A PIV real flow calibration device and method based on a wide speed ratio flow field

Abstract

The application discloses a PIV real flow calibration device and method based on a wide speed ratio flow field, and belongs to the field of non-contact flow field measurement equipment calibration. The application mainly comprises an air inlet pressure adjusting section, a transition section, a flow adjusting section, an air flow accelerating section, a flow speed adjusting first section, a standard flow field test section, a rear test cabin, a displacement mechanism, a flow speed adjusting second section, an air outlet section, a flow speed standard probe system and a control system, and the sections are sequentially connected. The application establishes the PIV real flow calibration device, meets the small size and high precision profile, adjusts the function of the key flow speed adjusting section nozzle and grid by real flow debugging, covers the sub-transonic and supersonic speed, realizes the wide speed ratio flow field construction, guarantees the flow field adjusting precision and stability, realizes the real flow calibration of the non-contact flow field measurement equipment PIV through the visual standard flow field test section and the rear test cabin. The application has the advantages of high measurement precision and easy realization.

Description

Technical Field

[0001] This invention belongs to the field of non-contact flow field measurement equipment calibration, and relates to a PIV actual flow calibration device and method based on a wide speed ratio flow field. Background Technology

[0002] Particle image velocimetry (PIV) is a type of visualization measurement technology. It is a new non-contact flow measurement technology developed using advanced image processing technology. Compared with other flow velocity measurement technologies, PIV technology, as a non-contact, non-disturbance flow field quantitative measurement and display technology, overcomes the limitations of single-point velocity measurement technology and can measure the velocity field distribution of the entire flow space.

[0003] In recent years, due to the outstanding characteristics of PIV (Probe-Induced Volume) technology, its application and promotion have been very rapid. It has been widely used in fields such as aero-engines, aircraft aerodynamics, wind tunnels, ships, and propellers. However, a common problem is that PIV systems are complex, involving the coordinated work of multiple components. Each component has certain influencing factors that affect the measurement results. Generally, PIV manufacturers will perform a simple system calibration before selling the instrument and propose an empirical index for speed accuracy. However, due to different standards, the calibration results are not the same. Most of the time, researchers cannot judge the accuracy of PIV measurement results. The reason for this is that there is a lack of PIV calibration methods, the evaluation standards are inconsistent, and the reliability of the measurement results cannot be evaluated. Therefore, PIV calibration is necessary.

[0004] Currently, the calibration of PIV in China mainly uses the method of simulating the scattered light of tracer particles in the flow field by simulating the reflected light of particles on a uniformly rotating disk. This method has the following three problems:

[0005] 1. The highest speed of the currently developed turntable calibration device is only about 10 m / s. However, in actual model development and large-scale tests, the airflow velocity in the flow field will mostly reach supersonic speed, and the turntable speed range is far from sufficient.

[0006] 2. PIV is a field measurement technique. The system measures the velocity information of a field, while the turntable calibration method can only calibrate the velocity at a single point and cannot calibrate the velocity field.

[0007] 3. The real application environment of PIV is the airflow state. The turntable calibration device cannot simulate the real use environment of PIV. There is no complete actual flow calibration device and method, which seriously restricts the quantitative application of PIV technology in model development and flow field testing of large-scale test facilities.

[0008] Based on the current situation, it is necessary to establish a calibration device for the current PIV measurement system, determine the system calibration method, and establish a measurement transfer and traceability system to better solve the flow field measurement problem. Summary of the Invention

[0009] The main objective of this invention is to provide a PIV (Polyvinyl Induction Vessel) real-flow calibration device and method based on a wide velocity ratio flow field. By establishing a PIV real-flow calibration device, while meeting the requirements of a small-size, high-precision profile, the device fits the adjustment functions of key velocity regulation sections (nozzle and grid finger) through real-flow tuning. This allows the calibration device's adjustment range to cover subsonic and transonic speeds, achieving the construction of a wide velocity ratio flow field while ensuring the accuracy and stability of flow field adjustment. Real-flow calibration of the non-contact flow field measurement device (PIV) is achieved through a visualized standard flow field test section and a rear test chamber. This invention has the advantages of high measurement accuracy and ease of implementation.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] This invention discloses a PIV (Pulse Injection Volume) actual flow calibration device based on a wide speed ratio flow field. It mainly consists of an inlet pressure regulation section, a transition section, a rectification section, an airflow acceleration section, a first flow velocity regulation section, a standard flow field test section, a rear test chamber, a displacement mechanism, a second flow velocity regulation section, an exhaust section, a flow velocity standard probe system, and a control system. These sections are connected sequentially. The object to be calibrated is a PIV system.

[0012] The system generates an airflow at a specified velocity through an intake pressure regulation section, a transition section, a rectification section, an airflow acceleration section, a first velocity regulation section, a second velocity regulation section, and a control system. A uniform and stable standard flow field is formed in the standard flow field test section, which has smooth solid walls on all four sides and optical glass windows on the side and top walls. The laser from the PIV system transmits through the optical glass on the top wall to generate a sheet light source in the test section, and a CCD camera captures the sheet light source area through the optical glass on the side walls. A flow velocity standard probe system is installed in the rear experimental chamber. The standard probe uses a displacement mechanism to measure the flow field in the sheet light source area, obtaining the velocity information of characteristic points throughout the field, thereby calibrating the PIV system.

