A system and method for measuring two-dimensional Mach number distribution field of supersonic flow

Abstract

The present invention relates to a system and method for measuring the two-dimensional Mach number distribution field of supersonic flow. Based on a femtosecond laser electron excitation marking velocity measurement system, the output laser beam is shaped into a dot matrix light by combining a diffraction optical element. This combination method can realize the transformation of FLEET technology from single point / line velocity measurement to two-dimensional flow field velocity measurement without a large loss of total laser energy. Secondly, a two-dimensional temperature field measurement device based on Rayleigh scattering uses a sheet light generation component to form a two-dimensional sheet laser, and conducts two-dimensional calibration data measurement under known conditions by monitoring the static pressure of the flow field and the laser energy. Combined with the two-dimensional Rayleigh scattering results of the formal test, the two-dimensional temperature distribution analysis of supersonic flow is realized. Using a signal synchronization generating device, a two-dimensional flow field velocity measurement device, a two-dimensional temperature field measurement device and a static pressure measurement are synchronously implemented to obtain simultaneous and frequency-coordinated experimental data, and then the two-dimensional Mach number distribution of supersonic flow can be constructed through the data.

Description

Technical Field

[0001] The invention relates to the technical field of supersonic airflow parameter testing, and in particular to a system and method for measuring a supersonic flow two-dimensional Mach number distribution field. Background Art

[0002] In the research of supersonic aircraft, ground tests, numerical calculations and flight tests are the three main means. The three research methods have their own advantages and disadvantages, so it is often necessary to combine the three to better understand, explain, design and optimize supersonic aircraft. In the field of aerodynamics, the combined analysis of the three is mainly based on the similarity conditions of certain specific dimensionless parameters, among which the Mach number is one of the most important dimensionless parameters. It is defined as the ratio of the object speed to the local sound speed. At the same time, its square can be used as a measure to compare the macroscopic flow kinetic energy of the gas and the random thermal motion energy of the molecules, and characterizes the degree of influence of the flow velocity change on the thermodynamic state. On another level, there is a special Mach cone structure in the disturbance propagation area of ​​the supersonic airflow. The Mach cone angle is directly related to the Mach number and directly affects the aerodynamic and aerothermal characteristics of the aircraft. In addition, the aircraft's attitude control, thermal protection, boundary layer control and other strategies also need to be formulated based on the flight Mach number. Therefore, in the three research methods of supersonic aircraft, accurately obtaining the Mach number is very important for experimental analysis, numerical model verification and ground-to-space correlation construction.

[0003] In numerical calculations, the Mach number can be directly inverted from the calculation results; in flight tests, the Mach airspeed meter installed on the aircraft is mainly used, which calculates the flight speed by measuring the static pressure / total pressure, and then measures the altitude of the aircraft. According to the linear relationship between the altitude and the speed of sound, the local speed of sound is obtained, and finally the flight Mach number is obtained; in ground tests, the supersonic flow is mainly formed through a wind tunnel, and the Mach number of the airflow at the outlet of the wind tunnel nozzle is generally calculated based on theoretical relationships such as aerodynamics and thermodynamics.

[0004] In the complex wind tunnel operation process, theoretical calculations often fail to take into account the impact of actual test factors, which is reflected in: 1) The theoretical calculation result is a single Mach number value. In actual wind tunnel tests, affected by the wall boundary layer and turbulence effects, the distribution of the Mach number is not uniform even in the core area; 2) Theoretical calculations inevitably make assumptions about ideal conditions. Since it is impossible to consider all physical processes in the actual test, the single numerical result calculated under ideal conditions is different from the characteristic Mach number under actual conditions. 3) The Mach number obtained by theoretical calculation is the Mach number at the nozzle outlet. In ground wind tunnel tests, the test piece is often fixed at a certain distance from the nozzle, so the Mach number at the nozzle outlet cannot fully represent the characteristic flow conditions at the installation position of the test piece.

[0005] Even so, ground tests still mainly use theoretically calculated Mach numbers as the characterization value of the test conditions. This is because it is extremely difficult to conduct Mach number tests. If we use the Mach number measurement method of flight tests as an analogy, it is necessary to place sensors that measure the airflow velocity and local sound speed (or temperature) in the test section with known gas components, and the invasive measurement method requires networking of sensors to obtain the distribution of parameters in space. Large brackets and a large number of sensors will inevitably affect the state of the incoming flow, resulting in the intrusive measurement also being unable to well characterize the incoming flow Mach number of ground tests. Faced with the difficulty of measuring the Mach number of supersonic incoming flow in ground tests of aircraft, the use of non-invasive measurement methods is a solution, but there are currently few public reports on related test systems and methods. Summary of the invention

[0006] The purpose of the present invention is to provide a system and method for measuring a two-dimensional Mach number distribution field of a supersonic flow, so as to achieve the measurement of a two-dimensional Mach number distribution field of a supersonic flow field by non-intrusive measurement means.

