the grid-shaped plasma exciter (1) to the plasma power supply (2), a strong electric field is formed near the latitude and longitude edges of the grid-shaped high-voltage electrode (11). A small number of free electrons in the air are accelerated in this electric field and collide with neutral particles at high speed, ionizing gas molecules and generating more positive and negative ions, thereby generating a non-equilibrium discharge plasma region between the two electrodes. Charged particles undergo directional acceleration under the action of the electric field, which is plasma aerodynamic excitation. The excitation first induces a starting vortex, which then evolves into a near-wall jet. Due to the presence of the block-shaped low-voltage electrode (12), High-voltage electrodes (11) are arranged around the perimeter, thus inducing an airflow that accelerates from the perimeter to the center inside each grid hole; from the perspective of the cross-sectional view, the two airflows on the left and right collide and merge in the middle, and then arch up to generate a vertical jet along the normal direction; the wall normal jets inside hundreds of grid holes are combined together to form a plasma jet array; when this plasma wall normal jet array is used in the turbulent boundary layer, it can produce an effect similar to micro-blowing: the jet array will cause disturbance to the boundary layer flow field, lift the fluid, destroy the near-wall vortex structure, and thus suppress the generation of near-wall turbulence, thereby reducing frictional resistance.

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