[0013] The intake pressure regulating section includes a main line and a bypass line; the main line and the bypass line are each equipped with two pressure regulating valves of different sizes. The larger valve is installed in the main line for coarse adjustment, and the smaller valve is installed in the bypass line for fine adjustment.

[0014] The transition section connects the pressure regulating section and the rectification section, and consists of a short straight pipe section and a diffuser section. When the length-to-diameter ratio of the straight pipe section is 5 to 10, the diffuser angle is 20° to 30°; when the length-to-diameter ratio of the straight pipe section is 3 to 5, the diffuser angle is 45° to 90°. When using a large-angle diffuser section, in order to alleviate severe separation within the diffuser section, to make the airflow as uniform as possible and to reduce losses, a flow diffuser device such as a metal mesh, a coaxial multi-layer diffuser section, or an open-hole contraction cone can be installed within the diffuser section.

[0015] The rectifying section is equipped with a rectifying device to suppress disturbances from the upstream valve, reduce turbulence, and improve the airflow quality of the test section. The rectifying device includes a honeycomb coil and a damping mesh. A stabilization section is located after the damping mesh, where standard total temperature and total pressure probes are arranged for control system feedback adjustment.

[0016] The airflow acceleration section accelerates the airflow to the speed of sound by using an appropriate contraction ratio, and ensures that the airflow velocity is evenly distributed. Generally, the contraction ratio should be above 10.

[0017] The first section of the flow rate regulation adopts a fully flexible wall structure nozzle, with flexible upper and lower walls and parallel rigid straight wall plates on both sides. The first section of the flow rate regulation mainly consists of upper and lower crossbeams, front and rear end plates, left and right side walls, a flexible plate and its actuator, and supports. The length of the flexible plate is denoted as D, extending from the inlet to the outlet. The outlet end of the flexible plate is fixed, while the inlet end slides to adapt to changes in length and slope when the flexible plate bends. Hinge support points are arranged on the backflow surface of the flexible plate and connected to the actuator. The bending shape of the flexible plate is controlled by controlling the stroke of the actuator to match the theoretical aerodynamic profile of the nozzle, thus obtaining nozzle profiles for different experimental Mach numbers Ma. Deformation starts from the flat plate, with the outlet point as the zero point. The relationship between the position x (0≤x≤D) of each support point and the displacement y is determined through debugging, forming an adjustment function. The typical operating condition adjustment function is as follows:

[0018]

[0019] Here, the coefficient matrix A is defined, and the coefficient matrix is ​​obtained by fitting the actual experimental curve:

[0020]

[0021] For ease of use, first retrieve the nozzle profile at Ma1.00. Using Ma1.00 as the initial calculation profile, and defining the elongation of each support point as 0 in the initial state, the adjustment function simplifies to:

[0022]

[0023] Here, the coefficient matrix B is defined, and the coefficient matrix is ​​obtained by fitting the actual experimental curve:

[0024]

[0025] The standard flow field test section has smooth solid walls on all four sides, optical glass windows on the side and top walls, and static pressure holes on the bottom wall. Flanges are located at the front and rear ends of the test section, connecting to the nozzle and the rear test chamber flanges respectively. Sealing strips are used to seal the front and rear sections. The test section has a diameter of L1×L1, and its area is denoted as S. 试验段 According to GJB 1179A-2012, the flow field stability generated by the standard flow field test section is better than 0.1%.

[0026] The rear test chamber is primarily used to install standard probes, achieving a sliding seal between the support arm and the test chamber. The rear test chamber mainly consists of a base plate, a lower pressure plate, an upper pressure plate, a square pressure plate, spring screws, and an L-shaped support arm. The lower pressure plate has an arc-shaped elongated hole. The lower and upper pressure plates are pressed onto the base plate by spring screws, and a fluororubber sealing ring is placed between the lower pressure plate and the base plate to achieve a sliding seal. The L-shaped support arm is fixed to the pressure plate by the square pressure plate and slides with the lower pressure plate. A sealing ring is used to seal between the square pressure plate and the lower pressure plate.

[0027] The second section for flow rate regulation involves installing a grid finger mechanism on the upper and lower wall panels, symmetrically arranged. This second section mainly consists of grid finger plates, grid finger connecting brackets, guide blocks and guide grooves, connecting rods, sealing covers, and electric cylinders. A total of n grid finger plates are installed, with the maximum thickness of a single grid finger denoted as H and the stroke as l1. During subsonic testing, the throttling area of ​​the calibration device is flexibly and accurately adjusted by controlling the extension and retraction of the grid fingers in real time; the flow channel area at the grid finger is denoted as S. 栅指 By blocking and throttling, the airflow velocity in the test section is established, controlled, and stabilized, effectively suppressing the adverse effects of probe wake and downstream airflow pressure pulsations and noise on the airflow quality of the test section. Using S... 栅指 / S 试验段 The following formula reflects the throttling situation:

[0028]

[0029] The relationship between throttling and Mach number, as determined by experiments, is as follows:

[0030] S 栅指 / S 试验段 =c0+c1Ma+c2Ma 2 (4)

