Method for simulating low nox air component plasma jet establishment

Abstract

The application discloses a method for establishing simulated air component low-NOx plasma jet, and solves the problem that high temperature of an electric arc causes O2 and N2 to dissociate when the electric arc heater heats air, and further causes changes in test gas components and aerodynamic parameters. The application is based on an electric arc heater, and an electric arc plasma discharge device is constructed. The electric arc heater is controlled to arc, and plasma jet step modulation and airflow adjustment are performed, so that a simulated air component low-NOx plasma jet with certain total enthalpy is formed through a nozzle.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aerodynamic test, and relates to a method for establishing a low-NOx plasma jet simulating air composition. BACKGROUND

[0002] In order to carry out tests in a laboratory environment under actual flight conditions of an aircraft in a supersonic or hypersonic airflow, a method for obtaining a high Mach number airflow of a certain temperature by heating test gas through an arc heater has been widely used in the development of hypersonic wind tunnels at home and abroad. However, when the arc heater heats air, the high temperature around the arc will cause O2 and N2 to dissociate and undergo chemical reactions, and the generated nitrogen oxides and ionized copper ions and copper oxide will pollute the test gas, causing changes in the composition and aerodynamic parameters of the test gas in the chamber. SUMMARY

[0003] The technical problem solved by the application is to overcome the shortcomings of the prior art and provide a method for establishing a low-NOx plasma jet simulating air composition, which can quickly, stably and efficiently establish a plasma jet under different Mach number conditions simulating real air composition through an arc heater; and eliminate the speed components of the gas jet in directions other than the forward direction of the airflow, thereby achieving uniform distribution of the axial speed of the airflow.

[0004] The technical scheme provided by the application is as follows:

[0005] A method for establishing a low-NOx plasma jet simulating air composition, comprising: S1, constructing an arc heater, a primary mixing chamber, a secondary mixing chamber, an airflow adjusting chamber, a nozzle and corresponding power supply, a water cooling system and a gas supply system connected in sequence; the water cooling system is used for cooling the arc heater, the primary mixing chamber, the secondary mixing chamber, the airflow adjusting chamber and the nozzle;

[0006] S2, introducing an arc starting medium into the arc chamber of the arc heater from the gas supply system, and starting the arc by power supply to build a plasma discharge channel between the positive and negative electrodes of the arc heater;

[0007] S3, after the arc is successfully started, switching the arc chamber of the arc heater to pure N2 medium to make the arc heater reach a preset working state;

[0008] S4, after the arc heater reaches the preset working state, injecting normal-temperature pure N2 medium into the primary mixing chamber;

[0009] S5, measuring the airflow temperature in the primary mixing chamber to obtain the average temperature of the primary mixed gas flow; adjusting the injection amount of the pure N2 medium in the primary mixing chamber according to the average temperature of the primary mixed gas flow until the temperature of the primary mixed gas flow is stabilized within a set value;

[0010] S6, injecting pure O2 medium into the secondary mixing chamber;

[0011] S7, calculating the total enthalpy of the gas flow sprayed out of the nozzle to obtain a calculation result;

[0012] S8, comparing the calculation result with the target gas flow enthalpy value, if the positive deviation is greater than 5%, normal temperature air is introduced into the gas flow adjustment chamber to adjust the enthalpy value, if the negative deviation is greater than 5%, the injection amount of pure N2 medium in the primary mixing chamber and the injection amount of pure O2 medium in the secondary mixing chamber are reduced in proportion until the requirement is met.

[0013] Further, the electric arc heater comprises a first electrode, a second electrode, a stainless steel shell and an air inlet ring, the first electrode and the second electrode are arranged in the stainless steel shell, there is a gap between the first electrode and the second electrode, the air inlet ring is embedded in the stainless steel shell, and the air inlet ring and the gap between the first electrode and the second electrode form an arc chamber; the air inlet ring has a series of tangential air inlet holes in the circumferential direction for inputting an electric arc heater working medium into the arc chamber, the electric arc heater working medium comprises an arc starting medium and pure N2 medium, the arc starting medium is used for the arc starting process of the electric arc heater, and the electric arc heater switches to pure N2 medium after the arc starting; the working medium obtains high-temperature plasma jet after passing through the electric arc heater;

[0014] The end of the second electrode away from the first electrode is in communication with the primary mixing chamber, the primary mixing chamber is provided with a pure N2 medium input port for inputting normal temperature pure N2 medium, the high-temperature plasma jet out of the electric arc heater is mixed with the normal temperature pure N2 medium to obtain primary mixed gas;

[0015] The secondary mixing chamber is provided with a pure O2 medium input port to mix the primary mixed gas with pure O2 medium to obtain secondary mixed gas;

[0016] The gas flow adjustment chamber is used for rectifying the secondary mixed gas, and the rectified gas is obtained through the transverse and longitudinal guide vanes arranged in the gas flow adjustment chamber; the rectified gas is sprayed out of the nozzle.

