A microfluidic enhanced vortex plasma turbulence drag reduction device and method

Abstract

The application discloses a kind of microfluidics enhanced vortex plasma turbulent drag reduction device and method, it is related to aerodynamics technical field, including dielectric barrier discharge excitation module and corona excitation module on aircraft skin;Wherein, dielectric barrier discharge excitation module includes bare electrode, covering electrode, insulating medium, jet square hole;Corona excitation module includes corona negative electrode, corona positive electrode, inner air blowing hole, porous medium. Normal micro air blowing generated by corona excitation module can eliminate the downwash drag-increasing effect of streamwise vortex induced by dielectric barrier discharge excitation module, and enhance the upwash drag-reducing effect, improve the overall drag-reducing effect, and enhance the drag-reducing ability at higher incoming flow speed.

Description

Technical Field

[0001] This invention relates to the field of aerodynamics. Background Technology

[0002] In the field of aerodynamics, drag reduction has always been a pursuit in aircraft aerodynamic design. When an aircraft cruises at subsonic speeds, about half of the drag comes from wall friction drag. Therefore, friction drag is directly related to fuel consumption.

[0003] To achieve drag reduction in aircraft, various flow control methods have been developed, mainly categorized into passive and active control. A typical passive flow control method primarily uses trenches. Trenches are flow-oriented protrusions periodically arranged along the spanwise direction on the surface of the aircraft. By separating the lower layer of the turbulent boundary layer, they can achieve a drag reduction effect of approximately 8% to 10%. However, their adaptability is poor, and their working range is limited. Most trenches can only achieve optimal drag reduction within a very small Reynolds number range. Once the design Reynolds number is deviated from due to changes in flight speed, altitude, or weather, the drag reduction effect will decrease significantly, or even increase drag. Furthermore, their disturbance effect is limited. When the incoming flow velocity increases, the fixed trench spacing cannot match the increased spacing of the turbulent boundary layer, making it difficult to effectively intervene in the turbulent boundary layer and thus losing the drag reduction effect. These changes are unavoidable in actual flight, making simple trenches difficult to apply for drag reduction in practical flight.

[0004] Typical active flow control methods include air blowing and spanwise wall oscillation, which are highly adaptable. Air blowing can achieve 20%–30% turbulent drag reduction, while spanwise wall oscillation can reduce turbulent frictional drag by 45%. However, active control methods often require complex bleed air pipelines, air sources, motors, and complex mechanical structures. Furthermore, traditional air blowing methods require bleed air from the engine, which can impair engine performance. The energy and costs of driving air blowing and spanwise wall oscillation outweigh the drag reduction benefits, making them impractical.

[0005] Plasma turbulence drag reduction is a novel active drag reduction method with advantages such as simple structure and low drag reduction cost. It is currently the most promising turbulence drag reduction method for practical applications and has become a research hotspot in recent years. Among plasma turbulence drag reduction methods, dielectric barrier discharge (DBD) is commonly used, which can achieve an 11% drag reduction effect on airfoil turbulent friction at an incoming flow velocity of 20 m / s. However, due to the very limited intensity of the dielectric barrier discharge (the induced velocity is generally only 2~3 m / s), when the incoming flow velocity increases to 30 m / s, the drag reduction effect rapidly decreases to 2.6%; when the incoming flow velocity increases further, the drag reduction effect disappears, making it difficult to implement in practice.

[0006] Therefore, there is an urgent need to seek more efficient and flexible methods for reducing drag in plasma turbulence, so as to achieve more efficient drag reduction at higher incoming flow velocities. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a microjet-enhanced vortex plasma turbulence drag reduction device.

[0008] To achieve the above objectives, the present invention specifically adopts the following technical solution: A microjet-enhanced vortex plasma turbulence drag reduction device includes a dielectric barrier discharge excitation module and a corona excitation module disposed on the skin of an aircraft. The dielectric barrier discharge excitation module includes an exposed electrode, a covering electrode, an insulating medium, and jet square holes. The exposed electrode is elongated and its long side is arranged along the flow direction, covering the entire drag reduction area. The short side of the exposed electrode is arranged along the spanwise direction. The covering electrode is also elongated and its long side is arranged along the flow direction, covering the drag reduction area. The insulating medium is tightly attached to various parts of the aircraft, including curved surfaces. The exposed electrode and the covering electrode are distributed on the upper and lower sides of the insulating medium. One exposed electrode and one covering electrode form an electrode group. Jet square holes are opened in the insulating medium between adjacent electrode groups. The corona excitation module includes a corona negative electrode, a corona positive electrode, an inner air hole, and a porous medium. The corona positive electrode is annular, and the inner air hole is located inside the annular corona positive electrode. The corona negative electrode is coaxially located at the lower end of the corona positive electrode, and the porous medium is located directly above the inner air hole. After assembling one corona negative electrode and one corona positive electrode, a corona discharge unit is formed. Multiple corona discharge units are arranged in an array at the normal projection position of the jet square hole to generate a corona normal jet in the internal blowing hole. The porous medium is embedded in the jet square hole, and the corona normal jet is rectified by the porous medium to form micro-blowing. Through the above scheme, the device achieves efficient drag reduction through the synergistic effect of the dielectric barrier discharge excitation module and the corona excitation module. The dielectric barrier discharge excitation module consists of exposed electrodes, covered electrodes, and an insulating medium. The electrodes are arranged along the flow direction and spanwise, and jet square holes are formed in the insulating medium. The corona excitation module includes corona positive and negative electrodes, internal blowing holes, and a porous medium, generating a normal jet through corona discharge. The corona discharge units are arrayed at the normal projection positions of the jet square holes. After being rectified by the porous medium, the corona normal jet forms a uniform micro-blowing air. The two modules work together to induce a stable flow-oriented vortex structure in the boundary layer, achieving drag reduction by changing the distribution of the underlying flow field. The normal micro-blowing air generated by the corona is used to actively control and enhance the stability and intensity of these vortices, thereby achieving synergistic reduction of turbulent frictional drag.

