A plasma-based variable Mach number wind tunnel design method

Abstract

The present invention discloses a plasma-based variable Mach number wind tunnel design method, which belongs to the technical field of aerospace aerodynamic wind tunnel design. The method solves the problem of low test efficiency of the conventional variable Mach number wind tunnel in the prior art due to the need to replace a specific nozzle; the present invention determines the overall aerodynamic parameters; determines the cross-sectional size of the stable section according to the wind tunnel flow, the set simulated temperature and the simulated pressure; constructs the axial Mach number distribution by setting the idea of ​​calculating the wall profile, designs the nozzle outlet Mach number in combination with the transonic theory, and verifies the nozzle outlet Mach number by the computational fluid dynamics method; controls the number of excited plasma generators, uses the phenomenological model to solve the volume force field generated by the plasma excitation, obtains the changed nozzle outlet Mach number, and completes the design of the variable Mach number wind tunnel. The present invention effectively improves the efficiency of the test using the variable Mach number wind tunnel, and can be applied to the design of the variable Mach number wind tunnel.

Description

Technical Field

[0001] The invention relates to a variable Mach number wind tunnel and a design method, in particular to a plasma-based variable Mach number wind tunnel design method, and belongs to the technical field of aerospace aerodynamics wind tunnel design. Background Art

[0002] The current important development trend in the aerospace field includes research on the reusability of hypersonic cruise vehicles, which has far-reaching strategic value. Wind tunnels are the most basic test devices for designing high Mach number aircraft. The performance of the nozzle in the wind tunnel has a decisive influence on the performance of the airflow in the wind tunnel. In the past, high-speed wind tunnels usually used fixed block nozzles. Although fixed block nozzles have the characteristics of good flow field quality and high flow field repetition accuracy, they can only be tested at a specific Mach number. If you want to test at different Mach numbers, you must replace the specific nozzle. This approach is very time-consuming and energy-consuming, and the test efficiency is low. Although the above problems can be alleviated to a certain extent by replacing only the throat of the nozzle through reasonable design, it is still impossible to continuously change the Mach number to truly and accurately simulate supersonic flow. At the same time, the soft wall nozzle can theoretically achieve infinite continuous adjustment, but its structure is complex and the cost is high. It cannot meet the needs of existing wind tunnels, which seriously restricts the effectiveness of ground tests.

[0003] In summary, a plasma-based variable Mach number wind tunnel design method is needed. Summary of the invention

[0004] A brief overview of the present invention is provided below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0005] In view of this, in order to solve the problem of low test efficiency of the traditional variable Mach number wind tunnel in the prior art due to the need to replace a specific nozzle, the present invention provides a plasma-based variable Mach number wind tunnel design method.

[0006] The technical solution is as follows: A plasma-based variable Mach number wind tunnel design method includes the following steps:

[0007] S1. Determine the overall aerodynamic parameters;

[0008] Specifically, the overall aerodynamic parameters include wind tunnel operating parameters and the relationship between total temperature and total pressure and static temperature and static pressure. Wind tunnel operating parameters include total temperature and total pressure of incoming flow, Mach number of test chamber, static temperature, static pressure and wind tunnel flow rate.

[0009] S2. Determine the cross-sectional dimensions of the stable section according to the wind tunnel flow rate, the set simulated temperature and the simulated pressure;

[0010] S3. According to the overall aerodynamic parameters, the axial Mach number distribution is constructed by following the Sivells method to calculate the wall profile by setting the axial Mach number distribution. The nozzle exit Mach number is designed in combination with the transonic theory, and the nozzle exit Mach number is verified by the computational fluid dynamics method.

