An evaluation method for the accuracy of a flat probe in high-temperature dynamic plasma diagnostics

Abstract

This application relates to the field of flush probe evaluation, and specifically discloses a method for evaluating the accuracy of flush probe in high-temperature dynamic plasma diagnosis. Through theoretical calculations and test results of a high-enthalpy wind tunnel, the accuracy of directly using flush probes for measuring the plasma concentration in a high-temperature dynamic flow field is quantitatively evaluated, and a comparative evaluation of the detection data between electrostatic probes and flush probes is achieved.

Description

Technical Field

[0001] This application relates to the technical field of flush probe evaluation, in particular to a test and analysis method for evaluating the diagnostic accuracy of flush probes used in high-temperature plasma tests, mainly including determination of test conditions, model design, and result analysis. Background Art

[0002] The plasma sheath generated by the interaction between hypersonic aircraft and the atmosphere is the fundamental cause of communication interruption. Comprehensively, objectively, and accurately understanding the characteristics of the plasma sheath is a prerequisite for studying the measurement and control communication problems under the plasma sheath, accurately predicting the blackout interruption interval, and exploring new methods to overcome the blackout.

[0003] The electrostatic probe (Langmuir probe) is one of the earliest diagnostic tools used to measure plasma characteristics. It has the characteristics of simple structure, easy setup, and high resolution. However, it will affect the aerodynamics in the hypersonic flow field environment and cannot resist ablation. Therefore, its application in flight tests is limited. The flush probe is a new plasma test method that can be used in hypersonic flight tests. It adopts an electrode-embedded structure, effectively solving the problems of easy ablation of the probe and interference with the flow field. It can survive in a complex plasma environment for a long time, but the theoretical model for its application in high-temperature flow environments has not been established yet. According to the probe measurement theory, the main sources of probe measurement uncertainty include collisions and dynamic flow fields. Collisions and flow fields will affect the number of electrons collected within the Debye sphere of the probe. Therefore, when processing data, it is necessary to correct the sheath expansion effect and flow effect caused by collisions. Currently, it is still impossible to accurately evaluate the influence of the above effects through theoretical calculations. Therefore, before applying the flush probe to the plasma flow field diagnosis of hypersonic flight tests, it is necessary to evaluate and analyze the diagnostic accuracy of the flush probe through a method combining experiments and theoretical calculations in the ground high-enthalpy wind tunnel flow field, providing support for the analysis of the test results of subsequent flight tests. Summary of the Invention

[0004] This application proposes an experimental model and evaluation method for analyzing the measurement accuracy of flush probes in high-temperature flow field dynamic plasmas. Through theoretical calculations and the test results of high-enthalpy wind tunnel tests, the accuracy of directly using flush probes to measure the plasma concentration in high-temperature dynamic flow fields is quantitatively evaluated, realizing the comparative evaluation of the detection data between electrostatic probes and flush probes.

[0005] This application adopts the following technical solutions:

[0006] Step 1: Use the CFD method for solving the thermochemical non-equilibrium NS equations to calculate the plasma flow field environment parameters (velocity, pressure, electron temperature, electron number density) under typical flight conditions (altitude, Mach number, angle of attack) of the flight trajectory profile, and determine the electron number density range [n of the flush probee1 , n e2 .

[0007] Step 2: According to the plasma flow field parameters T e (electron temperature), n e (electron number density) obtained in Step 1, solve for the plasma Debye length λ D :

[0008]

[0009] where T e is the electron temperature, and n e is the electron number density.

[0010] Step 3: According to the plasma Debye length λ D obtained in Step 2, and the plasma flow field parameters (pressure and velocity) obtained in Step 1, determine the pressure range [p1, p2] and velocity range [u1, u2] of the flow field at a height of λ D from the wall surface at the installation position of the flush-mounted probe;

