Air inlet pressure regulating system and pressure regulating method for low-density wind tunnel

Abstract

The invention provides a low-density wind tunnel inlet gas pressure regulating system and method, the system comprises a gas source module, a pressure regulating module, a heater and a spray pipe which are communicated in sequence, the gas source module comprises a nitrogen preparation station, a dynamic gas storage tank and an energy storage gas storage tank, and the dynamic gas storage tank and the energy storage gas storage tank are connected in parallel through a pipeline; valves are arranged at the inlet ends and the outlet ends of the dynamic gas storage tank and the energy storage gas storage tank; the pressure regulating module comprises a plurality of pressure regulating pipelines which are connected in parallel, and pressure regulating valves aiming at different volume flow rates are arranged on the different pressure regulating pipelines respectively. According to the pressure regulating method, the scheme of controlling the pressure drop of the gas storage tank, the initial pressure of the gas storage tank and various pressure regulating valves is adopted to replace the scheme of a partial pressure grade gas storage tank and a single-stage or multi-stage PID control pressure regulating valve of a conventional wind tunnel, and the inherent characteristics of poor high-precision valve position control continuity, narrow linear regulating interval, low pressure regulating precision and the like of a small-caliber pressure regulating valve are overcome; and high-precision pressure regulation requirements of small-volume flow rate and wide-volume flow rate range tests of the low-density wind tunnel are met.

Description

Technical Field

[0001] The invention relates to the technical field of wind tunnel testing, and in particular to an air intake pressure regulating system and a pressure regulating method for a low-density wind tunnel. Background Art

[0002] The low-density wind tunnel air intake pressure regulating system presents operating characteristics such as small volume flow rate and wide volume flow rate range, which is the core problem that needs to be solved when designing the low-density wind tunnel air intake pressure regulating system. The typical low-density wind tunnel Mach number range is 10-25, the total pressure range is 0.05MPa-1.5MPa (the pressure span is 30 times), the mass flow rate range is 1g / s-500g / s (the flow span is 500 times), the volume flow rate range is 0.4-120L / s (the volume flow rate span is 300 times), the gas source is a 2MPa medium-pressure gas source, and the gas source volume flow rate is 0.04-40L / s (the gas source volume flow rate span is 1000 times). It presents typical operating characteristics such as small volume flow rate and wide volume flow rate range.

[0003] The existing conventional wind tunnel air inlet pressure regulating system generally adopts medium-pressure gas source or high-pressure gas source, or both, and cooperates with single-stage or two-stage pressure regulating valve system to meet the wide range of pressure regulating function of conventional wind tunnel. The typical meter-scale conventional wind tunnel has a Mach number of 5 to 10, a total pressure adjustment range of 0.01MPa to 6MPa (adjusting pressure span 600 times), an adjustable mass flow range of 1kg / s to 200kg / s (adjusting flow span 200 times), and an adjustable volume flow of 800 to 8000L / s (adjusting volume flow rate span 10 times). The gas source includes a 20MPa high-pressure gas source and a 2MPa medium-pressure gas source, and the gas source volume flow rate is 30 to 900L / s (gas source volume flow rate span 30 times). It presents typical operating characteristics such as a wide operating pressure range and a moderate volume flow rate. Conventional wind tunnel air intake pressure regulating systems use air source systems with different pressure levels, combined with single-stage or multi-stage pressure regulating valves, and use two-stage pressure reduction or single-stage pressure reduction to meet different operating pressure tests, and then meet the wide operating pressure range pressure regulation requirements of conventional wind tunnels. Conventional wind tunnel air intake pressure regulating systems are only suitable for conventional wind tunnel pressure regulation requirements with medium volume flow rates. The pressure regulation accuracy of small-diameter pressure regulating valves below DN10 can only reach 5%, the high-precision valve position control of small-diameter pressure regulating valves of DN25 is discontinuous, and the linear adjustment range of small-diameter pressure regulating valves of DN40 is narrow. Due to the lack of suitable small-diameter high-precision pressure regulating valves, the existing small-diameter pressure regulating valve + conventional wind tunnel air intake pressure regulating system solution cannot meet the high-precision pressure regulation requirements of low-density wind tunnels.

[0004] The typical conventional wind tunnel air inlet pressure regulating system scheme is as follows:

[0005] [1] Patent CN201911204272.2 "A wide range air intake pressure regulating system for a hypersonic wind tunnel" discloses an air intake pressure regulating system for a conventional wind tunnel, which uses a high-pressure gas source and a medium-pressure gas source, and cooperates with a single-stage or two-stage pressure regulating valve. The first-stage pressure regulating valve is a bypass butterfly valve or a front-stage high-pressure pressure reducing valve, and the second-stage is a medium-pressure pressure regulating valve or a rear-stage high-pressure pressure regulating valve, respectively realizing the wide range high-precision air intake pressure regulating function of vacuum, medium-pressure, and high-pressure incoming pressure. The first-stage pressure regulating valve used in this air intake pressure regulating system is a bypass butterfly valve or a hydraulic pressure reducing valve, and the second-stage pressure regulating valve is a hydraulic plunger pressure regulating valve. Combined with the general PID pressure regulating method, it meets the wide range high-precision air intake pressure regulating requirements of conventional hypersonic vacuum, medium-pressure, and high-pressure incoming pressure. Due to the lack of high-precision small-diameter pressure regulating valves, it is impossible to meet the air intake pressure regulating requirements of low-density wind tunnels with small volume flow rates and a wide volume flow rate range.

[0006] [2] Patent CN201911204248.9 "A method for regulating vacuum pressure inlet pressure of a hypersonic wind tunnel" discloses a method for regulating vacuum inlet pressure of a conventional wind tunnel, which uses a medium-pressure gas source, a bypass valve and a two-stage pressure regulating system of a single-stage medium-pressure regulating valve. The first-stage bypass valve is a bypass butterfly valve, and the second-stage pressure regulating valve is a hydraulic plunger pressure regulating valve. Combined with the general PID pressure regulating method, the vacuum inlet pressure can be precisely controlled. Due to the lack of high-precision small-caliber pressure regulating valves, it is impossible to meet the requirements of low-density wind tunnels for small volume flow rates and wide volume flow rate ranges. Summary of the invention

[0007] The object of the present invention is to provide an air intake pressure regulating system and a pressure regulating method for a low-density wind tunnel, which are used to solve the problem of high-precision pressure regulation in a low-density wind tunnel with a small volume flow rate and a wide volume flow rate range.