[0017] Further, the S5 comprises: measuring the gas flow temperature in the primary mixing chamber, including: measuring the total enthalpy of the gas flow based on the instantaneous enthalpy probe or the double sound speed throat total enthalpy probe method of the equilibrium sound speed flow method, and then converting the average temperature of the gas to obtain the primary mixed gas temperature;

[0018] Alternatively, the average temperature of the gas flow in the primary mixing chamber is measured by the tunable diode laser absorption spectrum technology to obtain the primary mixed gas temperature.

[0019] Further, the amount of pure N2 medium injected into the primary mixing chamber satisfies that the primary mixed gas temperature is lower than the ionization temperature of nitrogen and oxygen.

[0020] Further, in the S6, the ratio of the injection amount of the pure O2 medium in the secondary mixing chamber to the total injection amount of the N2 medium of the arc heater and the primary mixing chamber is 21:79.

[0021] Further, the arc heater adopts a tubular hollow electrode arc heater as the plasma generation source.

[0022] Further, the arc starting process of the S2 is maintained for 500ms to 1000ms, pure N2 is used as the working medium after the arc heater successfully starts, and the intervention time of the pure N2 working medium is the moment when the arc starting process ends, and the time difference is controlled within ±50ms.

[0023] Further, in the S7, the total enthalpy of the gas flow sprayed by the nozzle is calculated to obtain a calculation result, which includes:

[0024]

[0025] Wherein, G is the mass flow of the gas flow sprayed by the nozzle; P0 is the total pressure of the gas flow before the nozzle throat; A eff is the effective cross-sectional area of the nozzle throat; H0 is the total enthalpy of the gas flow sprayed by the nozzle.

[0026] Further, the arc starting working medium of the arc heater includes: helium, neon, argon and other inert gases, or N2.

[0027] In summary, the present application at least includes the following beneficial technical effects:

[0028] The basic principle of the application is that the arc heater successfully starts under the inert gas, a stable and continuous arc plasma discharge channel is established, and then the pure N2 medium is passed through the arc heater to reach a predetermined arc heater working state; the plasma jet from the arc heater is a high-temperature nitrogen plasma jet with a temperature of 5000℃ or above, after the primary mixing chamber is fully mixed with the normal-temperature nitrogen gas and the high-temperature nitrogen plasma jet, the nitrogen plasma after ionization is rapidly cooled to form elemental nitrogen or nitrogen atoms; in the secondary mixing chamber, the low-temperature nitrogen gas flow is fully mixed with the normal-temperature oxygen gas, the gas flow temperature is further reduced, and a certain enthalpy value of high-temperature gas flow similar to air is formed through the nozzle outlet, effectively controlling the formation of nitrogen oxides in the plasma jet. At the same time, by adjusting the different gas inlets of the primary mixing chamber, the secondary mixing chamber and the gas flow adjusting chamber, a certain enthalpy value of high-temperature pure air jet is formed.

[0029] The application is a method for establishing simulated air component plasma jet, which comprises the following steps: constructing an arc plasma discharge device, controlling the arc heater to start arc, and modulating the plasma jet in steps and rotating the gas flow, and finally forming a simulated air component low NOx plasma jet with certain total enthalpy through a nozzle. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The application is a method for establishing simulated air component plasma jet, which comprises the following steps: constructing an arc plasma discharge device, controlling the arc heater to start arc, and modulating the plasma jet in steps and rotating the gas flow, and finally forming a simulated air component low NOx plasma jet with certain total enthalpy through a nozzle.

[0031] Figure 2 The application is a method for establishing simulated air component plasma jet, which comprises the following steps: constructing an arc plasma discharge device, controlling the arc heater to start arc, and modulating the plasma jet in steps and rotating the gas flow, and finally forming a simulated air component low NOx plasma jet with certain total enthalpy through a nozzle.

[0032] The application is a method for establishing simulated air component plasma jet, which comprises the following steps: constructing an arc plasma discharge device, controlling the arc heater to start arc, and modulating the plasma jet in steps and rotating the gas flow, and finally forming a simulated air component low NOx plasma jet with certain total enthalpy through a nozzle.

