Method for regulating and controlling hypersonic fusion separation bubbles through flow direction plasma excitation

Abstract

A double-incident shock wave / boundary layer interference model is designed, incoming flow is 4-7 Mach laminar flow, and an artificial transition tape is installed on the upstream of a separation area; multiple pairs of cylindrical stepped holes are evenly formed in the middle of the surface of the flat plate in the spanwise direction and used for assembling electrodes and high-voltage wires. The invention also provides a hypersonic velocity dual-incident shock wave / boundary layer interference model which comprises the shock wave generator and a dual-incident shock wave / boundary layer interference model below the shock wave generator. In addition, the invention provides a method for regulating and controlling the hypersonic fusion separation bubble through flow direction plasma excitation, high-energy plasma excitation is applied in front of a separation line through a plasma exciter, an intermittent high-energy disturbance effect is generated on a wave system structure through the strong impact effect of high-energy plasmas, the influence of the shock wave reverse pressure gradient on a boundary layer is reduced, and the separation effect of the hypersonic fusion separation bubble is improved. The size scale of separation bubble fusion is reduced, and flow separation induced by shock wave / wall surface boundary layer interference is relieved.

Description

Technical Field

[0001] The invention relates to the technical field of flow control, and in particular to a method for regulating and controlling hypersonic fusion separation bubbles. Background Art

[0002] The hypersonic inlet is an important component of the propulsion system of a hypersonic vehicle, and its performance has a crucial impact on the overall performance of the vehicle. In order to achieve deceleration and pressurization of the captured airflow, people use a multi-stage compression structure to form an incident shock wave system to complete this process. Under hypersonic conditions, a boundary layer is inevitably present on the surface of the inlet. When the incident shock wave meets the boundary layer, under the influence of the strong adverse pressure gradient of the shock wave, the flow direction of the inner layer of the boundary layer is reversed, forcing the incoming flow to be lifted away from the near wall, forming a flow separation phenomenon. In the area where the separation is more serious, the flow in the boundary layer flows strongly mixed with the return flow, forming a vortex structure of low-energy flow. Due to the great difference in flow field parameters, the outflow can only "bypass" this interference area, thus forming a unique flow structure-separation bubble. The external high-speed flow transfers mechanical energy to the separation bubble, and the vortex inside the separation bubble accelerates the flow in the separation zone until the reattachment process begins, so the separation bubble only plays an intermediate role in energy transfer and has a fairly stable flow field structure. The separation bubble can cause the flow field to be distorted, and its contraction and expansion movement will cause the shock wave to oscillate back and forth. The upper limit of the shock wave flow movement is called the separation line.

[0003] In the context of multiple incident shock waves interfering with the boundary layer, there is a flow scenario where when multiple shock wave interference regions approach each other, their combination will lead to the fusion of separation bubbles, thus inducing large-scale separation. Figure 1 As shown in the figure, the fused separation bubble absorbs the low-energy flow generated by multiple shock waves. Compared with the separation bubble induced by a single incident shock wave, the area of ​​the separation bubble is larger, and the induced separation shock wave has a stronger interference on the flow field. Since the fusion separation bubble has little energy loss in the process of mechanical energy transmission and the internal vortex structure is very stable, the obstruction to the streamwise flow is more obvious, which may be several times that of the state without separation bubbles. In severe cases, it often blocks the flow channel and aggravates the separation of the boundary layer. At the same time, the lift and momentum coefficients are also affected by the fusion separation bubble, which may cause control and stability problems of the aircraft, and have serious hazards to hypersonic navigation.

