Semiconductor-ignited superdense arc array turbulent friction drag reduction device and method
By using a semiconductor arc-initiating ultra-dense arc array device that forms an arc plasma chain in the flow field, the problem of poor drag reduction effect of turbulent friction under high incoming flow velocity is solved, and effective drag reduction and strong adaptability are achieved at higher speeds.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- AIR FORCE UNIV PLA
- Filing Date
- 2023-07-27
- Publication Date
- 2026-07-14
AI Technical Summary
Existing technologies struggle to effectively reduce drag from turbulent friction at high inflow velocities, the drag reduction effect of dielectric barrier discharge decreases rapidly, and active control methods are energy-intensive and have poor adaptability.
A semiconductor arc-initiating ultra-dense arc array device is used to generate thermal blockage along the flow direction by forming an arc plasma chain in the flow field, which separates the strip structure of the bottom layer of the turbulent boundary layer. Semiconductor materials are used to reduce the breakdown voltage to increase the spanwise density, thereby achieving active adjustment of discharge intensity and density.
It achieves effective drag reduction at higher inflow velocities, is highly adaptable, and has a significant drag reduction effect. It can be adjusted in real time to adapt to different flow field conditions and reduce turbulent frictional resistance.
Smart Images
Figure CN116847526B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of plasma flow control technology, and in particular to a novel plasma actuator for reducing frictional drag in turbulent boundary layers, specifically relating to a semiconductor arc-initiating ultra-dense arc array turbulent frictional drag reduction device and method. Background Technology
[0002] Increasing lift and reducing drag has always been a goal of aircraft aerodynamic design. For large transport aircraft and high-aspect-ratio UAVs, frictional drag accounts for nearly 50% of the total drag during cruise flight. 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.
[0003] Boundary layer flow drag reduction control technology is mainly divided into two types: passive control and active control. A typical passive flow control method relies on small ribs. Small ribs refer to flow-oriented protrusions periodically arranged along the spanwise direction at the boundary layer surface. By separating the striped structure of the turbulent boundary layer, they can achieve a drag reduction effect of about 8% to 10%. However, their adaptability is poor, and their working range is limited. Most small ribs 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 drop significantly, or even increase drag. These changes are unavoidable in actual flight, making it difficult for simple small ribs to achieve drag reduction applications in real-world flight.
[0004] Typical active flow control methods include air blowing and spanwise wall oscillation, which are highly adaptable. Air blowing can achieve 20%–30% turbulence drag reduction, while spanwise wall oscillation can reduce turbulent frictional drag by 45%. However, active control methods often require complex air intake pipes, air sources, motors, and complex mechanical structures. 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, making it the most promising turbulence drag reduction method for practical applications and a research hotspot in recent years. Among plasma turbulence drag reduction methods, dielectric barrier discharge is commonly used, which can achieve an 11% drag reduction effect on airfoil turbulence friction at an incoming flow velocity of 20 m / s. However, due to the limited intensity of dielectric barrier discharge (the induced velocity is generally only 2-3 m / s), the drag reduction effect rapidly decreases to 2.6% when the incoming flow velocity increases to 30 m / s; and disappears when the incoming flow velocity increases further. For typical UAVs (such as Wing Loong-2 and Rainbow-5), their flight speeds are generally greater than 50 m / s, while for large passenger aircraft (such as Airbus A320 and C919), their cruising speeds exceed 200 m / s. Therefore, there is an urgent need to find plasma discharge methods with stronger intensity to achieve effective drag reduction at higher incoming flow velocities. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a semiconductor arc-initiating ultra-dense arc array turbulence friction reduction device, comprising a semiconductor block 1, an electrode 2, a ceramic block 3, and a high-voltage pulse power supply 4; wherein...
[0007] Semiconductor block 1 is in the shape of a thin cuboid. Multiple cylindrical blind holes with the same spacing and even distribution are opened on the side of semiconductor block 1. The axes of these blind holes are on the same plane, which is parallel to the front and rear surfaces of semiconductor block 1.
[0008] Establish an xyz spatial coordinate system, with the positive x-axis pointing in the direction of the incoming flow, the positive y-axis pointing in the horizontal plane perpendicular to the direction of the incoming flow, and the positive z-axis pointing vertically upward. The front and rear surfaces of semiconductor block 1 are parallel to the xoz plane; the side of semiconductor block 1 with the cylindrical blind hole is parallel to the xoy plane.
[0009] The discharge electrode 2 is a solid cylindrical rod, the shape of which is adapted to the blind hole of the semiconductor block 1 and inserted therein. After the discharge electrode 2 is inserted, one end of it is flush with the side of the semiconductor block and exposed to the air, while the other end is inserted into the bottom of the blind hole.
[0010] The topmost of the multiple cylindrical blind holes has a perforation at the bottom for a wire to pass through, connecting the topmost electrode to the high-voltage output terminal of the high-voltage pulse power supply 4; the bottommost discharge electrode 2 is also grounded through a lead wire through the perforation at the bottom of the blind hole; the middle electrode is suspended and not connected in any way; the low-voltage output terminal of the high-voltage pulse power supply 4 is grounded.
[0011] The ceramic block 3 is a thin cuboid shape, and the projection of the front and rear surfaces of the ceramic block 3, which are parallel to the xoz plane, onto the xoz plane completely overlaps with the semiconductor block 1.
[0012] Multiple semiconductor blocks 1 and ceramic blocks 3 with inserted discharge electrodes 2 are arranged at intervals, with the outermost layer being ceramic blocks 3, so that the multiple discharge electrodes 2 inserted on the semiconductor blocks 1 form an electrode array, and each semiconductor block 1 uses a separate high-voltage pulse power supply 4.