[0011] Step 4: To ensure that the flush-mounted probe can be installed flush with the model surface and avoid ablation during the test due to protruding from the surface, and at the same time considering the size of the core area of the 20MW arc wind tunnel flow field, design the following 150mm×150mm flat plate test model for wind tunnel testing; it is required that the catalytic characteristics of the flat plate material are close to those of the aircraft surface material; arrange the flush-mounted probe and the electrostatic probe symmetrically on the flat plate, and the requirements are as follows: 1) The head of the electrostatic probe support and the two electrodes of the flat plate probe are located in the same cross-section; 2) 60 > D1 > 3R, 75 > D2 > 2R, where R is the radius of the flat plate probe device; 3) The size L1 of the head of the electrostatic probe support and the length L2 of the electrostatic probe satisfy The distance L3 of the electrostatic probe from the wall surface is > 10λ D ; The probe spacing d > 2λ D . By restricting D1, it is ensured that there is no interference between the electrostatic probe and the flush-mounted probe; by restricting D2, the two probes are as close as possible to the nozzle exit, weakening the influence caused by the flow field attenuation. The restriction on the relationship between L1 and L2 is to ensure that the electrostatic probe meets the usage requirements of the slender body assumption; the restriction on L3 is to avoid interference between the electrostatic probe and the flat plate model and affect the test results.

[0012] Step 5: Wind tunnel flow field debugging; generally, in an arc wind tunnel or a high-frequency induction heating plasma wind tunnel, the free jet test method is used to carry out the test, and the electron number density n e, the surface pressure p, and the flow velocity u are three simulation parameters, and their simulation ranges are determined according to Steps 1 and 3. Considering the limitations of the existing wind tunnel test capabilities, it is impossible to simultaneously simulate the above three parameters. Therefore, the test uses the method of partial parameter simulation to cover the ranges of the electron number density n e , the surface pressure p, and the flow velocity u one by one, and determine the wind tunnel operating parameters (voltage, current, air flow rate) and the model placement attitude angle that meet the simulation requirements.

[0013] Step 6: Wind tunnel test; According to the wind tunnel operating parameters and the model placement attitude angle determined in Step 5, after the flow field is stable, use the fast feeding mechanism to place the test model clockwise (not more than 2 s) in the core area of the flow field downstream of the wind tunnel nozzle, and it is required to ensure that the flow fields at the positions of the electrostatic probe and the flush-mounted probe above the test model are the same (the surface pressure and heat flux are the same). During the test, record the test data (plasma density) of the electrostatic probe and the flush-mounted probe.

[0014] Step 7: According to the wind tunnel operating parameters determined in Step 5, use the CFD method of solving thermochemical non-equilibrium NS to calculate the plasma flow field of the test in Step 6; Extract the plasma flow field parameter curves in the normal direction of the wall surface at the position of the flush-mounted probe from the calculation results, including the electron number density and pressure.

[0015] Step 8: If the deviation between the model surface pressure calculated in Step 7 and the pressure test result in Step 5 is less than 20%, it is considered that the calculation result of Step 7 meets the requirements, and Step 9 can be carried out; If the deviation is greater than 20%, it is considered that the calculation result of Step 7 does not meet the requirements, and it is necessary to adjust the thermochemical reaction model, calculation grid, and numerical discretization method and recalculate.

[0016] Step 9: According to the test results of the electrostatic probe in Step 6, correct the electron density curve in Step 7; Extract the electron number density Ne D at a distance λ from the wall surface from the curve. 标准 .

[0017] Step 10: Compare the electron number density Ne 标准 obtained in Step 9 with the test results of the flush-mounted probe in Step 6, and evaluate and determine the deviation between the two.

[0018] In summary, the present application includes at least the following beneficial technical effects:

[0019] (1) By setting up the experimental model and evaluation method, it is possible to find out the deviation between the measurement results of the electrostatic probe at the surface position and the measurement results of the flush-mounted probe at the spatial position above the surface, and it is possible to realize the comparative evaluation of the detection data between the electrostatic probe and the flush-mounted probe;

[0020] (2) By the method of the present application, a look-up table of electron number density and deviation is formed, and the deviation of plasma diagnosis of the flush-mounted probe in this state can be quickly found according to the electron number density actually diagnosed by the flush-mounted probe. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of the experimental model in the embodiment of the present application;

[0022] Figure 2 It is a schematic diagram of the physical structure of the experimental model in the embodiment of the present application;

[0023] Figure 3 It is a schematic diagram of the wind tunnel experiment in the embodiment of the present application;

[0024] Figure 4 It is a schematic diagram of calculating result correction according to the results of electrostatic probes in the embodiment of the present application. Detailed Embodiment

[0025] The present application will be further described in detail below with reference to the drawings and specific embodiments:

[0026] The embodiment of the present application discloses a method for evaluating the accuracy of high-temperature dynamic plasma diagnosis of a flush-mounted probe. Referring to Figures 1-4 , it includes the following steps:

[0027] S1: Determine the experimental model. To ensure that the flush-mounted probe can be installed flush with the model surface and avoid ablation during the test due to protruding from the surface, and considering the size of the core area of the flow field of the 20MW arc wind tunnel, the following test model is designed for the wind tunnel test:

[0028] The experimental model includes a flat plate. The catalytic characteristics of the flat plate material are close to those of the aircraft surface material. The flush-mounted probe and the electrostatic probe are connected to the same side of the flat plate. The measuring end of the flush-mounted probe is flush with the flat plate surface, the probe axis of the electrostatic probe is parallel to the flat plate surface, and the distance between the axis of the electrostatic probe and the axis of the flush-mounted probe is D1, where 0.4L > D1 > 3R, R is the radius of the flat plate probe device, L is the side length of the flat plate, and the flat plate is square. In this embodiment, the size of the flat plate is 150mm × 150mm; along the wind tunnel flow direction, the distance between the axis of the flush-mounted probe and the side of the flat plate facing the flow direction is D2, where 0.5L > D2 > 2R; the size L1 of the head of the electrostatic probe support and the probe length L2 of the electrostatic probe satisfy L1 < 1 / 4L2 < R; the electrostatic probe includes 3 probes, and the axes of the 3 probes are all parallel to the wall surface of the flat plate. The axes of the 3 probes are in the same plane and this plane is perpendicular to the wall surface of the flat plate. The distance L3 between the probe closest to the flat plate surface and the wall surface is L3 > 10λ D ; the probe spacing d > 2λ D ;

[0029] By restricting D1, it is ensured that there is no interference between the electrostatic probe and the flush-mounted probe, and they can be under the condition of a consistent flow field; by restricting D2, the two probes are as close as possible to the nozzle exit, weakening the influence brought by the flow field attenuation; the restriction on the relationship between L1 and L2 ensures that the electrostatic probe meets the usage requirements of the slender body hypothesis; the restriction on L3 avoids the interference between the electrostatic probe and the flat plate model and affects the test results.

[0030] S2: Use the CFD method of solving the thermochemical non-equilibrium NS equations to calculate the plasma flow field environment parameters under typical flight conditions (certain altitude, Mach number, angle of attack) of the flight ballistic profile, and obtain the calculated values of the velocity range, pressure range, electron temperature range, and electron number density range of the flow field.

[0031] S3: According to the range of electron temperature and the range of electron number density, solve to obtain the calculated value of the plasma Debye length λ D range of calculated values,

[0032]

[0033] where, T e is the electron temperature, n e is the electron number density, k is the Boltzmann constant, e is the charge, and ε0 is 1 / 4π.

[0034] S4: According to the range of plasma Debye length, velocity and pressure, determine the pressure range and velocity range of the flow field at a height of λ D from the wall surface in the normal direction of the installation position of the flush-mounted probe.

[0035] S5: Wind tunnel flow field debugging: Generally, in an arc wind tunnel or a high-frequency induction heating plasma wind tunnel, the free jet test method is used to carry out the test. Select the electron number density n e , surface pressure p, and flow velocity u as three simulation parameters. Among them, the target adjustment range of the electron number density includes the calculated value of the electron number density range obtained in S21, and the target adjustment ranges of the surface pressure and flow velocity include the pressure range and velocity range of the flow field at a height of λ D from the wall surface obtained in step S23;

[0036] Considering the limitations of the existing wind tunnel test capabilities, it is impossible to simultaneously simulate the above three parameters. Therefore, the test uses the method of partial parameter simulation to simulate the electron number density n eCover the target adjustment ranges of the electron number density, surface pressure p, and flow velocity u. Specifically, adjust the operating parameters of the wind tunnel and the model placement attitude angle so that the electron number density in the wind tunnel flow field, the surface pressure on the surface of the experimental model, and the flow velocity are within the target adjustment ranges. Record the determined wind tunnel operating parameters and model placement attitude angle. The wind tunnel operating parameters include voltage, current, and air flow rate.

[0037] S6: Wind tunnel test: According to the wind tunnel operating parameters and model placement attitude angle determined in S5, after the flow field is stable, use the rapid feeding mechanism to place the test model clockwise in the core area of the flow field downstream of the wind tunnel nozzle. It is required to ensure that the flow fields at the positions of the electrostatic probe and the flush-mounted probe above the test model are consistent (the surface pressures are the same). The time of the experimental model in the wind tunnel flow field is not more than 2 s. Record the electron number density Ne measured by the flush-mounted probe. 平测 and the electron number density Ne measured by the electrostatic probe 静测 .

