A flow field precision control system and control method for a DC transient transonic wind tunnel

Abstract

A flow field precision control system and control method for a direct current transient impulse transonic wind tunnel belong to the technical field of wind tunnel testing; the existing equipment fails and cannot brake in time; the system comprises a control center computer, an angle of attack control computer, a gate finger controller, a flow field controller, a gate finger driving device and a pressure regulating valve electro-hydraulic system; the gate finger driving device comprises a gate finger device, the gate finger device comprises gate finger segments arranged at the upper and lower wall plates of the second throat of the wind tunnel super expansion section, which are in two groups, each group of gate finger segments comprises 6 airfoil gate finger pieces, each group of gate finger segments is respectively fixed on two upper and lower gate finger trolleys, the gate finger trolley is provided with 4 rows of linear guide rails, and the servo electric cylinder is provided with a linear displacement sensor; thereby achieving the purpose of precisely controlling the Mach number of the flow field of the direct current transient impulse transonic wind tunnel; the method solves the problem of Mach number control accuracy within the range of 1.0≤M≤1.2 by adopting a PID control plus feedforward control control mode for the gate fingers and optimizing the flow field control.

Description

Technical Field

[0001] The invention belongs to the technical field of wind tunnel testing, and in particular relates to a flow field precision control system and a control method for a direct current transient transonic wind tunnel. Background Art

[0002] With the development of aerospace industry, the requirements for the accuracy of wind tunnel test data in aircraft design are getting higher and higher, especially the aircraft aerodynamic shape optimization selection test and the precise measurement test of external load resistance. At the same time, due to the increasing complexity of aircraft aerodynamic shape, wind tunnel test data is more sensitive to the influence of flow field Mach number control accuracy. Therefore, the requirements for wind tunnel Mach number control accuracy are also getting higher and higher.

[0003] Research shows that when the errors of balance, angle of attack, and pressure measurement are constant and the test angle of attack is a constant value, the error of the model aerodynamic coefficient decreases with the increase of Mach number. That is, the error of subsonic test data is the largest, followed by transonic speed, and the smallest at supersonic speed. It can be seen that for high subsonic cruising aircraft, the precise control and measurement of Mach number during wind tunnel tests is one of the key factors affecting the model aerodynamic coefficient.

[0004] For aircraft whose aerodynamic characteristics are very sensitive to Mach number changes, the drag measurement accuracy is not accurate enough using conventional Mach number control methods. Such drag measurement accuracy makes it difficult to accurately obtain the drag increment of external objects. It can be seen that it is difficult to meet the aircraft design requirements when using conventional Mach number control methods, and it is necessary to carry out research on the precise control technology of the flow field Mach number in the DC transient wind tunnel. Summary of the invention

[0005] The present invention overcomes the deficiencies of the above-mentioned prior art and provides a flow field precision control system and control method for a direct current transient transonic wind tunnel. The system controls the stroke of the gate fingers located at the second throat of the wind tunnel in real time to change the cross-sectional area of ​​the second throat, so that the airflow in the wind tunnel is throttled at the corresponding Mach number, thereby achieving the purpose of precisely controlling the Mach number of the flow field of the direct current transient transonic wind tunnel; the method solves the problem of Mach number control accuracy within the range of 1.0≤M≤1.2 by adopting a PID control plus feedforward control control mode for the gate fingers and optimizing the control of the flow field.

[0006] The technical solution of the present invention:

[0007] Technical Solution 1

[0008] A flow field precision control system for a direct current transient transonic wind tunnel, comprising a control center computer, an angle of attack control computer, a gate finger controller, a flow field controller, a gate finger driving device and a pressure regulating valve electro-hydraulic system; the control center computer is bidirectionally connected to the gate finger controller via Ethernet, the gate finger controller is bidirectionally connected to the gate finger driving device, the angle of attack control computer is bidirectionally connected to the flow field controller via Ethernet, and the flow field controller is bidirectionally connected to the pressure regulating valve electro-hydraulic system;

[0009] The gate finger driving equipment includes a gate finger device, which includes a gate finger segment, a gate finger trolley, a servo electric cylinder and a buffer cylinder; the gate finger segment is arranged at the upper and lower wall panels of the second throat of the wind tunnel super expansion section, and is divided into two groups, each group of gate finger segments includes 6 airfoil gate finger pieces, and the 6 airfoil gate finger pieces of each group of gate finger segments are respectively fixed on the upper and lower gate finger trolleys, the gate finger trolley is provided with 4 rows of linear guide rails, the gate finger trolley is connected to the servo electric cylinder, the servo electric cylinder is provided with a linear displacement sensor, and the gate finger trolley is connected to the buffer cylinder.