[0013] In one embodiment of the present invention, the length of the semiconductor block 1 in the x-direction is the same as that of the target area for drag reduction; the thickness in the y-direction is 1mm to 3mm; the width in the z-direction is 5mm to 10mm; the diameter of the blind hole should be at least 0.5mm smaller than the thickness of the semiconductor block; the depth of the blind hole should be at least 1mm smaller than the width of the semiconductor block 1; the spacing between adjacent blind holes on the same semiconductor block 1 should be greater than 0.1mm; there are a total of N cylindrical blind holes, N≥5, and the distance between the center of the first and last cylindrical blind holes and the edge of the semiconductor block 1 in the x-direction should be greater than 1mm.
[0014] In one specific embodiment of the present invention, the diameter of the blind hole is 0.5 mm to 2 mm; the depth of the blind hole is 4 mm to 9 mm.
[0015] In another specific embodiment of the present invention, the semiconductor block 1 has a thickness of 2 mm in the y direction, a width of 10 mm in the z direction, a blind hole diameter of 1 mm, a blind hole depth of 8 mm, a spacing of 4 mm between adjacent blind holes on the same semiconductor block 1, and a total of 5 cylindrical blind holes. The distance between the center of the first and last cylindrical blind holes and the edge of the semiconductor block 1 in the x direction is 2 mm.
[0016] In yet another specific embodiment of the present invention
[0017] A discharge electrode 2 is inserted into each cylindrical blind hole;
[0018] The ceramic block 3 has a length of 20 mm in the x direction, a width of 1 mm in the y direction, and a thickness of 10 mm in the z direction. The ceramic block 3 and the semiconductor block 1 into which the discharge electrode 2 is inserted are arranged at intervals to form an electrode array with a flow distance of 4 mm and a spanwise distance of 2 mm.
[0019] In another embodiment of the present invention, the semiconductor block 1 is made of silicon nitride semiconductor or ceramic material with cuprous oxide coating; the discharge electrode 2 is made of heat-resistant conductive metal material or non-metallic conductive material such as graphite; the high-voltage pulse power supply 4 is selected with voltage > 3kV and frequency > 1kHz, and the power supply volume and weight should be as small as possible.
[0020] In the specific installation of the aforementioned semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device, the device is embedded inside the surface where drag reduction is required, with the exposed side of the discharge electrode 2 flush with the surface. The size of the device and the number of semiconductor blocks 1, discharge electrodes 2, and ceramic blocks 3 are adjusted according to the size of the area requiring drag reduction, and the device is positioned slightly upstream in the drag reduction area. The spanwise spacing d of the discharge electrodes 2 is [not specified]. y Determined by the flow field conditions, the following must be satisfied:
[0021] d y =15~20δ v (1)
[0022] δ v =v / u τ (2)
[0023] Where v is the kinematic viscosity of air, d is the spanwise electrode spacing, and δ v For the boundary layer viscous length scale, u τ The boundary layer friction velocity is denoted by ; the flow spacing of the discharge electrode 2 is determined by the spanwise spacing and the breakdown voltage of the semiconductor material surface, ensuring discharge in the flow direction and no discharge in the spanwise direction.
[0024] The working process of the above-mentioned semiconductor arc-initiating ultra-dense arc array turbulence friction reduction device after a single semiconductor block 1 inserted into the discharge electrode 2 is energized is as follows:
[0025] High-voltage pulse power supply 4 generates a pulsed high voltage, which is applied to the array of discharge electrodes 2, creating a strong electric field between the discharge electrodes 2 and generating an initial current in semiconductor block 1. This heats the semiconductor in the current path. Because semiconductor materials have a negative temperature coefficient of resistance, when the voltage remains constant, the current in the initial current path will continuously increase due to the decrease in resistance, leading to a continuous enhancement of the heating effect. This forms a positive cycle of "enhanced heating - decreased resistance - increased current - further enhanced heating," causing most of the current in the circuit to concentrate in a narrow path on the side of the exposed discharge electrodes 2 of semiconductor block 1. Above, that is, the flow path connecting each relay discharge electrode 2; in this conductive path, the temperature rises rapidly, causing the semiconductor material to evaporate, forming a material vapor with a high degree of ionization but low electrical strength in the conductive path between the discharge electrodes 2; this material vapor further increases the conductivity of the discharge path, making the resistance of the discharge path extremely small, equivalent to a wire, the high-voltage pulse power supply 4 is short-circuited by the discharge path, generating a strong arc discharge in the discharge path, generating plasma, forming an explosive heating effect along the flow direction, generating thermal blockage in the flow field, forming a "virtual rib" in the flow direction; the discharge occurs along the setting direction of the semiconductor;
[0026] The working process of the semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device is as follows:
[0027] Individual semiconductor blocks 1 inserted into the discharge electrode 2 are arranged side by side in the longitudinal direction, and adjacent semiconductor blocks 1 are separated by ceramic blocks 3 to form a semiconductor arc-initiating ultra-dense arc array turbulence friction reduction device. Due to the presence of semiconductor blocks 1, the discharge electrode 2 is more likely to discharge along the flow direction to generate arc 5, but less likely to discharge along the longitudinal direction to form arc 5 along the flow direction. Under the action of the relay discharge electrode 2, each arc 5 is connected end to end along the flow direction to form an "arc plasma chain". It forms an array-like "virtual rib" effect in the flow field, that is, the thermal blocking effect generated by the arc 5 connected end to end, which separates the strip structure of the bottom layer of the boundary layer and achieves the purpose of turbulence friction reduction.
[0028] The last high-voltage pulse power supply 4 is in the off state, so the discharge electrode 2 on the last semiconductor block 1 does not discharge to generate an electric arc 5. The other high-voltage pulse power supplies 4 are turned on, forming an array of electric arcs 5 on the side of the device.
[0029] A method for operating a semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device is also provided:
[0030] When the incoming flow velocity is high, all high-voltage pulse power supplies 4 are turned on, so that each column of electrode groups generates an electric arc discharge. The discharge generates a heating effect in the boundary layer, which causes blockage of the flow field and forms virtual ribs. The virtual ribs separate the strip structure in the boundary layer, thereby suppressing turbulent pulsation and reducing turbulent frictional resistance.