[0007] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a supersonic flow two-dimensional Mach number distribution field measurement system, comprising a supersonic flow field generating device for simulating and generating observable high-altitude high-speed incoming flow conditions;

[0008] Also includes:

[0009] A static pressure measuring device for measuring the static pressure level of the area to be measured when supersonic airflow passes through or when no airflow passes through;

[0010] The two-dimensional flow field velocity measurement device based on femtosecond laser electronic excitation marking comprises a femtosecond laser, a first reflector, a lattice diffraction optical element, a plano-convex lens, and a dichroic mirror arranged in sequence, and is used to shape the laser light generated by the femtosecond laser into a lattice light and focus it on the area to be measured, and also includes a first image signal acquisition device for acquiring the positions of the marked molecules or atoms at different times;

[0011] The two-dimensional temperature field measuring device based on Rayleigh scattering comprises a high-frequency pump laser, a rotatable half-wave plate, a beam splitter and a sheet light generating component which are arranged in sequence. After the laser light generated by the high-frequency pump laser passes through the beam splitter, part of the laser light passes through the sheet light generating component and becomes a two-dimensional sheet laser light and can coincide with the plane of the lattice light, and the focal length of the two-dimensional sheet laser light can coincide with the center of the lattice light. The device also comprises a laser energy meter for receiving another part of the laser light after passing through the beam splitter, and also comprises a second image signal acquisition device for acquiring Rayleigh scattering signals.

[0012] A signal synchronization generating device is used for timing control of the supersonic flow field generating device, the two-dimensional flow field velocity measuring device and the two-dimensional temperature field measuring device.

[0013] Optionally, the first image signal acquisition device includes a first high-speed camera, a first high-speed image intensifier, an optical lens and a first optical filter, the optical lens is installed on the first high-speed camera through the first high-speed image intensifier, and the first optical filter is located in front of the optical lens.

[0014] Optionally, the second image signal acquisition device includes a second high-speed camera, a second high-speed image intensifier, an ultraviolet lens and a second optical filter, the ultraviolet lens is installed on the second high-speed camera through the second high-speed image intensifier, and the second optical filter is located in front of the ultraviolet lens.

[0015] Optionally, the supersonic flow field generating device includes a nozzle, a test section and a test section outlet with a vacuum pump, the test section outlet and the nozzle are respectively located at two ends of the test section and are connected to the test section, and the test section is also provided with a plurality of optical windows for the dot matrix light and two-dimensional sheet laser to enter the test section and for the first image signal acquisition device and the second image signal acquisition device to acquire signals in the test section.

[0016] Optionally, the static pressure measuring device is a static pressure probe, which is fixed in the test section, arranged in a position parallel to the direction of the maximum velocity component of the supersonic airflow, and located in a non-optical measurement area.

[0017] Optionally, the signal synchronization generating device includes a computer and a timing controller, the timing controller is respectively connected to the femtosecond laser, the first image signal acquisition device, the high-frequency pump laser, the second image signal acquisition device and the supersonic flow field generating device, the supersonic flow field generating device is signal connected to the static pressure measuring device, and the computer is respectively connected to the first image signal acquisition device, the second image signal acquisition device, the static pressure measuring device and the laser energy meter.

[0018] Optionally, the two-dimensional temperature field measuring device includes one or more reversing mirrors for reversing the optical path.

[0019] Optionally, the incoming flow of the supersonic gas flow is a thermally complete body.

[0020] In a second aspect, the present invention further provides a method for measuring a two-dimensional Mach number distribution field of a supersonic flow, which is performed using a two-dimensional Mach number distribution field measurement system for a supersonic flow according to any implementation of the first aspect, and comprises the following steps:

[0021] S100, calibrates the supersonic flow two-dimensional Mach number distribution field measurement system, including:

[0022] Camera window calibration, Rayleigh scattering laser polarization direction adjustment, Rayleigh scattering calibration field signal acquisition and first image signal acquisition device parameter determination;

[0023] S200, test data collection and processing analysis, including:

[0024] Obtain consistent frequency from laser energy meter f Laser energy data I ( t ), static pressure data is obtained by static pressure measuring device p ( t ), the flow displacement Δ of the femtosecond laser electron excitation marking signal is obtained by measuring the two-dimensional flow field velocity based on the femtosecond laser electron excitation marking. x ( x , y , t ) and tangential displacement Δ y ( x , y , t ), the Rayleigh scattering distribution field signal under the test condition is obtained by the two-dimensional temperature field measurement device based on Rayleigh scattering S ( x , y , t );The calibration field Rayleigh scattering signal is obtained by the calibration process S 0 ( x , y ), calibration field average temperature T 0 , average laser energy during calibration I 0 , calibration field static pressure level p 0 and the Rayleigh scattering cross section coefficient of the gas component during calibration Specific heat ratio γ , gas constant R and Rayleigh scattering cross section coefficient of the gas component during the experiment Obtained by looking up a table of known gas components;

[0025] The two-dimensional Mach number distribution field is obtained by processing and analyzing using the following formula:

[0026] .

[0027] Optionally, the camera window calibration uses a standard space three-dimensional calibration plate;

[0028] The spatial resolution test uses a standard resolution plate.

[0029] Optionally, the polarization direction of the Rayleigh scattered laser is adjusted using a half-wave plate frame that can automatically step, rotate and record, and the angle of the rotatable half-wave plate and the average Rayleigh scattering signal intensity of the measured area are recorded at the same time. A curve of the Rayleigh scattering intensity average value changing with the angle of the rotatable half-wave plate is plotted, and the result is approximately a sine curve, with the peak position corresponding to the vertical polarization angle and the trough position corresponding to the horizontal polarization angle.