[0011] S4. Control the number of excited plasma generators, use the phenomenological model to solve the volume force field generated by plasma excitation, obtain the changed nozzle outlet Mach number, and complete the variable Mach number wind tunnel design;

[0012] It also includes a fixed section, a plasma generator, a stabilizing section, a nozzle section, a test section, an expansion section, a straight discharge section and a vacuum unit;

[0013] The fixed section, stable section, nozzle section, test section, expansion section, straight-discharge section and vacuum unit are connected in sequence, and the plasma generator is arranged in the pressure equalizing holes evenly arranged on the surface of the stable section;

[0014] The fixed section is used to connect to a high-pressure gas source;

[0015] The plasma generator comprises an upper electrode, a lower electrode and an insulating layer, wherein the insulating layer is arranged between the upper electrode and the lower electrode, and the plasma generator is used to provide a plasma beam;

[0016] A rectifying orifice plate is arranged at the rear side of the stabilizing section, and the stabilizing section is used to rectify the plasma beam and output a high-pressure gas flow containing plasma;

[0017] The nozzle section is used to accelerate the high-pressure gas flow containing plasma to reach a desired Mach number, thereby obtaining a processed plasma gas beam;

[0018] The test section is used to provide an aerodynamic test site for hypersonic aerodynamic tests;

[0019] The expansion section is used to decelerate and pressurize the plasma gas beam after being processed by the hypersonic aerodynamic test;

[0020] The straight discharge section is used to recover the working fluid;

[0021] The vacuum unit is used to evacuate the straight-discharge section and provide a low-pressure environment.

[0022] Furthermore, in S1, the wind tunnel flow rate It is expressed as:

[0023] ;

[0024] in, To simulate the gas density under the envelope, is the cross-sectional area, is the flow rate.

[0025] Furthermore, in S2, the cross-sectional size of the stable section is It is expressed as:

[0026] ;

[0027] in, To simulate temperature, is the volume, is the gas constant, To simulate pressure.

[0028] Furthermore, in S3, computational fluid dynamics software is used to simulate the nozzle working condition, and the simulation process is to solve the three-dimensional NS equations and obtain the nozzle outlet Mach number by calculating the flow field in the nozzle;

[0029] The conservation form formula of the three-dimensional NS equation is expressed as:

[0030] ;

[0031] in, is a conserved variable, is the inviscid flux, =1, 2, or 3, is the viscous flux.

[0032] Furthermore, in the S4, the plasma excitation action area is simplified into a triangular OAB area, the volume force component of the OAB area is solved, and loaded into the plasma excitation area, the flow field is solved, the flow field distribution in the nozzle is obtained, and the changed nozzle outlet Mach number is calculated;

[0033] The electric field intensity E is distributed linearly in the OAB region;

[0034] Electric field strength distribution It is expressed as:

[0035] ;

[0036] in, is the electric field strength at the origin, , is the maximum voltage applied between the electrodes, is the distance between the two electrodes, is the first constant, is the second constant;

[0037] The first constant It is expressed as:

[0038] ;

[0039] in, is the distance of the plasma excitation action area in the OB direction, is the breakdown voltage of the plasma flow boundary;

[0040] The second constant It is expressed as:

[0041] ;

[0042] in, is the distance of the plasma excitation action area in the OA direction;

[0043] The electric field intensity component in the direction It is expressed as:

[0044] ;

[0045] The electric field intensity component in the direction It is expressed as:

[0046] ;

[0047] The body force component in the direction is expressed as:

[0048] ;

[0049] in, is the charge density, is the elementary charge, is the power supply discharge frequency, is the plasma action time in one excitation cycle;

[0050] The body force component in the direction is expressed as:

[0051] ;

[0052] The volume force generated by the directional motion of plasma under the action of the electric field is added to the source term of the momentum equation to obtain the volume force equation induced by plasma.

[0053] The plasma-induced volume force equation is expressed as:

[0054] ;

[0055] in, is the first velocity component, is the second velocity component, are the coordinate components, is the sub-grid stress, is the plasma-induced volume force, is the statistical weight of the ion, For pressure;

[0056] According to the above calculation model of plasma excitation and the plasma-induced volume force equation, the plasma-induced volume force is solved. , plasma-induced volume forces are implemented by a custom program Loading of the plasma excitation region in the momentum equation source term and the inner wall of the stable segment.