[0008] The present invention provides an air intake pressure regulating system for a low-density wind tunnel, comprising an air source module, a pressure regulating module, a heater and a nozzle which are connected in sequence, wherein the air source module comprises a nitrogen preparation station, a dynamic air storage tank and an energy storage air storage tank, the dynamic air storage tank and the energy storage air storage tank are connected in parallel through a pipeline, and valves are arranged at the inlet end and the outlet end of the dynamic air storage tank and the energy storage air storage tank; the pressure regulating module comprises a plurality of pressure regulating pipelines which are connected in parallel, and pressure regulating valves for different volume flow rates are arranged on different pressure regulating pipelines.

[0009] Furthermore, the dynamic gas storage tank and the energy storage tank are both medium-pressure gas storage tanks with a maximum operating pressure of 2 MPa.

[0010] Furthermore, both the dynamic gas storage tank and the energy storage tank are provided with a deflation pipeline, and the deflation pipeline is provided with a deflation valve.

[0011] Furthermore, the pressure regulating module includes a first pressure regulating pipeline, a second pressure regulating pipeline, a third pressure regulating pipeline and a fourth pressure regulating pipeline connected in parallel, the first pressure regulating pipeline is provided with a positioning pressure reducing valve a and a solenoid valve a, the second pressure regulating pipeline is provided with a positioning pressure reducing valve b and a solenoid valve b, the third pressure regulating pipeline is provided with an electric pressure regulating valve, and the fourth pressure regulating pipeline is provided with a hydraulic pressure regulating valve.

[0012] Furthermore, the inlet end of the dynamic gas storage tank is provided with a gas source preparation valve a, and the outlet end is provided with a gas source management valve a; the inlet end of the energy storage gas storage tank is provided with a gas source preparation valve b, and the outlet end is provided with a gas source management valve b.

[0013] A pressure regulating method for an air intake pressure regulating system for a low-density wind tunnel adopts different combinations of medium-pressure gas storage tanks according to different volume flow rate test requirements, and controls the pressure drop ratio of the medium-pressure gas storage tanks during the effective test process, thereby reducing the difficulty of designing a pressure regulating valve of a downstream pressure regulating module and meeting the high-precision pressure regulating requirements of a small volume flow rate test; according to different outlet volume flow rates of the pressure regulating module, the pressure regulating method is divided into three working conditions: extremely small, moderate and large;

[0014] In the test of the outlet volume flow rate range of the pressure regulating module under extremely small working conditions, the pressure regulation method is as follows:

[0015] a1: Select a dynamic gas storage tank to supply gas for the test within the minimum test volume flow range;

[0016] a2: Release air by opening the air release valve a to reduce the initial pressure of the dynamic air storage tank, or increase the initial pressure of the dynamic air storage tank by opening the air source management valve a and the air source management valve b to charge the dynamic air storage tank from the energy storage tank, and accurately control the initial pressure of the dynamic air storage tank required by the test state, so that the initial pressure accuracy is controlled within 1%;

[0017] a3: Open the gas source management valve a;

[0018] a4: According to the test state requirements, open the solenoid valve a and / or the solenoid valve b, use the positioning pressure reducing valve a and / or the positioning pressure reducing valve b to reduce the pressure, and after the reduced pressure airflow is heated by the heater, a test airflow medium with a stable total pressure and total temperature is formed at the nozzle inlet, and the pressure regulation control accuracy is within 1.5%;

[0019] In the test of the outlet volume flow rate range of the pressure regulating module under moderate working conditions, the pressure regulation method is as follows:

[0020] b1: Select a dynamic gas storage tank to supply gas for the test within a moderate test volume flow range;

[0021] b2: Release the gas by opening the vent valve a to reduce the initial pressure of the dynamic gas storage tank, or increase the initial pressure of the dynamic gas storage tank by opening the gas source management valve a and the gas source management valve b to charge the dynamic gas storage tank from the energy storage tank, and accurately control the initial pressure of the dynamic gas storage tank required by the test state, so that the initial pressure accuracy is controlled within 1%;

[0022] b3: Open the gas source management valve a;

[0023] b4: According to the test state requirements, open the electric pressure regulating valve to a certain opening and maintain it. After the decompressed airflow is heated by the heater, a test airflow medium with a stable total pressure and total temperature is formed at the nozzle inlet. The pressure regulation control accuracy is within 2%;

[0024] In the test of the outlet volume flow rate range of the pressure regulating module under larger working conditions, the pressure regulation method is as follows:

[0025] c1: Select dynamic gas storage tanks and energy storage tanks to supply gas for the test with a larger test volume flow range;

[0026] c2: According to the test requirements, the initial pressures of the dynamic gas storage tank and the energy storage tank are reduced by opening the bleed valve a and the bleed valve b to release gas, or the initial pressures of the dynamic gas storage tank and the energy storage tank are increased by opening the nitrogen preparation station and the gas source preparation valve a and the gas source preparation valve b to charge the tanks, and the initial pressures of the two gas tanks are set so that the pressure regulating valve operates within its linear adjustment range;

[0027] c3: Open the gas source management valve a and the gas source management valve b;

[0028] c4: The PID control strategy is used to implement feedback control of the valve position of the hydraulic pressure regulating valve. After the airflow is heated by the heater, a test airflow medium with stable total pressure and total temperature is formed at the nozzle inlet, and the pressure regulation control accuracy is within 2%.

[0029] Furthermore, during the effective test process, the pressure drop ratio control of the medium-pressure gas storage tank adopts a classification control strategy based on the gas volume flow rate at the outlet of the pressure regulating module, specifically:

[0030] Minimum working condition: When the outlet volume flow rate range of the pressure regulating module is 0L / s<G≤5L / s, a dynamic gas storage tank is used for gas supply, and the single effective test duration is ≥30s. The pressure drop ratio of the medium-pressure gas storage tank during the effective test is controlled to be ε≤1%;

[0031] Moderate working conditions: When the outlet volume flow rate of the pressure regulating module is in the range of 5L / s<G≤20L / s, a dynamic gas storage tank is used for gas supply, and the single test duration is ≥30s. The pressure drop ratio of the medium-pressure gas storage tank during the effective test is controlled to be ε≤2%;

[0032] Larger working conditions: When the outlet volume flow rate range of the pressure regulating module is 20L / s<G≤120L / s, the dynamic gas tank and the energy storage gas tank are used to supply gas together. The single test duration is ≥30s, and the pressure drop ratio of the medium-pressure gas tank during the effective test is controlled to be ε≤8%.