[0031] The adjustment function coefficients c0, c1, and c2 are obtained by fitting the actual experimental curve. Using formulas (3) and (4), the relationship between the grating finger elongation s and the Mach number Ma is obtained, forming the adjustment function as follows:

[0032]

[0033] By employing two sections of flow rate regulation, the regulation range covers subsonic and transonic speeds, enabling the construction of a wide-ratio flow field. At subsonic and transonic speeds, the nozzle profile remains unchanged. The Mach number at the reference point of the test section is monitored in real-time by adjusting the extension of the grid fingers and the opening of the pressure regulating valve, ensuring the flow rate in the test section reaches the set value. At supersonic speeds, the total pressure in the stable section is monitored in real-time by adjusting the nozzle profile and the opening of the pressure regulating valve, ensuring the flow rate in the test section reaches the set value.

[0034] The flow velocity standard probe system measures pressure and temperature information using a total static pressure probe and a total temperature probe, calculates the Mach number and flow velocity at the measurement points, and displays the data. The total static pressure probe and total temperature probe must be calibrated before use.

[0035] The working method of the PIV actual flow calibration device based on a wide velocity ratio flow field disclosed in this invention is as follows:

[0036] Step 1: Set up the test system and determine the camera working distance based on the PIV laser chip light source focusing range requirements, the size of the measurement working area, the camera lens focal length, and the chip size requirements.

[0037] Step 2: Equipment inspection and connection. Check the power supply, laser, synchronizer and other subsystems of the PIV to ensure that the power is turned on, the laser is turned on and preheated, the synchronizer is connected, the camera is connected and the PIV is adjusted to standby state under normal working conditions.

[0038] Step 3: Adjust the laser position so that the sheet light source generated by the laser can illuminate the measured flow field area on the axial plane of the standard flow field test section of the calibration device;

[0039] Step 4: Adjust the camera position so that the camera is perpendicular to the laser sheet light source and the particles in the measured flow field can be clearly imaged;

[0040] Step 5: Install the standard probe. Place the standard probe on the cross section of the sheet light source. The initial position of the measurement point is at the center of the PIV field of view, facing the direction of the airflow. The calibration wind speed should be selected as the upper and lower limits of the range and the middle value of the range. The calibration speed can also be set according to the test requirements.

[0041] Step 6: Run the calibration device, adjust the airflow speed to the preset calibration point, observe the stability of the flow field, and start the calibration test after the requirements are met;

[0042] Step 6.1: Turn on the calibration device control system and input the corresponding working condition flow field control parameters according to the test requirements. The working condition flow field control parameters include flow velocity, control accuracy, flexible wall nozzle shape, grid finger position, etc.

[0043] Step 6.2: Turn on the pressure regulating section of the calibration device and ventilate the calibration device. When the flow field in the test section reaches the predetermined wind speed, it will enter automatic adjustment. Through the feedback of the total temperature, total pressure and static pressure of the test section wall arranged in the rectifier section, the opening of the pressure regulating valve and the extension of the grid finger are further adjusted to achieve the specified airflow speed.

[0044] Step 7: Turn on the tracer particle generator and allow the tracer particles to flow through the test section of the calibration device with the airflow; adjust the concentration of the tracer particles so that there are more than 6 particles in each discrimination zone of the PIV field of view, and collect data. Take the velocity value collected at the center of the average flow field of view as the effective value of a single acquisition. Collect 6 sets of data continuously at this calibration point and record them as v. piv1-i ~v piv6-i Calculate the average of the 6 groups as the calibrated velocity value v at the calibration point. piv-i ;

[0045] Step 8: Place the standard probe on the cross-section of the sheet light source, with the measurement point at the center of the PIV field of view, directly facing the direction of the incoming airflow. Collect the flow velocity at this point for 1 minute and calculate the average value over the collection time, denoted as v. 标准-i ;

[0046] Step 9: Adjust the flow rate of the calibration device to the next calibration point, and repeat steps 7 to 8. When selecting the calibration point, the PIV shooting screen can be divided into areas, and the center point of each area can be used as the calibration point. The number of areas is determined according to the actual situation.

[0047] Step 10: After the above calibration process is completed, turn off the calibration device, PIV system, particle generator, etc., to complete this calibration.

[0048] Step 11: Calculate the indication error of the PIV being calibrated. At a certain speed, the indication error Δv of the PIV being calibrated is... i Calculate according to formula (6):

[0049] Δv i =v piv-i -v 标准-i (6)

[0050] Among them, v piv-i Let v be the corrected velocity value of PIV at the i-th velocity. 标准-i This represents the standard speed value at the i-th speed calibration point;

[0051] Calculate the indication error of the PIV instrument being calibrated at m calibration points within this range:

[0052]

[0053] PIV actual flow calibration is performed based on the indicated error.

[0054] Beneficial effects:

[0055] 1. The present invention discloses a PIV real flow calibration device and method based on a wide speed ratio flow field. By constructing a standard flow field test section, it realizes for the first time the calibration of non-contact flow field measurement equipment in a real airflow environment. Compared with the currently used turntable calibration method, it not only greatly expands the calibration range, but also realizes the leap from single-point calibration to whole-field calibration.