[0057] The beneficial effects of the present invention are as follows: the present invention adopts a dielectric barrier plasma generator to change the airflow properties in a traditional wind tunnel, thereby changing the Mach number of the test chamber, that is, a rectifying orifice plate is arranged on the rear side of the stable section to rectify the plasma beam and output a high-pressure airflow containing plasma, thereby realizing the change of the Mach number by using a solid block nozzle, saving test time, compensating for design errors, and saving energy. The plasma-based variable Mach number wind tunnel designed by the present invention has a Mach number change range of ±0.2 in the test section, an effective working time of more than 1 minute, and no pollution to the environment, while realizing energy conservation and utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0059] Figure 1 The figure is a flow chart of a design method of a plasma-based variable Mach number wind tunnel;

[0060] Figure 2 It is a partial enlarged schematic diagram of the stable segment;

[0061] Figure 3 It is a structural schematic diagram of the stable segment;

[0062] Figure 4 Schematic diagram of the structure of a plasma-based variable Mach number wind tunnel. DETAILED DESCRIPTION

[0063] In order to make the technical solutions and advantages of the embodiments of the present invention more clearly understood, the exemplary embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0064] Example: Reference Figure 1-Figure 4 The present embodiment is described in detail, a plasma-based variable Mach number wind tunnel design method, specifically comprising the following steps:

[0065] S1. Determine the overall aerodynamic parameters;

[0066] Specifically, the overall aerodynamic parameters include wind tunnel operating parameters and the relationship between total temperature and total pressure and static temperature and static pressure. Wind tunnel operating parameters include total temperature and total pressure of incoming flow, Mach number of test chamber, static temperature, static pressure and wind tunnel flow rate.

[0067] S2. Determine the cross-sectional dimensions of the stable section according to the wind tunnel flow rate, the set simulated temperature and the simulated pressure;

[0068] S3. According to the overall aerodynamic parameters, the idea of ​​calculating the wall profile by setting the axial Mach number distribution according to the Sivells method is adopted. The assumption of the spring flow area is abandoned, the axial Mach number distribution is constructed, and the nozzle outlet Mach number is designed in combination with the transonic theory. The nozzle outlet Mach number is verified by the computational fluid dynamics method, that is, the design method with controllable nozzle length is obtained;

[0069] S4. Control the number of excited plasma generators, use the phenomenological model to solve the volume force field generated by plasma excitation, obtain the changed nozzle outlet Mach number, and complete the variable Mach number wind tunnel design;

[0070] It also includes a fixed section 1, a plasma generator 2, a stabilizing section 3, a nozzle section 4, a test section 5, an expansion section 6, a straight discharge section 7 and a vacuum unit 8;

[0071] The fixed section 1, the stable section 3, the nozzle section 4, the test section 5, the expansion section 6, the straight section 7 and the vacuum unit 8 are connected in sequence, and the plasma generator 2 is arranged in the pressure equalizing holes evenly arranged on the surface of the stable section 3;

[0072] The fixed section 1 is used to connect to a high-pressure gas source;

[0073] The plasma generator 2 comprises an upper electrode 9, a lower electrode 10 and an insulating layer 11, wherein the insulating layer 11 is arranged between the upper electrode 9 and the lower electrode 10, and the plasma generator 2 is used to provide a plasma beam;

[0074] A rectifying orifice plate 12 is disposed at the rear side of the stabilizing section 3, and the stabilizing section 3 is used to rectify the plasma beam and output a high-pressure gas flow containing plasma;

[0075] The nozzle section 4 is used to accelerate the high-pressure gas flow containing plasma. The gas flow is accelerated to the speed of sound through the contraction profile at the inlet, and the gas flow near the speed of sound is accelerated to the supersonic speed through the expansion profile at the outlet, so that the gas flow reaches the desired Mach number, thereby obtaining a processed plasma gas beam.