[0031] When the incoming flow velocity is not high, the spanwise spacing is larger than when the incoming flow velocity is high. According to the actual incoming flow velocity requirements, the form of inter-column discharge is adopted to increase the spanwise spacing of the virtual ribs. In order to adapt to a wider incoming flow velocity scenario, the spanwise spacing of the discharge electrode 2 is made as small as possible. The flow direction spacing of the discharge electrode 2 is determined according to the spanwise spacing, ensuring that there is no discharge along the spanwise direction.
[0032] In addition, a method for reducing turbulent friction drag using an ultra-dense electric arc array based on semiconductor arc initiation is also provided. This method is based on the aforementioned semiconductor arc initiation ultra-dense electric arc array turbulent friction drag reduction device, and the specific process is as follows:
[0033] Step S1: The sensor collects flow field data. The sensor is placed in the flow field to collect information such as temperature, pressure, velocity, and wall shear stress in the flow field in real time, and inputs the data into the controller.
[0034] Step S2: Analyze the data collected by the sensors in the controller, and determine the mainstream speed u measured by the sensors. ∞ Take the friction speed u τ =0.035u ∞ Kinematic viscosity v = 1.51 × 10 -5 m2 / s, based on equation (2), the boundary layer viscous length scale δ is calculated. v ,
[0035] δ v =v / u τ (2)
[0036] Therefore, the spanwise spacing d of the current electric arc 5 can be determined. y Is it located between 15 and 20δ? v between;
[0037] Step S3: Based on the calculation and analysis results, select the appropriate operating mode and parameters through the control circuit. Different modes correspond to different spanning distances, thus adjusting the spanning distance d of the arc 5. y Maintain at 15-20δ v between;
[0038] The controller determines the required discharge strategy based on equations (1) and (2).
[0039] d y =15~20δ v (1)
[0040] If the current spanwise spacing of the small ribs is d y >15~20δ v , where δ v To test the obtained boundary layer viscous length scale, it is necessary to control the discharge of more electrode groups by controlling the switching of the high-voltage pulse power supply 4, and to densify the spanwise of the arc 5; if the current spanwise spacing d of the small ribs... y <15~20δ v Then, the number of discharge electrode groups needs to be reduced by controlling the switch of the high-voltage pulse power supply 4, so that the arc 5 becomes sparser along the span direction, in order to meet the flow field's requirements for drag reduction.
[0041] Step S4: The sensor collects flow field data again to gather flow field information after the arc discharge.
[0042] Step S5: Analyze the data collected by the sensor again in the controller, compare the information before and after the arc discharge, and compare the changes in frictional resistance measured before and after the arc discharge under the temperature, pressure and speed conditions. If the measured frictional resistance is less than the frictional resistance before the arc discharge, the expected drag reduction effect is achieved and the work ends. Otherwise, select a new working mode or a new discharge state from step S1 based on the flow field information.
[0043] This invention arranges a discharge electrode array along the flow direction on the wall surface, generating an array-type arc discharge in the flow field. The arc discharge, with a greater intensity than dielectric barrier discharge, creates stronger disturbances in the flow field, thereby achieving turbulent friction drag reduction at higher flow velocities. The arc discharge generates rapid heating, producing hot air masses in the flow field and creating thermal blockage. In this invention, the electrodes are arranged along the flow direction, thus forming a flow-direction thermal blockage zone in the flow field, producing a "virtual rib" effect similar to the rib drag reduction method. This separates the strip structure at the bottom layer of the turbulent boundary layer, thereby achieving the effect of turbulent friction drag reduction.
[0044] As the incoming flow velocity increases, the required spanwise spacing of the ribs becomes denser. However, since arc discharge always occurs on the two closest electrodes, the spanwise spacing of the electrode array cannot exceed its flow-direction spacing, limiting performance improvement. Therefore, to further improve the effective drag reduction for incoming flow velocities, based on the aforementioned arc array turbulent friction drag reduction device, the characteristics of semiconductor materials in reducing arc discharge breakdown voltage are utilized to induce arcs along the flow direction, further increasing the spanwise density of the arc array and thus further improving the effective drag reduction for incoming flow velocities. Since arc discharge is commonly used in flow control in supersonic flow fields (incoming flow velocities greater than 340 m / s), compared to typical plasma turbulent drag reduction methods based on dielectric barrier discharge, the device of this invention has a greater discharge intensity, enabling drag reduction at higher incoming flow velocities. Compared to traditional passive control methods such as rib drag reduction, this invention is an active method with greater adaptability, capable of adjusting the discharge intensity and density in real time according to the incoming flow conditions to meet drag reduction needs under different incoming flow conditions. It can also achieve effective drag reduction in actual flight where incoming flow conditions change rapidly. Attached Figure Description
[0045] Figure 1 A schematic diagram of the overall structure of an ultra-dense arc array turbulent friction drag reduction device based on semiconductor arc initiation is shown.
[0046] Figure 2 The electrode geometry diagram is shown.
[0047] Figure 3 The diagram shows the geometric structure of the ceramic block;
[0048] Figure 4 The diagram shows the geometric structure of the semiconductor block.
[0049] Figure 5 A schematic diagram of a forward cycle that triggers semiconductor discharge is shown;
[0050] Figure 6 This diagram illustrates the drag reduction mode of turbulent friction at high speeds.
[0051] Figure 7The spanwise profile is shown under the turbulent friction drag reduction mode at high speeds;
[0052] Figure 8 This diagram illustrates the drag reduction mode of turbulent friction at lower speeds.
[0053] Figure 9 A flowchart of a method for reducing drag due to turbulence friction using an ultra-dense arc array based on semiconductor arc initiation is shown.
[0054] Figure 10 The diagram shows the relationship between the various parts of the turbulent friction drag reduction method based on semiconductor arc induction and ultra-dense arc array.