[0010] Furthermore, a cylinder sealing ring is provided on the servo electric cylinder, and the servo electric cylinder is connected to the gate finger trolley through a first joint bearing.

[0011] Furthermore, a cylinder sealing ring is provided on the buffer cylinder, and the buffer cylinder is connected to the gate finger trolley through a second joint bearing.

[0012] Furthermore, the gate finger device also includes a gate finger shell, a left mounting flange, a right mounting flange, a flange upper sealing gasket and a flange lower sealing gasket; the gate finger shell is respectively connected to the upper and lower wall panels of the second throat of the wind tunnel super-expansion section through a left mounting flange and a right mounting flange, and the left mounting flange and the right mounting flange are both installed with a flange upper sealing gasket and a flange lower sealing gasket.

[0013] Technical Solution 2

[0014] A control method implemented on a flow field precision control system of a direct current transient transonic wind tunnel according to technical solution 1 comprises the following steps:

[0015] Step 1: Start by determining whether the line position sensor reading is normal. If it is abnormal, an alarm will be given and the process will end. Otherwise, proceed to step 2.

[0016] Step 2: Before blowing, adjust each node of the wind tunnel super expansion section to a given initial size, and then move the gate finger section to a preset position;

[0017] Step 3: Open the pressure regulating valve to control the total pressure in the stable section to ensure that the total pressure in the stable section is stable within the error band;

[0018] Step 4: After the total pressure is stable, a gate finger controller is used to control the gate finger driving device to perform Mach number control so that the Mach number is kept within the error band;

[0019] Step 5: Start the angle of attack to a given value. If the Mach number deviates from the target Mach number, use the gate finger Mach number control system to control the Mach number so that the Mach number remains within the error band, and then perform data acquisition;

[0020] Step 6: After the data collection of the last angle of attack position is completed, the gate finger segment is locked at the current position, the angle of attack returns to zero, the pressure regulating valve is closed, and the blowing ends.

[0021] Further, in order to realize the control of Mach number by the gate finger Mach number control system in steps 3 to 5, the following steps are performed:

[0022] Step 51, the pressure regulating valve control system is open-loop control at the initial stage of flow field establishment, so that the wind tunnel approaches the set point at the fastest speed;

[0023] Step 52, the gate finger segment moves to the preset position s0 before starting, and the gate finger segment remains in the initial stage of flow field establishment;

[0024] Step 53, the pressure regulating valve controls the total pressure to be stable;

[0025] Step 54: After the total pressure is stabilized, the Mach number is adjusted through the gate finger Mach number control system to make the gate finger Mach number control system perturb near the set point.

[0026] Furthermore, the method for the pressure regulating valve to control the total pressure to be stable in step 53 includes adopting an incremental PID algorithm including output limiting to complete the feedback control of the total pressure, as follows;

[0027] Assuming the control error at time k is e(k), the control output is formula (7):

[0028] u(k)=u(k-1)+K p [e(k)-e(k-1)]+K i e(k) (7)

[0029] The above formula is the incremental PID algorithm, where K p is the proportionality coefficient, K i is the integral coefficient; since the integral output is a cumulative amount, in order to prevent integral saturation and ensure the safe operation of the equipment, u(k) is output limited, taking the linear area of ​​the main pressure regulating valve, and limiting it to 3% to 70% of the full displacement;

[0030] During the blowing process, due to the continuous decrease of the spherical tank pressure, in order to compensate for the total pressure change caused by the decrease of the spherical tank pressure, static feedforward compensation is added on the basis of feedback control, and the compensation coefficient changes with different given values;

[0031] The control output at time k after considering feedback and feedforward is formula (8):

[0032] u(k)=u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K co Tc (8)

[0033] Where K co is the compensation coefficient, and Tc is the control period.