[0076] The test section 5 is used to provide an aerodynamic test site for hypersonic aerodynamic tests;

[0077] The expansion section 6 is used to decelerate and pressurize the plasma gas beam after being processed by the hypersonic aerodynamic test;

[0078] The straight discharge section 7 is used to recover the working fluid;

[0079] The vacuum unit 8 is used to evacuate the straight-discharge section 7 to provide a low-pressure environment.

[0080] Specifically, the high-pressure airflow passes through the fixed section 1, the stable section 3, and the nozzle section 4 in sequence, reaches the desired Mach number and undergoes a wind tunnel test in the test section 5, and then is recovered through the expansion section 6, the straight-discharge section 7, and the vacuum unit 8;

[0081] The stable segment 3 has a built-in equalizing hole, and the plasma generator 2 is evenly distributed in the equalizing hole of the stable segment 3. The upper electrode 9 is slightly higher than the thickness of the inner shell of the stable segment 3 to facilitate the discharge of plasma. The upper electrode 9 is slightly smaller than the diameter of the equalizing hole of the stable segment 3 to maintain the original function of the stable segment. The lower electrode 10 has the same structure as the upper electrode 9 and is dispersed on the outside of the insulating layer 11. The insulating layer 11 evenly wraps the inner shell of the stable segment 3. The principle of the plasma generator 2 is to break through the insulating layer 11 by gradually increasing the voltage to generate plasma near the upper electrode 9. It is characterized in that it can generate stable low-temperature plasma under atmospheric pressure without a vacuum device.

[0082] During the plasma excitation process, the collision between electrons and neutral gas molecules will cause the ionization, dissociation and excitation of the molecules, and the excited gas molecules will further dissociate due to processes such as recombination and collision extinction, which will have a significant impact on the gas composition. Due to the increase in charged particles, the plasma region has a very high conductivity, and the high current flux will cause Joule heating. The increase in air temperature will further increase the conductivity, intensifying the significant changes in physical parameters, thereby achieving an improvement in aerodynamic performance.

[0083] When high-frequency alternating current is applied, the gas between the electrodes is broken down to produce plasma, and the density of high-energy electrons generated is 1010-1012, in cm -3 However, because there is an insulating material between the electrodes, the size of the discharge current is limited by the displacement current of the insulating material, and the power consumption is low. The high-energy electrons in the plasma collide with the surrounding gas molecules to produce a large number of excited atoms and ions, which are helpful for the ionization of the sample molecules. The ionization efficiency is very high;

[0084] The stabilizing section 3 has a built-in pressure equalizing hole, and the plasma generator 2 is evenly distributed in the evenly distributed hole. The evenly distributed hole can increase the number of excited ions and adjust the physical properties of the airflow. The rectifying orifice plate 12 of the stabilizing section 3 is formed by evenly processing a cylinder on a metal plate. The rectifying orifice plate 12 provides a uniform and stable flow to prevent airflow separation.

[0085] Test section 5 is the wind tunnel body.

[0086] Furthermore, in S1, the wind tunnel flow rate It is expressed as:

[0087] ;

[0088] in, To simulate the gas density under the envelope, is the cross-sectional area, is the flow rate.

[0089] Furthermore, in S2, the cross-sectional size of the stable section is It is expressed as:

[0090] ;

[0091] in, To simulate temperature, is the volume, is the gas constant, To simulate pressure.

[0092] Furthermore, in S3, computational fluid dynamics software (CFD) is used to simulate the nozzle working condition, and the simulation process is to solve the three-dimensional NS equations and calculate the flow field in the nozzle to obtain the nozzle exit Mach number;

[0093] The conservation form of the three-dimensional NS equation is expressed as:

[0094] ;

[0095] in, is a conserved variable, is the inviscid flux, =1, 2, or 3, is the viscous flux.