[0009] Furthermore, the corona negative electrode is cylindrical, made of an ablation-resistant conductive material, with a bottom diameter of 0.5-2mm and a height of 5-20mm, and the upper end face of the corona negative electrode is sharpened. The cylindrical shape with a tapered tip, as described above, is designed to concentrate the electric field using the tip effect, thereby making it easier and more stable to induce corona discharge. Its size range (0.5-2 mm diameter, 5-20 mm height) is optimized based on discharge efficiency, mechanical strength, and manufacturing feasibility.

[0010] Furthermore, the corona positive electrode is circular and connected to the positive terminal of a high-voltage DC power supply. It is made of an ablation-resistant conductive material and embedded in the aircraft skin, which is also made of conductive material. The corona positive electrode is wrapped with an insulating material. The normal distance between the upper end face of the corona negative electrode and the lower end face of the corona positive electrode is 5-20 mm. All corona positive electrodes are connected to the positive terminal of the high-voltage DC power supply in parallel, and all corona negative electrodes are grounded. All exposed electrodes are connected to the positive terminal of a high-voltage sinusoidal power supply in parallel, and all covered electrodes are grounded. The above scheme clarifies the connection, installation, and insulation details of the corona positive electrode. Connecting the corona positive electrode to a high-voltage DC power supply and embedding it in a conductive skin, then wrapping it with insulating material, strictly confines the discharge to the area between the annular positive electrode and the needle-shaped negative electrode, preventing current diffusion in other directions and ensuring the safety and controllability of the discharge. Simultaneously, it defines the distance range between the positive and negative electrodes, which is crucial for maintaining stable corona discharge rather than spark discharge. All corona negative electrodes are connected in parallel and grounded, while all exposed electrodes are connected in parallel to a high-voltage sinusoidal power supply. This electrical configuration ensures the uniformity and consistency of operation of each discharge unit, while simplifying the complexity of the external power supply system and improving system reliability.

[0011] Furthermore, the inner diameter of the corona positive electrode ring is 10-30mm, the outer diameter is 2-6mm larger than the inner diameter, and the ring wall thickness is 1-3mm. With the above scheme, the outer diameter is slightly larger than the inner diameter and the wall thickness is 1-3mm. This ensures that the electrode has sufficient mechanical strength and conductive cross-section to withstand long-term discharge. At the same time, its annular structure helps to generate a uniform annular electric field, thereby promoting the formation of a uniform normal jet, laying the foundation for the subsequent generation of uniform micro-blowing gas through porous media.

[0012] Furthermore, the porous medium has a porosity of 20-50%, a pore size of 0.1-1mm, and is cut into a square shape. Its flow direction and spanwise dimensions are the same as those of the jet square hole, and its thickness is the same as that of the aircraft skin. The above scheme optimizes porosity and pore size to effectively rectify, diffuse, and slow down the high-speed but non-uniform transient jet generated by corona discharge, transforming it into a low-speed, uniform, and stable "micro-blowing gas." Fabricating it into a square shape identical to the jet's square aperture and keeping it flush with the skin ensures complete embedding within the gas path without interfering with the mainstream flow, guaranteeing smooth injection of the micro-blowing gas into the boundary layer for more effective interaction with the generated vortices.

[0013] This invention also discloses an assembly method for a microjets-enhanced vortex plasma turbulence drag reduction device, applied to the aforementioned device, comprising the following steps: Step S1: First, attach the cover electrode and then attach the insulating medium tightly on top of it; Step S2: Attach the exposed electrode. The exposed electrode is attached above the insulating medium. One exposed electrode and one covered electrode form an electrode group, which is assembled into a dielectric barrier discharge excitation module. Step S3: First, embed the corona positive electrode into the aircraft skin, ensuring that the circular axis of the corona positive electrode is parallel to the normal. Then, install the corona negative electrode below the corona positive electrode, ensuring that the bottom circle of the corona negative electrode is coaxial with the bottom circle of the corona positive electrode. Assemble to form a corona discharge unit. Step S4: Inside the aircraft skin, multiple corona discharge units are arranged in an array at the normal projection position of the jet square hole to generate a corona normal jet in the internal blowing hole. The porous medium is embedded in the jet square hole, and the corona normal jet is rectified by the porous medium to form micro-blowing air. Then, a micro-jet enhanced vortex plasma turbulence reduction device is assembled. The above scheme follows a logical sequence from bottom to top, from single module to system integration: S1 attaching the covering electrode and insulating medium; S2 attaching the exposed electrode to form the dielectric barrier discharge excitation module; S3 installing the corona positive and negative electrodes to form the corona unit; and S4 integrating the array and porous medium. This method ensures that each precision component can be accurately positioned and fixed, especially guaranteeing the precise spatial alignment of the jet square hole of the dielectric barrier discharge excitation module and the corona normal jet outlet, which is a prerequisite for achieving functional synergy between the two.