[0030] Optionally, if the area to be tested is located in the test section of the wind tunnel, a known gas is selected as the test gas for Rayleigh scattering calibration field signal collection, the gas is left to stand still and stabilize, the pressure of the test section is maintained at the atmospheric pressure level, the temperature of the test section is collected by a thermocouple, and the calibration field Rayleigh scattering signal collects the results under the vertical polarization and horizontal polarization of the laser respectively to eliminate the influence of other interference signals;

[0031] If the area to be tested is located in an open space, which is connected to the atmosphere, air is used as the test gas for Rayleigh scattering calibration field signal collection. The gas is left to stand still and the pressure in the open space is maintained at the atmospheric pressure level. The temperature in the open space is collected by a thermocouple. The calibration field Rayleigh scattering signal collects the results under vertical and horizontal polarization of the laser respectively to eliminate the influence of other interference signals.

[0032] Optionally, when determining the parameters of the first image signal acquisition device, after reducing the visible light interference in the area to be measured to the minimum, three specific processes of theoretical calculation, physical delay measurement and actual operation adjustment are adopted to complete the determination of the acquisition system parameters.

[0033] The above technical solution of the present invention has the following advantages:

[0034] The supersonic flow two-dimensional Mach number distribution field measurement system provided by the present invention is based on the femtosecond laser electron excitation mark velocity measurement system, combined with a diffractive optical element, so that the output laser beam is shaped into a dot matrix light. This combination method can realize the transformation of the femtosecond laser electron excitation mark measurement technology from single point / line velocity measurement to two-dimensional flow field velocity measurement without a large loss of total laser energy. Secondly, a two-dimensional temperature field measurement device based on Rayleigh scattering uses a sheet light generation component to form a two-dimensional sheet laser, and conducts two-dimensional calibration data measurement under known conditions by monitoring the static pressure of the flow field and the laser energy. Combined with the two-dimensional Rayleigh scattering results of the formal test, the two-dimensional temperature distribution analysis of supersonic flow is realized. Then, a signal synchronization generating device is used to synchronously implement a two-dimensional flow field velocity measurement device, a two-dimensional temperature field measurement device and a static pressure measurement to obtain simultaneous and frequency test data. Then, the two-dimensional velocity and temperature distribution can be inverted by an algorithm, and the specific heat ratio and gas constant can be obtained based on the known test gas components. Finally, according to the definition of Mach number, the four data parameters of specific heat ratio, gas constant, flow velocity and temperature distribution are used to construct the two-dimensional Mach number distribution of supersonic flow.

[0035] The supersonic flow two-dimensional Mach number distribution field measurement method provided by the present invention adopts a supersonic flow two-dimensional Mach number distribution field measurement system to measure the supersonic flow two-dimensional Mach number distribution field, and obtains the two-dimensional Mach number distribution of the supersonic flow field by non-invasive measurement means. Compared with the traditional invasive measurement means, it basically eliminates the interference of the test element on the flow field, reduces the error caused by the insufficient response time of the test element, and improves the temporal and spatial resolution of the test results. In addition, the present invention uses a diffractive optical element to achieve the ability to improve the test dimension of the femtosecond laser electron excitation marking technology, from the traditional one-dimensional single point / quasi-two-dimensional single line to the two-dimensional multi-point / two-dimensional dot matrix test level. In addition, based on the excitation and marking of molecules / atoms in the supersonic flow field, the two-dimensional velocity and temperature distribution of the supersonic flow can be obtained simultaneously and at the same place. Under the known gas composition and the measured static pressure level, the two-dimensional Mach number distribution can be inverted. The important flow field information of velocity, temperature and Mach number distribution obtained by the test can support experimental analysis, numerical model verification and earth-sky correlation construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings of the present invention are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not necessarily be consistent with the actual products.

[0037] Figure 1 It is a structural schematic diagram of a supersonic flow two-dimensional Mach number distribution field measurement system in an embodiment of the present invention;

[0038] Figure 2 yes Figure 1 Schematic diagram of the structure of the mid-supersonic flow two-dimensional Mach number distribution field measurement system after cutting off part of the test section and removing the test section outlet;

[0039] Figure 3 It is a schematic flow chart of a method for measuring a two-dimensional Mach number distribution field of a supersonic flow in an embodiment of the present invention.

[0040] In the figure: 1: nozzle; 2: test section; 3: test section outlet; 4: static pressure probe; 5: first high-transmittance ultraviolet window; 6: high-transmittance near-infrared window; 7: second high-transmittance ultraviolet window; 8: femtosecond laser; 9: first reflector; 10: diffraction optical element; 11: plano-convex lens; 12: dichroic mirror; 13: first optical filter; 14: optical lens; 15: first high-speed image intensifier; 16: first high-speed camera; 17: high-frequency pump laser; 18: first reversing reflector; 19: second reversing reflector; 20: rotatable half-wave plate; 21: beam splitter; 22: laser energy meter; 23: third reversing reflector; 24: sheet light generating component; 25: second optical filter; 26: ultraviolet lens; 27: second high-speed image intensifier; 28: second high-speed camera; 29: timing controller; 30: computer. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not 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.