[0096] Furthermore, in the S4, the plasma excitation action area is simplified into a triangular OAB area, the volume force component of the OAB area is solved, and loaded into the plasma excitation area, the flow field is solved, the flow field distribution in the nozzle is obtained, and the changed nozzle outlet Mach number is calculated;

[0097] The electric field intensity E is distributed linearly in the OAB region;

[0098] Electric field strength distribution It is expressed as:

[0099] ;

[0100] in, is the electric field strength at the origin, , is the maximum voltage applied between the electrodes, is the distance between the two electrodes, is the first constant, is the second constant;

[0101] The first constant It is expressed as:

[0102] ;

[0103] in, is the distance of the plasma excitation action area in the OB direction, is the breakdown voltage of the plasma flow boundary;

[0104] The second constant It is expressed as:

[0105] ;

[0106] in, is the distance of the plasma excitation action area in the OA direction;

[0107] The electric field intensity component in the direction It is expressed as:

[0108] ;

[0109] The electric field intensity component in the direction It is expressed as:

[0110] ;

[0111] The body force component in the direction is expressed as:

[0112] ;

[0113] in, is the charge density, is the elementary charge, is the power supply discharge frequency, is the plasma action time in one excitation cycle;

[0114] The body force component in the direction is expressed as:

[0115] ;

[0116] The volume force generated by the directional motion of plasma under the action of the electric field is added to the source term of the momentum equation to obtain the volume force equation induced by plasma.

[0117] The plasma-induced volume force equation is expressed as:

[0118] ;

[0119] in, is the first velocity component, is the second velocity component, are the coordinate components, is the sub-grid stress, is the plasma-induced volume force, is the statistical weight of the ion, For pressure;

[0120] According to the above-mentioned calculation model of plasma excitation, namely the phenomenological model and the plasma-induced volume force equation, the plasma-induced volume force is solved. , plasma-induced volume forces are implemented by a custom program (UDF) Loading of the plasma excitation region in the momentum equation source term and the inner wall of the stable segment.

[0121] Specifically, the first constant and the second constant Breakdown voltage at the plasma flow boundary related;

[0122] The volume force generated by plasma excitation can be represented by the electric field force. The direction of the electric field force is parallel to the AB side of the OAB region and points diagonally downward. After plasma excitation, the temperature increases and the kinetic energy of the gas increases, which changes the flow field state in the nozzle, thereby changing the Mach number at the nozzle outlet. The specific Mach number change is controlled by the number of excited plasma generators.

[0123] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

Claims

1. A plasma-based variable Mach number wind tunnel design method, characterized in that: The following steps are involved: S1. Determine the overall aerodynamic parameters; Specifically, the overall aerodynamic parameters include wind tunnel operating parameters and the relationship between total temperature and total pressure and static temperature and static pressure. Wind tunnel operating parameters include total temperature and total pressure of incoming flow, Mach number of test chamber, static temperature, static pressure and wind tunnel flow rate. S2. Determine the cross-sectional dimensions of the stable section according to the wind tunnel flow rate and the set simulated temperature and simulated pressure; S3. According to the overall aerodynamic parameters, the axial Mach number distribution is constructed by following the Sivells method to calculate the wall profile by setting the axial Mach number distribution. The nozzle exit Mach number is designed in combination with the transonic theory, and the nozzle exit Mach number is verified by the computational fluid dynamics method. S4. Control the number of excited plasma generators, use the phenomenological model to solve the volume force field generated by plasma excitation, obtain the changed nozzle outlet Mach number, and complete the variable Mach number wind tunnel design; It also includes a fixed section (1), a plasma generator (2), a stabilizing section (3), a nozzle section (4), a test section (5), an expansion section (6), a straight-discharge section (7) and a vacuum unit (8); The fixed section (1), the stable section (3), the nozzle section (4), the test section (5), the expansion section (6), the straight-discharge section (7) and the vacuum unit (8) are connected in sequence, and the plasma generator (2) is arranged in pressure equalizing holes evenly arranged on the surface of the stable section (3); The fixed section (1) is used to connect to a high-pressure gas source; The plasma generator (2) comprises an upper electrode (9), a lower electrode (10) and an insulating layer (11), wherein the insulating layer (11) is arranged between the upper electrode (9) and the lower electrode (10), and the plasma generator (2) is used to provide a plasma beam; A rectifying orifice plate (12) is arranged at the rear side of the stabilizing section (3), and the stabilizing section (3) is used to rectify the plasma beam and output a high-pressure gas flow containing plasma; The nozzle section (4) is used to accelerate the high-pressure gas flow containing plasma to reach a desired Mach number, thereby obtaining a processed plasma gas beam; The test section (5) is used to provide an aerodynamic test site for hypersonic aerodynamic tests; The expansion section (6) is used to decelerate and pressurize the plasma gas beam after being processed by the hypersonic aerodynamic test; The straight discharge section (7) is used to recover the working fluid; The vacuum unit (8) is used to evacuate the straight-discharge section (7) to provide a low-pressure environment.