[0014] Furthermore, in step S1, a groove of the same size as the covering electrode is pre-processed below the position of the covering electrode on the upper surface of the aircraft skin. After the covering electrode is embedded in the groove, an insulating medium is attached to ensure that the normal projection of one long side of the exposed electrode is aligned with one long side of the covering electrode. A jet square hole is opened on the insulating medium between adjacent electrode groups. The jet square hole is a square through hole with the same flow length as the exposed electrode and a spanwise width slightly smaller than the electrode group spacing by 1 mm. It is used to embed the porous medium to cooperate with the corona excitation module to generate a normal jet. The above-described method involves pre-machining grooves for the cover electrode so that it is flush with the skin after embedding. This "hidden" installation is crucial in preventing any surface protrusions from disrupting the external aerodynamic shape and flow field. The exposed electrode is explicitly aligned with the long side of the cover electrode to ensure uniform distribution of the plasma and horizontal jet generated by the dielectric barrier discharge excitation module along the spanwise direction. The size design of the jet orifice maximizes the effective blowing area while allowing for the installation edge.

[0015] Furthermore, in step S2, the spanwise spacing between corresponding positions of adjacent electrode groups should be between 750δν and 1450δν, where δν is the viscous length scale of the boundary layer, which can be calculated according to the following formula. In the formula, ν is the kinematic viscosity of the fluid, u τ Let τ be the boundary layer friction velocity. w Let ρ be the wall shear stress and ρ be the fluid density.

[0016] Through the above scheme, this distance ensures that the generated streamwise vortices can be embedded into the inherent structure of the background flow field at the most effective interval, thereby optimally interfering with the turbulence generation process and achieving maximum drag reduction. This makes the design of the device scientifically sound and adaptable.

[0017] Furthermore, in step S4, the high-voltage DC power supply is turned on, and the output voltage amplitude is adjusted to ensure a stable corona discharge between the corona positive and negative electrodes, forming a corona. The high-voltage sinusoidal power supply is turned on, and a high-voltage sinusoidal wave is applied between the exposed electrode and the covered electrode, thereby generating a strong spanwise electric field between the exposed electrode and the covered electrode. Under the constraint of the insulating medium, the air on the surface of the insulating medium directly above the covered electrode will be ionized by the strong electric field between the electrodes, forming a dielectric barrier discharge, which will then generate a horizontal jet in the spanwise direction from the exposed electrode to the covered electrode. In the boundary layer where the mainstream velocity is along the flow direction, the above-mentioned horizontal jet will interact with the boundary layer flow, forming vortices in the boundary layer, forming a flow vortex along the electrode direction. On the upward washing side of the flow vortex, the low-speed fluid at the bottom of the boundary layer sweeps upward, reducing the bottom velocity and Reynolds stress of the boundary layer, and reducing the frictional resistance. Conversely, on the downward washing side, the high-speed fluid at the top of the boundary layer accumulates towards the wall, increasing the bottom velocity and Reynolds stress, and increasing the frictional resistance.

[0018] The beneficial effects of this invention are as follows: 1. This invention, based on the vortices generated by typical spanwise DBD (Deep Bore Discharge) systems, couples a normal microjets generated by corona discharge to form a microjets-enhanced vortex-type plasma turbulence drag reduction device and method, providing a new technical approach for efficient drag reduction at higher incoming flow velocities. Specifically, porous dielectric materials are embedded between each group of DBD discharge units, and corona discharge is used below the porous dielectric to generate airflow, forming normal microjets. This simultaneously generates vortices and normal microjets in the boundary layer. The efficient coupling of the flow-oriented vortices and normal microjets improves drag reduction capability. The corona-induced normal microjets eliminate the drag-increasing effect of the downwash caused by DBD-induced flow-oriented vortices and enhance the upsweep drag reduction effect, thereby achieving effective drag reduction at higher incoming flow velocities. 2. This invention, through the organic coupling of vortices and microjets, not only enhances the local drag reduction effect, but also promotes the mixing of microjets and boundary layers by utilizing the effect of vortices. This allows the drag reduction effect generated by the microjets to propagate downstream to a more distant region. Compared with existing drag reduction methods based solely on dielectric barrier discharge or corona discharge, this invention utilizes DBD-induced flow vortices to promote the downstream transport of the low-speed fluid layer generated by the microjets, increasing the drag reduction area downstream of the blowing zone, thereby enhancing the overall drag reduction effect and resulting in a larger overall drag reduction range. 3. Compared with conventional dielectric barrier discharge, corona discharge has an order of magnitude higher mechanical efficiency. This invention introduces the role of corona discharge into dielectric barrier discharge, resulting in higher overall mechanical efficiency compared with existing dielectric barrier discharge turbulence drag reduction methods. It can achieve considerable drag reduction effect with less energy consumption, thereby improving drag reduction energy efficiency. 4. Compared with the simple method of using bleed air to achieve drag reduction, the present invention does not require drawing high-pressure air from the engine or other parts, and does not damage the engine's performance and operational stability. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall assembly structure of the present invention; Figure 2 This is an assembly structure diagram of the dielectric barrier discharge excitation module of the present invention; Figure 3 This is an assembly structure diagram of the corona excitation module of the present invention; Figure 4 This is an exploded structural diagram of the corona excitation module of the present invention; Figure 5 This is an assembly structure diagram of a single corona discharge unit of the present invention; Figure 6 This is a schematic diagram of the working process of the microjet-enhanced vortex plasma turbulence drag reduction device of the present invention.