[0033] Furthermore, according to the pressure regulation requirements of different pressure regulating module outlet volume flow rate range tests, pressure regulation accuracy control strategies based on different types of pressure regulating valves are adopted to meet the high-precision pressure regulation requirements of low-density wind tunnel small volume flow rate tests, as follows:

[0034] When the outlet volume flow rate of the pressure regulating module is 0.4L / s≤G≤5L / s, the pressure regulating valve adopts positioning pressure reducing valve a and positioning pressure reducing valve b, and accurately controls the initial pressure of the dynamic gas storage tank so that the pressure regulating accuracy is within 1.5%;

[0035] When the outlet volume flow rate of the pressure regulating module is 5L / s<G≤20L / s, a DN25 electric pressure regulating valve is used to accurately control the initial pressure of the dynamic gas storage tank so that the pressure regulation accuracy is within 2%;

[0036] When the outlet volume flow rate of the pressure regulating module is 20L / s<G≤120L / s, a DN40 hydraulic pressure regulating valve is used in conjunction with PID control technology to control the positioning accuracy of the pressure regulating valve to within 0.3%, so that its pressure regulation accuracy is within 2%.

[0037] Further: when the outlet volume flow rate range of the pressure regulating module is 0.4L / s≤G≤5L / s, positioning pressure reducing valve a and positioning pressure reducing valve b are used as pressure regulating valves, which are fixed throat orifice plates or flow nozzles, to accurately control the initial pressure of the dynamic gas storage tank, with a repeatable control accuracy within 1%, so that the pressure regulation accuracy is within 1.5%;

[0038] When the outlet volume flow rate range of the pressure regulating module is 5L / s<G≤20L / s, the pressure regulating valve adopts a DN25 electric pressure regulating valve to accurately control the initial pressure of the dynamic gas storage tank, with a repeatable control accuracy within 1%, so that the pressure regulation accuracy is within 2%;

[0039] When the outlet volume flow rate range of the pressure regulating module is 20L / s<G≤120L / s, the pressure regulating valve adopts a DN40 hydraulic pressure regulating valve in combination with PID control technology as the pressure regulating valve. The positioning accuracy of the pressure regulating valve is within 0.3%, so that the pressure regulation accuracy is within 2%.

[0040] Furthermore, in the test in which the outlet volume flow rate of the pressure regulating module ranges from 0.4L / s≤G≤5L / s, both the positioning pressure reducing valve a and the positioning pressure reducing valve b adopt a fixed throat orifice plate or a throttling nozzle.

[0041] The beneficial effects of the technical solution are as follows: the present invention provides an air intake pressure regulating system for a low-density wind tunnel and a pressure regulating method for different volume flow rates after pressure regulating valves. It adopts the method of controlling the pressure drop of an air storage tank, controlling the initial pressure of an air storage tank and controlling a variety of pressure regulating valves to replace the conventional wind tunnel's pressure grade air storage tank + single-stage or multi-stage PID controlled pressure regulating valve solution, overcomes the inherent characteristics of small-caliber pressure regulating valves such as poor continuity of high-precision valve position control, narrow linear adjustment range, and low pressure regulation accuracy, and meets the high-precision pressure regulation requirements of low-density wind tunnel tests with small volume flow rates and a wide volume flow rate range. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a system principle diagram of the present invention.

[0044] Explanation of the accompanying drawings: 1-nitrogen preparation station; 2-gas source preparation valve a; 3-gas source preparation valve b; 4-dynamic gas storage tank; 5-energy storage tank; 6-air release valve a; 7-air release valve b; 8-gas source management valve a; 9-gas source management valve b; 10-solenoid valve a; 11-solenoid valve b; 12-positioning pressure reducing valve a; 13-positioning pressure reducing valve b; 14-electric pressure regulating valve; 15-hydraulic pressure regulating valve; 16-heater; 17-nozzle. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0047] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] Example 1

[0049] like Figure 1 As shown, the present invention provides an air intake pressure regulating system for a low-density wind tunnel, comprising an air source module, a pressure regulating module, a heater 16 and a nozzle 17 connected in sequence, the air source module comprising a nitrogen preparation station 1, a dynamic air storage tank 4 and an energy storage air storage tank 5, the dynamic air storage tank 4 and the energy storage air storage tank 5 are connected in parallel through a pipeline, the dynamic air storage tank 4 and the energy storage air storage tank 5 are both provided with a venting pipeline, the venting pipeline of the dynamic air storage tank 4 is provided with a venting valve a6, and the venting pipeline of the energy storage air storage tank 5 is provided with a venting valve b7; the inlet end of the dynamic air storage tank 4 is provided with an air source preparation valve a2, and the outlet end is provided with an air source management valve a8; the inlet end of the energy storage air storage tank 5 is provided with an air source preparation valve b3, and the outlet end is provided with an air source management valve b9. The pressure regulating module includes multiple pressure regulating pipelines connected in parallel, and pressure regulating valves for different volume flow rates are respectively arranged on different pressure regulating pipelines. Specifically: the pressure regulating module includes a first pressure regulating pipeline, a second pressure regulating pipeline, a third pressure regulating pipeline and a fourth pressure regulating pipeline connected in parallel, the first pressure regulating pipeline is provided with a positioning pressure reducing valve a12 and a solenoid valve a10, the second pressure regulating pipeline is provided with a positioning pressure reducing valve b13 and a solenoid valve b11, the third pressure regulating pipeline is provided with an electric pressure regulating valve 14, and the fourth pressure regulating pipeline is provided with a hydraulic pressure regulating valve 15.

[0050] The dynamic gas storage tank 4 and the energy storage tank 5 are medium-pressure gas storage tanks, which are used to store medium-pressure nitrogen for low-density wind tunnel tests, with a maximum operating pressure of 2MPa. According to the requirements of different volume flow rate tests, different combinations of medium-pressure gas storage tanks are used, and the pressure drop ratio of the medium-pressure gas storage tanks during the effective test process is controlled to reduce the difficulty of designing the pressure regulating valve of the downstream pressure regulating module and meet the high-precision pressure regulation requirements (within 2%) of small volume flow rate tests. During the effective test process (after the total pressure and total temperature at the inlet of the wind tunnel nozzle 17 are stable), the pressure drop ratio of the gas storage tank is defined by the following formula:

[0051]

[0052] Where P q1 Indicates the pressure of the medium pressure gas storage tank at the initial moment of the effective test process; P q2 Indicates the pressure of the medium pressure gas storage tank at the end of the effective test process; ΔP q It is the pressure drop of the medium pressure gas tank during the effective test; It is the average pressure of the medium pressure gas storage tank during the effective test process, and it is considered that the pressure of the medium pressure gas storage tank decreases approximately linearly.