[0055] Attached image annotations:
[0056] 1. Semiconductor block 2. Electrode 3. Ceramic block 4. High-voltage pulse power supply 5. Electric arc 6. Virtual rib Detailed Implementation
[0057] This invention provides a semiconductor arc-initiating ultra-dense arc array turbulence friction reduction device, comprising a semiconductor block 1, an electrode 2, a ceramic block 3, and a high-voltage pulse power supply 4, such as... Figure 1 As shown.
[0058] like Figure 4 As shown, semiconductor block 1 is a thin cuboid shape, made of silicon carbide semiconductor material, or it can be an alumina ceramic block with a cuprous oxide semiconductor glaze coated on its surface. Multiple evenly spaced, cylindrical blind holes are formed on the side (thickness direction) of semiconductor block 1 for inserting discharge electrodes 2. After insertion, one end of the discharge electrode 2 is flush with the side of the semiconductor block and exposed to the air, while the other end is closed. The axes of these cylindrical blind holes are in a plane parallel to the front and rear surfaces of semiconductor block 1. The bottom of the uppermost blind hole is perforated to allow a wire to pass through, connecting the uppermost electrode to a high-voltage pulse power supply 4. The high-voltage pulse power supply 4 is located inside the cabin, with leads from the inside of the wing skin connecting to semiconductor block 1 and discharge electrodes 2 on the aircraft surface. The lowermost discharge electrode 2 is also grounded via a lead through a perforated bottom of a blind hole. The middle electrode is suspended and not connected to any part, serving as a relay. All other electrical connections employ conventional techniques in the art and will not be described further.
[0059] Establish an xyz spatial coordinate system. The positive x-axis points towards the incoming flow direction, which is the length direction of semiconductor block 1. The positive y-axis points in the horizontal plane perpendicular to the incoming flow direction, which is the thickness direction of semiconductor block 1. The positive z-axis points vertically upward, which is the width direction of semiconductor block 1. The front and rear surfaces of semiconductor block 1 are parallel to the xoz plane. The side of semiconductor block 1 with the cylindrical blind hole is parallel to the xoy plane.
[0060] Discharge electrode 2 is a solid cylindrical rod, such as Figure 2 As shown, the size is exactly the same as (or slightly smaller than) the cylindrical hole on the side of semiconductor block 1 for easy insertion, and discharge electrode 2 is inserted into the cylindrical blind hole. Discharge electrode 2 is usually made of copper or tungsten.
[0061] Ceramic block 3 is a thin cuboid shape, used to separate adjacent semiconductor blocks. For example... Figure 3 As shown, the projections of the front and rear surfaces of the ceramic block 3, which are parallel to the xoz plane, onto the xoz plane completely overlap with those of the semiconductor block 1. Multiple semiconductor blocks 1 and ceramic blocks 3 with inserted discharge electrodes 2 are arranged at intervals, with the outermost layer being ceramic blocks 3 (therefore, there is one more ceramic block 3 than semiconductor block 1). This allows the multiple discharge electrodes 2 inserted on the semiconductor blocks 1 to form an electrode array, constituting the main structure of the semiconductor arc-initiating ultra-dense arc array turbulence friction reduction device of the present invention. In one embodiment of the present invention, the ceramic block 3 is made of alumina ceramic insulating material.
[0062] The high-voltage pulse power supply 4 is used to generate pulsed high voltage to drive the electrode array to discharge. Its positive terminal is connected to the uppermost electrode of the semiconductor block 1, and its negative terminal is grounded. When the high-voltage pulse power supply 4 is turned on, it will break down the air between the electrodes, generating an electric arc 5 between the electrodes. Each semiconductor block 1 is connected to one high-voltage pulse power supply 4. The high-voltage pulse power supplies 4 can be connected in parallel or operate independently, and each high-voltage pulse power supply 4 can be controlled independently.
[0063] In a specific embodiment of the present invention, semiconductor block 1 is made of silicon carbide semiconductor material. Its length in the x-direction is the same as the target area for drag reduction, which is 20 mm in this embodiment; its thickness in the y-direction can be 1 mm to 3 mm, which is 2 mm in this embodiment; its width in the z-direction can be adjusted according to specific circumstances, generally 5 mm to 10 mm, which is 10 mm in this embodiment. The diameter of the cylindrical blind holes on semiconductor block 1 should be at least 0.5 mm smaller than the thickness of the semiconductor block, generally 0.5 mm to 2 mm, which is 1 mm in this embodiment; the depth of the blind holes should be at least 1 mm smaller than the width of semiconductor block 1, generally 4 mm to 9 mm, which is 8 mm in this embodiment; the spacing between adjacent cylindrical blind holes on the same semiconductor block 1 should be greater than 0.1 mm, which is 4 mm in this embodiment; there are a total of 5 cylindrical blind holes, and the distance between the center of the first and last cylindrical blind holes and the edge of the semiconductor block 1 in the x-direction should be greater than 1 mm, which is 2 mm in this embodiment.
[0064] The discharge electrode 2 is made of copper and its size is exactly the same as the cylindrical blind hole on the semiconductor block 1 (in this embodiment, the cross-sectional diameter is 1 mm and the length is 8 mm). One discharge electrode 2 is inserted into each cylindrical blind hole.
[0065] The ceramic block 3 is made of alumina ceramic material. In a specific embodiment of the present invention, the ceramic block 3 is exactly the same size as the semiconductor block 1. The ceramic block 3 has a length of 20 mm in the x direction, a width of 1 mm in the y direction, and a thickness of 10 mm in the z direction. The ceramic block 3 and the semiconductor block 1 into which the discharge electrode 2 is inserted are arranged at intervals to form an electrode array with a flow direction (i.e., x-axis direction) distance of 4 mm and a span direction (i.e., y-axis direction) distance of 2 mm.
[0066] The high-voltage pulse power supply 4 adopts an airborne miniaturized microsecond pulse power supply, and each semiconductor block 1 uses a separate high-voltage pulse power supply 4.