[0020] Reference numerals: 100, dielectric barrier discharge excitation module; 110, exposed electrode; 120, covered electrode; 130, insulating dielectric; 160, electrode group; 170, jet square hole; 200, corona excitation module; 210, corona negative electrode; 220, corona positive electrode; 230, internal air blowing hole; 240, porous dielectric; 300, aircraft skin. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] Example 1 This invention, based on the vortices generated by typical spanwise deep-diffusion (DBD), couples a normal microjets generated by corona discharge to form a microjets-enhanced vortex-type plasma turbulence drag reduction device, providing a new technical approach for efficient drag reduction at higher incoming flow velocities. Specifically, porous medium 240 material is embedded between each group of DBD discharge units, and corona discharge is used below the porous medium 240 to generate airflow, forming normal microjets. This simultaneously generates vortices and normal microjets in the boundary layer. Through the efficient coupling of flow-oriented vortices and normal microjets, drag reduction capability is improved. The mechanism is as follows: the corona-induced normal microjets eliminate the drag-increasing effect of the downwash generated by DBD-induced flow-oriented vortices and enhance the drag reduction effect of the upsweep, thereby achieving effective drag reduction at higher incoming flow velocities. Simultaneously, the DBD-induced flow-oriented vortices promote the downstream transport of the low-speed fluid layer generated by the microjets, increasing the drag reduction area downstream of the airflow zone, thus enhancing the overall drag reduction effect. While improving drag reduction effect and increasing drag reduction energy savings, a portion of the DBD discharge power is allocated to high-efficiency corona discharge, reducing the overall energy consumption of the system and thus achieving the goal of improving energy efficiency. Specific embodiments are described below.

[0024] like Figures 1 to 6 As shown, this embodiment provides a microjet-enhanced vortex plasma turbulence drag reduction device, including a dielectric barrier discharge excitation module 100 and a corona excitation module 200 disposed on the aircraft skin 300.

[0025] Reference Figure 1 and Figure 2 The dielectric barrier discharge excitation module 100 includes exposed electrodes 110, covered electrodes 120, insulating dielectric 130, jet square holes 170, etc. Figure 2 As shown. The exposed electrode 110 is a strip of copper foil with a thickness of 0.01-0.1 mm (preferably 0.05 mm). The long side of the exposed electrode 110 is arranged along the flow direction (x direction), and its length covers the entire drag reduction area; the short side is arranged along the span direction (y direction), and its width is 0.5-3 mm (preferably 1 mm). The covering electrode 120 is also a strip of copper foil with the same thickness as the exposed electrode 110. The long side of the covering electrode 120 is also arranged along the flow direction (x direction), and its length covers the entire drag reduction area; the short side is arranged along the span direction (y direction), and its width is 3-10 mm (preferably 5 mm). The insulating medium 130 is made of polyimide film with a thickness of 0.05-0.5 mm (preferably 0.18 mm). Because polyimide film is a flexible material, it can be tightly attached to various parts of an aircraft, including curved surfaces. In specific applications, when the curvature of the aircraft skin is not large, the polyimide material can be replaced with materials such as alumina ceramic sheets as needed to improve its durability.

[0026] During assembly, the cover electrode 120 is first attached. If the aircraft skin 300 is an insulating material, the cover electrode 120 can be directly attached to the top of the aircraft skin 300 (positive y-direction). If the aircraft skin 300 is a conductive material, an insulating film (such as polyimide) must first be attached to the surface of the aircraft skin 300, and then the cover electrode 120 is attached on top of the insulating film. After the cover electrode 120 is attached, the insulating medium 130 is tightly attached on top of it to ensure that there is no air around the cover electrode 120. To ensure the sealing of the insulating medium 130 to the cover electrode 120, a groove of the same size as the cover electrode 120 can be pre-machined below the position of the cover electrode 120 on the upper surface of the aircraft skin 300. After the cover electrode 120 is embedded in the groove, the insulating medium 130 is then attached. Subsequently, the exposed electrode 110 is attached above the insulating medium 130, ensuring that the normal projection of one long side of the exposed electrode 110 is aligned with one long side of the covering electrode 120. One exposed electrode 110 and one covering electrode 120 form an electrode group 160. The spanwise spacing between corresponding positions of adjacent electrode groups 160 should be between 750δν and 1450δν, where δ ν The viscous length of the boundary layer is measured by the following formula: In the formula, ν is the kinematic viscosity of the fluid, u τ Let τ be the boundary layer friction velocity. wρ represents the wall shear stress, and ρ represents the fluid density. Furthermore, jet orifices 170 are formed in the insulating medium 130 between adjacent electrode groups 160. The jet orifices 170 are square through holes with a flow length identical to the exposed electrode 110 and a spanwise width slightly smaller than the spacing between electrode groups 160 by 1 mm. They are used to embed the porous medium 240 to cooperate with the corona excitation module 200 in generating a normal jet.