[0053] 1. During the effective test, the pressure drop ratio control of the medium-pressure gas storage tank adopts a classification control strategy based on the outlet gas volume flow rate of the pressure regulating module. According to the different outlet volume flow rates of the pressure regulating module, the pressure regulation method is divided into three working conditions: extremely small, moderate and large, as follows:

[0054] a): Test on the outlet volume flow rate range of the pressure regulating module under extremely small working conditions (0L / s<G≤5L / s), using dynamic gas storage tank 4 (volume V1) to supply gas, with a single effective test duration of ≥30s, and controlling the pressure drop ratio of the medium-pressure gas storage tank ε≤1% during the effective test.

[0055] b) Test the outlet volume flow rate range of the pressure regulating module under moderate working conditions (5L / s<G≤20L / s), using dynamic gas storage tank 4 (volume V1) to supply gas, with a single test duration of ≥30s, and controlling the pressure drop ratio of the medium-pressure gas storage tank ε≤2% during the effective test.

[0056] c) For the outlet volume flow rate range test of the pressure regulating module under larger working conditions (20L / s<G≤120L / s), the dynamic gas storage tank 4 (volume V1) and the energy storage tank 5 (volume V1) are used to supply gas together. The single test duration is ≥30s, and the pressure drop ratio of the medium-pressure gas storage tank during the effective test is controlled to be ε≤8%.

[0057] 2. In the low-density wind tunnel test, the outlet volume flow rate of the pressure regulating module is mainly determined by the throat cross-sectional area of ​​the selected test nozzle 17. According to the requirements of different test conditions of the low-density wind tunnel, the total pressure, total temperature and Mach number requirements of the wind tunnel test are determined, the nozzle 17 is selected, and the test mass flow rate is calculated according to the following formula:

[0058]

[0059] Wherein, G is the test mass flow rate, kg / s; C is the nitrogen flow coefficient, 0.04; The average total pressure of the wind tunnel test airflow under the selected test conditions of the low-density wind tunnel, Pa; A * is the throat cross-sectional area of ​​the selected nozzle 17, m 2 ; T0 is the average total temperature of the wind tunnel test airflow under the selected test conditions of the low-density wind tunnel, K.

[0060] According to the experimental mass flow conservation, the mass flow rate G at the outlet of the pressure regulating module t Equal to the mass flow rate at the inlet of nozzle 17, then:

[0061] G t =G (3);

[0062] Ignoring the internal pressure loss of the heater 16, the volume flow rate at the outlet of the pressure regulating module is approximately calculated by the following formula:

[0063]

[0064]

[0065] in, The average stagnation density at the outlet of the pressure regulating module under the selected test conditions of the low-density wind tunnel, kg / s; is the average stagnation density of the pressure regulating module outlet under the selected test state of the low-density wind tunnel, Pa; R is the nitrogen gas constant, 297 J / (kg*K); T 0t The average stagnation temperature at the outlet of the pressure regulating module under the test conditions selected for the low-density wind tunnel is approximately room temperature, 288K. Combining formulas (1) to (6), we can obtain:

[0066]

[0067] From the above formula, we can see that: C, R are constants, T 0t Approximately room temperature; T0 is the total test temperature, which is mainly determined by the anti-condensation relationship of the selected nozzle 17. Limited by the heating technology, the total test temperature of the nozzle 17 with different Mach numbers varies relatively little, approximately 2 times; A * It is determined by the throat area of ​​the selected nozzle 17. The overall variation range of the nozzle 17 tests with different Mach numbers is wide, with a difference of more than 200 times. It can be seen that the outlet volume flow rate of the pressure regulating module is mainly determined by the throat cross-sectional area of ​​the selected nozzle 17. Formula (7) shows that in the low-density wind tunnel test, the classification basis of the medium-pressure gas tank pressure drop ratio classification control strategy is the different Mach number nozzle 17 tests, using different medium-pressure gas tank operation strategies.

[0068] 3. According to the classification control strategy of the pressure drop ratio of the medium-pressure gas storage tank during the effective test, the medium-pressure gas storage tank is designed to meet the small volume flow and high-precision test requirements of the low-density wind tunnel. According to the law of conservation of mass, the mass of the gas flowing out of the nozzle 17 during the effective test is equal to the mass of the gas flowing out of the medium-pressure gas storage tank, then:

[0069] Δm=GΔt=m q1 -m q2 (8);

[0070] Among them, Δm is the mass of gas flowing out during the effective test, kg; Δt is the effective test time, s; m q1 is the gas mass of the medium pressure gas storage tank at the initial moment of the effective test process, kg; m q2 is the gas mass in the medium-pressure gas storage tank at the end of the effective test process, kg. The low-density wind tunnel test is a small flow test. It can be assumed that the gas temperature in the medium-pressure gas storage tank remains unchanged. The gas mass in the medium-pressure gas storage tank at different times is:

[0071] m q1 =ρ q1 V q (9);

[0072] m q2 =ρ q2 V q (10);

[0073]

[0074] Among them, ρ q1 is the gas density of the medium pressure gas storage tank at the initial moment of the effective test process, kg / m 3 ρ q2 The gas density of the medium pressure gas storage tank at the end of the effective test process, kg / m 3 ; V q is the volume of the medium pressure gas storage tank, m 3 ; T q is the gas temperature of the medium pressure gas storage tank, approximately room temperature, 288K. Combining formulas (1), (2), (7) to (12), the gas source volume V q Determined by the following formula:

[0075]

[0076] The lowest medium pressure gas storage tank operating pressure at the initial moment of the effective test process is usually selected as:

[0077]

[0078] Where η is the loss adjustment ratio of the voltage regulating module, which is usually selected to be 1.4 to 1.6. Combining formulas (13) and (14), we get:

[0079]