[0033] 11, first electrode; 12, second electrode; 13, arc chamber; 14, stainless steel shell; 15, gas inlet ring

[0034] 21, pure N2 medium input port; 31, pure O2 medium input port; 41, normal temperature air inlet; 51, throat DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the application clearer, the embodiments disclosed by the application will be further described in detail below with reference to the drawings.

[0036] As shown in the drawings, the application discloses a method for establishing simulated air component plasma jet, which comprises the following steps: Figure 1

[0037] Step 1, constructing a plasma jet generation system device, which comprises, in order, an arc heater 1, a primary mixing chamber 2, a secondary mixing chamber 3, a gas flow adjusting chamber 4 and a nozzle 5.

[0038] As shown in the drawings, the application discloses a method for establishing simulated air component plasma jet, which comprises the following steps: Figure 2 ​As shown, the arc heater 1 adopts a hollow copper electrode AC arc heater with a star structure as a plasma generation source. The arc heater 1 includes a first electrode 11, a second electrode 12, a stainless steel shell 14, and an air inlet ring 15. The first electrode 11 and the second electrode 12 are tubular and coaxially arranged in the stainless steel shell 14, and there is a gap between the first electrode 11 and the second electrode 12. The air inlet ring 15 is embedded in the stainless steel shell 14 and has a series of tangential air inlet holes in the circumferential direction. The arc chamber 13 is formed between the first electrode 11, the second electrode 12, the stainless steel shell 14, and the air inlet ring 15. The series of tangential air inlet holes in the circumferential direction of the air inlet ring 15 are used to input the working medium of the arc heater 1. The first electrode 11 is a positive electrode, and the end of the first electrode 11 away from the second electrode 12 is closed. The second electrode 12 is a negative electrode, and the end of the second electrode 12 away from the first electrode 11 is the outlet of the arc heater 1. The working medium of the arc heater 1 includes an arc starting medium and pure N2 medium. The arc starting medium is used for the arc starting process of the arc heater 1, and the arc heater 1 switches to pure N2 medium after starting the arc. The working medium obtains high-temperature plasma jet after passing through the arc heater 1;

[0039] The outlet of the arc heater 1 is communicated with the primary mixing chamber 2. The primary mixing chamber 2 is provided with a pure N2 medium input port 21 for inputting normal-temperature pure N2 medium. The high-temperature plasma jet from the arc heater 1 mixes with the normal-temperature pure N2 medium to obtain primary mixed gas.

[0040] The secondary mixing chamber 3 is provided with a pure O2 medium input port 31 to mix the primary mixed gas with pure O2 medium to obtain secondary mixed gas.

[0041] The gas flow adjusting chamber 4 is provided with a normal-temperature air inlet 41 for inputting normal-temperature air to adjust the enthalpy of the secondary mixed gas. The gas flow adjusting chamber 4 is used to rectify the secondary mixed gas by the transverse and longitudinal guide vanes arranged inside the gas flow adjusting chamber 4 to obtain rectified gas. The rectified gas is sprayed out through the nozzle 5. The nozzle 5 is provided with a throat 51.

[0042] Step 2: The arc heater 1 is used as a plasma generation source. Pure Ar gas medium or pure N2 medium is tangentially input into the inter-electrode gap of the arc heater 1. Under this condition, the arc heater 1 is instantaneously short-circuited between the electrodes to start the arc. Alternatively, pure Ar gas medium is tangentially input into the inter-electrode gap of the arc heater 1 under low vacuum conditions to perform high-voltage breakdown. A plasma discharge channel is constructed in the arc chamber between the electrodes of the arc heater 1 to achieve successful arc starting to heat the working medium.

[0043] Step 3: After successful arc starting, the working medium of the arc heater 1 is switched to pure N2 medium by a control program to make the arc heater 1 reach a preset working state.

[0044] Step 4, after the heater reaches normal working condition, pure N2 medium is injected into the primary mixing chamber 2 at the rear end of the arc heater 1 through a series of tangential inlet holes;

[0045] Step 5, the temperature of the gas flow in the primary mixing chamber 2 is measured, and when the temperature of the gas flow in the primary mixing chamber 2 is higher than a certain value, the injection amount of pure N2 medium in step 3 is increased until the temperature of the gas flow in the primary mixing chamber 2 is stabilized within a certain value;

[0046] Step 6, pure O2 medium is injected into the secondary mixing chamber 3 through tangential inlet holes, and the ratio of the injection amount of O2 medium to the total injection amount of N2 medium is about 21:79;

[0047] Step 7, the gas flow is adjusted in the gas flow adjustment chamber 4, the gas flow is adjusted to be axial parallel to the flow field by setting a flow guide vane to eliminate the rotation of the gas flow, the flow field temperature is adjusted to make the distribution more uniform, and further air medium is injected for total enthalpy adjustment of the mixed gas.