[0056] 2. The present invention discloses a PIV actual flow calibration device based on a wide speed ratio flow field. It mainly constructs a wide speed ratio standard flow field through the first section and the second section of flow velocity adjustment. Through actual flow debugging, the present invention fits the adjustment functions of the above two key flow velocity adjustment sections, realizing small-size and high-precision profile adjustment. On the one hand, it realizes continuous adjustment of the supersonic flow field. On the other hand, it can effectively suppress the adverse effects of subsonic airflow pressure pulsation and noise on the airflow quality of the test section, ensuring the continuity and stability of the flow field of the calibration device.

[0057] 3. The present invention discloses a PIV actual flow calibration device based on a wide speed ratio flow field. The standard probe is installed on the displacement mechanism and calibration is performed by moving the probe through the displacement mechanism. By designing a rear test chamber, a part of the displacement mechanism is placed in the rear test chamber. While ensuring good airtightness of the device and realizing the calibration function, the interference of the displacement mechanism on the standard flow field is avoided, thus ensuring the independence of the standard flow field test section and the reliability of the calibration results.

[0058] 4. The present invention discloses a PIV actual flow calibration method based on a wide speed ratio flow field. Relying on an actual flow calibration device, it proposes an operable PIV actual flow calibration method for the first time, which solves the problems of the lack of PIV actual flow calibration methods and the inability to evaluate the reliability of measurement results. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of a PIV real-flow calibration device based on a wide speed ratio flow field according to the present invention;

[0060] Wherein: 1—Inlet pressure regulation section, 2—Transition section, 3—Rectification section, 4—Airflow acceleration section, 5—Flow velocity regulation first section, 6—Standard flow field test section, 7—Rear test chamber, 8—Displacement mechanism, 9—Flow velocity regulation second section, 10—Exhaust section, 11—Flow velocity standard probe system, 12—Control system;

[0061] Figure 2 This is a schematic diagram of the first section of the flexible-wall nozzle structure of the PIV actual flow calibration device based on a wide velocity ratio flow field according to the present invention.

[0062] Wherein: 51—upper and lower crossbeams, 52—front and rear end plates, 53—left and right side walls, 54—flexible plate, 55—actuator, 56—support;

[0063] Figure 3 This is a schematic diagram of the standard flow field test section structure of a PIV actual flow calibration device based on a wide speed ratio flow field according to the present invention.

[0064] Wherein: 61—cylinder, 62—optical glass window, 63—static pressure hole, 64—flange;

[0065] Figure 4 This is a schematic diagram of the rear test chamber structure of a PIV actual flow calibration device based on a wide speed ratio flow field according to the present invention. Figure 4 a) is a schematic diagram of the aft experimental module structure. Figure 4 b) is a sectional view of the bottom of the test chamber;

[0066] Wherein: 71—top plate, 72—test chamber body, 73—L-shaped support arm, 74—bottom plate, 75—spring screw, 76—square pressure plate, 77—upper pressure plate, 78—lower pressure plate;

[0067] Figure 5 This is a schematic diagram of the displacement mechanism structure of a PIV actual flow calibration device based on a wide speed ratio flow field according to the present invention.

[0068] Among them: 81—Y-axis displacement module, 82—servo motor, 83—X-axis displacement module;

[0069] Figure 6 This is a schematic diagram of the second section grid finger structure of a PIV actual flow calibration device based on a wide velocity ratio flow field according to the present invention.

[0070] Wherein: 91—grid finger piece, 92—grid finger connecting bracket, 93—guide block and guide groove, 94—connecting rod, 95—sealing cover, 96—electric cylinder;

[0071] Figure 7 This is a schematic diagram of the calibration test system layout of the present invention;

[0072] Among them: 13—laser, 14—camera, 15—synchronizer, 16—standard probe, 17—particle generator;

[0073] Figure 8 This is the calibration area division diagram of the present invention. Detailed Implementation

[0074] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0075] Example 1:

[0076] See appendix Figure 1This embodiment discloses a PIV (Pilot-Induced Airflow) calibration device based on a wide speed ratio (Mach number 0.3–2.0) flow field. It mainly consists of an inlet pressure regulating section 1, a transition section 2, a rectification section 3, an airflow acceleration section 4, a first flow velocity regulating section 5, a standard flow field test section 6, a rear test chamber 7, a displacement mechanism 8, a second flow velocity regulating section 9, an exhaust section 10, a flow velocity standard probe system 11, and a control system 12. These sections are connected sequentially. The object being calibrated is the PIV system.

[0077] The system generates an airflow at a specified velocity through the intake pressure regulation section 1, transition section 2, rectification section 3, airflow acceleration section 4, flow velocity regulation section 5, flow velocity regulation section 9, and control system 12. A uniform and stable standard flow field is formed in the standard flow field test section 6. The four walls of the test section are smooth solid walls, and optical glass windows are opened on the side walls and the top wall. The laser of the PIV system generates a sheet light source in the test section through the optical glass on the top wall, and the CCD camera takes pictures of the sheet light source area through the optical glass on the side walls. A flow velocity standard probe system 11 is installed in the rear experimental chamber 7. The standard probe moves and measures the flow field in the sheet light source area through the displacement mechanism 8 to obtain the velocity information of the feature points of the entire field, thereby realizing the calibration of the PIV system.