[0080] According to different test conditions of the low-density wind tunnel, the parameters such as the throat cross-sectional area and total temperature of the nozzle 17 are determined, and the corresponding pressure regulating module outlet volume flow G is determined using formula (7) tv ; Using the pressure drop ratio classification control strategy of the medium-pressure gas storage tank, the maximum G under three types of working conditions is determined respectively. tv, pressure drop ratio ε, effective test time Δt, and use formula (15) to calculate the volume V of the medium-pressure gas storage tank under the three working conditions q The classified medium-pressure gas storage tank use strategy based on the pressure drop ratio classification control strategy of the medium-pressure gas storage tank is:

[0081] V1=V q1

[0082] V1=V q2

[0083] V1+V2=V q3 (16);

[0084] The calculated volumes of the dynamic gas tank 4V1 and the energy storage tank 5V2 are as follows:

[0085] V1=max (V q1 ,V q2 ) (17);

[0086] V2=V q3 -max (V q1 ,V q2 ) (18);

[0087] In order to further improve the interchangeability efficiency of the dynamic gas storage tank 4 and the energy storage gas storage tank 5, the dynamic gas storage tank 4 and the energy storage gas storage tank 5 adopt an equal volume design strategy, then:

[0088] V1=V2=max (max (V q1 ,V q2 ),V q3 -max (V q1 ,V q2 )) (19).

[0089] 4. According to the pressure regulation requirements of different pressure regulating module outlet volume flow rate range tests, pressure regulation accuracy control strategies based on different types of pressure regulating valves are adopted to meet the high-precision pressure regulation requirements of low-density wind tunnel small volume flow rate tests. The details are as follows:

[0090] a. For the test of the outlet volume flow rate range of the pressure regulating module under extremely small working conditions (0.4L / s≤G≤5L / s), the pressure regulating valves use the positioning pressure reducing valve a12 and the positioning pressure reducing valve b13. Both pressure reducing valves are equipped with a fixed throat orifice plate or a throttling nozzle, and accurately control the initial pressure of the dynamic air storage tank 4 (with a repeatable control accuracy within 1%), so that the pressure regulation accuracy is within 1.5%, meeting the high-precision pressure regulation requirements of the extremely small volume flow range of the low-density wind tunnel.

[0091] b. For the test of the outlet volume flow rate range of the pressure regulating module under moderate working conditions (5L / s<G≤20L / s), the pressure regulating valve adopts a small-diameter (DN25) electric pressure regulating valve 14, which has a high-precision positioning discontinuous characteristic, adopts a high-precision positioning opening method, and accurately controls the initial pressure of the dynamic air storage tank 4 (repeat control accuracy within 1%), so that its pressure regulation accuracy reaches within 2%, meeting the high-precision pressure regulation requirements of the moderate volume flow range of the low-density wind tunnel.

[0092] c. For the test of the outlet volume flow rate range of the pressure regulating module under larger working conditions (20L / s<G≤120L / s), the pressure regulating valve adopts a moderate caliber (DN40) hydraulic pressure regulating valve 15 with PID control technology, so that the positioning accuracy of the pressure regulating valve is within 0.3%, and the pressure regulation accuracy is within 2%, which meets the high-precision test requirements of the low-density wind tunnel with a larger volume flow range.

[0093] 5. In the test of the volume flow rate range of the pressure regulating module outlet under extremely small working conditions, the pressure regulating valve adopts a fixed throat orifice plate or a throttling nozzle, and the pressure regulating accuracy is within 1.5% through the following control method. At the initial moment of the effective test process of the low-density wind tunnel, the test gas mass flow rate is:

[0094]

[0095] At the end of the effective test process in the low-density wind tunnel, the test gas mass flow rate is:

[0096]

[0097] Ignore the pipeline flow resistance. During the effective test, the pressure regulating valve is a fixed throat orifice plate or a throttling nozzle, and its throat cross-sectional area A t ; To simplify the analysis, it is assumed that the throat of the pressure regulating valve operates under the sonic speed condition. At the initial moment of the effective test process of the low-density wind tunnel, the gas mass flow rate of the pressure regulating valve is:

[0098]

[0099] At the end of the effective test process in the low-density wind tunnel, the gas mass flow rate of the pressure regulating valve is determined by the following formula:

[0100]

[0101] According to the law of conservation of mass, the gas mass flow rate at the initial and final moments is conserved, so:

[0102] G1=G t1 (twenty four);

[0103] G2=G t2 (25);

[0104] The pressure regulation accuracy during the effective wind tunnel test is determined by the following formula:

[0105]

[0106] Combining formulas (1), (20) to (26), we can obtain:

[0107]

[0108] In the test of the outlet volume flow rate of the extremely small pressure regulating module, it can be seen from formula (27) that the pressure regulating accuracy of a single test during the effective test process using a pressure regulating valve with a fixed throat orifice is only related to the pressure drop ratio of the medium-pressure gas storage tank, and is half of the pressure drop ratio. According to the pressure drop ratio classification control strategy of the medium-pressure gas storage tank, when testing in the extremely small volume flow range, the pressure drop ratio of the medium-pressure gas storage tank ε≤1%, and the pressure regulation accuracy of a single test reaches 0.5%.

[0109] In many tests, the initial pressure P of the medium pressure gas storage tank was precisely controlled. q1 , so that its repeatability η≤1%. Assuming that P q1 The mean value of but:

[0110]

[0111] From formula (1), we can know that:

[0112]

[0113] Combining formulas (28) to (30), we can obtain:

[0114]

[0115] Combined with formula (27), the maximum deviation in multiple pressure regulation tests is determined by the maximum possible pressure difference. Therefore, the pressure regulation accuracy in multiple tests is:

[0116]

[0117] Combining formulas (27), (28), (32), (33) and (34), and ignoring high-order small quantities because ε and η are small quantities, we can obtain:

[0118]

[0119] It can be seen from formula (35) that in the test of the outlet volume flow rate of the extremely small pressure regulating module, the pressure regulation accuracy in multiple tests is jointly determined by the single test accuracy and the repeatability accuracy of the initial pressure of the medium-pressure gas tank, and they are linearly superimposed. Based on the above analysis, in the test of the outlet volume flow rate of the extremely small pressure regulating module, it can be known from the classification control strategy of the pressure drop ratio of the medium-pressure gas tank that ε≤1%, and from the pressure regulation accuracy control strategy based on different types of pressure regulating valves that η≤1%, then the pressure regulation accuracy of multiple tests Δ≤1.5%, which meets the pressure regulation control accuracy of the low-density wind tunnel.