[0027] Reference Figures 1 to 5 The corona excitation module 200 mainly consists of a corona negative electrode 210, a corona positive electrode 220, an internal air blowing hole 230, and a porous medium 240, etc. Figure 3 As shown. For ease of observation, Figure 3 In the demonstration, the aircraft skin 300 was made transparent. In reality, the aircraft skin 300 is usually made of aluminum alloy, titanium alloy, or composite materials, and is not a transparent material. The corona negative electrode 210 is cylindrical and made of ablation-resistant metals such as copper or tungsten, or graphite materials. The diameter of the bottom surface of the cylinder is 0.5-2mm (preferably 1mm), and the height of the cylinder is 5-20mm (preferably 10mm). In practical applications, the upper end face (positive z-direction) of the corona negative electrode 210 can be sharpened to achieve stronger discharge. The corona positive electrode 220 is annular and made of ablation-resistant metals such as copper or tungsten, or graphite materials. It is embedded in the aircraft skin 300. If the aircraft skin 300 is a conductive material, an insulating material needs to be wrapped around the outside of the corona positive electrode 220 during embedding. After embedding, the inner ring of the corona positive electrode 220 forms an inner air blowing hole 230. The inner diameter of the corona positive electrode 220 ring is 10-30mm (preferably 20mm), and the outer diameter is 2-6mm (preferably 4mm) larger than the inner diameter, ensuring a ring wall thickness of 1-3mm (preferably 2mm). The porous medium 240 can be made of sintered stainless steel, three-dimensional woven composite materials, etc., ensuring a porosity of 20-50% (preferably 25%) and a pore size of 0.1-1mm (preferably 0.2mm). It is cut into a square shape, and its flow direction and spanwise dimensions are the same as those of the jet square hole 170, and its thickness is the same as that of the aircraft skin 300.

[0028] Based on the aircraft skin 300, the corona positive electrode 220, corona negative electrode 210, dielectric barrier discharge excitation module 100, and porous dielectric 240 are sequentially assembled to form the aircraft skin. Figure 1 The microjets-enhanced vortex plasma turbulence drag reduction device is shown. For ease of observation, Figure 1 The third porous medium 240 from the left is not shown. Meanwhile, the aircraft skin 300 has been made transparent. In actual application, all porous media 240 should be fully assembled. At the same time, the aircraft skin 300 is generally made of opaque materials such as metal and composite materials.

[0029] This embodiment also discloses an assembly method for a microjets-enhanced vortex plasma turbulence drag reduction device, applied to the above-mentioned device, including the following steps: Step S1: First attach the cover electrode 120, and then attach the insulating medium 130 tightly on top of it; Step S2: Attach the exposed electrode 110. The exposed electrode 110 is attached above the insulating medium 130. One exposed electrode 110 and one covered electrode 120 form an electrode group 160, which is assembled into a dielectric barrier discharge excitation module 100. Step S3: First, embed the corona positive electrode 220 into the aircraft skin 300, ensuring that the annular axis of the corona positive electrode 220 is parallel to the normal. Then, install the corona negative electrode 210 below the corona positive electrode 220, ensuring that the bottom circle of the corona negative electrode 210 is coaxial with the bottom annular circle of the corona positive electrode 220, and assemble to form a corona discharge unit. Step S4: Inside the aircraft skin 300, multiple corona discharge units are arranged in an array at the normal projection position of the jet square hole 170 to generate a corona normal jet in the internal blowing hole 230. The porous medium 240 is embedded in the jet square hole 170, and the corona normal jet is rectified by the porous medium 240 to form micro-blowing air. Figure 1 (As shown by the middle arrow), and then assembled to form a microjet-enhanced vortex plasma turbulence drag reduction device.

[0030] In step S1, a groove of the same size as the cover electrode 120 is pre-processed below the position of the cover electrode 120 on the upper surface of the aircraft skin 300. After the cover electrode 120 is embedded in the groove, an insulating medium 130 is attached to ensure that the normal projection of one long side of the exposed electrode 110 is aligned with one long side of the cover electrode 120. A jet square hole 170 is opened on the insulating medium 130 between adjacent electrode groups 160. The jet square hole 170 is a square through hole with the same flow length as the exposed electrode 110 and a spanwise width that is slightly smaller than the spacing between electrode groups 160 by 1 mm. It is used to embed the porous medium 240 to cooperate with the corona excitation module 200 to generate a normal jet.

[0031] In step S4, the high-voltage DC power supply is turned on, and the output voltage amplitude is adjusted to ensure a stable corona discharge between the corona positive electrode 220 and the corona negative electrode 210, thus forming a corona discharge. Figure 6(Middle purple part) When the high-voltage sinusoidal power supply is turned on, a high-voltage sinusoidal wave is applied between the exposed electrode 110 and the covered electrode 120, thereby generating a strong spanwise electric field between the exposed electrode 110 and the covered electrode 120. Under the constraint of the insulating medium 130, the air on the surface of the insulating medium 130 directly above the covered electrode 120 will be ionized by the strong electric field between the electrodes, forming a dielectric barrier discharge. This will generate a horizontal jet in the spanwise direction from the exposed electrode 110 to the covered electrode 120. In the boundary layer where the mainstream velocity is along the flow direction, the above-mentioned horizontal jet will interact with the boundary layer flow, forming vortices in the boundary layer and forming a flow vortex along the electrode direction. On the upward washing side of the flow vortex, the low-speed fluid at the bottom of the boundary layer sweeps upward, the bottom velocity and Reynolds stress of the boundary layer decrease, and the frictional resistance decreases. Conversely, on the downward washing side, the high-speed fluid at the top of the boundary layer accumulates towards the wall, the bottom velocity and Reynolds stress both increase, and the frictional resistance increases.

