A method for measuring the stagnation enthalpy of a super-high-enthalpy non-equilibrium gas flow

Abstract

This invention relates to a method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation points, used for ground tests of arc wind tunnel thermal protection systems. Specifically, it pertains to the field of aircraft ground aerodynamic thermal testing research. Based on a developed dual-band laser absorption spectroscopy method, it measures the non-equilibrium temperature of the airflow on the surface of a water-cooled stagnation point model and the component concentrations of atomic nitrogen and oxygen, obtaining the internal energy enthalpy and chemical enthalpy of the stagnation point model, thereby achieving the measurement of the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation points. This method complements existing methods and fills the gap in enthalpy measurement in the 50-100 MJ / kg range for aerodynamic thermal testing. Furthermore, this method is not limited to measuring airflow parameters during the testing and commissioning phase; it can also achieve full-process flow field parameter monitoring for aerodynamic thermal evaluation tests of aircraft thermal protection materials.

Description

Technical Field

[0001] This invention relates to the measurement of airflow parameters in ground tests of aircraft, for use in ground tests of thermal protection systems in electric arc wind tunnels, and particularly to a method for measuring the enthalpy of stagnation points in ultra-high enthalpy non-equilibrium airflow, belonging to the field of research on ground aerodynamic and thermal tests of aircraft. Background Technology

[0002] As spacecraft reentry speeds increase, reaching Mach numbers of Ma=30 and enthalpy values ​​exceeding 45 MJ / kg, and with reentry speeds reaching the second cosmic velocity and enthalpy values ​​around 60 MJ / kg, ground-based wind tunnels are commonly used to simulate the reentry process of these spacecraft. These typically employ high-frequency induction plasma heating wind tunnels and MPD magnetic acceleration plasma wind tunnels. For ground simulations of these two types of wind tunnels, the most critical environmental factor is the calibration of ground-based airflow parameters, with the measurement of enthalpy values ​​for ultra-high enthalpy incoming flow conditions being of paramount importance.

[0003] Regarding the measurement of enthalpy of ultra-high enthalpy gas flows, current methods based on lower enthalpy conditions are still used. The stagnation enthalpy is obtained by back-calculating the stagnation pressure and stagnation heat flux using a stagnation test specimen. This method is based on the classic Fay-Riddell formula. This formula makes many assumptions and does not consider the non-equilibrium effects at high enthalpy, generally only applicable to enthalpy measurements below 30 MJ / kg. At higher enthalpy conditions, due to the questionable accuracy of the formula itself, and the fact that radiative heat flux can no longer be ignored under ultra-high enthalpy conditions, the stagnation heat flux exhibits significant measurement errors. Therefore, this method is unsuitable for enthalpy measurement. The enthalpy measurement method I developed (ZL201910440190.1) is based on flow conservation and NASA thermochemical equilibrium calculations, and is applicable to enthalpy measurement in the range of 1-25 MJ / kg. The patent (ZL201811494282.X) considers enthalpy measurement under low enthalpy conditions, ignores the chemical enthalpy generated by gas dissociation, and obtains the local total enthalpy of the gas flow at the nozzle outlet by measuring the temperature and velocity of the free flow at the nozzle outlet of the electric arc heater, and is applicable to enthalpy measurement in the range of 1.5 MJ / kg-7.5 MJ / kg. The patents (ZL202111015133.2, ZL202111012554.X) respectively consider the conditions of pure air medium and mixed medium with arc-starting argon gas, and extend the applicable range of gas flow enthalpy to 50 MJ / kg. The above work did not involve the measurement of gas flow enthalpy under higher enthalpy conditions (≥50MJ / kg) and strong nonequilibrium effects.