[0067] First, the working process of a single semiconductor block 1 after being energized is described. A high-voltage pulse power supply 4 generates a pulsed high voltage, which is applied to the array of discharge electrodes 2, creating a strong electric field between the electrodes and inducing an initial current in the semiconductor block 1, thus heating the semiconductor in the current path. Because semiconductor materials such as silicon carbide and cuprous oxide have negative temperature coefficients of resistance (i.e., the higher the temperature, the lower the resistance), according to Ohm's law, when the voltage remains constant, the current in the initial current path will continuously increase due to the decrease in resistance, leading to a continuous enhancement of the heating effect. This forms a positive cycle of "enhanced heating - decreased resistance - increased current - further enhanced heating," as shown below. Figure 5 As shown, this ultimately leads to the majority of the current in the circuit concentrating on a narrow path on the side of the exposed discharge electrode 2 of semiconductor block 1, i.e., the flow path connecting each relay discharge electrode 2. In this conductive path, the temperature rises rapidly, causing the semiconductor material to evaporate and forming highly ionized material vapor with low dielectric strength in the conductive path between the discharge electrodes 2. This material vapor further increases the conductivity of the discharge path (i.e., reduces the resistance of the discharge path), eventually making the resistance of the discharge path extremely small, equivalent to a wire. The high-voltage pulse power supply 4 is short-circuited by the discharge path, generating a strong arc discharge in the discharge path, producing plasma, and creating an explosive heating effect along the flow direction, generating thermal blockage in the flow field, forming a "virtual rib" in the flow direction. Unlike ordinary arc discharge, which requires extremely high voltage to directly break down air, the above process only requires a small initial current to gradually induce arc discharge in the semiconductor. The breakdown voltage of the discharge is very low, making it easy for the discharge to occur along the semiconductor's orientation (x-direction).
[0068] The working process of the semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device is described below. Individual semiconductor blocks 1 inserted into the discharge electrode 2 are arranged side-by-side along the spanwise direction (i.e., the y-axis direction), and adjacent semiconductor blocks 1 are separated by ceramic blocks 3, forming the semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device. Due to the presence of the semiconductor blocks 1, the discharge electrode 2 is more likely to discharge along the flow direction (x-direction) to generate an arc 5, but less likely to discharge along the spanwise direction (y-direction). Therefore, although the spanwise spacing between the electrodes (d...)... y =2mm) ratio of flow direction spacing (d) x Even with a diameter of 4 mm, the arc discharge will still occur along the flow direction (x direction), forming an arc 5 along the flow direction. Under the action of the relay discharge electrode 2, each arc 5 connects end to end along the flow direction, forming an "arc plasma chain". This creates an array-like "virtual rib" effect in the flow field (i.e., the thermal blocking effect generated by the connected arc 5 strings), separating the strip structure of the boundary layer, thus achieving the effect of turbulent friction drag reduction. Figure 1 As shown. Figure 1 The last high-voltage pulse power supply 4 is in the off state, so the discharge electrode 2 on the last semiconductor block 1 does not discharge to generate an electric arc 5. The other high-voltage pulse power supplies 4 are turned on, forming an array of electric arcs 5 on the side of the device.
[0069] In the specific implementation process, since the breakdown voltage between adjacent discharge electrodes 2 along the flow direction (x direction) can be reduced by one order of magnitude by using semiconductor materials, the spanwise (y direction) spacing of discharge electrodes 2 can be reduced to one-tenth of its flow direction spacing. Assuming the flow direction spacing of discharge electrodes 2 is 4 mm, its spanwise spacing can be as small as 0.4 mm, which can adapt to the boundary layer strip structure spacing under higher incoming flow velocities and significantly improve the effective drag reduction speed range.
[0070] In specific implementation, the semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device of the present invention is embedded into the surface where drag reduction is required. The exposed side of the discharge electrode 2 is flush with the surface where drag reduction is required. Figure 6 As shown. The size of the device and the number of semiconductor block 1, discharge electrode 2, and ceramic block 3 can be adjusted according to the required drag reduction area. Since the drag reduction effect can persist for a distance after leaving the device in the flow field, in specific arrangements, the device of the present invention can be placed in a position slightly upstream of the drag reduction area to save discharge energy and improve drag reduction efficiency. The spanwise spacing (d) of the discharge electrode 2 y Determined by the flow field conditions, it should satisfy:
[0071] d y =15~20δ v (1)
[0072] δ v =v / u τ(2)
[0073] Where v is the kinematic viscosity of air, d is the spanwise electrode spacing, and δ v For the boundary layer viscous length scale, u τ The boundary layer friction velocity is generally the mainstream velocity u. ∞ The viscosity is approximately 0.035, therefore, as the mainstream velocity increases, the viscous length scale decreases, and the spanwise electrode spacing must also decrease accordingly to achieve a better drag reduction effect. The flow-direction spacing of the discharge electrodes 2 is determined based on the spanwise spacing and the breakdown voltage of the semiconductor material surface, ensuring discharge in the flow direction and no discharge in the spanwise direction. In this embodiment, the turbulent friction drag reduction device based on the semiconductor arc-initiated ultra-dense arc array is 20mm long in the flow direction and 22mm wide in the spanwise direction, with a spanwise spacing d = 2mm between the electrodes.
[0074] The semiconductor block 1 is preferably made of silicon nitride semiconductor, but ceramic materials with a cuprous oxide coating can also be used, with alumina being a suitable ceramic material. The discharge electrode 2 can be made of heat-resistant and conductive metals such as copper or tungsten, or non-metallic conductive materials such as graphite. Due to tungsten's excellent wear resistance and heat resistance, tungsten is the preferred material for discharge electrode 2, followed by copper, and lastly non-metallic conductive materials such as graphite. The ceramic block 3 can be made of any insulating ceramic material; common alumina ceramic is chosen here, but organic materials such as PEEK and plexiglass can also be used as substitutes. However, considering the mechanical properties of the materials, alumina and other ceramic materials are preferred. The high-voltage pulse power supply 4 can be any high-voltage pulse power supply with a voltage >3kV and a frequency >1kHz. The power supply's volume and weight should be as small as possible to reduce the structural weight of the device and adapt to applications with space and load constraints, such as drones.