[0120] 6. In the moderate pressure regulating module outlet volume flow rate range test, the pressure regulating valve uses a small-diameter (e.g. DN25) electric pressure regulating valve 14, and the pressure regulating accuracy is achieved within 2% through the following control method. The small-diameter electric pressure regulating valve 14 does not have the high positioning accuracy control function of the continuous opening of the valve core position, but only has the high positioning accuracy control of the stepped opening of the valve core position (e.g. stroke interval 1mm). When conducting a moderate pressure regulating module outlet volume flow rate range test, the pressure regulating valve is always opened to a certain valve opening in the single-state test, and the opening is kept unchanged during the effective test process, so that the cross-sectional area of ​​the throttling throat remains unchanged. Using the same analysis method as the pressure regulation progress of the extremely small pressure regulating module outlet volume flow rate range test, the pressure regulation accuracy calculation results such as formulas (27) and (35) can be obtained. Based on this analysis, in the moderate pressure regulating module outlet volume flow rate test, in the single-state test, the pressure regulating valve is moderately opened at a certain valve opening. The medium-pressure gas tank pressure drop ratio classification control strategy shows that ε≤2%, and the pressure regulation accuracy control strategy based on different types of pressure regulating valves shows that η≤1%. Therefore, the pressure regulation accuracy of multiple tests Δ≤2% meets the pressure regulation control accuracy of the low-density wind tunnel.

[0121] 7. In the test of the outlet volume flow rate range of the larger pressure regulating module, the pressure regulating valve adopts a moderate caliber (DN40) hydraulic pressure regulating valve 15, and combined with the PID pressure regulating control method, the positioning accuracy of the pressure regulating valve is 0.3%, so that the pressure regulating accuracy is within 2%. Under such test conditions, the minimum volume flow after the pressure regulating valve is 20L / s, and a DN40 liquid cave pressure regulating valve is used. According to the calculation method of the valve regulation characteristic, the velocity coefficient of the pipeline after the pressure regulating valve is greater than 0.05. When an elliptical valve core is used, the pressure recovery coefficient in the linear regulation range is 0.1-0.8, and the valve stroke ratio is 10%-40%. For the volume flow test of 20L / s, according to the positioning accuracy of the valve core of the regulating valve within 0.3%, the pressure recovery coefficient is within 0.3-0.8, combined with the PID control strategy, the pressure regulation accuracy can reach within 2%, which meets the pressure regulation requirements of low-density wind tunnels.

[0122] 8. Based on the above-designed intake pressure regulating system, in the pressure regulating module outlet volume flow rate range test under extremely small working conditions, the pressure regulating method is as follows:

[0123] a1: Select dynamic gas storage tank 4 as the test gas supply for the minimum test volume flow range;

[0124] a2: The initial pressure of the dynamic gas storage tank 4 is reduced by opening the air release valve a6 to release air from the dynamic gas storage tank 4 to the environment, or the initial pressure of the dynamic gas storage tank 4 is increased by quickly opening the gas source management valve a8 and the gas source management valve b9 to charge the dynamic gas storage tank 5 from the energy storage tank 5, and the initial pressure of the dynamic gas storage tank 4 required by the test state is accurately controlled to ensure that the initial pressure accuracy is controlled within 1%;

[0125] a3: Open the gas source management valve a8;

[0126] a4: According to the test state requirements, choose to open the solenoid valve a10, or choose to open the solenoid valve b11, or choose to open the solenoid valve a10 and the solenoid valve b11 at the same time, and then use the positioning pressure reducing valve a12, or the positioning pressure reducing valve b13, or both to reduce the pressure. After the pressure is reduced, the airflow is heated by the heater 16 to form a test airflow medium with a stable total pressure and total temperature at the inlet of the nozzle 17, and the pressure regulation control accuracy is within 1.5%.

[0127] IX. Based on the above-designed intake pressure regulating system, in the pressure regulating module outlet volume flow rate range test under moderate working conditions, the pressure regulating method is as follows:

[0128] b1: Select dynamic gas storage tank 4 to supply gas for the test within a moderate test volume flow range;

[0129] b2: The initial pressure of the dynamic gas storage tank 4 is reduced by opening the air release valve a6 to release air from the dynamic gas storage tank 4 to the environment, or the initial pressure of the dynamic gas storage tank 4 is increased by quickly opening the gas source management valve a8 and the gas source management valve b9 to charge the dynamic gas storage tank 5 from the energy storage tank 5, and the initial pressure of the dynamic gas storage tank 4 required by the test state is accurately controlled to ensure that the initial pressure accuracy is within 1%;

[0130] b3: Open the gas source management valve a8;

[0131] b4: According to the test state requirements, open the electric pressure regulating valve 14 to a certain opening and maintain it. After the decompressed air flow is heated by the heater 16, a test air flow medium with stable total pressure and total temperature is formed at the inlet of the nozzle 17. The pressure regulation control accuracy is within 2%.

[0132] 10. Based on the above-designed intake pressure regulating system, in the pressure regulating module outlet volume flow rate range test under larger working conditions, the pressure regulating method is as follows:

[0133] c1: Dynamic gas storage tank 4 and energy storage gas storage tank 5 are selected to supply gas for the test with a larger test volume flow range;

[0134] c2: According to the test requirements, the initial pressure of the dynamic gas storage tank 4 and the energy storage gas storage tank 5 is lowered by opening the air release valve a6 and the air release valve b7 to release air to the environment, or the initial pressure of the dynamic gas storage tank 4 and the energy storage gas storage tank 5 is increased by opening the nitrogen preparation station 1, the gas source preparation valve a2 and the gas source preparation valve b3 to charge the tanks, and a certain level of initial pressure of the gas storage tank is set (for example, 1.8MPa, 1.0MPa), so that the pressure regulating valve operates within its linear adjustment range;

[0135] c3: Open the air source management valve a8 and the air source management valve b9;

[0136] c4: The PID control strategy is used to implement feedback control of the valve position of the hydraulic pressure regulating valve 15. After the airflow is heated by the heater 16, a test airflow medium with a stable total pressure and total temperature is formed at the inlet of the nozzle 17. The pressure regulation control accuracy is within 2%.

[0137] The present invention provides an air intake pressure regulating system and a pressure regulating valve method for three different volume flow rates after pressure regulating valves. The system adopts a variety of pressure regulating valves to control the pressure drop of an air storage tank, control the initial pressure of an air storage tank, and replace the conventional wind tunnel's pressure grade air storage tank + single-stage or multi-stage PID control pressure regulating valve solution, thereby overcoming the inherent characteristics of small-caliber pressure regulating valves such as poor continuity of high-precision valve position control, narrow linear adjustment range, and low pressure regulation accuracy, and meeting the high-precision pressure regulation requirements of low-density wind tunnel tests with small volume flow rates and a wide volume flow rate range.