[0004] The enthalpy of a gas flow is essentially composed of three components: internal enthalpy, kinetic enthalpy, and chemical enthalpy. Internal enthalpy is related to the gas flow temperature, kinetic enthalpy is related to the gas flow velocity, and chemical enthalpy is related to the gas composition and its mass fraction. When a flat-top stagnation model is used for calibration, the enthalpy experienced on the model's surface is the stagnation enthalpy. Since the gas flow is stagnant at the model's surface with zero velocity, its kinetic enthalpy is zero. Furthermore, for high-enthalpy gas flows, when the enthalpy is sufficiently high, corresponding to a very high temperature, the air undergoes sufficient dissociation and ionization, resulting in the absence of molecular oxygen and nitrogen. Calculations show that in the temperature range of 6000-10000 K, the gas composition is predominantly atomic oxygen and nitrogen, with a low content of electronic components, whose contribution to the chemical enthalpy of formation is negligible. The chemical enthalpy can be obtained by measuring the concentrations of N and O. Moreover, the non-equilibrium effects present in ultra-high enthalpy gas flows mean that gas component concentrations cannot be simply used for temperature and pressure calculations. A major challenge for ultra-high enthalpy gas flows is the high enthalpy non-equilibrium effect, meaning that the gas thermodynamic temperature cannot be characterized by a single temperature, and the thermodynamic temperatures corresponding to different atoms in the gas components are not consistent. High-temperature models generally need to use a two- or three-temperature approach to describe the gas. To quantify the internal enthalpy of ultra-high enthalpy gas flows, the gas temperature needs to obtain the temperatures of at least two energy levels, and then further perform temperature coupling to achieve the quantification of internal enthalpy. Summary of the Invention

[0005] The technical problem solved by this invention is to propose a method for measuring the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow. Based on the developed dual-band laser absorption spectroscopy method, the non-equilibrium temperature of the airflow on the surface of a water-cooled stagnation point model and the component concentrations of atomic nitrogen and oxygen are measured to obtain the internal energy enthalpy and chemical enthalpy of the stagnation point model, thereby realizing the measurement of the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow.

[0006] The technical solution of the present invention is as follows:

[0007] A method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow includes the following steps:

[0008] (1) Establish a stable flow field environment for ultra-high enthalpy non-equilibrium airflow. Place the water-cooled model in the forward direction downstream of the ultra-high enthalpy non-equilibrium airflow and measure the stagnation pressure P of the airflow. s ;

[0009] (2) The transmitting end of the dual-band absorption spectroscopy measurement system generates an incident laser signal. The laser signal passes along the surface of the water-cooled model and is received by the receiving end on the other side of the dual-band absorption spectroscopy measurement system to obtain the transmitted laser signal. The integration area A of each of the two bands is obtained based on the incident laser signal and the transmitted laser signal. N A O and the Gauss full width at half maximum (FWHM) Δν of the spectral lines N Δν OThe subscripts N and O represent atomic nitrogen and atomic oxygen, respectively.

[0010] (3) Based on the Gaussian half-width Δν of the spectral line N Δν O To obtain the temperatures T of atomic nitrogen and atomic oxygen under non-equilibrium conditions. N T O ;

[0011] (4) Based on the respective temperatures T of atomic nitrogen and atomic oxygen under the aforementioned non-equilibrium conditions N T O Obtain the coupling temperature T s ,in,

[0012] (5) Based on the coupling temperature T s and stationary pressure P s Obtain the specific heat C at constant pressure p ;

[0013] (6) Based on the specific heat C at constant pressure p and coupling temperature T s , obtain internal energy enthalpy h s ;

[0014] (7) Based on the integral area A N A O The temperatures T of atomic nitrogen and atomic oxygen N T O And the diameter D of the water-cooled model, to obtain the mole fraction X of atomic nitrogen and atomic oxygen. N and X O ;

[0015] (8) The molar concentrations of the atomic nitrogen and atomic oxygen X N and X O Converted to the mass fraction ω of atomic nitrogen and atomic oxygen N and ω O ;

[0016] (9) Based on the mass fractions ω of atomic nitrogen and atomic oxygen N and ω O Obtain chemical enthalpy h c ;

[0017] (10) Based on the internal energy enthalpy h s and chemical enthalpy h c We obtained the ultra-high enthalpy non-equilibrium gas stagnation point enthalpy H0.

[0018] In the above-mentioned method for measuring the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow, the water-cooled model is a cylindrical shell structure with internal cold water pipes, and the shell material is copper.

[0019] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (2) involves dividing the incident laser signal and the transmitted laser signal by their respective logarithms, and then fitting the data using the Voigt function to obtain the integration area A of each of the two bands. N A O and the Gauss full width at half maximum (FWHM) Δν of the spectral lines N Δν O .

[0020] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (3) is based on the Gauss full width at half maximum (FWHM) Δν of the spectral line. N Δν O To obtain the temperatures T of atomic nitrogen and atomic oxygen under non-equilibrium conditions. N T O ,include:

[0021] T N =14(λ) N ·Δν N ) 2

[0022] T O =16(λ) O ·Δν O ) 2

[0023] Where, λ N , λ O These are the center wavelengths of the two bands in the dual-band laser absorption spectroscopy measurement system.