[0075] In the implementation of specific drag reduction applications, when the incoming flow velocity is high, all high-voltage pulse power supplies 4 are turned on, causing arc discharge in each electrode group. The discharge generates heating in the boundary layer, causing blockage in the flow field and thus forming virtual ribs, such as... Figure 6 , Figure 7 As shown in the figure, U ∞ This represents the incoming flow velocity. Virtual ribs separate the strip structures in the boundary layer, thereby suppressing turbulent pulsations and reducing turbulent frictional resistance.
[0076] When the incoming flow velocity is low, the spanwise spacing required to achieve the best drag reduction effect is larger than when the incoming flow velocity is high. Therefore, depending on the actual incoming flow velocity requirements, an inter-column discharge configuration can be adopted (e.g., inter-column discharge). Figure 8(Multiple rows can also be spaced out) to increase the spanwise spacing of the virtual ribs, thus maintaining optimal drag reduction. To adapt to wider incoming flow velocities, the arc-inducing performance of semiconductor materials in reducing breakdown voltage should be fully utilized to minimize the spanwise spacing of discharge electrodes 2. The flow-direction spacing of discharge electrodes 2 is determined based on the spanwise spacing, ensuring that discharge does not occur along the spanwise direction.
[0077] Based on the above-mentioned device, the present invention also proposes a method for reducing turbulent frictional drag using an ultra-dense arc array based on semiconductor arc initiation, the process of which is as follows: Figure 9 As shown.
[0078] Step S1: The sensor collects flow field data. The sensor is placed in the flow field to collect information such as temperature, pressure, velocity, and wall shear stress in the flow field in real time, and inputs the data into the controller.
[0079] Step S2: Analyze the data collected by the sensors in the controller, and determine the mainstream speed u measured by the sensors. ∞ Take the friction speed u τ =0.035u ∞ Kinematic viscosity v = 1.51 × 10 -5 m 2 / s, based on equation (2), the boundary layer viscous length scale δ is calculated. v This allows us to determine the spanwise spacing d of the current electric arc 5. y Is it located between 15 and 20δ? v between.
[0080] Step S3: Based on the calculation and analysis results, select the appropriate operating mode and parameters through the control circuit. Different modes correspond to different spanning distances, thus adjusting the spanning distance d of the arc 5. y Maintain at 15-20δ v between.
[0081] Specifically, the controller can determine the required discharge strategy based on equations (1) and (2). If the current spanwise spacing d of the small ribs... y >15~20δ v , where δ v To test the obtained boundary layer viscous length scale, it is necessary to control the discharge of more electrode groups by controlling the switching of the high-voltage pulse power supply 4, and actively densify the spanwise of the arc 5; if the current spanwise spacing d of the small ribs y <15~20δ v Then, the number of discharge electrode groups needs to be reduced by controlling the switch of the high-voltage pulse power supply 4, so that the arc 5 becomes sparser along the span direction, in order to meet the flow field's requirements for drag reduction.
[0082] In step S4, the sensor collects flow field data again to gather flow field information after the arc discharge.
[0083] Step S5: The data collected by the sensor is analyzed again in the controller. The information before and after the arc discharge is compared. Under the given temperature, pressure, and speed conditions, the changes in frictional resistance measured before and after the arc discharge are compared. If the measured frictional resistance is less than the frictional resistance before the arc discharge, the expected drag reduction effect is achieved; otherwise, a new working mode or a new discharge state is selected based on the flow field information. In a specific embodiment of the present invention, a surface shear stress sensor such as a hot-film sensor (publication number: CN111351609A) is used to measure the surface frictional resistance. The changes in frictional resistance measured before and after the arc discharge are compared. If the measured frictional resistance is less than the frictional resistance before the arc discharge, the expected drag reduction effect is achieved, and the operation ends; otherwise, a new working mode or a new discharge state is selected again from step S1 based on the flow field information.
[0084] In the implementation of the turbulent friction drag reduction method for ultra-dense arc arrays based on semiconductor arc initiation, the relationships between the various parts of the method are as follows: Figure 10 As shown.
[0085] The differences between this invention and other technologies in the same field are as follows:
[0086] Currently, most turbulence drag reduction methods are simply passive drag reduction methods based on small ribs. In the use of plasma discharge for turbulence drag reduction, the discharge methods used are all dielectric barrier discharge. There is no technology that uses arc discharge for turbulence drag reduction. Similarly, there is no technology that uses semiconductor materials to reduce the breakdown voltage, thereby increasing the arc spanwise arrangement and improving the effective drag reduction speed range.
[0087] In flow control technologies employing arc plasma discharge, the controlled objects are mostly supersonic shock waves, shock wave-boundary layer interference, or the arc plasma discharge is used to control high angle-of-attack stall separation of subsonic wings, thereby increasing lift, delaying stall, and reducing pressure drag at high angles of attack. However, there is currently no technology utilizing arc discharge for turbulent friction drag reduction. Aircraft drag can be classified into pressure drag, friction drag, and induced drag. During cruise, friction drag can account for more than 50% of the total drag. Using arc discharge to reduce friction drag caused by turbulent flow can effectively reduce friction drag during cruise, thereby reducing the total flight drag. For typical passenger aircraft, cruise accounts for more than 80% of the entire flight process, while the rapid increase in pressure drag only occurs at high angles of attack (takeoff and landing phases, accounting for less than 20% of the flight process). Therefore, existing technologies using arc discharge to control high angle-of-attack flow separation to reduce pressure drag are fundamentally different from the turbulent friction drag reduction device and method based on semiconductor arc induction ultra-dense arc array proposed in this invention. Compared with these, this invention has unique advantages.