[0138] ① Air intake pressure regulating system and pressure regulating method for the test of volume flow rate (0.4L / s~5L / s) after the pressure regulating valve under extremely small working conditions. By controlling the pressure drop of the medium-pressure gas storage tank during the effective test to ≤1%, and using a fixed throat orifice plate or a throttling nozzle to reduce pressure, the pressure regulation accuracy of a single test is within 0.5%; by controlling the initial pressure accuracy of the medium-pressure gas storage tank to within 1%, combined with the single pressure regulation accuracy control technology, the pressure regulation accuracy of multiple tests is within 1.5%. The pressure regulation scheme of controlling the gas source pressure drop ratio, the initial pressure of the gas source gas storage and combining a fixed throttling diameter pressure reducing valve is adopted to replace the ultra-small diameter (DN10 or less) variable throttling throat pressure regulating valve (pressure regulation accuracy is less than 5%) scheme, to overcome the insufficient pressure regulation accuracy of the ultra-small diameter pressure regulating valve, and meet the high-precision pressure regulation requirements of the extremely small volume flow test in the low-density wind tunnel.

[0139] ② Air intake pressure regulating system and pressure regulating method for the test of volume flow rate (5L / s~20L / s) after the pressure regulating valve under moderate working conditions. By controlling the pressure drop of the medium-pressure gas storage tank during the effective test to ≤2%, and using the electric pressure regulating valve 14 with a fixed opening, the pressure regulating accuracy of a single test is within 1%; by controlling the initial pressure accuracy of the medium-pressure gas storage tank to within 1%, combined with the single pressure regulating accuracy control technology, the pressure regulating accuracy of multiple tests is within 2%. The pressure regulating scheme of controlling the gas source pressure drop ratio, the initial pressure of the gas source gas storage and combining the fixed opening setting of the pressure regulating valve is adopted to overcome the discontinuous characteristics of high-precision valve position control of small-caliber (e.g. DN25) pressure regulating valves, and meet the high-precision pressure regulation requirements of moderate volume flow tests in low-density wind tunnels. Compared with the air intake pressure regulating system for the extremely small volume flow test, a single electric pressure regulating valve 14 with a fixed opening setting is adopted. By setting different valve position openings, multiple pressure reducers with fixed throat diameters can be obtained, so that the initial pressure setting of a single gas storage tank can meet the pressure regulation requirements of more different test conditions.

[0140] ③ The air intake pressure regulating system and pressure regulating method for the test of the volume flow rate (20L / s~120L / s) after the pressure regulating valve under larger working conditions. By controlling the pressure drop of the medium-pressure gas storage tank during the effective test to ≤8%, the initial pressure of the medium-pressure gas storage tank is controlled in stages according to the test requirements (e.g. 1MPa, 1.8MPa), and the medium-caliber (DN40) hydraulic pressure regulating valve 15 with high positioning accuracy is controlled by PID, so that the test pressure regulation accuracy is within 2%. By controlling the initial pressure of the medium-pressure gas storage tank in stages, the pressure recovery coefficient before and after the pressure regulating valve is moderate, and then the hydraulic pressure regulating valve 15 is always operated in the high-precision linear adjustment range, overcoming the problem of narrow linear adjustment range of small-caliber pressure regulating valves.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An air intake pressure regulating system for a low-density wind tunnel, characterized in that: It comprises an air source module, a pressure regulating module, a heater and a nozzle which are connected in sequence. The air source module comprises a nitrogen preparation station, a dynamic air storage tank and an energy storage air storage tank. The dynamic air storage tank and the energy storage air storage tank are connected in parallel through pipelines. The inlet and outlet ends of the dynamic air storage tank and the energy storage air storage tank are both provided with valves. The pressure regulating module comprises a plurality of pressure regulating pipelines which are connected in parallel. Pressure regulating valves for different volume flow rates are respectively provided on different pressure regulating pipelines.

2. The air intake pressure regulating system for a low-density wind tunnel according to claim 1, characterized in that: The dynamic gas storage tank and the energy storage tank are both medium-pressure gas storage tanks with a maximum operating pressure of 2MPa.

3. The air intake pressure regulating system for a low-density wind tunnel according to claim 2, characterized in that: The dynamic gas storage tank and the energy storage gas storage tank are both provided with a deflation pipeline, and the deflation pipeline is provided with a deflation valve.

4. The air intake pressure regulating system for a low-density wind tunnel according to claim 1, characterized in that: The pressure regulating module includes a first pressure regulating pipeline, a second pressure regulating pipeline, a third pressure regulating pipeline and a fourth pressure regulating pipeline which are connected in parallel with each other. The first pressure regulating pipeline is provided with a positioning pressure reducing valve a and a solenoid valve a, the second pressure regulating pipeline is provided with a positioning pressure reducing valve b and a solenoid valve b, the third pressure regulating pipeline is provided with an electric pressure regulating valve, and the fourth pressure regulating pipeline is provided with a hydraulic pressure regulating valve.

5. The air intake pressure regulating system for a low-density wind tunnel according to claim 1, characterized in that: The inlet end of the dynamic gas storage tank is provided with a gas source preparation valve a, and the outlet end is provided with a gas source management valve a; the inlet end of the energy storage gas storage tank is provided with a gas source preparation valve b, and the outlet end is provided with a gas source management valve b.