[0038] S7: According to the wind tunnel operating parameters determined in S5, use the CFD method for solving thermochemical non-equilibrium NS to calculate the plasma flow field of the wind tunnel test to obtain the total incoming flow temperature T0, the position of the flush-mounted probe, and the plasma flow field parameter curves in the wall normal direction. The flow field parameter curves include Y - electron number density, Y - pressure, and plasma Debye length λ. D1 , where Y is the height from the wall.

[0039] S8: Under the condition of the same Y, if the deviation between the pressure obtained from the Y - pressure parameter curve in step S7 and the surface pressure of the wind tunnel flow field in S5 is less than 20%, proceed to S9; if the deviation is greater than 20%, then adjust the CFD method for solving the thermochemical non-equilibrium NS equation. Specifically, adjust the thermal chemical reaction model, computational grid, and numerical discretization method in the CFD method for solving the thermochemical non-equilibrium NS equation, and repeat S2 - S7.

[0040] S9: Repeat steps S5 - S8 to measure multiple groups of electron number densities under different wind tunnel flow field conditions.

[0041] S10: According to the electron number density measured by the electrostatic probe in S9, correct the Y - electron number density parameter curve in S7 to obtain the corrected electron number density curve. Extract the electron number density Ne at a distance from the wall equal to the plasma Debye length λ D1 from the corrected electron number density curve. 标准 .

[0042] S11: According to the electron number density Ne 标准 and the electron number density Ne measured by the flush-mounted probe in S6 平测 , evaluate the deviation. The deviation = |Ne 标准 - Ne 平测 | / Ne标准 × 100%, and a deviation lookup table is formed according to the electron number density and the corresponding deviation.

[0043] In this embodiment, the simulation ranges of the electron number density, pressure, and velocity are determined according to the flight profile of the aircraft, and tests are carried out in a 20MW arc wind tunnel (see Figure 2 ), combining the test results and the flow field calculation results, the diagnostic accuracy of the flush-mounted probe is analyzed. The height of the electrostatic probe is 10 mm from the flat wall surface, and the test result is 4.5×10 12 cm -3 ; the test result of the flush-mounted probe is 5.5×10 11 cm -3 .

[0044] According to the operating state of the wind tunnel, the test flow field is calculated, and the electron number density curve in the wall normal direction is obtained, and the curve is corrected according to the results of the electrostatic probe. Since the test result of the flush-mounted probe is the result at a position λ D (about 1 mm) from the wall surface, the result at a distance of 1 mm from the wall surface can be extracted from the corrected curve, which is about 2.1×10 12 cm -3 ;

[0045] Therefore, the test deviation of the flush-mounted probe is determined to be 1.55×10 12 cm -3 , about 74%.

[0046] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. An evaluation method for the high-temperature dynamic plasma diagnostic accuracy of a flush-mounted probe, characterized in that: Including: S1: Determine an experimental model, which includes a flat plate, a flush-mounted probe and an electrostatic probe connected to the same side of the flat plate. The measuring end of the flush-mounted probe is flush with the surface of the flat plate, and the probe axis of the electrostatic probe is parallel to the surface of the flat plate; S2: Determine the target adjustment ranges of the electron number density in the wind tunnel flow field, the surface pressure on the surface of the experimental model, and the flow velocity; S3: Wind tunnel flow field debugging: Debug the operating parameters of the wind tunnel and the model placement attitude angle so that the electron number density in the wind tunnel flow field, the surface pressure on the surface of the experimental model, and the flow velocity are within the target adjustment ranges, and record the determined operating parameters of the wind tunnel and the model placement attitude angle; S4: Wind tunnel test: Place the experimental model into the wind tunnel flow field according to the model placement attitude angle, and record the electron number density Ne measured by the flush-mounted probe 平测 and the electron number density Ne measured by the electrostatic probe 静测 ; S5: According to the wind tunnel operation parameters, the CFD method for solving thermochemical non-equilibrium NS is used to calculate the plasma flow field of the wind tunnel test to obtain the total incoming flow temperature T0, the position of the flush-mounted probe, and the plasma flow field parameter curves in the wall normal direction. The flow field parameter curves include the Y-electron number density, Y-pressure, and the plasma Debye length λ D1 , where Y is the height from the wall surface; S6: Under the same Y conditions, if the deviation between the pressure obtained from the Y-pressure parameter curve in step S5 and the surface pressure in the wind tunnel flow field in S3 is less than 20%, perform S7; if the deviation is greater than 20%, then adjust the methods for calculating the electron number density in the wind tunnel flow field, the surface pressure on the surface of the experimental model, and the flow velocity in step S2, and repeat S2 - S5; S7: Repeat steps S5 - S6 to measure the electron number density under multiple different wind tunnel flow field conditions; S8: According to the electron number density measured by the electrostatic probe in S7, correct the Y-electron number density parameter curve in S5 to obtain the corrected electron number density curve, and extract the electron number density Ne at a distance of the plasma Debye length λ from the wall surface from the corrected electron number density curve D1 ; 标准 ; S9: Evaluate the deviation according to the electron number density Ne 标准 and the electron number density Ne measured by the flush-mounted probe in S4 平测 .