[0004] At present, there are few studies on the mutual interference between multi-channel incident shock waves and boundary layers at home and abroad, and there are no literature reports on the flow control research of fusion and separation bubbles in this field. Plasma flow control is a new type of flow control method with advantages such as simple structure, wide bandwidth, fast response, and no moving parts. Its excellent control ability of regulating flow separation phenomena has been verified on models such as hypersonic compression corners and flat plates. Therefore, it is feasible to innovatively apply plasma technology to the study of separation bubble fusion control under hypersonic conditions to further improve flow separation. Summary of the invention

[0005] The present invention proposes a method for regulating hypersonic fusion separation bubbles by using plasma flow. In view of the requirements for double-incident shock wave / boundary layer interference regulation and the characteristics of high-altitude and high-speed flight environment, plasma technology is applied to the field of hypersonic flow control. Under the condition of Mach number 5, a high-energy plasma array is arranged in front of the separation line, and the strong impact effect of high-energy plasma is used to generate intermittent high-energy disturbances on the wave system structure, thereby reducing the impact of the shock wave reverse pressure gradient on the boundary layer, reducing the size of the separation bubble fusion, and slowing down the flow separation induced by the shock wave / wall boundary layer interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 The effect diagram showing the interference between the incident shock wave and the boundary layer to form a fusion separation bubble;

[0007] Figure 2 A specific design diagram of a double-incident shock wave / boundary layer interference model is shown, wherein Figure 2 (a) shows the side view of the model, Figure 2 (b) shows a top view of the model;

[0008] Figure 3 Showing the high energy discharge circuit diagram of the present invention;

[0009] Figure 4 The diagram shows the effect of shock wave disturbance on fusion and separation bubbles;

[0010] Figure 5 The separation bubble shrinkage effect diagram is shown, where Figure 5 (a) shows the baseline flow field effect, Figure 5 (b) shows the effect after stimulation;

[0011] Figure 6 The separation shock wave control effect diagram is shown, where Figure 6 (a) shows the reference flow field, Figure 6 (b) shows the flow field after excitation. DETAILED DESCRIPTION

[0012] The present invention is applicable to the flow control test for the fusion of hypersonic separation bubbles. The design scheme of the applied model in the present invention is as follows: the design state Mach number should be between Mach 4 and 5 to meet the hypersonic conditions; the forebody is compressed in two or more stages, and at the same time, it is ensured that under the design state, the multiple forebody shock waves have a clear separation intersection point to ensure the fusion of the separation bubbles; the flow channel should have a large aspect ratio; the model manufacturing material should ensure that it has the characteristics of high strength, deformation resistance and wear resistance to ensure the working safety under hypersonic conditions.

[0013] like Figure 2 As shown in the figure, taking the double incident shock wave / boundary layer interference model as an example, the model length should be between 420mm-480mm, the width should not exceed 260mm, and the channel aspect ratio should be greater than 2. In order to make the shock wave / boundary layer interference and flow separation more obvious, the total deflection angle of the forebody is preferably greater than 12°, and the difference between adjacent deflection angles should not exceed 2°. Finally, the separation bubbles induced by each level of incident shock wave should be merged. The incoming flow is 4-7 Mach laminar flow, and an artificial transition zone with a width of 6-12mm is installed upstream of the separation zone to ensure that the laminar flow is transformed into boundary turbulence before the separation line.

[0014] Multiple pairs (three pairs are shown in the figure) of cylindrical stepped holes are evenly arranged along the span direction in the middle of the flat surface. The multiple pairs of cylindrical stepped holes are symmetrical about the central axis of the flat surface, which are used to assemble electrodes and high-voltage wires. The stepped holes are punched vertically inward along the flat surface. The small cylinder close to the flat surface has a small aperture and is used to assemble copper electrodes; the large cylinder far from the flat surface has a large aperture and is used to assemble high-voltage wires; the high-voltage wires are sealed in the large cylinder by high-temperature resistant insulating sealant. The diameter of the electrode on the flat surface is between 0.5-1.5mm (this is also the aperture of the small cylinder close to the flat surface, and the electrode is inserted into the small cylinder hole, and the two are tightly matched). The distance between a pair of positive and negative electrodes should be kept at about 5mm, and the distance between two adjacent pairs of electrodes should be more than 20mm. The distance is set to prevent the electrodes from being too close to cause creepage, and to prevent the distance from being too far to form an excitation scale. The electrode installation position is more than 8mm before the separation line, but not higher than 12mm, because the discharge excitation effect is more ideal in this position range. The surface of each part of the model should be smooth, the material hardness should meet the requirements, the installed parts should fit tightly, the airtightness should be good, and there should be no obvious protrusions or recessed gaps.