[0048] Step 8, the total enthalpy of the gas flow after the arc heater nozzle is calculated by using the equilibrium sound velocity flow method. Starting from the equation of one-dimensional isentropic equilibrium flow of high-temperature gas, the enthalpy value (H0) of the gas flow is determined by measuring the mass flow (G), the total pressure of the gas flow before the throat (P0) and the effective cross-sectional area of the nozzle throat (A eff ), and the calculation formula is as follows:

[0049]

[0050] Step 9, the calculated plasma jet with a certain total enthalpy is compared with the target gas flow enthalpy value, if the positive deviation is greater than 5%, the enthalpy value is adjusted by entering normal temperature air into the gas flow adjustment chamber, if the negative deviation is greater than 5%, the injection amount of pure N2 medium in the primary mixing chamber and the injection amount of pure O2 medium in the secondary mixing chamber are reduced in proportion until the requirement is met.

[0051] Wherein, the injection amount of pure N2 medium in the primary mixing chamber and the injection amount of pure O2 medium in the secondary mixing chamber are reduced in proportion, that is, the injection amount of pure N2 medium in the primary mixing chamber is reduced by 5%, and the injection amount of pure O2 medium in the secondary mixing chamber is also reduced by 5%.

[0052] The time of maintaining the step 2 arc starting process is between 500 ms and 1000 ms, and after the arc heater is successfully started, pure N2 is used as the working medium, and the intervention time of the pure N2 working medium is the moment when the step 2 ends, and the time difference is controlled within 50 ms. Specifically, when argon is used for arc starting, the pure N2 working medium needs to be switched; when nitrogen is used for arc starting, the nitrogen input pipeline with larger flow needs to be switched, and the pure N2 working medium also needs to be re-switched.

[0053] The total enthalpy of the airflow in the primary mixing chamber is measured by using a transient enthalpy probe based on the balanced sound velocity flow method or a double sound velocity throat total enthalpy probe method, and then converted into the average temperature of the gas; or the average temperature of the airflow in the primary mixing chamber is measured by using a tunable diode laser absorption spectrum technology.

[0054] The amount of pure N2 medium injected into the primary mixing chamber needs to meet the requirement that the temperature of the plasma jet after passing through the primary mixing chamber is lower than the ionization temperature of nitrogen and oxygen.

[0055] The jet formed at the outlet of the secondary mixing chamber is a fully mixed N2 and O2 mixed gas, and the ratio is approximately the same as the composition ratio of nitrogen and oxygen in air. Moreover, the mixed gas has a tangential rotational speed component in the direction of downstream movement, and by arranging the horizontal and vertical guide vanes in the airflow adjusting chamber arranged downstream, the horizontal and vertical speed components of the incoming airflow are eliminated, so that the incoming airflow moves forward in the axial direction.

[0056] The nozzle can be a circular or rectangular nozzle.

[0057] The contents not described in detail in the specification are the known technologies of those skilled in the art.

[0058] The application is described in detail above in combination with the specific embodiments and exemplary examples, but these descriptions cannot be understood as limitations of the application. Those skilled in the art understand that the technical solutions and embodiments of the application can be variously replaced, modified or improved without deviating from the spirit and scope of the application, and these all fall within the scope of the application. The protection scope of the application is subject to the appended claims.

Claims

1. A method for simulating air component low NOx plasma jet creation, characterized by, The method comprises the following steps: S1, constructing an electric arc heater (1), a primary mixing chamber (2), a secondary mixing chamber (3), a gas flow adjusting chamber (4) and a nozzle (5) connected in sequence; S2, passing an arc starting medium into the arc chamber (13) of the electric arc heater (1) to start the arc, so as to construct a plasma discharge channel between the positive electrode and the negative electrode of the electric arc heater (1); S3, after the arc starting is successful, switching the arc chamber (13) of the electric arc heater (1) to pure N2 medium, so that the electric arc heater (1) reaches a preset working state; S4, after the electric arc heater (1) reaches the preset working state, injecting normal-temperature pure N2 medium into the primary mixing chamber (2); the amount of the pure N2 medium injected into the primary mixing chamber (2) satisfies that the temperature of the primary mixed gas flow is lower than the ionization temperature of nitrogen and oxygen; S5, measuring the temperature of the gas flow in the primary mixing chamber (2) to obtain the average temperature of the primary mixed gas flow; adjusting the injection amount of the pure N2 medium in the primary mixing chamber (2) according to the average temperature of the primary mixed gas flow until the temperature of the primary mixed gas flow is stable within the set value; S6, injecting pure O2 medium into the secondary mixing chamber (3); S7, calculating the total enthalpy of the gas flow sprayed from the nozzle (5) to obtain a calculation result; S8, comparing the calculation result with the target gas flow enthalpy value; if the positive deviation is greater than 3%, injecting normal-temperature air into the gas flow adjusting chamber (4) to adjust the enthalpy value; if the negative deviation is greater than 3%, reducing the total injection amount of the N2 medium in the arc chamber (13) and the primary mixing chamber (2) and the injection amount of the pure O2 medium injected into the secondary mixing chamber (3) in a proportion, until the requirement is met.