[0078] The intake pressure regulating section 1 includes a main line and a bypass line; the main line and the bypass line are each equipped with two pressure regulating valves of different sizes, the larger valve is installed in the main line for coarse adjustment, and the smaller valve is installed in the bypass line for fine adjustment.

[0079] The transition section 2 connects the pressure regulating section and the rectifier section, and consists of a short straight pipe section and a diffuser section with a diffusion angle of 20°.

[0080] The rectifying section 3, with a diameter of 450mm, is equipped with rectifying devices such as honeycomb coils and damping nets to suppress upstream valve disturbances, reduce turbulence, and improve the airflow quality of the test section. A static flow section is set after the damping net, and standard total temperature and total pressure probes are arranged for control system feedback adjustment.

[0081] The airflow acceleration section 4 has a contraction ratio of 20, which accelerates the airflow to the speed of sound and makes the airflow speed distribution uniform.

[0082] The structure of the first section 5 for flow rate regulation is shown in the appendix. Figure 2The nozzle employs a fully flexible wall structure, with flexible upper and lower walls and parallel rigid straight walls on both sides. It consists of upper and lower crossbeams 51, front and rear end plates 52, left and right side walls 53, a flexible plate 54, an actuator 55, and supports 56. The nozzle's designed length is 850mm. The flexible plate extends from the inlet to the outlet, with the outlet end fixed and the inlet end sliding to accommodate changes in length and slope during bending. The nozzle can achieve aerodynamic profile curves at four typical Mach numbers: 1.0, 1.5, 1.75, and 2.0. Hinge support points are arranged on the backflow surface of the flexible plate and connected to the actuator. By controlling the stroke of the actuator, the bending shape of the flexible plate is controlled to match the nozzle's theoretical aerodynamic profile, thus obtaining nozzle profiles for different experimental Mach numbers Ma. Deformation starts from a flat plate, with the outlet point as the zero point. The relationship between the position x (0≤x≤850mm) of each support point and the displacement y is determined through debugging. The debugging results are shown in Table 1.

[0083] Table 1 shows the deformation y (mm) starting from the flat plate.

[0084]

[0085] The fitting process generates an adjustment function, and the typical operating condition adjustment function is as follows:

[0086]

[0087] For ease of use, the nozzle profile at Ma1.00 can be selected first. Using Ma1.00 as the initial calculation profile, the elongation of each support point is defined as 0 in the initial state. The elongation results of the deformed surface are shown in Table 2.

[0088] Table 2 shows the initial surface deformation y (mm) with Ma1.00 as the initial value.

[0089]

[0090] The adjustment function can be simplified to:

[0091]

[0092] The structure of the standard flow field test section 6 is shown in the appendix. Figure 4 The cylinder 61 has smooth solid walls on all four sides, optical glass windows 62 on the side walls and the top wall, and static pressure holes 63 on the bottom wall. The front and rear ends of the test section have flanges 64, which are connected to the nozzle and the flange of the rear test chamber, respectively. They are sealed with sealing strips to the front and rear sections. The test section is 90mm×90mm in size.

[0093] The rear test chamber 7 is mainly used to install standard probes and achieve a sliding seal between the support arm and the test chamber. It consists of a top plate 71, a test chamber body 72, an L-shaped support arm 73, a bottom plate 74, etc., as shown in the attached diagram. Figure 4a) The internal structural diagram of the test chamber is attached. Figure 4 As shown in b), the main components include a base plate 74, a lower pressure plate 78, an upper pressure plate 77, a square pressure plate 76, a spring screw 75, and an L-shaped support arm 73. The lower pressure plate 78 has an arc-shaped elongated hole. The lower pressure plate 78 and the upper pressure plate 77 are pressed onto the base plate 74 by the spring screw 75. A fluororubber sealing ring is provided between the lower pressure plate 78 and the base plate 74 to achieve a sliding seal. The L-shaped support arm 73 is fixed to the pressure plate by the square pressure plate and slides with the lower pressure plate 78. A sealing ring is provided between the square pressure plate 76 and the lower pressure plate 78 to achieve a seal.

[0094] The structure of the second section 9 for flow rate regulation is shown in the appendix. Figure 3 A grid finger mechanism is installed on the upper and lower wall panels, symmetrically arranged. It consists of grid finger pieces 91, grid finger connecting brackets 92, guide blocks and guide grooves 93, connecting rods 94, sealing covers 95, and electric cylinders 96. A total of four grid finger pieces are installed, with a maximum thickness of 40mm and a stroke of 55mm for each finger. During subsonic testing, the throttling area of ​​the calibration device is flexibly and accurately adjusted by real-time control of the grid finger extension and retraction. This blocking and throttling effect establishes, controls, and stabilizes the airflow velocity in the test section, effectively suppressing the adverse effects of probe wake and downstream airflow pressure pulsations and noise on the airflow quality of the test section. The relationship between the grid finger elongation *s* and the Mach number *Ma* was determined through debugging, and the debugging results are shown in Table 3.