[0042] The present invention is based on two non-invasive laser diagnostic technologies, femtosecond laser electronic excitation tagging (FLEET) and Rayleigh scattering (RS). Femtosecond laser electronic excitation tagging is a molecular tracing test technology. When a femtosecond laser of a specific wavelength is used to irradiate the molecule to be measured, the molecule is dissociated by the high energy density laser and transitions from the ground state to the excited state. The dissociated products in the excited state will spontaneously repolymerize and return to the ground state, and fluorescence will be emitted in the process to track the position of the molecule. Rayleigh scattering is a common elastic scattering phenomenon in nature, which occurs when the wavelength of the excitation light is much larger than the characteristic scale of the substance to be measured. The scattering signal intensity of Rayleigh scattering is related to the molecular number density and the type of substance. By constructing the relationship between the molecular number density of known substances in the measured field and the temperature and pressure, the state of the field to be measured can be characterized. Since Rayleigh scattering is elastic scattering, the wavelength of the scattering signal is consistent with the excitation wavelength. The present invention utilizes the synchronous measurement of the dot matrix FLEET technology and the two-dimensional RS technology, realizes the synchronous measurement of the two-dimensional velocity and temperature of the supersonic flow field by two sets of laser diagnostic test devices and optical paths, and constructs a two-dimensional Mach number distribution field accordingly.

[0043] It should be noted that, generally speaking, the scenarios in which the technology of the present invention is used to implement two-dimensional Mach number distribution measurement already have facilities for realizing observable high-altitude and high-speed incoming flow conditions. Therefore, the supersonic flow field generating device in this embodiment is only for illustrative purposes.

[0044] In the present invention, the area to be tested can be the test section of the wind tunnel or an open space. It should be noted that "open space" refers to a space connected to the atmosphere, that is, a space with low or no requirements for sealing.

[0045] In this embodiment, the supersonic airflow is formed by a wind tunnel, and its theoretical incoming flow Mach number is obtained by calculation. The working fluid of the supersonic airflow is preferably air or nitrogen.

[0046] like Figure 1 and Figure 2As shown, the supersonic flow field generating device in the embodiment of the present invention includes a nozzle 1, a test section 2 and a test section outlet 3 with a vacuum pump, the test section outlet 3 and the nozzle 1 are respectively located at two ends of the test section 2 and are connected to the test section 2, and a plurality of optical windows are also provided on the test section 2. In the present embodiment, the plurality of optical windows include a first high-transmittance ultraviolet window 5, a high-transmittance near-infrared window 6 and a second high-transmittance ultraviolet window 7, which are used for the dot matrix light and the two-dimensional sheet laser to enter the test section 2 and for the first image signal acquisition device and the second image signal acquisition device to acquire signals in the test section 2.

[0047] See also Figure 1~Figure 3 As shown, the following constructs a supersonic flow two-dimensional Mach number distribution field measurement system based on the above-mentioned supersonic flow field generating device and uses it to perform supersonic flow two-dimensional Mach number distribution field measurement:

[0048] The first step is to construct supersonic flow conditions: a variety of technologies can be used to realize a high-temperature and high-pressure gas source upstream of the nozzle 1, which expands through the nozzle 1 to form a supersonic airflow, and then the supersonic airflow flows through the test section 2 and the test section outlet 3 with a vacuum pump to complete the airflow path. A static pressure probe 4 is installed in the test section 2 to measure the static pressure level in the test section 2 when the supersonic airflow passes or no airflow passes. The test section 2 is composed of a first high-transmittance ultraviolet window 5 facing the two-dimensional temperature field measurement device, a high-transmittance near-infrared window 6 facing the two-dimensional flow field velocity measurement device, and a second high-transmittance ultraviolet window 7 arranged perpendicular to the supersonic incoming flow and the first high-transmittance ultraviolet window 5. The optical window of the test section 2 is sealed. It should be noted that if the facility for realizing supersonic airflow is in an open space, the construction of the supersonic flow condition in this measurement system diagram only needs to retain the nozzle 1.

[0049] In this embodiment, the incoming flow of the supersonic gas flow is hot perfect gas, that is, the incoming flow pressure is not higher than the pressure at which the gas is liquefied, the temperature is not lower than the temperature at which the gas is liquefied, and the incoming flow temperature is not higher than the temperature at which the gas dissociates, ionizes or chemically reacts.

[0050] In this embodiment, the first image signal acquisition device includes a first high-speed camera 16, a first high-speed image intensifier 15, an optical lens 14 and a first optical filter 13. The optical lens 14 is installed on the first high-speed camera 16 through the first high-speed image intensifier 15, and the first optical filter 13 is located in front of the optical lens 14. The second image signal acquisition device includes a second high-speed camera 28, a second high-speed image intensifier 27, an ultraviolet lens 26 and a second optical filter 25. The ultraviolet lens 26 is installed on the second high-speed camera 28 through the second high-speed image intensifier 27, and the second optical filter 25 is located in front of the ultraviolet lens 26.