[0034] Furthermore, in step 54, the gate finger Mach number control system includes a gate finger Mach number controller, and the gate finger Mach number controller is a feedback-feedforward composite controller combining an open and closed loop. The control method includes the following steps:

[0035] Step 54-1, before the total pressure is stabilized, the gate finger is in open loop control, and the gate finger is kept at a preset position s0. The preset position s0 needs to be close to the gate finger position when the Mach number is stable. There is a certain deviation between the preset position s0 obtained by theoretical calculation and the actual preset position s0. By debugging each Mach number, the actual preset position s0 corresponding to each Mach number is obtained, and then the relationship formula between the two is fitted through the corresponding relationship between the Mach number and s0. The preset position s0 of the gate finger corresponding to any Mach number is calculated by the empirical formula (9) fitted through the actual blowing data;

[0036]

[0037] Step 54-2, after the total pressure stabilizes, the gate finger is put into closed-loop control. The gate finger controller in the closed-loop control stage is in the form of incremental control, which is divided into two parts: a feedback controller and a feedforward controller. The feedback controller is a PID controller, and the feedforward controller is a static feedforward form. The system intelligently selects a combination of controllers based on a given Mach number and current angle of attack.

[0038] Furthermore, the feedback controller is a Mach number feedback controller, i.e., formula (10), which is the same as the total pressure PID controller and adopts an incremental PID algorithm;

[0039] Δs1(k)=K p [e(k)-e(k-1)]+K i e(k) (10)

[0040] Furthermore, the feedforward controller adds feedforward compensation based on the change of the angle of attack on the basis of feedback control, as shown in formula (11);

[0041] Δs2=K ff Δα=K(α,M0)Δα (11)

[0042] Where Kff is the feedforward coefficient, unit: mm / °, this value is related to the current angle of attack α and the given Mach number M0.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention provides a flow field precision control system and control method for a direct current transient transonic wind tunnel. The system controls the stroke of the grating fingers located at the second throat of the wind tunnel in real time to change the cross-sectional area of ​​the second throat, so that the airflow in the wind tunnel is throttled at a corresponding Mach number. At this time, the Mach number is a function of the cross-sectional area of ​​the second throat. As long as the total pressure of the front chamber is sufficient to maintain the throttling condition, the Mach number of the test section will remain stable, thereby achieving the purpose of precise control of the flow field of the direct current transient transonic wind tunnel.

[0045] This method solves the problem of Mach number control accuracy in the range of 0.3≤M<1.0; by adopting PID control plus feedforward control for the gate finger and optimizing the control of the flow field, the problem of Mach number control accuracy in the range of 1.0≤M≤1.2 is solved. The flow field Mach number control accuracy reaches 0.001, so that the subsonic flow field control level of the DC transient wind tunnel reaches the domestic leading level, the drag accuracy of the wind tunnel test data at subsonic speed can reach the international advanced level of 0.0001, and the accuracy of the transonic wind tunnel test data reaches or approaches the advanced indicators required by the national military standard. It fundamentally solves the problem that the accuracy of the test data does not meet the development requirements of new aircraft due to the low flow field control accuracy. In addition, the Mach number precision control technology significantly improves the test efficiency during step measurement, and saves about 25% to 40% energy when M=1.0~1.2. The advancedness of the flow field precision control method of a DC transient transonic wind tunnel disclosed by the present invention reaches the engineering application level. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the architecture diagram of the present invention;

[0047] Figure 2 It is the main view of the gate finger structure;

[0048] Figure 3 is a side view of the gate finger structure;

[0049] Figure 4 It is a flow chart of the present invention;

[0050] Figure 5 It is the principle diagram of precise control of flow field;

[0051] Figure 6 This is the schematic diagram of the Mach number controller;

[0052] Figure 7 It is a functional diagram of the present invention.

[0053] In the figure: 1, a gate finger trolley, 2, a servo electric cylinder, 3, a buffer cylinder, 4, a gate finger plate, 5, a linear guide rail, 6, a first joint bearing, 7, a second joint bearing, and 8, a gate finger housing. DETAILED DESCRIPTION

[0054] The present invention will be described in detail below with reference to the accompanying drawings. Specific implementation method 1