[0095] Table 3. Debugging Results of the Relationship between Grid Finger Elongation and Mach Number

[0096] Ma number Actual insertion depth / mm Ratio of flow channel area at the gate to the test section area 0.4 46 0.5943 0.5 39 0.7266 0.6 33 0.8415 0.7 28 0.9389 0.8 24 1.0159 0.9 21 1.0756 1.0 19 1.1221

[0097] Based on the debugging results in Table 3 and formula (3), the adjustment function coefficients are obtained as c0 = -0.11, c1 = 2.12, and c2 = -0.89. Substituting these values ​​into formula (5), the relationship between the grating finger elongation and the Mach number is obtained, forming the adjustment function as follows:

[0098]

[0099] By adjusting the first section 5 and the second section 9 of the flow velocity regulation, the regulation range covers subsonic and transonic speeds, achieving the construction of a wide speed ratio flow field. At subsonic and transonic speeds, the nozzle profile remains unchanged. By adjusting the extension of the grid fingers in conjunction with the opening of the pressure regulating valve, the Mach number at the reference point of the test section is monitored in real time to ensure the flow velocity in the test section reaches the set value. At supersonic speeds, by adjusting the nozzle profile in conjunction with the opening of the pressure regulating valve, the total pressure in the stable section is monitored in real time to ensure the flow velocity in the test section reaches the set value.

[0100] The flow velocity standard probe system 11 measures pressure and temperature information through a total static pressure probe and a total temperature probe, calculates the Mach number and flow velocity at the measuring points, and displays the data. The total static pressure probe and the total temperature probe must be calibrated before use.

[0101] Example 2

[0102] Based on the apparatus and its application in Embodiment 1, this application, in another aspect, proposes a method for implementing the above-described PIV actual flow calibration method based on a wide velocity ratio flow field, comprising the following steps:

[0103] Step 1: Set up the test system, such as Figure 7 As shown, the working distance of camera 14 is determined based on the focusing range requirements of the PIV laser 13 light source, the size of the measurement working area, the focal length of the camera 14 lens, and the chip size requirements.

[0104] Step 2: Equipment inspection and connection. Check the power supply, laser 13, synchronizer 15 and other subsystems of the PIV. Ensure that the power supply is turned on, the laser 13 is turned on and preheated, synchronizer 15 is connected, camera 14 is connected and the PIV is adjusted to standby state under normal working conditions.

[0105] Step 3: Adjust the laser position so that the sheet light source generated by the laser can illuminate the measured flow field area on the axial plane of the standard flow field test section of the calibration device;

[0106] Step 4: Adjust the position of camera 14 so that the camera is perpendicular to the laser sheet light source and the particles in the measured flow field can be clearly imaged;

[0107] Step 5: Install the standard probe 16. Place the standard probe on the cross section of the sheet light source. The initial position of the measurement point is at the center of the PIV field of view, facing the direction of the airflow. Select the calibration wind speed as the upper and lower limits of the range and the middle value of the range.

[0108] Step 6: Run the calibration device, adjust the airflow speed to the preset calibration point, observe the stability of the flow field, and start the calibration test after the requirements are met;

[0109] Step 6.1: Turn on the calibration device control system and input the corresponding working condition flow field control parameters according to the test requirements. The working condition flow field control parameters include flow velocity, control accuracy, flexible wall nozzle shape, grid finger position, etc.

[0110] Step 6.2: Turn on the pressure regulating section of the calibration device and ventilate the calibration device. When the flow field in the test section reaches the predetermined wind speed, it will enter automatic adjustment. Through the feedback of the total temperature, total pressure and static pressure of the test section wall arranged in the rectifier section, the opening of the pressure regulating valve and the extension of the grid finger are further adjusted to achieve the specified airflow speed.

[0111] Step 7: Turn on the tracer particle generator 17, allowing the tracer particles to flow through the test section of the calibration device with the airflow; adjust the concentration of the tracer particles so that there are more than 6 particles in each discrimination zone of the PIV field of view, and collect data. Take the velocity value collected at the center of the average flow field of view as the effective value of a single acquisition. Collect 6 sets of data continuously at this calibration point and record them as v. piv1-i ~v piv6-i Calculate the average of the 6 groups as the calibrated velocity value v at the calibration point. piv-i ;

[0112] Step 8: Place the standard probe 16 on the cross-section of the light source, with the measurement point at the center of the PIV field of view, directly facing the direction of the incoming airflow. Collect the flow velocity at this point for 1 minute and calculate the average value over the collection time, denoted as v. 标准-i ;

[0113] Step 9: Divide the PIV shooting screen into 9 areas, take the center point of each area as the calibration point, adjust the flow rate of the calibration device to the next calibration point, and repeat steps 7 to 8.

[0114] Step 10: After the above calibration process is completed, turn off the calibration device, PIV system, particle generator 17, etc., to complete this calibration;

[0115] Step 11: Calculate the indication error of the PIV being calibrated. At a certain speed calibration point, the indication error Δv of the PIV being calibrated is... i The indication error Δv of the PIV instrument being calibrated is calculated according to formula (6) at m calibration points in this range.

[0116] PIV actual flow calibration is performed based on the indicated error.