[0015] The circuit connection scheme of the present invention is as follows: Figure 3As shown, a pair of electrodes has two poles, and the adjacent electrodes are connected end to end according to the conventional method in this field, and the electrodes maintain a series relationship. The poles close to the outside of the first and last pairs of electrodes are connected to the high-voltage wire that enters from the bottom to the top through the large cylindrical hole on the lower side of the plate. The output end of the high-voltage pulse power supply is connected to a high-voltage wire through the first diode, and the other high-voltage wire is grounded. The negative end of the high-voltage pulse power supply is grounded, thereby forming a closed circuit loop. The positive end of the first diode is connected to the output end of the high-voltage pulse power supply, and the negative end of the first diode is connected to the high-voltage wire. The preferred working voltage of the high-voltage pulse power supply is 0 to 20kV and the frequency is 0 to 20kHz. The DC power supply, the current limiting resistor, and the capacitor are connected in series in sequence, the positive end of the DC power supply is connected to the current limiting resistor, the negative end is grounded, one end of the capacitor is connected to the current limiting resistor, and the other end is grounded to form a loop. The positive end of the second diode is connected to the connection point between the current limiting resistor and the capacitor, and the negative end of the second diode is grounded. Specific embodiments

[0017] Figure 2 A specific example of the present invention is shown. Figure 2 This is a specific design drawing of the hypersonic double-incident shock wave / boundary layer interference model, which consists of a shock wave generator and a flat plate below it. The relative positions are well known to those skilled in the art and will not be repeated here. This model is a forebody two-stage compression model with a design state of Mach number 5. In order to reduce the counterweight, the model is made of 7075 aviation super-hard aluminum. The shock wave generator is 207.31mm long and 240mm wide. The upper surface of the shock wave generator is 120mm high from the upper surface of the flat plate. The first and second stage angles are 10° and 9°, respectively. After experimental verification, the intersection of the separation shock wave and the wall of this model corresponds to an average separation position of x=270.236mm. The unique separation bubble is obtained by observing the schlieren image, as shown in Figure 2 The dotted bulge on the upper surface of the middle and lower plate indicates that the separation bubbles generated by the two shock waves have merged. The experimental phenomenon is as follows Figure 1 shown.

[0018] The shock wave generator is connected to the flat plate through a support bracket (not shown in the figure, its general position and fixed connection method are well known to those skilled in the art), both of which are 240mm wide and have an installation height of H=120mm. The support bracket is shaped on the windward side to reduce interference with the flow field, and the specific shaping method is known to those skilled in the art. The leading edge of the shock wave generator and the leading edge of the flat plate have the same flow direction position, the wedge angle of the leading edge of the flat plate is 10°, the total length of the flat plate is 465mm, and the displacement mechanism adopts the tail support. A rectangular coordinate system is established with the outer vertex of the leading edge of the flat plate as the coordinate origin O. The flow direction is the positive direction of the x-axis, and the vertical upward direction is the positive direction of the y-axis. A transition zone is installed between the flow range of x=10mm and x=20mm, and the transition zone extends along the span direction to ensure that the boundary layer quickly develops into a turbulent boundary layer. Except for the metal leading edge, the flat plate is processed with the insulating material PEEK. The structure and position relationship between the metal material and the insulating material are known to those skilled in the art and will not be repeated. Under the condition of ensuring Mach number 5, the two forebody shock waves have a clear intersection point, which meets the rated working state requirements. The channel of the hypersonic model (i.e. the channel between the shock generator and the flat plate) is 240mm wide and 80mm high, with an aspect ratio of 3, which meets the conventional requirement of an aspect ratio greater than 2.