[0056] A precise flow control system for a DC transient transonic wind tunnel. Figure 1 As shown, it includes a control center computer, an angle of attack control computer, a gate finger controller, a flow field controller, a gate finger driving device and a pressure regulating valve electro-hydraulic system; the control center computer is bidirectionally connected to the gate finger controller via Ethernet, the gate finger controller is bidirectionally connected to the gate finger driving device, the angle of attack control computer is bidirectionally connected to the flow field controller via Ethernet, and the flow field controller is bidirectionally connected to the pressure regulating valve electro-hydraulic system;

[0057] Working process: The control center computer is connected to the gate finger controller through the test site industrial Ethernet to control the gate finger drive equipment, and at the same time controls the pressure regulating valve electro-hydraulic system through the flow field controller. Figure 7 As shown, the host computer sends a start or end command to PXI, namely PCI extensions for Instrumentation, which is a PCI extension for instrumentation systems. PXI sends position and speed control commands to the gate finger system. The gate finger system transmits status information such as actual position, speed, limit information, and alarm information to PXI, and PXI sends this information to the host computer for display. The host computer includes a control center computer and an angle of attack control computer.

[0058] The gate finger driving device comprises a gate finger device such as Figure 2 and Figure 3 As shown, the gate finger device includes a gate finger segment, a gate finger trolley 1, a servo electric cylinder 2 and a buffer cylinder 3; the gate finger segment is arranged at the upper and lower wall panels of the second throat of the wind tunnel super expansion section, and is divided into two groups, each group of gate finger segments includes 6 airfoil gate finger pieces 4, and the 6 airfoil gate finger pieces 4 of each group of gate finger segments are respectively fixed on the upper and lower gate finger trolleys 1, the gate finger trolley 1 is provided with 4 rows of linear guide rails 5, the gate finger trolley 1 is connected to the servo electric cylinder 2, the servo electric cylinder 2 is provided with a linear displacement sensor, and the gate finger trolley 1 is connected to the buffer cylinder 3.

[0059] Working process: The finger section is located at the upper and lower wall plates of the second throat of the wind tunnel super expansion section. There are two groups in total. Each group of fingers is composed of 6 airfoil finger pieces 4. The 6 airfoil finger pieces 4 of each group of fingers are fixed on the upper and lower finger trolleys 1 respectively. Under the drive control of the servo electric cylinder 2 on each side and the linear displacement sensor attached to the electric cylinder, the two finger trolleys 1 move synchronously along their respective 4 rows of linear guides 5 to achieve the extension and retraction of the fingers, so as to achieve the purpose of controlling the Mach number of the test section. A buffer cylinder is configured next to the servo electric cylinder 2 to prevent the finger trolley 1 from falling quickly when the electric cylinder fails.

[0060] Specifically, a cylinder sealing ring is provided on the servo electric cylinder 2 , and the servo electric cylinder 2 is connected to the gate finger trolley 1 through a first joint bearing 6 .

[0061] Specifically, a cylinder sealing ring is provided on the buffer cylinder 3 , and the buffer cylinder 3 is connected to the gate finger trolley 1 through a second joint bearing 7 .

[0062] Specifically, the gate finger device also includes a gate finger shell 8, a left mounting flange, a right mounting flange, a flange upper gasket and a flange lower gasket; the gate finger shell 8 is respectively connected to the upper and lower wall panels of the second throat of the wind tunnel super-expansion section through a left mounting flange and a right mounting flange, and the left mounting flange and the right mounting flange are both installed with a flange upper gasket and a flange lower gasket. Specific implementation method 2

[0064] A control method implemented on a flow field precision control system of a direct current transient transonic wind tunnel according to the first embodiment, such as Figure 4 As shown, the following steps are included:

[0065] Step 1: Start by determining whether the line position sensor reading is normal. If it is abnormal, an alarm will be given and the process will end. Otherwise, proceed to step 2.

[0066] Step 2: Before blowing, adjust each node of the wind tunnel super expansion section to a given initial size, and then move the gate finger section to a preset position;

[0067] Step 3: Open the pressure regulating valve to control the total pressure in the stable section to ensure that the total pressure in the stable section is stable within the error band;

[0068] Step 4: After the total pressure is stable, a gate finger controller is used to control the gate finger driving device to perform Mach number control so that the Mach number is kept within the error band;

[0069] Step 5: Start the angle of attack to a given value. If the Mach number deviates from the target Mach number, use the gate finger Mach number control system to control the Mach number so that the Mach number remains within the error band, and then perform data acquisition;

[0070] Step 6: After the data collection of the last angle of attack position is completed, the gate finger segment is locked at the current position, the angle of attack returns to zero, the pressure regulating valve is closed, and the blowing ends.