[0051] The second step is to build the optical path of the two-dimensional flow field velocity measurement device based on femtosecond laser electron excitation labeling: the laser generated by the femtosecond laser 8 (the laser wavelength depends on the test component, for example, when the measurement object is N2, an 800 nm laser can be selected) is adjusted in the emission direction through the first reflector 9, and an M×M lattice diffractive optical element 10 is introduced. According to the emission light separation angle and full-angle parameters of the diffractive optical element 10, and the optical distance between the plane of the test area of ​​the test section 2 and the diffractive optical element 10, a plano-convex lens 11 with a suitable focal length and size is selected, so that the lattice light can be contained in the plano-convex lens 11, and after changing the direction again through the dichroic mirror 12, the lattice light can be well focused on the test area of ​​the test section 2. In one example, a femtosecond laser with a wavelength of 800 nm, a pulse width of less than 150 fs, a frequency of more than 1 kHz, and a pulse energy that satisfies: the pulse energy reaches more than 6 mJ at a frequency of 1 kHz; a first high-speed camera, an optical lens, and a first optical filter that have a strong response to optical signals in the range of 380-450 nm are selected, and the frequencies of the first high-speed camera and the first high-speed image intensifier are more than 10 kHz; a diffractive optical element with a separation angle of less than 2° is selected to facilitate the flexible construction of the optical path; and a dichroic mirror that fully reflects 800 nm and transmits visible light is selected.

[0052] The third step is to build an optical path for a two-dimensional temperature field measurement device based on Rayleigh scattering: the laser generated by the high-frequency pump laser 17 (a laser wavelength that does not interfere with the overall system can be selected, such as a high-frequency 355 nm ultraviolet laser) is adjusted in the emission direction and emission height via the first reversing reflector 18 and the second reversing reflector 19, and then passes through the rotatable half-wave plate 20 to adjust the laser polarization direction. The laser then passes through the beam splitter 21 to reflect a small portion of the energy (for example, less than 10%) of the laser to the laser energy meter 22. The remaining large amount of laser energy passes through the beam splitter 21, and the incident direction is adjusted by the third reversing reflector 23 and introduced into the sheet light generating component 24. The angle of the lens in the sheet light generating component 24 is adjusted so that the two-dimensional sheet laser is parallel to the plane of the dot matrix light. The distance between the lenses in the sheet light generating component 24 is adjusted so that the two-dimensional sheet laser coincides with the center of the dot matrix light. In one example, a high-frequency pumped Nd:YAG laser with a wavelength of 355 nm, a frequency of more than 10 kHz, and a pulse energy that satisfies: the pulse energy reaches more than 300 mJ at a frequency of 10 kHz; a 355±10 nm bandpass filter, a lens with high ultraviolet light transmittance, and a second high-speed camera with strong ultraviolet light response are selected, and the frequencies of the second high-speed camera and the second high-speed image intensifier are more than 10 kHz; a half-wave plate that can adjust the polarization direction of the 355 nm laser is selected; a plano-concave lens, a plano-convex lens, and a plane mirror assembly are selected to modulate the laser beam into laser sheet light, and the focal length and length of the sheet light are adjustable.

[0053] It is worth noting that, in this embodiment, the first reversing reflector 18, the second reversing reflector 19 and the third reversing reflector 23 mainly play the role of reversing the light path in the light path, which facilitates the layout of the light path and the collection device.

[0054] The fourth step is the calibration of the camera windows of the first image signal acquisition device and the second image signal acquisition device: under the condition of removing the first optical filter 13 and the second optical filter 25, according to the required shooting window size, adjust the distance between the first image signal acquisition device, the second image signal acquisition device and the test section 2, and adjust the focal length of the optical lens 14 and the ultraviolet lens 26 respectively, so that the first image signal acquisition device and the second image signal acquisition device can image clearly and the window positions are approximately consistent. Place a calibration plate in the test section 2, adjust the gate width and magnification factor of the first high-speed image intensifier 15 and the second high-speed image intensifier 27 respectively, and complete the simultaneous shooting of the calibration plate image. The calibration plate image shot at the same time will be used as a reference for the subsequent image alignment processing. After completing the focus and field of view calibration, install the first optical filter 13 and the second optical filter 25. In one example, the camera window calibration uses a standard spatial three-dimensional calibration plate, such as calibration plate 106-10, LaVision; the spatial resolution test uses a standard resolution plate, such as resolution plate USAF-1951.

[0055] Step 5, RS laser polarization direction adjustment: fill the test section 2 with gas of known components, and close the upstream and downstream flow paths of the test section 2. Use the timing controller 29 to trigger the high-frequency pump laser 17, the second high-speed image intensifier 27 and the second high-speed camera 28 separately, adjust the gate width, magnification factor and delay of the second high-speed image intensifier 27, observe and compare the signals of the laser light passing through the area and the signal of the area not passing through in the imaging results, and greatly adjust the angle of the rotatable half-wave plate 20 to confirm whether the Rayleigh scattering signal can be collected. After determining that the signal can be collected, finely adjust the angle of the rotatable half-wave plate 20 and record the imaging signal. According to the relationship between the imaging signal and the change of the half-wave plate angle, determine the angle of the rotatable half-wave plate 20 corresponding to the vertical polarization (strongest signal) and horizontal polarization (weakest signal) of the laser for subsequent RS signal collection settings. In one example, the rotatable half-wave plate 20 is adjusted by a half-wave plate frame that can automatically step, rotate and record. A half-wave plate suitable for 355 nm laser is used, and the half-wave plate angle and the average RS signal intensity of the target test area are recorded at the same time. A curve of the average RS signal intensity changing with the half-wave plate angle is plotted. The result is similar to a sine curve, with the peak position corresponding to the vertical polarization angle and the trough position corresponding to the horizontal polarization angle.