[0032] Reference Figures 1 to 6 During the assembly of the corona excitation module 200, the corona positive electrode 220 is first embedded into the aircraft skin 300, ensuring that the annular axis of the corona positive electrode 220 is parallel to the normal (z-direction). Subsequently, the corona negative electrode 210 is installed below the corona positive electrode 220 (in the negative z-direction), ensuring that the bottom circle of the corona negative electrode 210 is coaxial with the bottom annular surface of the corona positive electrode 220, and the normal distance between the upper end face of the corona negative electrode 210 and the lower end face of the corona positive electrode 220 is 5-20 mm (preferably 10 mm). After the assembly of one corona negative electrode 210 and one corona positive electrode 220, a corona discharge unit is formed. Inside the aircraft skin 300, multiple corona discharge units are arranged in an array at the normal projection position of the jet square hole 170 to generate a corona normal jet in the internal air blowing hole 230. Based on this, the porous medium 240 is embedded in the jet square hole 170, and the corona normal jet is rectified by the porous medium 240 to form micro-blowing air.

[0033] Reference Figures 1 to 6 The working method of the above-mentioned microjets-enhanced vortex plasma turbulence drag reduction device is described as follows: 1. Connect all corona positive electrodes 220 to the positive terminal of the high-voltage DC power supply, with all corona positive electrodes 220 connected in parallel, and all corona negative electrodes 210 grounded; simultaneously connect all exposed electrodes 110 to the positive terminal of the high-voltage sinusoidal power supply, with all exposed electrodes 110 connected in parallel, and all covering electrodes 120 grounded. The above connection method is a common method in the field of electrical and electronic engineering, and will not be described in detail here.

[0034] 2. Turn on the high-voltage DC power supply and adjust the output voltage amplitude to ensure a stable corona discharge between the corona positive electrode 220 and the corona negative electrode 210, thus forming a corona. The output voltage amplitude of the high-voltage DC power supply should be within a reasonable range. If the voltage amplitude is too small, corona will not be generated, while if the voltage amplitude is too large, unexpected arc discharge will occur. The above-mentioned output voltage amplitude range is related to the distance between the corona positive electrode 220 and the corona negative electrode 210, and should be adjusted as needed in practical applications. The corona discharge ionizes the air between the electrodes, generating a large number of negative ions. Under the influence of the electric field between the electrodes, the ionized negative ions move from the lower corona negative electrode to the upper corona positive electrode, and continuously collide with air molecules, forming an upward ion wind ( Figure 1 A purple region is located between the corona positive electrode 220 and the corona negative electrode 210. Under the induction of particle wind, an upward (positive z-direction) normal jet can be generated in the internal blowing hole 230. After the normal jet is rectified by the porous medium 240, it can form micro-blowing on the surface of the aircraft.

[0035] 3. Turn on the high-voltage sinusoidal power supply and apply a high-voltage sinusoidal wave between the exposed electrode 110 and the covered electrode 120, thereby generating a strong electric field in the spanwise direction (positive y-direction) between the exposed electrode 110 and the covered electrode 120. Under the constraint of the insulating medium 130, the air on the surface of the insulating medium 130 directly above the covered electrode 120 will be ionized by the strong electric field between the electrodes, forming a dielectric barrier discharge. According to the principle of dielectric barrier discharge, this will further generate a horizontal jet in the spanwise direction (positive y-direction) pointing from the exposed electrode 110 to the covered electrode 120. In the boundary layer where the main flow velocity is along the flow direction (positive x-direction), the above-mentioned horizontal jet will interact with the boundary layer flow, forming vortices in the boundary layer, forming vortices axially along the electrode direction (x-direction), called flow-direction vortices. On the upward-washing side (positive y-direction side) towards the vortex, low-velocity fluid sweeps upward from the bottom of the boundary layer, reducing the velocity and Reynolds stress at the bottom of the boundary layer, thus decreasing frictional resistance. Conversely, on the downward-washing side (negative y-direction side), high-velocity fluid accumulates towards the wall at the top of the boundary layer, increasing both the velocity and Reynolds stress at the bottom of the layer, thus increasing frictional resistance. Figure 5 The fifth and sixth corona discharge units from the left in the middle are shown. (And...) Figure 1 Similarly, for ease of comparison and explanation, Figure 5 The fifth and sixth corona discharge units from the left in the middle were not connected to the high-voltage DC power supply. Only the dielectric barrier discharge module was active at this location, which was used to compare the drag reduction effect of microjets enhanced vortex plasma turbulence with other locations.