[0071] Specifically, the precise control of the flow field of the DC transient transonic wind tunnel described in steps 3 to 5 is achieved by the main pressure regulating valve control and the gate finger control. Under this control mode, the wind tunnel is equivalent to a two-input and two-output multivariable coupling system, and the changes in the air source pressure and the angle of attack are regarded as disturbances, such as Figure 5 As shown, in order to realize the gate finger Mach number control system controlling the Mach number in steps 3 to 5, the following steps are performed:

[0072] Step 51, according to the one-dimensional pipe flow continuity equation, there is relation (1):

[0073]

[0074] Where P0 is the total airflow pressure in the stable section of the wind tunnel or the total airflow pressure in the test section, P 0e is the total airflow pressure at the entrance of the second throat, A is the cross-sectional area of ​​the test section, is the cross-sectional area of ​​the second throat; M is the Mach number of the wind tunnel test section; γ is the air specific heat ratio.

[0075] From formula (1), we can see that under certain pressure ratio conditions, changing the cross-sectional area of ​​the second throat can achieve the purpose of changing the Mach number of the test section. To achieve this goal, a finger-type two-throat is used in the DC transient wind tunnel, and the cross-sectional area of ​​the second throat can be quickly changed by changing the finger stroke.

[0076] According to the super expansion section and the gate finger structure, there are two throat cross-sectional area relations (2):

[0077]

[0078] In the formula, S 超 is the cross-sectional area of ​​the wind tunnel super-expansion section, the size is obtained by actual measurement, H is the maximum thickness of a single finger, and S is the finger stroke.

[0079] Take γ = 1.4, substitute the corresponding wind tunnel parameters into equations (1) and (2) and take the derivative, then,

[0080]

[0081] That is, the relationship between the change in Mach number and the change in the finger stroke is as follows:

[0082]

[0083] ΔM=M 名义 -M 实际 (5)

[0084] According to the law of flow conservation, we can get:

[0085]

[0086] The above formulas (4), (5) and (6) are the gate finger control formulas. Where q(λ) is the flow coefficient, M 名义 is the target Mach number of the flow field precision control system, M 实际 It is the incoming flow Mach number actually measured in the wind tunnel test section.

[0087] According to the above principle, the premise of the gate finger controlling the Mach number is that the total pressure in the front chamber meets the throttling condition. In order to ensure the stability of the gate finger regulation and reduce the coupling degree of the wind tunnel system, the pressure regulating valve control system is open-loop control in the early stage of the flow field establishment, so that the wind tunnel approaches the set point at the fastest speed.

[0088] Step 52, the gate finger segment moves to the preset position s0 before starting, and the gate finger segment remains in the initial stage of flow field establishment;

[0089] Step 53, the pressure regulating valve controls the total pressure to be stable;

[0090] Step 54: After the total pressure is stabilized, the Mach number is adjusted through the gate finger Mach number control system to make the gate finger Mach number control system perturb near the set point.

[0091] At this time, the control system can be approximately regarded as two independent closed-loop cascade systems, the outer loop is total pressure / Mach number control, and the inner loop is pressure regulating valve / gate finger position control.

[0092] Specifically, the method for the pressure regulating valve to control the total pressure to be stable in step 53 includes adopting an incremental PID algorithm including output limiting to complete the feedback control of the total pressure, as follows;

[0093] Assuming the control error at time k is e(k), the control output is formula (7):

[0094] u(k)=u(k-1)+K p [e(k)-e(k-1)]+K i e(k) (7)

[0095] The above formula is the incremental PID algorithm, where K p is the proportionality coefficient, K i is the integral coefficient, u(k-1) is the control output at time k-1; since the integral output is a cumulative amount, in order to prevent integral saturation and ensure the safe operation of the equipment, u(k) is output limited, taking the linear area of ​​the main pressure regulating valve, and limiting it to 3% to 70% of the full displacement;

[0096] During the blowing process, due to the continuous decrease of the spherical tank pressure, in order to compensate for the total pressure change caused by the decrease of the spherical tank pressure, static feedforward compensation is added on the basis of feedback control, and the compensation coefficient changes with different given values;

[0097] The control output at time k after considering feedback and feedforward is formula (8):

[0098] u(k)=u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K co Tc (8)

[0099] Where K co is the compensation coefficient, and Tc is the control period.