[0019] like Figure 2 As shown, with the short side of the plate as the axis of symmetry, three discharge excitations are arranged in the span direction, corresponding to the flow position x=255mm, the electrode spacing is 5mm, and the spacing between the two is 60mm. A cylindrical stepped hole is provided on the plate, which is punched inward perpendicular to the surface of the plate. A cylindrical hole with a diameter of 1mm is close to the upper surface of the plate, and a copper electrode with a diameter of 1mm is installed. The surface of the electrode copper needle is flush with the surface of the plate to prevent the introduction of additional disturbances. Away from the upper surface of the plate is a cylindrical hole with a diameter of 4mm, and a 4mm high-voltage wire is installed. The lower end of the cylindrical hole is open, so the cylindrical stepped hole is a through hole. The high-voltage wire is sealed to the through hole and connected to the electrode above by high-temperature resistant insulating sealant, while ensuring that the upper surface of the plate and the electrode are flat.

[0020] The high-voltage pulse power supply can break through the air medium and form a short plasma path between the electrodes. The pulse discharge voltage is set to 20kv, the discharge frequency is set to 500Hz, the rising edge is 100ns, the falling edge is 100ns, and the pulse width is 100ns.

[0021] The plasma path lasts only a short time in the air, so a high-power charging current is needed to compensate for the loss. The capacitor is charged by a DC source, and after the plasma path is formed, a strong current is released through the electrode to maintain the plasma path. The DC source is set to a constant voltage of 1kV and a capacitor of 2μf.

[0022] The voltage acquisition system and current acquisition system are composed of high-voltage voltage probe and current probe respectively, which can measure the voltage and current changes over time simultaneously. The sampling frequency of the oscilloscope to record single-cycle discharge parameters is 100MHz.

[0023] During the implementation of the present invention, a plasma exciter is used to apply high-energy plasma excitation in front of the separation line, and the strong impact effect of the high-energy plasma is used to produce intermittent high-energy disturbances on the wave system structure, thereby reducing the influence of the shock wave reverse pressure gradient on the boundary layer, reducing the size scale of the separation bubble fusion, and slowing down the flow separation induced by the shock wave / wall boundary layer interference.

[0024] Before excitation: The hypersonic double incident shock wave / boundary layer interference model is in the design state of Mach 5. The shock wave generator performs two-stage compression on the incoming flow, generating two incident shock waves that intersect on the flat surface, that is, the model is in the rated working state. The forebody boundary layer develops into a turbulent boundary after passing through the transition zone. Due to the induction of the strong adverse pressure gradient of the double incident shock wave, the incoming flow boundary layer no longer adheres to the wall, and flow separation occurs, resulting in the fusion of the separation bubble. The stream length is 25.8 mm, and the area size is S = 4.4186×10 3 mm 2 The separation bubble forces the upstream airflow to deflect, resulting in the formation of a separation shock wave. The separation shock wave foot moves back and forth in the intermittent zone, further strengthening the shock wave / boundary layer interference, causing more serious flow separation and having a serious impact on the hypersonic flow field structure.

[0025] After excitation: High-energy plasma excitation is applied to the three discharge regions simultaneously, such as Figure 4 As shown in Figure 1, the discharge excitation generates high-energy shock waves, which strongly impact the separation zone. The separation bubble is significantly regulated by the impact disturbance, as shown in Figure 1. Figure 5 As shown in the figure, after calculation and analysis, the flow length of the separation bubble is reduced to 16.4 mm, and the area is S = 3.96115 × 10 3 mm 2 , the regional scale shrank by 10.35%. Figure 6 As shown in the figure, the excitation also has a significant regulating effect on the separation shock wave. The shock wave structure breaks up the foot of the separation shock wave, and the angle between the separation shock wave and the wall is reduced by 1.11°. In the process of backward movement, the entire separation shock wave is lifted up, and at the same time, it couples with the expansion wave system and the reattachment shock wave, changing the original shape of the spatial interference zone. At this time, the low-frequency instability of the separation shock wave has been improved to a certain extent, and the influence on the adverse pressure gradient of the boundary layer has been greatly weakened, which improves the boundary layer flow separation phenomenon.