[0088] Compared with other turbulence drag reduction methods, the present invention has the following advantages:
[0089] 1. Enhanced adaptability. Compared to traditional passive drag reduction methods, the semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device and method proposed in this invention is an active method. It can adjust the discharge intensity and density in real time and change the control mode according to the changes in the flow field during actual flight to adapt to the drag reduction requirements. It can effectively adapt to the rapidly changing flow field conditions during actual flight and maintain the optimal drag reduction state at all times, thus significantly enhancing its adaptability and practicality.
[0090] 2. Greater effective incoming flow velocity. Compared with plasma turbulence drag reduction methods based on dielectric barrier discharge, the semiconductor arc-initiated ultra-dense arc array turbulence friction drag reduction device and method proposed in this invention employs a larger arc discharge intensity, which can generate effective disturbances at a greater incoming flow velocity, thereby producing a wider effective drag reduction incoming flow velocity range. This effectively solves the problems of low discharge intensity and extremely limited effective drag reduction velocity range existing in existing plasma turbulence drag reduction technologies based on dielectric barrier discharge, and has stronger application prospects in drag reduction applications for various aircraft.
[0091] 3. Excellent drag reduction effect. In turbulent boundary layer drag reduction applications, the higher the incoming flow velocity, the smaller the spanwise spacing of the boundary layer's bottom stripe structure, requiring denser arc discharges and virtual ribs to achieve better drag reduction. This invention introduces semiconductor materials into the arc array, reducing the breakdown voltage from approximately 3 kV / mm² to several hundred V / mm², a reduction of orders of magnitude. This significantly increases the spanwise density of the arc array while ensuring normal discharge along the flow direction, resulting in better turbulent friction drag reduction at higher incoming flow velocities.
Claims
1. A semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device, characterized in that, It includes a semiconductor block (1), electrodes (2), a ceramic block (3), and a high-voltage pulse power supply (4); wherein The semiconductor block (1) is a thin cuboid shape. Multiple cylindrical blind holes with the same spacing and uniform distribution are opened on the side of the semiconductor block (1). The axes of these blind holes are on the same plane, which is parallel to the front and rear surfaces of the semiconductor block (1). Establish an xyz spatial coordinate system, with the positive x-axis pointing to the direction of the incoming flow, the positive y-axis pointing to the direction perpendicular to the direction of the incoming flow in the horizontal plane, and the positive z-axis pointing vertically upward. The front and rear surfaces of the semiconductor block (1) are parallel to the xoz plane; the side of the semiconductor block (1) with the cylindrical blind hole is parallel to the xoy plane. The discharge electrode (2) is a solid cylindrical rod with a shape that conforms to the blind hole of the semiconductor block (1) and is inserted therein. After the discharge electrode (2) is inserted, one end of it is flush with the side of the semiconductor block and exposed to the air, while the other end is inserted into the bottom of the blind hole. The topmost blind hole among multiple cylindrical blind holes has a perforation at the bottom for passing through a wire to connect the topmost electrode to the high-voltage output terminal of the high-voltage pulse power supply (4); the bottommost discharge electrode (2) is also grounded through a lead wire perforated at the bottom of the blind hole; the middle electrode is suspended and not connected in any way; the low-voltage output terminal of the high-voltage pulse power supply (4) is grounded. The ceramic block (3) is a thin cuboid shape. The projection of the front and rear surfaces of the ceramic block (3) parallel to the xoz plane onto the xoz plane completely overlaps with the semiconductor block (1). Multiple semiconductor blocks (1) with inserted discharge electrodes (2) are arranged at intervals with ceramic blocks (3), and the outermost layer is ceramic block (3), so that multiple discharge electrodes (2) inserted on semiconductor blocks (1) form an electrode array, and each semiconductor block (1) uses a high-voltage pulse power supply (4) alone.
2. The semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device as described in claim 1, characterized in that, The length of the semiconductor block (1) in the x direction is the same as the target area for drag reduction; the thickness in the y direction is 1mm to 3mm; the width in the z direction is 5mm to 10mm; the diameter of the blind hole should be more than 0.5mm smaller than the thickness of the semiconductor block; the depth of the blind hole should be more than 1mm smaller than the width of the semiconductor block (1); the spacing between adjacent blind holes on the same semiconductor block (1) should be greater than 0.1mm; there are N cylindrical blind holes in total, N≥5, and the distance between the center of the first and last cylindrical blind holes and the edge of the semiconductor block (1) in the x direction should be greater than 1mm.
3. The semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device as described in claim 2, characterized in that, The diameter of the blind hole is 0.5mm to 2mm; the depth of the blind hole is 4mm to 9mm.
4. The semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device as described in claim 2, characterized in that, The semiconductor block (1) has a thickness of 2 mm in the y direction, a width of 10 mm in the z direction, a blind hole diameter of 1 mm, and a blind hole depth of 8 mm. The spacing between adjacent blind holes on the same semiconductor block (1) is 4 mm; there are a total of 5 cylindrical blind holes, and the distance between the center of the first and last cylindrical blind holes and the edge of the semiconductor block (1) in the x direction is 2 mm.
5. The semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device as described in claim 1, characterized in that, A discharge electrode (2) is inserted into each cylindrical blind hole; The ceramic block (3) has a length of 20 mm in the x direction, a width of 1 mm in the y direction, and a thickness of 10 mm in the z direction. The ceramic block (3) and the semiconductor block (1) into which the discharge electrode (2) is inserted are arranged at intervals to form an electrode array with a flow distance of 4 mm and a span distance of 2 mm.
6. The semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device as described in claim 1, characterized in that, The semiconductor block (1) is made of silicon nitride semiconductor or ceramic material with cuprous oxide coating; the discharge electrode (2) is made of heat-resistant conductive metal material or non-metal conductive material; the high voltage pulse power supply (4) is selected with a voltage > 3kV and a frequency > 1kHz.