[0056] Step 6, RS calibration field signal acquisition: Take the known component gas filled into the test section 2 in the fifth step as the test object, adjust the rotatable half-wave plate 20 to the vertical polarization position, make the laser energy meter 22 and the static pressure probe 4 enter the state of preparation for acquisition, and arrange several thermocouples in the area of ​​the test section that does not interfere with RS shooting. After completing the above operations, confirm that the second optical filter 25 has been installed and the focal length of the ultraviolet lens 26 is appropriate, and use the gate width, magnification factor and delay parameters of the second high-speed image intensifier 27 determined in the fifth step to collect RS calibration field signals. After completing the signal acquisition, record the calibration field signal S 0, the laser energy obtained by the laser energy meter 22 during calibration I 0, static pressure obtained by static pressure probe 4 during calibration p 0, the average temperature obtained by several thermocouples during calibration T 0, gas composition during calibration X 0, to support the subsequent signal processing of the two-dimensional temperature field. After the calibration is completed, take out the thermocouple installed in the test section 2 to prevent it from interfering with the flow field during subsequent tests. In one example, nitrogen is used as the test gas for RS calibration field signal acquisition. The gas is left to stand still and the pressure of the test section is maintained at atmospheric pressure. The temperature of the test section is collected by thermocouples, and the calibration field Rayleigh scattering signal collects the results under vertical polarization and horizontal polarization of the laser respectively to eliminate the influence of other interference signals. It should be noted that any gas of known composition can be selected as the test gas when collecting Rayleigh scattering calibration field signals. Of course, it is preferred to select the gas required for the test to avoid preparing multiple gas sources.

[0057] Step 7: The parameters of the first image signal acquisition device are determined in three aspects: 1. Theoretical calculation is used to determine the field width in the direction of the expected maximum mainstream velocity based on the field size determined in step 4. L e . According to the expected speed U e , calculate the expected signal out of the window time Δ t e , Δ t e = L e / U e According to the expected number of FLEET single shot shots N e , calculate the expected acquisition frequency of the first high-speed image intensifier 15 and the first high-speed camera 16 f e , f e = N e / Δ te 2. Physical delay measurement: the trigger frequency of the femtosecond laser 8 f fe Set to 1 / Δ t e . After completing the calculation and setting, introduce a supersonic airflow of known components into the test section 2, and use an oscilloscope and a photomultiplier tube to preliminarily determine the approximate range of the delay time between the laser trigger signal and the fluorescence signal. Adjust the delay, gate width and amplification factor of the first high-speed image intensifier 15 until the signal can be collected. Then give a moderate amplification factor, gradually reduce the gate width, and match the appropriate delay to minimize interference signals entering the camera. Finally, determine the delay under a smaller gate width and increase the amplification factor until obvious salt and pepper noise appears and stop. 3. Actual operation adjustment. After completing the parameter setting of the first high-speed image intensifier 15, test the effect of the expected acquisition frequency parameters, adjust them according to the actual situation, and obtain the appropriate number of FLEET single-shot excitation shots. N , the acquisition frequency of the first high-speed image intensifier 15 and the first high-speed camera 16 f , the trigger frequency of the femtosecond laser 8 f f .

[0058] Step 8, synchronization of the two-dimensional flow field velocity measurement device and the two-dimensional temperature field measurement device: In this embodiment, the signal synchronization generating device includes a computer 30 and a timing controller 29, the timing controller 29 is respectively connected to the femtosecond laser 8, the first image signal acquisition device, the high-frequency pump laser, the second image signal acquisition device, and the supersonic flow field generating device, the supersonic flow field generating device is connected to the static pressure measuring device, and the computer is respectively connected to the first image signal acquisition device, the second image signal acquisition device, the static pressure measuring device and the laser energy meter. Figure 1 and Figure 2As shown, the timing controller 29 is connected to the upstream trigger device of the nozzle 1, the femtosecond laser 8, the first image signal acquisition device, the second image signal acquisition device, and the high-frequency pump laser 17 by using signal lines (lines shown by dotted lines in the figure). The upstream trigger device of the nozzle 1 is connected to the static pressure probe 4 by using signal lines. At the beginning of the test, the upstream sensor of the nozzle 1 receives the airflow flow signal, the output level is increased, and the static pressure probe 4 is triggered to work. The timing controller 29 works with the set output frequency, output voltage, and pulse width, and triggers the two-dimensional flow field velocity measurement device and the two-dimensional temperature field measurement device to run in different channels respectively. The rising edge of the received signal of the laser energy meter 22 corresponds to the trigger point of the signal synchronization generating device, so as to realize the simultaneous operation of each measuring device. Of course, according to the functional scope of the timing controller 29, in some embodiments, additional relays or more timing controllers can be added to the measurement system to realize the above-mentioned synchronization method, which will not be repeated here. In other embodiments, synchronization can use relays to realize the function of single triggering to start the cycle operation, and can also use multiple timing controllers in parallel to realize the function of synchronous operation of different frequency devices.