[0036] 4. Since the corona excitation modules 200 are all located between adjacent electrode groups 160 of the dielectric barrier discharge excitation module 100, the micro-blowing air generated by the corona excitation module 200 is also located between adjacent flow vortices, thus generating complex interactions, such as... Figure 5As shown. Specifically, on the upward sweeping side (positive y-direction side) of the flow-directing vortex, the low-velocity fluid at the bottom of the boundary layer sweeps upward, reducing frictional resistance. The micro-blowing promotes the upward sweeping effect of the flow-directing vortex, further enhancing the drag reduction effect. On the downward sweeping side (negative y-direction side) of the flow-directing vortex, the high-velocity fluid at the top of the boundary layer accumulates towards the wall, increasing frictional resistance. At this time, the micro-blowing can suppress the drag increase caused by the downward sweeping of the flow-directing vortex and produce an upward sweeping effect similar to that on the upward sweeping side.

[0037] Implementation Principle: The corona excitation module 200 generates normal micro-blowing air, which eliminates the drag-increasing effect of the downwash caused by the flow vortex induced by the dielectric barrier discharge excitation module 100, and enhances the drag reduction effect of the upsweep, thereby improving the overall drag reduction effect and enhancing the drag reduction capability at higher incoming flow velocities. Simultaneously, the flow vortex induced by the dielectric barrier discharge excitation module 100 promotes the downstream transport of the low-speed fluid layer generated by the micro-blowing air, increasing the drag reduction area downstream of the blowing zone and further enhancing the overall drag reduction effect. While improving the drag reduction effect and increasing drag reduction energy savings, by distributing a portion of the discharge power of the dielectric barrier discharge excitation module 100 to the high-efficiency corona excitation module 200, the overall energy consumption of the system is reduced, thus achieving the goal of improving energy efficiency.

[0038] Existing dielectric barrier discharge actuators work by coupling drag reduction and drag enhancement effects on the boundary layer, resulting in limited overall drag reduction and poor performance under high-speed flow conditions. This invention employs corona micro-blowing, which counteracts the drag enhancement effect of the dielectric barrier discharge actuator while simultaneously enhancing its drag reduction effect, thus significantly improving the overall drag reduction performance and enhancing drag reduction capabilities under high-speed conditions. Through the organic coupling of vortices and microjets, this invention not only enhances local drag reduction but also promotes mixing between the microjets and the boundary layer using the vortex effect, allowing the drag reduction effect generated by the microjets to propagate downstream to a more distant region. Compared to existing drag reduction methods based solely on dielectric barrier discharge or corona discharge, the overall drag reduction range is larger. Corona discharge has an order of magnitude higher mechanical efficiency than conventional dielectric barrier discharge. This invention introduces the effect of corona discharge into dielectric barrier discharge, resulting in higher overall mechanical efficiency compared to existing dielectric barrier discharge turbulent drag reduction methods. It achieves considerable drag reduction with lower energy consumption, thereby improving the energy efficiency of drag reduction.

[0039] It should be noted that the connection relationships of components not specifically mentioned in this application are all assumed to be based on existing technology. Since they do not involve the inventive point and are commonly used in existing technology, the structural connection relationships are not described in detail.

Claims

1. A microjets-enhanced vortex plasma turbulence drag reduction device, characterized in that, Includes a dielectric barrier discharge excitation module (100) and a corona excitation module (200) mounted on the aircraft skin (300). The dielectric barrier discharge excitation module (100) includes an exposed electrode (110), a cover electrode (120), an insulating medium (130), and a jet square hole (170). The exposed electrode (110) is elongated and its long side is arranged along the flow direction, covering the entire drag reduction area. The exposed electrode (110) is arranged along the spanwise direction. The cover electrode (120) is elongated and its long side is arranged along the flow direction, covering the drag reduction area. The short side is arranged along the spanwise direction. The insulating medium (130) is closely attached to various parts of the aircraft, including curved surfaces. The exposed electrode (110) and the cover electrode (120) are distributed on the upper and lower sides of the insulating medium (130). One exposed electrode (110) and one cover electrode (120) form an electrode group (160). The jet square hole (170) is opened on the insulating medium (130) between adjacent electrode groups (160). The corona excitation module (200) includes a corona negative electrode (210), a corona positive electrode (220), an inner air blowing hole (230), and a porous medium (240). The corona positive electrode (220) is annular. The inner air blowing hole (230) is located inside the annular corona positive electrode (220). The corona negative electrode (210) is coaxially located at the lower end of the corona positive electrode (220). The porous medium (240) is located directly above the inner air blowing hole (230). After the corona negative electrode (210) and the corona positive electrode (220) are assembled, they form a corona discharge unit. Multiple corona discharge units are arranged in an array at the normal projection position of the jet square hole (170) to generate a corona normal jet in the internal blowing hole (230). The porous medium (240) is embedded in the jet square hole (170), and the corona normal jet is rectified by the porous medium (240) to form micro-blowing.

2. The microjets-enhanced vortex plasma turbulence drag reduction device according to claim 1, characterized in that, The corona negative electrode (210) is cylindrical and made of ablation-resistant conductive material. The diameter of the bottom surface of the cylinder is 0.5-2mm and the height of the cylinder is 5-20mm. The upper end face of the corona negative electrode (210) is sharpened.