[0026] The description of the present invention is illustrative, but it is also applicable to other separation bubble fusion models. The present invention is proposed to provide a method for regulating the fusion of separation bubbles by flow-directed plasma excitation. A high-energy plasma array is arranged in front of the separation line, and the strong impact effect of high-energy plasma is used to produce intermittent high-energy disturbances on the wave system structure, reduce the impact of the shock wave reverse pressure gradient on the boundary layer, reduce the size of the separation bubble fusion, and slow down the flow separation induced by the shock wave / wall boundary layer interference. This method gives full play to the excellent regulation effect of plasma, and at the same time achieves the control goals of reducing the scale of separation bubble fusion and improving the stability of the flow field, which is of great significance to improving hypersonic flow separation.

Claims

1. A double-incident shock wave / boundary layer interference model, the incoming flow is 4-7 Mach laminar flow, characterized in that: Installation of an artificial transition zone upstream of the separation zone; A plurality of pairs of cylindrical stepped holes are evenly arranged along the span direction at the rear of the middle of the plate surface. The plurality of pairs of cylindrical stepped holes are symmetrical about the central axis of the plate span direction and are used to assemble electrodes and high-voltage wires. The stepped holes are punched vertically inward along the plate surface. The small cylinder close to the plate surface has a small hole diameter and is used to assemble copper electrodes; the large cylinder far from the plate surface has a large hole diameter and is used to assemble high-voltage wires. The electrode is installed in front of the separation line.

2. The double-incident shock wave / boundary layer interference model according to claim 1, characterized in that: The model length is between 420mm and 480mm, the width does not exceed 260mm, and the channel width-to-height ratio is greater than 2; the total deflection angle of the forebody is greater than 12°, and the difference between adjacent deflection angles does not exceed 2°; The width of the artificial transition zone is between 6-12mm. The high-voltage wires are sealed in a large cylinder using a high-temperature resistant insulating sealant; The hole diameter of the small cylinder and the diameter of the electrode are between 0.5-1.5 mm; the electrode is inserted into the hole of the small cylinder, and the two are tightly matched; The distance between a pair of positive and negative electrodes is about 5mm, and the distance between two adjacent pairs of electrodes is more than 20mm; The electrode installation position is more than 8mm in front of the separation line, but not higher than 12mm; The surface of the model is flat everywhere, the material hardness meets the requirements, the installed parts fit tightly, the airtightness is good, and there are no obvious protrusions or recessed gaps.

3. The double-incident shock wave / boundary layer interference model according to claim 1 or 2, characterized in that: The circuit connection scheme of the model is as follows: a pair of electrodes has two poles, and adjacent electrode pairs are connected end to end, and the electrode pairs maintain a series relationship; the poles close to the outside of the first and last pairs of electrodes are connected to the high-voltage wire that enters from the bottom to the top through the large cylindrical hole on the lower side of the plate; the output end of the high-voltage pulse power supply is connected to a high-voltage wire through the first diode, and the other high-voltage wire is grounded, and the negative end of the high-voltage pulse power supply is grounded to form a closed circuit loop, the positive end of the first diode is connected to the output end of the high-voltage pulse power supply, and the negative end of the first diode is connected to the high-voltage wire; the DC power supply, the current limiting resistor, and the capacitor are connected in series in sequence, the positive end of the DC power supply is connected to the current limiting resistor, and the negative end is grounded, one end of the capacitor is connected to the current limiting resistor, and the other end is grounded to form a loop; the positive end of the second diode is connected to the connection point between the current limiting resistor and the capacitor, and the negative end of the second diode is grounded.