[0117] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A PIV (Pulse-Induced Flow) calibration device based on a wide velocity ratio flow field, characterized in that: It mainly consists of an intake pressure regulation section, a transition section, a rectification section, an airflow acceleration section, a first flow velocity regulation section, a standard flow field test section, a rear test chamber, a displacement mechanism, a second flow velocity regulation section, an exhaust section, a flow velocity standard probe system, and a control system. These sections are connected sequentially. The object being calibrated is the PIV system. An airflow with a specified velocity is generated through an intake pressure regulation section, a transition section, a rectification section, an airflow acceleration section, a first velocity regulation section, a second velocity regulation section, and a control system. A uniform and stable standard flow field is formed in the standard flow field test section. The four walls of the test section are smooth solid walls, and optical glass windows are opened on the side walls and the top wall. The laser of the PIV system generates a sheet light source in the test section through the optical glass on the top wall, and the CCD camera takes pictures of the sheet light source area through the optical glass on the side wall. A flow velocity standard probe system is installed in the rear experimental chamber. The standard probe moves and measures the flow field in the sheet light source area through a displacement mechanism to obtain the velocity information of the feature points of the entire field, thereby realizing the calibration of the PIV system. The first section of the flow rate regulation adopts a fully flexible wall structure nozzle, with flexible upper and lower walls and parallel rigid straight wall plates on both sides. The first section mainly consists of upper and lower crossbeams, front and rear end plates, left and right side walls, a flexible plate and its actuator, and supports. The length of the flexible plate is denoted as D, extending from the inlet to the outlet. The outlet end of the flexible plate is fixed, while the inlet end slides to adapt to changes in length and slope during bending. Hinge support points are arranged on the backflow surface of the flexible plate and connected to the actuator. The bending shape of the flexible plate is controlled by controlling the stroke of the actuator to match the theoretical aerodynamic profile of the nozzle, thus obtaining nozzle profiles for different experimental Mach numbers Ma. Deformation starts from the flat plate, with the outlet point as the zero point. The relationship between the position x (0≤x≤D) of each support point and the displacement y is determined through debugging, forming an adjustment function. The typical operating condition adjustment function is as follows: Here, the coefficient matrix A is defined, and the coefficient matrix is ​​obtained by fitting the actual experimental curve: For ease of use, first retrieve the nozzle profile at Ma1.

00. Using Ma1.00 as the initial calculation profile, and defining the elongation of each support point as 0 in the initial state, the adjustment function simplifies to: Here, the coefficient matrix B is defined, and the coefficient matrix is ​​obtained by fitting the actual experimental curve:

2. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The intake pressure regulating section includes a main line and a bypass line; the main line and the bypass line are each equipped with two pressure regulating valves, one large and one small. The large valve is installed in the main line for coarse adjustment, and the small valve is installed in the bypass line for fine adjustment. The transition section connects the pressure regulating section and the rectification section, and consists of a short straight pipe section and a diffuser section. When the length-to-diameter ratio of the straight pipe section is 5 to 10, the diffuser angle is 20° to 30°; when the length-to-diameter ratio of the straight pipe section is 3 to 5, the diffuser angle is 45° to 90°. When using a large-angle diffuser section, in order to alleviate severe separation in the diffuser section, uniform airflow, and reduce losses, a metal mesh, a coaxial multi-layer diffuser section, and an open-hole contraction cone diffuser device are installed in the diffuser section.

3. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The rectifying section is equipped with a rectifying device to suppress disturbances from the upstream valve, reduce turbulence, and improve the airflow quality of the test section. The rectifying device includes a honeycomb structure and a damping mesh. A static flow section is set after the damping mesh, and standard total temperature and total pressure probes are arranged therefor to control system feedback adjustment.

4. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The airflow acceleration section accelerates the airflow to the speed of sound by using an appropriate contraction ratio, and ensures that the airflow velocity is evenly distributed, with the contraction ratio being above 10.

5. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The standard flow field test section has smooth solid walls on all four sides, optical glass windows on the side and top walls, and static pressure holes on the bottom wall. Flanges are located at the front and rear ends of the test section, connecting to the nozzle and the rear test chamber flanges respectively. Sealing strips are used to seal the front and rear sections. The test section has a diameter of L1×L1, and its area is denoted as S. 试验段 According to GJB 1179A-2012, the flow field stability generated by the standard flow field test section is better than 0.1%.

6. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The rear test chamber is mainly used to install standard probes and achieve a sliding seal between the support arm and the test chamber. The rear test chamber mainly consists of a base plate, a lower pressure plate, an upper pressure plate, a square pressure plate, spring screws, and an L-shaped support arm. The lower pressure plate has an arc-shaped elongated hole. The lower pressure plate and the upper pressure plate are pressed onto the base plate by spring screws. There is a fluororubber sealing ring between the lower pressure plate and the base plate to achieve a sliding seal. The L-shaped support arm is fixed to the pressure plate by the square pressure plate and slides with the lower pressure plate. The square pressure plate and the lower pressure plate are sealed by a sealing ring.

7. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The second section for flow rate regulation includes a grid finger mechanism installed symmetrically on the upper and lower wall panels. This second section mainly consists of grid finger plates, grid finger connecting brackets, guide blocks and guide grooves, connecting rods, sealing covers, and electric cylinders. A total of n grid finger plates are installed, with the maximum thickness of a single grid finger denoted as H and the stroke as l1. During subsonic testing, the throttling area of ​​the calibration device is flexibly and accurately adjusted by real-time control of the grid finger extension and retraction. The flow channel area at the grid finger is denoted as S. 栅指 By blocking and throttling, the airflow velocity in the test section is established, controlled, and stabilized, effectively suppressing the adverse effects of probe wake and downstream airflow pressure pulsations and noise on the airflow quality of the test section; using S 栅指 / S 试验段 The following formula reflects the throttling situation: The relationship between throttling and Mach number, as determined by experiments, is as follows: S 栅指 / S 试验段 =c0+c1Ma+c2Ma 2 (4) The adjustment function coefficients c0, c1, and c2 are obtained by fitting the actual experimental curve; the relationship between the grating finger elongation s and the Mach number Ma is obtained through formulas (3) and (4), forming the adjustment function as follows: By adjusting the first and second sections of the flow rate regulation, the regulation range covers subsonic and transonic speeds, enabling the construction of a wide speed ratio flow field. At subsonic and transonic speeds, the nozzle profile remains unchanged, and the Mach number at the reference point of the test section is monitored in real time by adjusting the extension of the grid fingers in conjunction with the opening of the pressure regulating valve, so that the flow rate in the test section reaches the set value. At supersonic speeds, the total pressure in the stable section is monitored in real time by adjusting the nozzle profile in conjunction with the opening of the pressure regulating valve, so that the flow rate in the test section reaches the set value.

8. The PIV actual flow calibration device based on a wide velocity ratio flow field as described in claim 1, characterized in that: The flow velocity standard probe system measures pressure and temperature information through total static pressure probe and total temperature probe, calculates and displays the Mach number and flow velocity at the measuring point; the total static pressure probe and total temperature probe need to be calibrated before use.

9. A PIV actual flow calibration method based on a wide velocity ratio flow field, implemented based on a PIV actual flow calibration device based on a wide velocity ratio flow field as described in any one of claims 1 to 8, characterized in that: Includes the following steps, Step 1: Set up the test system and determine the camera working distance based on the PIV laser chip light source focusing range requirements, the size of the measurement working area, the camera lens focal length, and the chip size requirements. Step 2: Equipment inspection and connection. Check the power supply, laser, synchronizer and other subsystems of the PIV. Ensure that the power supply, laser and preheating are turned on, synchronizer and camera are connected, and PIV is adjusted to standby mode under normal working conditions. Step 3: Adjust the laser position so that the sheet light source generated by the laser can illuminate the measured flow field area on the axial plane of the standard flow field test section of the calibration device; Step 4: Adjust the camera position so that the camera is perpendicular to the laser sheet light source and the particles in the measured flow field can be clearly imaged; Step 5: Install the standard probe. Place the standard probe on the cross section of the sheet light source. The initial position of the measurement point is at the center of the PIV field of view, facing the direction of the airflow. The calibration wind speed should be selected as the upper and lower limits of the range and the middle value of the range. At the same time, the calibration speed should be set according to the test requirements. Step 6: Run the calibration device, adjust the airflow speed to the preset calibration point, observe the stability of the flow field, and start the calibration test after the requirements are met; Step 6.1: Turn on the calibration device control system and input the corresponding working condition flow field control parameters according to the test requirements. The working condition flow field control parameters include flow velocity, control accuracy, flexible wall nozzle shape, and grid finger position. Step 6.2: Turn on the pressure regulation section of the calibration device, and the calibration device will be ventilated. When the flow field in the test section reaches the predetermined wind speed, it will enter automatic regulation. By using the total temperature, total pressure and static pressure of the test section wall as feedback, the opening of the pressure regulating valve and the extension of the grid fingers will be adjusted to achieve the specified airflow speed. Step 7: Turn on the tracer particle generator and allow the tracer particles to flow through the test section of the calibration device with the airflow; adjust the concentration of the tracer particles so that there are more than 6 particles in each discrimination zone of the PIV field of view, and collect data. Take the velocity value collected at the center of the average flow field of view as the effective value of a single acquisition. Collect 6 sets of data continuously at this calibration point and record them as v. piv1-i ~v piv6-i Calculate the average value of the 6 groups as the calibrated velocity value v at the calibration point. piv-i ; Step 8: Place the standard probe on the cross-section of the sheet light source, with the measurement point at the center of the PIV field of view, directly facing the direction of the incoming airflow. Collect the flow velocity at this point for 1 minute and calculate the average value over the collection time, denoted as v. 标准-i ; Step 9: Adjust the flow rate of the calibration device to the next calibration point, and repeat steps 7 to 8. When selecting the calibration point, the PIV shooting screen is divided into areas, and the center point of each area is used as the calibration point. The number of areas is determined according to the actual situation. Step 10: After the above calibration process is completed, turn off the calibration device, PIV system, and particle generator to complete this calibration. Step 11: Calculate the indication error of the PIV being calibrated. At a certain speed, the indication error Δv of the PIV being calibrated is... i Calculate according to formula (6): Δv i =v piv-i -v 标准-i (6) Among them, v piv-i Let v be the corrected velocity value of PIV at the i-th velocity. 标准-i This represents the standard speed value at the i-th speed calibration point; Calculate the indication error of the PIV instrument being calibrated at m calibration points within this range: PIV actual flow calibration is performed based on the indicated error.

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