7. The semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device as described in claim 1, characterized in that, During installation, the device is embedded into the surface requiring drag reduction, with the exposed discharge electrode (2) of the device flush with the surface. The size of the device and the number of semiconductor blocks (1), discharge electrodes (2), and ceramic blocks (3) are adjusted according to the size of the area requiring drag reduction, and the device is positioned slightly upstream in the drag reduction area. The spanwise spacing d of the discharge electrodes (2) is... y Determined by the flow field conditions, the following must be satisfied: d y =15~20δ v (1) δ v =v / u τ (2) Where v is the kinematic viscosity of air, d is the spanwise electrode spacing, and δ v For the boundary layer viscous length scale, u τ The boundary layer friction velocity is denoted by ; the flow spacing of the discharge electrode (2) is determined by the spanwise spacing and the breakdown voltage of the semiconductor material surface, ensuring that the flow direction discharges while the spanwise direction does not discharge.
8. A method for reducing turbulent frictional drag using an ultra-dense electric arc array based on semiconductor arc initiation, wherein the method is based on the semiconductor arc initiation ultra-dense electric arc array turbulent frictional drag reduction device as described in any one of claims 1-6, characterized in that, The specific process is as follows: Step S1: The sensor collects flow field data. The sensor is placed in the flow field to collect temperature, pressure, velocity, and wall shear stress information in the flow field in real time, and inputs the data into the controller. Step S2: Analyze the data collected by the sensors in the controller, and determine the mainstream speed u measured by the sensors. ∞ Take the friction speed u τ =0.035u ∞ Kinematic viscosity v = 1.51 × 10 -5 m 2 / s, based on equation (2), the boundary layer viscous length scale δ is calculated. v , δ v =v / u τ (2) Therefore, it can be determined whether the spanwise spacing dy of the current electric arc (5) is located between 15 and 20δ. v between; Step S3: Based on the calculation and analysis results, select the appropriate working mode and parameters through the control circuit. Different modes correspond to different spanning distances, so that the spanning distance d of the arc (5) is adjusted. y Maintain at 15-20δ v between; The controller determines the required discharge strategy based on equations (1) and (2). d y =15~20δ v (1) If the current spanwise spacing of the small ribs is d y >15~20δ v , where δ v To test the obtained boundary layer viscous length scale, it is necessary to control the discharge of more electrode groups by controlling the switching of the high-voltage pulse power supply (4) to densify the arc (5) in the spanwise direction; if the current spanwise spacing d of the small ribs y <15~20δ v Then, the number of discharge electrode groups needs to be reduced by controlling the switch of the high-voltage pulse power supply (4) so that the arc (5) becomes sparser along the span direction to meet the flow field's requirements for drag reduction. Step S4: The sensor collects flow field data again to gather flow field information after the arc discharge. Step S5: Analyze the data collected by the sensor again in the controller, compare the information before and after the arc discharge, and compare the changes in frictional resistance measured before and after the arc discharge under the temperature, pressure and speed conditions. If the measured frictional resistance is less than the frictional resistance before the arc discharge, the expected drag reduction effect is achieved and the work ends. Otherwise, select a new working mode or a new discharge state from step S1 based on the flow field information.
9. The method for reducing turbulent frictional drag of an ultra-dense arc array based on semiconductor arc initiation as described in claim 8, characterized in that, The working process of a single semiconductor block (1) with the discharge electrode (2) inserted after being energized is as follows: The high-voltage pulse power supply (4) generates a pulsed high voltage, which is applied to the array of discharge electrodes (2), generating a strong electric field between the discharge electrodes (2) and generating an initial current in the semiconductor block (1), which heats the semiconductor in the current path. Since the semiconductor material has a negative temperature coefficient of resistance, when the voltage is constant, the current in the initial current path will continuously increase due to the decrease in resistance, which leads to a continuous enhancement of the heating effect, thus forming a positive cycle of "heating enhancement - resistance reduction - current increase - further heating enhancement". This causes most of the current in the circuit to concentrate on a narrow strip on the side of the exposed discharge electrode (2) of the semiconductor block (1). In the narrow path, that is, the flow path connecting each relay discharge electrode (2); in this conductive path, the temperature rises rapidly, causing the semiconductor material to evaporate, forming a material vapor with a high degree of ionization but low electrical resistance in the conductive path between the discharge electrodes (2); these material vapors further increase the conductivity of the discharge path, making the resistance of the discharge path extremely small, equivalent to a wire, the high voltage pulse power supply (4) is short-circuited by the discharge path, generating a strong arc discharge in the discharge path, generating plasma, forming an explosive heating effect along the flow direction, generating thermal blockage in the flow field, forming a "virtual rib" in the flow direction; the discharge occurs along the setting direction of the semiconductor; The working process of the semiconductor arc-initiating ultra-dense arc array turbulent friction drag reduction device is as follows: The individual semiconductor blocks (1) inserted into the discharge electrode (2) are arranged side by side in the longitudinal direction, and the adjacent semiconductor blocks (1) are separated by ceramic blocks (3) to form a semiconductor arc-initiating ultra-dense arc array turbulence friction reduction device. Due to the presence of the semiconductor blocks (1), the discharge electrode (2) is more likely to discharge along the flow direction to generate an arc (5), but it is not easy to discharge along the longitudinal direction to form an arc (5) along the flow direction. Under the action of the relay discharge electrode (2), each arc (5) is connected end to end along the flow direction to form an "arc plasma chain". It forms an array-like "virtual rib" effect in the flow field, that is, the thermal blocking effect generated by the arc (5) connected end to end separates the strip structure of the bottom layer of the boundary layer to achieve the purpose of turbulence friction reduction. The last high-voltage pulse power supply (4) is in the off state, so the discharge electrode (2) on the last semiconductor block (1) does not discharge to generate an electric arc (5), and the other high-voltage pulse power supplies (4) are turned on, forming an array of electric arcs (5) on the side of the device.