4. A hypersonic double-incidence shock wave / boundary layer interference model, hereinafter referred to as the "model", is characterized by: The model includes a shock wave generator and a double-incident shock wave / boundary layer interference model as claimed in claim 1 or 2 below the shock wave generator, and the double-incident shock wave / boundary layer interference model is hereinafter referred to as a "flat plate"; the model is a forebody two-stage compression model with a design state Mach number of 5, and the model is made of 7075 aviation super-hard aluminum. The shock wave generator is 207.31 mm long and 240 mm wide. The upper surface of the shock wave generator is 120 mm high from the upper surface of the flat plate, and the first and second stage angles are 10° and 9° respectively; The shock wave generator is connected to the flat plate through a supporting bracket, the width of both is 240mm, and the installation height is H=120mm; the flow direction positions corresponding to the leading edge of the shock wave generator and the pointed leading edge of the flat plate are the same, the wedge angle of the leading edge of the flat plate is 10°, the total length of the flat plate is 465mm, and the displacement mechanism adopts the tail support, and a rectangular coordinate system is established with the outer vertex of the leading edge of the flat plate as the coordinate origin O, the flow direction is the positive direction of the x-axis, and the vertical upward is the positive direction of the y-axis; a transition belt is installed between the flow range of x=10mm and x=20mm, and the transition belt extends along the span direction; Except for the metal front edge, the flat plate is made of insulating material PEEK; the channel of this model is 240mm wide and 80mm high, with an aspect ratio of 3; With the short side of the plate as the axis of symmetry, three discharge excitations are arranged in the span direction, with the corresponding flow position x=255mm, the electrode spacing being 5mm, and the two-way spacing being 60mm; a cylindrical stepped hole is arranged on the plate, with a 1mm diameter cylindrical hole close to the upper surface of the plate, on which a 1mm diameter copper electrode is mounted, and the surface of the electrode copper needle is flush with the surface profile of the plate; a 4mm diameter cylindrical hole is far from the upper surface of the plate, on which a 4mm high-voltage wire is mounted, the lower end of the cylindrical hole is open, and the cylindrical stepped hole is a through hole; the high-voltage wire is sealed into the through hole with a high-temperature resistant insulating sealant and connected to the electrode above, while ensuring that the upper surface of the plate and the electrode are flat.

5. The hypersonic double-incident shock wave / boundary layer interference model as described in claim 4, when working, the power supply parameters of the flat plate are set as follows based on claim 3: the pulse discharge voltage is set to 20kV, the discharge frequency is set to 500Hz, the rising edge is 100ns, the falling edge is 100ns, and the pulse width is 100ns; the DC source is set to a constant voltage of 1kV and a capacitance of 2μf.

6. A method for regulating hypersonic fusion separation bubbles by flow-directed plasma excitation, which is based on the hypersonic double-incident shock wave / boundary layer interference model as claimed in claim 4, the design state Mach number should be between Mach 4 and 5; the forebody is compressed in two or more stages, and it is ensured that under the design state, the multiple forebody shock waves have a clear separation intersection point; the flow channel has a large aspect ratio; and it is characterized in that: Before excitation: In the hypersonic double-incident shock wave / boundary layer interference model, under the design state of Mach 5, the shock wave generator performs two-stage compression on the incoming flow, generating two incident shock waves that intersect on the flat surface, that is, the model is in the rated working state; the forebody boundary layer develops into a turbulent boundary after passing through the transition zone. Due to the induction of the strong adverse pressure gradient of the double-incident shock wave, the incoming flow boundary layer no longer adheres to the wall, and flow separation occurs, leading to the fusion of separation bubbles; the separation bubble forces the upstream airflow to deflect, resulting in the formation of a separation shock wave, and the separation shock wave foot moves back and forth in the intermittent zone, further strengthening the shock wave / boundary layer interference, causing more serious flow separation, and having a serious impact on the hypersonic flow field structure; After excitation: high-energy plasma excitation is applied to the three discharge areas at the same time, and the discharge excitation generates high-energy shock waves, which strongly impact and disturb the separation zone; the separation bubble is significantly regulated by the impact disturbance; the excitation also has a significant regulatory effect on the separation shock wave, and the shock wave structure breaks up the foot of the separation shock wave, reducing the angle between the separation shock wave and the wall, and lifting the entire separation shock wave in the process of backward movement, while coupling with the expansion wave system and the reattachment shock wave, changing the original shape of the spatial interference zone; at this time, the low-frequency instability of the separation shock wave is improved to a certain extent, and the influence on the adverse pressure gradient of the boundary layer has been greatly weakened, which improves the boundary layer flow separation phenomenon.

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