[0100] Specifically, the gate finger Mach number control system in step 54 includes a gate finger Mach number controller, and the gate finger Mach number controller is a feedback-feedforward composite controller combining an open-loop and a closed-loop, such as Figure 6 As shown, the control method includes the following steps:

[0101] Step 54-1, before the total pressure stabilizes, the gate finger is open-loop controlled, and the gate finger remains at the preset position s0. The reason for presetting the gate finger position is mainly to shorten the blowing time and reduce costs. Unlike the pressure regulating valve, the Mach number is more sensitive to the action of the gate finger. In order to ensure the adjustment speed and stability, the preset position s0 needs to be close to the gate finger position when the Mach number is stable. There is a certain deviation between the preset position s0 obtained by theoretical calculation and the actual preset position s0. By debugging each Mach number, the actual preset position s0 corresponding to each Mach number is obtained, and then the relationship formula between the two is fitted through the corresponding relationship between Mach number and s0. The gate finger preset position s0 corresponding to any Mach number is calculated by the empirical formula (9) fitted through the actual blowing data;

[0102]

[0103] Step 54-2, after the total pressure stabilizes, the gate finger is put into closed-loop control. The gate finger controller in the closed-loop control stage is in the form of incremental control, which is divided into two parts: a feedback controller and a feedforward controller. The feedback controller is a PID controller, and the feedforward controller is a static feedforward form. The system intelligently selects a combination of controllers based on a given Mach number and current angle of attack.

[0104] Specifically, the feedback controller is a Mach number feedback controller, i.e., formula (10), which is the same as the total pressure PID controller and adopts an incremental PID algorithm;

[0105] Δs1(k)=K p [e(k)-e(k-1)]+K i e(k) (10)

[0106] Specifically, for small Mach number conditions, the Mach number is insensitive to the change of the angle of attack, and a good control effect can be achieved only by feedback control; with the increase of the Mach number, the impact of the change of the angle of attack on the flow field becomes more and more obvious. Feedback control can only respond to the change of the Mach number in the next cycle after the impact occurs, and there is an inherent hysteresis. In order to solve this problem, the feedforward controller adds a feedforward compensation Δs2 based on the change of the angle of attack on the basis of feedback control, as shown in formula (11):

[0107] Δs2=K ff Δα=K(α,M0)Δα (11)

[0108] In the formula, K ff is the feedforward coefficient, unit: mm / °. This value is related to the current angle of attack α and the given Mach number M0 and is determined by the relationship K(α,M0). Δα is the change in angle of attack.