3. The microjets-enhanced vortex plasma turbulence drag reduction device according to claim 1, characterized in that, The corona positive electrode (220) is annular and is connected to the positive terminal of a high-voltage DC power supply. It is made of an ablation-resistant conductive material and is embedded in the aircraft skin (300). The aircraft skin (300) is also made of conductive material. The corona positive electrode (220) is wrapped with an insulating material. The normal distance between the upper end face of the corona negative electrode (210) and the lower end face of the corona positive electrode (220) is 5-20 mm. All corona positive electrodes (220) are connected to the positive terminal of the high-voltage DC power supply and are connected in parallel. All corona negative electrodes (210) are grounded. All exposed electrodes (110) are connected to the positive terminal of a high-voltage sinusoidal power supply and are connected in parallel. All covered electrodes (120) are grounded.

4. The microjets-enhanced vortex plasma turbulence drag reduction device according to claim 1, characterized in that, The inner diameter of the corona positive electrode (220) ring is 10-30mm, the outer diameter is 2-6mm larger than the inner diameter, and the ring wall thickness is 1-3mm.

5. The microjets-enhanced vortex plasma turbulence drag reduction device according to claim 1, characterized in that, The porous medium (240) has a porosity of 20-50% and a pore size of 0.1-1mm. It is cut into a square shape, and its flow direction and spanwise dimensions are the same as those of the jet square hole (170). Its thickness is the same as that of the aircraft skin (300).

6. A method for assembling a microjets-enhanced vortex plasma turbulence drag reduction device, characterized in that, Applied to any one of claims 1 to 5 above, it includes the following steps: Step S1: First attach the cover electrode (120), and then attach the insulating medium (130) tightly on top of it; Step S2: Attach the exposed electrode (110). The exposed electrode (110) is attached above the insulating medium (130). One exposed electrode (110) and one covered electrode (120) form an electrode group (160) and are assembled into a dielectric barrier discharge excitation module (100). Step S3: First, embed the corona positive electrode (220) into the aircraft skin (300), ensuring that the annular axis of the corona positive electrode (220) is parallel to the normal. Then, install the corona negative electrode (210) below the corona positive electrode (220), ensuring that the bottom circle of the corona negative electrode (210) is coaxial with the bottom annular circle of the corona positive electrode (220), and assemble to form a corona discharge unit. Step S4: Inside the aircraft skin (300), multiple corona discharge units are arranged in an array at the normal projection position of the jet square hole (170) to generate a corona normal jet in the internal blowing hole (230). The porous medium (240) is embedded in the jet square hole (170). After the corona normal jet is rectified by the porous medium (240), it forms a micro-blowing air, which is then assembled to form a micro-jet enhanced vortex plasma turbulence drag reduction device.

7. The assembly method of the microjets-enhanced vortex plasma turbulence drag reduction device according to claim 6, characterized in that, In step S1, a groove of the same size as the cover electrode (120) is pre-processed below the position of the cover electrode (120) on the upper surface of the aircraft skin (300). After the cover electrode (120) is embedded in the groove, an insulating medium (130) is attached to ensure that the normal projection of one long side of the exposed electrode (110) is aligned with one long side of the cover electrode (120). The jet square hole (170) is opened on the insulating medium (130) between adjacent electrode groups (160). Its flow length is the same as that of the exposed electrode (110), and its span width is 1 mm smaller than the spacing between the electrode groups (160). It is used to embed the porous medium (240) to cooperate with the corona excitation module (200) to generate a normal jet.

8. The assembly method of the microjets-enhanced vortex plasma turbulence drag reduction device according to claim 6, characterized in that, In step S2, the spanwise spacing between adjacent electrode groups (160) should be between 750δν and 1450δν, where δν is the viscous length scale of the boundary layer, which can be calculated according to the following formula. In the formula, ν is the kinematic viscosity of the fluid, u τ Let τ be the boundary layer friction velocity. w Let ρ be the wall shear stress and ρ be the fluid density.

9. The assembly method of the microjets-enhanced vortex plasma turbulence drag reduction device according to claim 6, characterized in that, In step S4, the high-voltage DC power supply is turned on, and the output voltage amplitude is adjusted to ensure a stable corona discharge between the corona positive electrode (220) and the corona negative electrode (210), thus forming a corona. The high-voltage sinusoidal power supply is turned on, and a high-voltage sinusoidal wave is applied between the exposed electrode (110) and the covered electrode (120), thereby generating a strong spanwise electric field between the exposed electrode (110) and the covered electrode (120). Under the constraint of the insulating medium (130), the air on the surface of the insulating medium (130) directly above the covered electrode (120) will be electrified by the strong electric field between the electrodes. The separation forms a dielectric barrier discharge, which in turn generates a horizontal jet pointing from the bare electrode (110) to the covered electrode (120) in the spanwise direction. In the boundary layer where the mainstream velocity is along the flow direction, the horizontal jet will interact with the boundary layer flow, forming vortices in the boundary layer and forming a flow vortex along the electrode direction. On the upwash side of the flow vortex, the low-speed fluid at the bottom of the boundary layer sweeps upward, and the velocity and Reynolds stress of the bottom layer of the boundary layer decrease, thus reducing the frictional resistance. Conversely, on the downwash side, the high-speed fluid at the top of the boundary layer accumulates towards the wall, and the velocity and Reynolds stress of the bottom layer both increase, thus increasing the frictional resistance.

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