2. The evaluation method for the accuracy of a flat probe high-temperature dynamic plasma diagnosis according to claim 1, characterized in that: The electrostatic probe includes a support and a probe connected to the support. The axis of the probe connected to the support is parallel to the flat plate. The cross-section passing through the two electrode axes of the flush-mounted probe is the positioning cross-section, and the boundary position between the support and the first probe is coplanar with the positioning cross-section.

3. The evaluation method for the accuracy of a paperback probe in high-temperature dynamic plasma diagnosis according to claim 2, wherein: The distance between the axis of the electrostatic probe and the axis of the flush-mounted probe is D1, and 0.4L > D1 > 3R, where R is the radius of the flat plate probe device, L is the side length of the flat plate, and the flat plate is square.

4. A method for evaluating the accuracy of a flat probe high-temperature dynamic plasma diagnosis according to claim 3, characterized in that: Along the wind tunnel incoming flow direction, the distance between the axis of the flush-mounted probe and the side of the flat plate facing the incoming flow direction is D2, and 0.5L > D2 > 2R; the size L1 of the head of the electrostatic probe support and the probe length L2 of the electrostatic probe satisfy L1 < 1 / 4L2 < R.

5. The evaluation method for the high-temperature dynamic plasma diagnosis accuracy of a flat probe according to claim 2, characterized in that: The electrostatic probe includes three probes, and the distance L3 between the probe closest to the flat surface and the wall surface satisfies L3 > 10λ D ; the probe spacing d > 2λ D .

6. The evaluation method for the high-temperature dynamic plasma diagnostic accuracy of a flat probe according to claim 1, characterized in that: The plasma Debye length λ D1 :

7. A method for evaluating the accuracy of a flat probe high-temperature dynamic plasma diagnosis according to claim 1, characterized in that: Step S2 includes, S21: Use the CFD method for solving the thermochemical non-equilibrium NS equations to calculate the plasma flow field environment parameters under typical flight conditions of the flight ballistic profile, and obtain the calculated value range of the flow velocity, the calculated value range of the pressure, the calculated value range of the electron temperature, and the calculated value range of the electron number density in the flow field; S22: Solve to obtain the plasma Debye length λ according to the ranges of the electron temperature and the electron number density D Range calculated value Among them, T e is the electron temperature, and n e is the electron number density; S23: Determine the pressure range and velocity range of the flow field at a height of λ from the wall surface in the normal direction of the installation position of the flush probe according to the ranges of the plasma Debye length, velocity, and pressure. D where the pressure range and velocity range of the flow field are determined; The target adjustment range of the electron number density of the wind tunnel flow field includes the calculated value of the electron number density range obtained by S21, and the target adjustment ranges of the surface pressure and the flow velocity include the pressure range and the velocity range of the flow field at a distance of λ from the wall surface obtained in step S23. D The flow field pressure range and velocity range at this location.

8. The evaluation method for the accuracy of a flat probe high-temperature dynamic plasma diagnosis according to claim 1, characterized in that: The time of the experimental model in the wind tunnel flow field is not more than 2 s.

9. The evaluation method for the accuracy of a flat probe high-temperature dynamic plasma diagnosis according to claim 1, wherein: The deviation = |Ne 标准 - Ne 平测 | / Ne 标准 × 100%.

10. A method for evaluating the accuracy of a flat probe high-temperature dynamic plasma diagnosis according to claim 1, characterized in that: Form a deviation lookup table according to the electron number density and the corresponding deviation.

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