6. A pressure regulating method for an air intake pressure regulating system for a low-density wind tunnel, characterized in that: According to the requirements of different volume flow rate tests, different combinations of medium-pressure gas storage tanks are used to control the pressure drop ratio of the medium-pressure gas storage tanks during the effective test process, and pressure regulation accuracy control strategies based on different types of pressure regulating valves are used to meet the high-precision pressure regulation requirements of small volume flow rate tests; according to the different outlet volume flow rates of the pressure regulating module, the pressure regulation methods are divided into three working conditions: extremely small, moderate and large; In the test of the outlet volume flow rate range of the pressure regulating module under extremely small working conditions, the pressure regulation method is as follows: a1: Select a dynamic gas storage tank to supply gas for the test within the minimum test volume flow range; a2: Release air by opening the air release valve a to reduce the initial pressure of the dynamic air storage tank, or increase the initial pressure of the dynamic air storage tank by opening the air source management valve a and the air source management valve b to charge the dynamic air storage tank from the energy storage tank, and accurately control the initial pressure of the dynamic air storage tank required by the test state, so that the initial pressure accuracy is controlled within 1%; a3: Open the gas source management valve a; a4: According to the test state requirements, open the solenoid valve a and / or the solenoid valve b, use the positioning pressure reducing valve a and / or the positioning pressure reducing valve b to reduce the pressure, and after the reduced pressure airflow is heated by the heater, a test airflow medium with a stable total pressure and total temperature is formed at the nozzle inlet, and the pressure regulation control accuracy is within 1.5%; In the test of the outlet volume flow rate range of the pressure regulating module under moderate working conditions, the pressure regulation method is as follows: b1: Select a dynamic gas storage tank to supply gas for the test within a moderate test volume flow range; b2: Release the gas by opening the vent valve a to reduce the initial pressure of the dynamic gas storage tank, or increase the initial pressure of the dynamic gas storage tank by opening the gas source management valve a and the gas source management valve b to charge the dynamic gas storage tank from the energy storage tank, and accurately control the initial pressure of the dynamic gas storage tank required by the test state, so that the initial pressure accuracy is controlled within 1%; b3: Open the gas source management valve a; b4: According to the test state requirements, open the electric pressure regulating valve to a certain opening and maintain it. After the decompressed airflow is heated by the heater, a test airflow medium with a stable total pressure and total temperature is formed at the nozzle inlet. The pressure regulation control accuracy is within 2%; In the test of the outlet volume flow rate range of the pressure regulating module under larger working conditions, the pressure regulation method is as follows: c1: Select dynamic gas storage tanks and energy storage tanks to supply gas for the test with a larger test volume flow range; c2: According to the test requirements, the initial pressures of the dynamic gas storage tank and the energy storage tank are reduced by opening the bleed valve a and the bleed valve b to release gas, or the initial pressures of the dynamic gas storage tank and the energy storage tank are increased by opening the nitrogen preparation station and the gas source preparation valve a and the gas source preparation valve b to charge the tanks, and the initial pressures of the two gas tanks are set so that the pressure regulating valve operates within its linear adjustment range; c3: Open the gas source management valve a and the gas source management valve b; c4: The PID control strategy is used to implement feedback control of the valve position of the hydraulic pressure regulating valve. After the airflow is heated by the heater, a test airflow medium with stable total pressure and total temperature is formed at the nozzle inlet, and the pressure regulation control accuracy is within 2%.

7. The pressure regulating method of the air intake pressure regulating system for a low-density wind tunnel according to claim 6, characterized in that: During the effective test, the pressure drop ratio control of the medium-pressure gas storage tank adopts a classification control strategy based on the gas volume flow rate at the outlet of the pressure regulating module, specifically: Minimum working condition: When the outlet volume flow rate range of the pressure regulating module is 0L / s<G≤5L / s, a dynamic gas storage tank is used for gas supply, and the single effective test duration is ≥30s. The pressure drop ratio of the medium-pressure gas storage tank during the effective test is controlled to be ε≤1%; Moderate working conditions: When the outlet volume flow rate of the pressure regulating module is in the range of 5L / s<G≤20L / s, a dynamic gas storage tank is used for gas supply, and the single test duration is ≥30s. The pressure drop ratio of the medium-pressure gas storage tank during the effective test is controlled to be ε≤2%; Larger working conditions: When the outlet volume flow rate range of the pressure regulating module is 20L / s<G≤120L / s, the dynamic gas tank and the energy storage gas tank are used to supply gas together. The single test duration is ≥30s, and the pressure drop ratio of the medium-pressure gas tank during the effective test is controlled to be ε≤8%.

8. The pressure regulating method of the air intake pressure regulating system for a low-density wind tunnel according to claim 7, characterized in that: According to the pressure regulation requirements of different pressure regulating module outlet volume flow rate range tests, pressure regulation accuracy control strategies based on different types of pressure regulating valves are adopted to meet the high-precision pressure regulation requirements of low-density wind tunnel small volume flow rate tests, as follows: When the outlet volume flow rate of the pressure regulating module is 0.4L / s≤G≤5L / s, the pressure regulating valve adopts positioning pressure reducing valve a and positioning pressure reducing valve b, and accurately controls the initial pressure of the dynamic gas storage tank so that the pressure regulating accuracy is within 1.5%; When the outlet volume flow rate of the pressure regulating module is 5L / s<G≤20L / s, a DN25 electric pressure regulating valve is used to accurately control the initial pressure of the dynamic gas storage tank so that the pressure regulation accuracy is within 2%; When the outlet volume flow rate of the pressure regulating module is 20L / s<G≤120L / s, a DN40 hydraulic pressure regulating valve is used in conjunction with PID control technology to control the positioning accuracy of the pressure regulating valve to within 0.3%, so that its pressure regulation accuracy is within 2%.

9. The pressure regulating method of the air intake pressure regulating system for a low-density wind tunnel according to claim 8, characterized in that: When the outlet volume flow rate range of the pressure regulating module is 0.4L / s≤G≤5L / s, the positioning pressure reducing valve a and the positioning pressure reducing valve b are used as the pressure regulating valves to accurately control the initial pressure of the dynamic gas storage tank, with a repeatable control accuracy within 1%, so that the pressure regulation accuracy is within 1.5%; When the outlet volume flow rate range of the pressure regulating module is 5L / s<G≤20L / s, the pressure regulating valve adopts a DN25 electric pressure regulating valve to accurately control the initial pressure of the dynamic gas storage tank, with a repeatable control accuracy within 1%, so that the pressure regulation accuracy is within 2%; When the outlet volume flow rate range of the pressure regulating module is 20L / s<G≤120L / s, the pressure regulating valve adopts a DN40 hydraulic pressure regulating valve in combination with PID control technology as the pressure regulating valve. The positioning accuracy of the pressure regulating valve is within 0.3%, so that the pressure regulation accuracy is within 2%.

10. The pressure regulating method of the air intake pressure regulating system for a low-density wind tunnel according to claim 9, characterized in that: In the test where the outlet volume flow rate of the pressure regulating module ranges from 0.4L / s≤G≤5L / s, both the positioning pressure reducing valve a and the positioning pressure reducing valve b adopt a fixed throat orifice plate or a throttling nozzle.

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