[0059] Step 9, formal test, signal acquisition: Use signal lines to connect the computer 30 to the first image signal acquisition device, the second image signal acquisition device, the laser energy meter 22, and the static pressure probe 4. Start the supersonic flow field generating device. When the incoming flow passes through the sensor upstream of the nozzle 1, the static pressure probe 4 and the timing controller 29 are triggered to start working. At the same time, the femtosecond laser 8 and the high-frequency pump laser 17 start working at the set frequency and delay. Part of the laser energy emitted by the high-frequency pump laser 17 I' ( t ) is received by the laser energy meter 22. The above process computer 30 will obtain the static pressure test data related to time p ( t ) and laser energy test data I ( t )= I' ( t ) / C, where C is the ratio coefficient of the laser energy allocated by the beam splitter 21 to the laser energy meter 22. When the supersonic flow passes through the area to be measured, the computer 30 will receive the FLEET signal and the RS signal. The FLEET signal image is generated at each shooting time interval 1 / f Obvious displacement can be observed in the internal energy, and the test condition Rayleigh scattering distribution field signal S ( x , y , t ) are also recorded.

[0060] Step 10: FLEET image signal processing: First, the centroid method is used to accurately obtain the spatial position of each point in the femtosecond laser dot matrix. Combined with the Rayleigh scattering results, interpolation processing is used in the continuously changing area to enrich the number of measurement points. After that, the displacement of each measurement point Δ can be analyzed from multiple test results. s ( x , y , t ), and decompose it into the flow displacement Δ x ( x , y , t ) and tangential displacement Δ y ( x , y , t ). Based on the shooting time interval of FLEET signal 1 / f Under the premise that the supersonic jet flows in the tangential direction is isotropic, the velocity at each laser dot array measurement point at each moment is obtained. .

[0061] Step 11: RS image signal processing: Based on the Rayleigh scattering signal intensity relationship, the two-dimensional temperature field is obtained in combination with the calibration results of step 6. Test conditions: Rayleigh scattering distribution field signal is ,in C s is a constant related to the optical system. When the system is fixed, the constant will no longer change; X i The gas component i The mole fraction of For gas components i The scattering cross-section coefficient of , both of which can be obtained by looking up the table under the condition of known gas composition and excitation wavelength; k is the Boltzmann constant. The calibration field signal is By performing ratio processing on the Rayleigh scattering distribution field signal under the test condition and the calibration field signal, the optical system related constants and the Boltzmann constant can be eliminated, and finally the two-dimensional temperature distribution can be obtained: .

[0062] Step 12: Calculation of the two-dimensional Mach number distribution field results: Combined with the calibration plate images taken by the first image signal acquisition device and the second image signal acquisition device in step 4, the velocity results and temperature results obtained in steps 10 and 11 are analyzed by image stretching and cropping algorithms, and finally the results of the two are made consistent in space, dimension and time. On this basis, using the two-dimensional temperature results of step 11, the two-dimensional distribution of local sound speed can be obtained. ,in γ is the specific heat ratio, R is the gas constant, which can be obtained by looking up the table under known composition and state conditions. According to the calculation formula of Mach number Substituting the two-dimensional velocity result of step 10 and the two-dimensional distribution of local sound speed mentioned above, we can get the two-dimensional Mach number distribution field ,Right now .

[0063] The above embodiments are for the case where the supersonic airflow is formed by a wind tunnel, that is, the waiting area is located in a wind tunnel test. It is worth noting that if the measurement is performed in an open space, the measurement method and the measurement device used are basically the same, except that there is no need to set an optical window and collect signals through the optical window. The measurement method and the measurement device have been specifically described in the above embodiments and will not be repeated here.

[0064] Any details not described in detail in the present invention are common knowledge or prior art in the art.

[0065] 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 not every embodiment contains only one independent technical solution. In the absence of a conflict of solutions, the various technical features mentioned in each embodiment can be combined in any manner to form other implementation methods that can be understood by those skilled in the art.