[0024] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (5) is based on the coupled temperature T. s and stationary pressure P s Obtain the specific heat C at constant pressure p ,include:

[0025] C p =0.9938 - 7.787 × 10 -4 P s +1.98×10 -4 T s +7.067×10 -7 P s ·T s -4.587×10 -8 T s 2 -1.25×10 -10 P s ·T s 2 +4.19×10-12 T s 3

[0026] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (6) is based on the isobaric specific heat C. p and coupling temperature T s , obtain internal energy enthalpy h s ,include:

[0027] h s =C P ×T s .

[0028] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (7) is based on the integral area A. N A O The temperatures T of atomic nitrogen and atomic oxygen N T O And the diameter D of the water-cooled model, to obtain the mole fraction X of atomic nitrogen and atomic oxygen. N and X O ,include:

[0029]

[0030] Among them, S(T) N ), S(T O The values ​​represent the line intensities of the spectral lines in the two bands of the dual-band laser absorption spectroscopy measurement system, respectively.

[0031] In the above-mentioned method for measuring the stagnation point enthalpy of ultra-high enthalpy non-equilibrium airflow, step (8) involves determining the molar concentrations X of atomic nitrogen and atomic oxygen. N and X O Converted to the mass fraction ω of atomic nitrogen and atomic oxygen N and ω O ,include:

[0032]

[0033] Among them, M air Let be the molar mass of air.

[0034] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (9) is based on the mass fractions ω of atomic nitrogen and atomic oxygen. N and ω O Obtain chemical enthalpy h c ,include:

[0035] h c =aω N +bω O

[0036] Where a and b are the dissociation energies of atomic nitrogen and atomic oxygen, respectively, with values ​​of a = 33.7 and b = 15.6.

[0037] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, step (10) is based on the internal energy enthalpy h. s and chemical enthalpy h c To obtain the enthalpy H0 of the ultra-high enthalpy non-equilibrium gas stagnation point, including:

[0038] H0 = h s +h c .

[0039] In the above-mentioned method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, the dual-band λ of the dual-band absorption spectroscopy measurement system... N , λ O The value λ satisfies: N =868.03nm, λ O =777.19nm.

[0040] In the above-mentioned method for measuring the stagnation point enthalpy of ultra-high enthalpy non-equilibrium airflow, the ultra-high enthalpy non-equilibrium airflow is generated by a high-frequency induction plasma heating wind tunnel or by an MPD magnetic acceleration plasma wind tunnel.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] (1) The present invention proposes a method for measuring the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow. Based on the developed dual-band laser absorption spectroscopy measurement method, the non-equilibrium temperature of the airflow on the surface of the water-cooled stagnation point model and the component concentrations of atomic nitrogen and oxygen are measured to obtain the internal energy enthalpy and chemical enthalpy of the stagnation point model, thereby realizing the measurement of the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow.

[0043] (2) The present invention proposes a method for measuring the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow. Based on the developed dual-band laser absorption spectroscopy measurement method, it can realize the measurement of airflow enthalpy under ultra-high enthalpy and non-equilibrium conditions, filling the gap of existing methods and applicable to the quantitative measurement of flow field under strong thermodynamic non-equilibrium conditions.

[0044] (3) The present invention proposes a method for measuring the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow. The enthalpy value of the method is applicable in the range of 30-100 MJ / kg, which can complement the existing methods and fill the gap in the measurement of enthalpy value in the range of 50-100 MJ / kg in aerodynamic thermal experiments.

[0045] (4) The present invention proposes a method for measuring the stagnation point enthalpy of ultra-high enthalpy non-equilibrium airflow, which can realize rapid and long-term measurement of ultra-high enthalpy airflow state with a response frequency of 100-1000Hz and a measurement time of 100-3600s. Therefore, this method is not limited to the measurement of airflow parameters in the test and debugging stage, but can also realize the monitoring of flow field parameters throughout the aerodynamic thermal test of aircraft thermal protection materials. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the layout of a method for measuring the enthalpy of stagnation point of ultra-high enthalpy non-equilibrium airflow according to an embodiment of the present invention. Detailed Implementation

[0047] The accompanying drawings and embodiments provide a more detailed description of the present invention:

[0048] The diagram shows a layout schematic of a method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to an embodiment of the present invention. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point includes the following steps:

[0049] (I) Establish a stable flow field environment for ultra-high enthalpy non-equilibrium airflow. Place the water-cooled model in the forward direction downstream of the ultra-high enthalpy non-equilibrium airflow and measure the stagnation pressure P of the airflow. s .