Claims

1. A control method implemented on a flow field precision control system of a direct current transient transonic wind tunnel, the flow field precision control system comprising a control center computer, an angle of attack control computer, a gate finger controller, a flow field controller, a gate finger drive device and a pressure regulating valve electro-hydraulic system; the control center computer is bidirectionally connected to the gate finger controller via Ethernet, the gate finger controller is bidirectionally connected to the gate finger drive device, the angle of attack control computer is bidirectionally connected to the flow field controller via Ethernet, and the flow field controller is bidirectionally connected to the pressure regulating valve electro-hydraulic system; The gate finger driving device comprises a gate finger device, the gate finger device comprises a gate finger segment, a gate finger trolley (1), a servo electric cylinder (2) and a buffer cylinder (3); the gate finger segment is arranged at the upper and lower wall plates of the second throat of the wind tunnel super expansion section, and is in two groups, each group of gate finger segments comprises six airfoil gate finger pieces (4), the six airfoil gate finger pieces (4) of each group of gate finger segments are respectively fixed on the upper and lower gate finger trolleys (1), the gate finger trolley (1) is provided with four rows of linear guide rails (5), the gate finger trolley (1) is connected to the servo electric cylinder (2), the servo electric cylinder (2) is provided with a linear displacement sensor, and the gate finger trolley (1) is connected to the buffer cylinder (3); It is characterized in that The following steps are involved: Step 1: Start by determining whether the line position sensor reading is normal. If it is abnormal, an alarm will be given and the process will end. Otherwise, proceed to step 2. Step 2: Before blowing, adjust each node of the wind tunnel super expansion section to a given initial size, and then move the gate finger section to a preset position; Step 3: Open the pressure regulating valve to control the total pressure in the stable section to ensure that the total pressure in the stable section is stable within the error band; Step 4: After the total pressure is stable, a gate finger controller is used to control the gate finger driving device to perform Mach number control so that the Mach number is kept within the error band; Step 5: Start the angle of attack to a given value. If the Mach number deviates from the target Mach number, use the gate finger Mach number control system to control the Mach number so that the Mach number remains within the error band, and then perform data acquisition; Step 6: After the last angle of attack position data is collected, the gate finger segment is locked at the current position, the angle of attack returns to zero, the pressure regulating valve is closed, and the blowing ends; In order to realize the gate finger Mach number control system in step 3 to step 5 to control the Mach number, the following steps are performed: Step 51, the pressure regulating valve control system is open-loop control at the initial stage of flow field establishment, so that the wind tunnel approaches the set point at the fastest speed; Step 52, the gate finger segment moves to the preset position s0 before starting, and the gate finger segment remains in the initial stage of flow field establishment; Step 53, the pressure regulating valve controls the total pressure to be stable; Step 54, after the total pressure is stabilized, the Mach number is adjusted through the gate finger Mach number control system, so that the gate finger Mach number control system is perturbed near the set point; The method for the pressure regulating valve to control the total pressure to be stable in step 53 includes using an incremental PID algorithm including output limiting to complete the feedback control of the total pressure, as follows; Assuming the control error at time k is e(k), the control output is formula (7): u(k)=u(k-1)+K p [e(k)-e(k-1)]+K i e(k) (7) The above formula is the incremental PID algorithm, where K p is the proportionality coefficient, K i is the integral coefficient; since the integral output is a cumulative amount, in order to prevent integral saturation and ensure the safe operation of the equipment, u(k) is output limited, taking the linear area of ​​the main pressure regulating valve, and limiting it to 3% to 70% of the full displacement; During the blowing process, due to the continuous decrease of the spherical tank pressure, in order to compensate for the total pressure change caused by the decrease of the spherical tank pressure, static feedforward compensation is added on the basis of feedback control, and the compensation coefficient changes with different given values; The control output at time k after considering feedback and feedforward is formula (8): u(k)=u(k-1)+K p [e(k)-e(k-1)]+K i e(k)+K co Tc (8) Where K co is the compensation coefficient, Tc is the control period; In step 54, the gate finger Mach number control system includes a gate finger Mach number controller, and the gate finger Mach number controller is a feedback-feedforward composite controller combining an open-loop and a closed-loop. The control method includes the following steps: Step 54-1, before the total pressure is stabilized, the gate finger is in open loop control, and the gate finger is kept at a preset position s0. The preset position s0 needs to be close to the gate finger position when the Mach number is stable. There is a certain deviation between the preset position s0 obtained by theoretical calculation and the actual preset position s0. By debugging each Mach number, the actual preset position s0 corresponding to each Mach number is obtained, and then the relationship formula between the two is fitted through the corresponding relationship between the Mach number and s0. The preset position s0 of the gate finger corresponding to any Mach number is calculated by the empirical formula (9) fitted through the actual blowing data; Step 54-2, after the total pressure stabilizes, the gate finger is put into closed-loop control. The gate finger controller in the closed-loop control stage is in the form of incremental control, which is divided into two parts: a feedback controller and a feedforward controller. The feedback controller is a PID controller, and the feedforward controller is a static feedforward form. The system intelligently selects a combination of controllers based on a given Mach number and current angle of attack.

2. The method for precise flow field control of a DC transient transonic wind tunnel according to claim 1, characterized in that: The feedback controller is a Mach number feedback controller, i.e., formula (10), which is the same as the total pressure PID controller and adopts an incremental PID algorithm; Δs1(k)=K p [e(k)-e(k-1)]+K i e(k) (10).

3. The method for precise flow field control of a DC transient transonic wind tunnel according to claim 2 is characterized in that: The feedforward controller adds feedforward compensation based on the change of the angle of attack on the basis of feedback control, as shown in formula (11); Δs2=K ff Δα=K(α,M0)Δα (11) Where K ff is the feedforward coefficient, unit: mm / °, this value is related to the current angle of attack α and the given Mach number M0.

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