2. The method of claim 1, wherein: The electric arc heater (1) comprises a first electrode (11), a second electrode (12), a stainless steel shell (14) and a gas inlet ring (15); the first electrode (11) and the second electrode (12) are arranged in the stainless steel shell (14) and have a gap therebetween; the gas inlet ring (15) is embedded in the stainless steel shell (14) and forms an arc chamber (13) with the gap between the first electrode (11) and the second electrode (12); the gas inlet ring (15) has a series of tangential gas inlet holes in the circumferential direction for inputting the working medium of the electric arc heater (1) into the arc chamber (13); the working medium of the electric arc heater (1) comprises arc starting medium and pure N2 medium; the arc starting medium is used for the arc starting process of the electric arc heater (1), and the electric arc heater (1) is switched to pure N2 medium after the arc starting; the working medium obtains high-temperature plasma jet after passing through the electric arc heater (1); The end portion of the second electrode (12) away from the first electrode (11) is communicated with the primary mixing chamber (2); the primary mixing chamber (2) is provided with a pure N2 medium input port (21) for inputting normal-temperature pure N2 medium; the high-temperature plasma jet from the electric arc heater (1) is mixed with the normal-temperature pure N2 medium to obtain primary mixed gas; The secondary mixing chamber (3) is provided with a pure O2 medium input port (31) to mix the primary mixed gas with the pure O2 medium to obtain secondary mixed gas; The gas flow adjusting chamber (4) is used for adjusting the secondary mixed gas, and the adjusted gas is obtained by the transverse and longitudinal guide vanes arranged in the gas flow adjusting chamber (4); and the adjusted gas is sprayed out through the nozzle (5).

3. The method of claim 2, wherein the air component is simulated by a low-NOx plasma jet. The method comprises the steps of: The arc starting medium is pure Ar or pure N2.

4. The method for establishing a simulated low-NOx plasma jet based on air composition according to claim 1, characterized in that: In the step S5, the temperature of the gas flow in the primary mixing chamber is measured, which comprises the following steps: the total enthalpy of the gas flow is measured by using the instantaneous enthalpy probe based on the balanced sound velocity flow method or the double sound velocity throat total enthalpy probe method, and then the average temperature of the gas is converted to obtain the temperature of the primary mixed gas flow; Or, the average temperature of the gas flow in the primary mixing chamber is measured by using the tunable diode laser absorption spectrum technology to obtain the temperature of the primary mixed gas flow.

5. The method for establishing a simulated low-NOx plasma jet based on air composition according to claim 1, characterized in that: In the step S6, the ratio of the injection amount of the pure O2 medium in the secondary mixing chamber to the total injection amount of the N2 medium of the arc heater and the primary mixing chamber is 21:

79.

6. The method for establishing a simulated low-NOx plasma jet based on air composition according to claim 1, characterized in that: The arc heater adopts a tubular hollow electrode arc heater as the plasma generating source.

7. The method for establishing a simulated low-NOx plasma jet based on air composition according to claim 1, characterized in that: The arc starting process in the step S2 is maintained for 500 ms to 1000 ms, the pure N2 is used as the working medium after the arc heater is successfully started, and the intervention time of the pure N2 working medium is a moment before the end of the arc starting process, and the time difference is controlled to be within 50 ms.

8. The method for establishing a simulated low-NOx plasma jet based on air composition according to claim 1, characterized in that: In the step S7, the total enthalpy of the gas flow sprayed out of the nozzle is calculated to obtain a calculation result, which comprises the following steps: ； Wherein, G is the mass flow of the gas flow sprayed by the nozzle; P0 is the total pressure of the gas flow before the throat of the nozzle; A eff is the effective cross-sectional area of the throat of the nozzle; H0 is the total enthalpy of the gas flow sprayed by the nozzle.

Images