2. The plasma-based variable Mach number wind tunnel design method according to claim 1, characterized in that: The S1, wind tunnel flow It is expressed as: ； in, To simulate the gas density under the envelope, is the cross-sectional area, is the flow rate.

3. The plasma-based variable Mach number wind tunnel design method according to claim 2, characterized in that: In S2, the cross-sectional size of the stable section It is expressed as: ； in, To simulate temperature, is the volume, is the gas constant, To simulate pressure.

4. The plasma-based variable Mach number wind tunnel design method according to claim 3, characterized in that: In S3, computational fluid dynamics software is used to simulate the nozzle working condition, and the simulation process is to solve the three-dimensional NS equations and obtain the nozzle outlet Mach number by calculating the flow field in the nozzle; The conservation form formula of the three-dimensional NS equation is expressed as: ； in, is a conserved variable, is the inviscid flux, =1, 2, or 3, is the viscous flux.

5. The plasma-based variable Mach number wind tunnel design method according to claim 4, characterized in that: In the S4, the plasma excitation action area is simplified to a triangular OAB area, the volume force component of the OAB area is solved, and loaded into the plasma excitation area, the flow field is solved, the flow field distribution in the nozzle is obtained, and the changed nozzle outlet Mach number is calculated; The electric field intensity E is distributed linearly in the OAB region; Electric field strength distribution It is expressed as: ； in, is the electric field strength at the origin, , is the maximum voltage applied between the electrodes, is the distance between the two electrodes, is the first constant, is the second constant; The first constant It is expressed as: ； in, is the distance of the plasma excitation action area in the OB direction, is the breakdown voltage of the plasma flow boundary; The second constant It is expressed as: ； in, is the distance of the plasma excitation action area in the OA direction; The electric field intensity component in the direction It is expressed as: ； The electric field intensity component in the direction It is expressed as: ； The body force component in the direction is expressed as: ； in, is the charge density, is the elementary charge, is the power supply discharge frequency, is the plasma action time in one excitation cycle; The body force component in the direction is expressed as: ； The volume force generated by the directional motion of plasma under the action of the electric field is added to the source term of the momentum equation to obtain the volume force equation induced by plasma. The plasma-induced volume force equation is expressed as: ； in, is the first velocity component, is the second velocity component, are the coordinate components, is the sub-grid stress, is the plasma-induced volume force, is the statistical weight of the ion, For pressure; According to the above calculation model of plasma excitation and the plasma-induced volume force equation, the plasma-induced volume force is solved. , plasma-induced volume forces are implemented by a custom program Loading of the plasma excitation region in the momentum equation source term and the inner wall of the stable segment.

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