[0050] In one optional embodiment, the water-cooled model is a flat-topped cylindrical model, that is, a cylindrical shell structure with internal cold water pipes and a pressure measuring device, and the shell material is copper.

[0051] In one optional embodiment, the ultra-high enthalpy non-equilibrium airflow is generated by a high-frequency induction plasma heating wind tunnel or by an MPD magnetic acceleration plasma wind tunnel.

[0052] (II) The transmitting end of the dual-band absorption spectroscopy measurement system generates an incident laser signal. The laser signal passes along the surface of the water-cooled model and is received by the receiving end on the other side of the dual-band absorption spectroscopy measurement system to obtain the transmitted laser signal. The logarithm of the division between the incident laser signal and the transmitted laser signal is used, and the integral area A of each band is obtained by fitting the data using the Voigt function. N A O and the Gauss full width at half maximum (FWHM) Δν of the spectral lines N Δν O The subscripts N and O represent atomic nitrogen and atomic oxygen, respectively.

[0053] In one optional embodiment, the dual-band absorption spectroscopy measurement system has dual-band λ N , λ O The value λ satisfies: N =868.03nm, λ O =777.19nm.

[0054] (III) Based on the Gaussian half-width Δν of the spectral line N Δν O To obtain the temperatures T of atomic nitrogen and atomic oxygen under non-equilibrium conditions. N T O The specific calculation formula is as follows:

[0055] T N =14(λ) N ·Δν N ) 2

[0056] T O =16(λ) O ·Δν O ) 2

[0057] Where, λ N , λ O These are the center wavelengths of the two bands in the dual-band laser absorption spectroscopy measurement system.

[0058] (iv) Based on the respective temperatures T of atomic nitrogen and atomic oxygen under non-equilibrium conditions N T O Obtain the coupling temperature T s ,in,

[0059] (V) Based on coupling temperature T s and stationary pressure P s Obtain the specific heat C at constant pressure p The specific calculation formula is as follows:

[0060] C p =0.9938 - 7.787 × 10 -4 P s +1.98×10 -4 T s +7.067×10 -7 P s ·T s -4.587×10 -8 T s 2 -1.25×10 -10 P s ·T s 2 +4.19×10 -12 T s 3

[0061] (vi) Based on the specific heat of constant pressure C p and coupling temperature Ts , obtain internal energy enthalpy h s The specific calculation formula is as follows:

[0062] h s =C P ×T s

[0063] (vii) Based on the integral area A N A O The temperatures T of atomic nitrogen and atomic oxygen N T O And the diameter D of the water-cooled model, to obtain the mole fraction X of atomic nitrogen and atomic oxygen. N and X O The specific calculation formula is as follows:

[0064]

[0065] Among them, S(T) N ), S(T O The values ​​represent the line intensities of the spectral lines in each of the two bands of the dual-band laser absorption spectroscopy measurement system, and the spectral parameters and T values ​​based on the atomic spectral database. N T O You can get it immediately.

[0066] (viii) The molar concentrations X of atomic nitrogen and atomic oxygen N and X O Converted to the mass fractions ω of atomic nitrogen and atomic oxygen N and ω O The specific calculation formula is as follows:

[0067] include:

[0068]

[0069] Among them, M air Let be the molar mass of air.

[0070] (ix) Based on the mass fractions ω of atomic nitrogen and atomic oxygen N and ω O Obtain chemical enthalpy h c The specific calculation formula is as follows:

[0071] h c =aω N +bω O

[0072] Where a and b are the dissociation energies of atomic nitrogen and atomic oxygen, respectively, with values ​​of a = 33.7 and b = 15.6.

[0073] (x) Based on the internal energy enthalpy h sand chemical enthalpy h c The enthalpy H0 of the ultra-high enthalpy non-equilibrium gas stagnation point is obtained using the following specific calculation formula:

[0074] H0 = h s +h c

[0075] The proposed method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point is based on a developed dual-band laser absorption spectroscopy method. It measures the non-equilibrium temperature of the airflow on the surface of a water-cooled stagnation point model and the component concentrations of atomic nitrogen and oxygen, thereby obtaining the internal energy enthalpy and chemical enthalpy of the stagnation point model and thus realizing the measurement of the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point.

[0076] The above description is only the best specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

[0077] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for measuring the enthalpy of stagnation point in ultra-high enthalpy non-equilibrium airflow, characterized in that, Includes the following steps: (1) Establish a stable flow field environment for ultra-high enthalpy non-equilibrium airflow. Place the water-cooled model in the forward direction downstream of the ultra-high enthalpy non-equilibrium airflow and measure the stagnation pressure P of the airflow. s ; (2) The transmitting end of the dual-band absorption spectroscopy measurement system generates an incident laser signal. The laser signal passes along the surface of the water-cooled model and is received by the receiving end on the other side of the dual-band absorption spectroscopy measurement system to obtain the transmitted laser signal. The integration area A of each of the two bands is obtained based on the incident laser signal and the transmitted laser signal. N A O and the Gauss full width at half maximum (FWHM) of the spectral lines The subscripts N and O represent atomic nitrogen and atomic oxygen, respectively. (3) Based on the Gaussian half-width of the spectral line To obtain the temperatures T of atomic nitrogen and atomic oxygen under non-equilibrium conditions. N T O ; (4) Based on the respective temperatures T of atomic nitrogen and atomic oxygen under the aforementioned non-equilibrium conditions. N T O Obtain the coupling temperature T s , in, ; (5) Based on the coupling temperature T s and stationary pressure P s Obtain the specific heat C at constant pressure p ; (6) Based on the specific heat C at constant pressure p and coupling temperature T s , obtain internal energy enthalpy ; (7) Based on the integral area A N A O The temperatures T of atomic nitrogen and atomic oxygen N T O And the diameter D of the water-cooled model, to obtain the mole fraction X of atomic nitrogen and atomic oxygen. N and X O ; (8) The molar concentrations X of the atomic nitrogen and atomic oxygen are... N and X O Converted to mass fractions of atomic nitrogen and atomic oxygen and ; (9) Based on the mass fractions of the atomic nitrogen and atomic oxygen. and Obtain chemical enthalpy ; (10) Based on the internal energy enthalpy and chemical enthalpy Obtain the enthalpy of the ultra-high enthalpy non-equilibrium gas stagnation point. ; In step (2), the incident laser signal and the transmitted laser signal are divided, and the logarithm is taken. Then, the Voigt function is used for fitting to obtain the integration area A of each of the two bands. N A O and the Gauss full width at half maximum (FWHM) of the spectral lines .

2. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, The water-cooled model is a cylindrical shell structure with internal cold water pipes, and the shell material is copper.

3. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (3), the Gaussian half-width of the spectral line is used as a basis. To obtain the temperatures T of atomic nitrogen and atomic oxygen under non-equilibrium conditions. N T O , include: in, , These are the center wavelengths of the two bands in the dual-band laser absorption spectroscopy measurement system.

4. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (5), the temperature T based on coupling s and stationary pressure P s Obtain the specific heat C at constant pressure p , include: 。 5. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (6), the specific heat at constant pressure C is used as a basis. p and coupling temperature T s , obtain internal energy enthalpy ,include: 。 6. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (7), the integral area A is used as the basis. N A O The temperatures T of atomic nitrogen and atomic oxygen N T O And the diameter D of the water-cooled model, to obtain the mole fraction X of atomic nitrogen and atomic oxygen. N and X O , include: in, , These represent the line intensities of the spectral lines in each of the two bands of the dual-band laser absorption spectroscopy measurement system.

7. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (8), the molar concentrations X of atomic nitrogen and atomic oxygen are... N and X O Converted to mass fractions of atomic nitrogen and atomic oxygen and ,include: in, Let be the molar mass of air.

8. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (9), the mass fractions of atomic nitrogen and atomic oxygen are used as the basis for the calculation. and Obtain chemical enthalpy ,include: in, , These are the dissociation energies of atomic nitrogen and atomic oxygen, respectively, and their values ​​are... .

9. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, In step (10), the internal energy enthalpy is used as the basis. and chemical enthalpy Obtain the enthalpy of the ultra-high enthalpy non-equilibrium gas stagnation point. ,include: 。 10. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, The dual-band absorption spectroscopy measurement system , The value satisfies: =868.03nm, =777.19nm.

11. The method for measuring the enthalpy of ultra-high enthalpy non-equilibrium airflow stagnation point according to claim 1, characterized in that, The ultra-high enthalpy non-equilibrium airflow is generated by a high-frequency induction plasma heating wind tunnel or by an MPD magnetic acceleration plasma wind tunnel.

Images