[0066] In addition, without departing from the scope of the present invention, the technical solutions described in the aforementioned embodiments may be modified, or some of the technical features may be replaced by equivalents, without causing the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A supersonic flow two-dimensional Mach number distribution field measurement system, comprising a supersonic flow field generating device, for simulating and generating observable high-altitude high-speed incoming flow conditions, characterized in that: Also includes: A static pressure measuring device for measuring the static pressure level of the area to be measured when supersonic airflow passes through or when no airflow passes through; The two-dimensional flow field velocity measurement device based on femtosecond laser electronic excitation marking comprises a femtosecond laser, a first reflector, a lattice diffraction optical element, a plano-convex lens, and a dichroic mirror arranged in sequence, and is used to shape the laser light generated by the femtosecond laser into a lattice light and focus it on the area to be measured, and also includes a first image signal acquisition device for acquiring the positions of the marked molecules or atoms at different times; The two-dimensional temperature field measuring device based on Rayleigh scattering comprises a high-frequency pump laser, a rotatable half-wave plate, a beam splitter and a sheet light generating component which are arranged in sequence. After the laser light generated by the high-frequency pump laser passes through the beam splitter, part of the laser light passes through the sheet light generating component and becomes a two-dimensional sheet laser light and can coincide with the plane of the lattice light, and the focal length of the two-dimensional sheet laser light can coincide with the center of the lattice light. The device also comprises a laser energy meter for receiving another part of the laser light after passing through the beam splitter, and also comprises a second image signal acquisition device for acquiring Rayleigh scattering signals. A signal synchronization generating device for timing control of the supersonic flow field generating device, the two-dimensional flow field velocity measuring device and the two-dimensional temperature field measuring device; Obtain consistent frequency from laser energy meter f Laser energy data I ( t ), static pressure data is obtained by static pressure measuring device p ( t ), the flow displacement Δ of the femtosecond laser electron excitation marking signal is obtained by measuring the two-dimensional flow field velocity based on the femtosecond laser electron excitation marking. x ( x , y , t ) and tangential displacement Δ y ( x , y , t ), the Rayleigh scattering distribution field signal under the test condition is obtained by the two-dimensional temperature field measurement device based on Rayleigh scattering S ( x , y , t );The calibration field Rayleigh scattering signal is obtained by the calibration process S 0 ( x , y ), calibration field average temperature T 0 , average laser energy during calibration I 0 , calibration field static pressure level p 0 and the Rayleigh scattering cross section coefficient of the gas component during calibration Specific heat ratio γ , gas constant R and Rayleigh scattering cross section coefficient of the gas component during the experiment Obtained by looking up a table of known gas components; The two-dimensional Mach number distribution field is obtained by processing and analyzing using the following formula: 。 2. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 1, characterized in that: The first image signal acquisition device includes a first high-speed camera, a first high-speed image intensifier, an optical lens and a first optical filter. The optical lens is installed on the first high-speed camera through the first high-speed image intensifier, and the first optical filter is located in front of the optical lens.

3. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 1, characterized in that: The second image signal acquisition device includes a second high-speed camera, a second high-speed image intensifier, an ultraviolet lens and a second optical filter. The ultraviolet lens is installed on the second high-speed camera through the second high-speed image intensifier, and the second optical filter is located in front of the ultraviolet lens.

4. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 1, characterized in that: The supersonic flow field generating device includes a nozzle, a test section and a test section outlet with a vacuum pump. The test section outlet and the nozzle are respectively located at two ends of the test section and are connected to the test section. The test section is also provided with a plurality of optical windows for the dot matrix light and the two-dimensional sheet laser to enter the test section and for the first image signal acquisition device and the second image signal acquisition device to acquire signals in the test section.

5. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 4, characterized in that: The static pressure measuring device is a static pressure probe, which is fixed in the test section, arranged in a position parallel to the direction of the maximum velocity component of the supersonic airflow, and located in a non-optical measurement area.

6. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 1, characterized in that: The signal synchronization generating device includes a computer and a timing controller. The timing controller is respectively connected to the femtosecond laser, the first image signal acquisition device, the high-frequency pump laser, the second image signal acquisition device and the supersonic flow field generating device by signal. The supersonic flow field generating device is connected to the static pressure measuring device by signal. The computer is respectively connected to the first image signal acquisition device, the second image signal acquisition device, the static pressure measuring device and the laser energy meter by signal.

7. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 1, characterized in that: The two-dimensional temperature field measuring device includes one or more reversing reflectors for reversing the optical path.

8. The supersonic flow two-dimensional Mach number distribution field measurement system according to claim 1, characterized in that: The incoming flow of supersonic airflow is a thermally complete body.

9. A method for measuring a two-dimensional Mach number distribution field of a supersonic flow, characterized in that: The measurement is performed using the supersonic flow two-dimensional Mach number distribution field measurement system as described in any one of claims 1 to 8, comprising the following steps: S100, calibrates the supersonic flow two-dimensional Mach number distribution field measurement system, including: Camera window calibration, Rayleigh scattering laser polarization direction adjustment, Rayleigh scattering calibration field signal acquisition and first image signal acquisition device parameter determination; S200, test data collection and processing analysis, including: Obtain consistent frequency from laser energy meter f Laser energy data I ( t ), static pressure data is obtained by static pressure measuring device p ( t ), the flow displacement Δ of the femtosecond laser electron excitation marking signal is obtained by measuring the two-dimensional flow field velocity based on the femtosecond laser electron excitation marking. x ( x , y , t ) and tangential displacement Δ y ( x , y , t ), the Rayleigh scattering distribution field signal under the test condition is obtained by the two-dimensional temperature field measurement device based on Rayleigh scattering S ( x , y , t );The calibration field Rayleigh scattering signal is obtained by the calibration process S 0 ( x , y ), calibration field average temperature T 0 , average laser energy during calibration I 0 , calibration field static pressure level p 0 and the Rayleigh scattering cross section coefficient of the gas component during calibration Specific heat ratio γ , gas constant R and Rayleigh scattering cross section coefficient of the gas component during the experiment Obtained by looking up a table of known gas components; The two-dimensional Mach number distribution field is obtained by processing and analyzing using the following formula: 。 10. The method for measuring the two-dimensional Mach number distribution field of supersonic flow according to claim 9, characterized in that: The camera window calibration uses a standard space three-dimensional calibration plate; The spatial resolution test uses a standard resolution plate.

11. The method for measuring the two-dimensional Mach number distribution field of supersonic flow according to claim 9, characterized in that: The polarization direction of the Rayleigh scattered laser is adjusted using a half-wave plate frame that can automatically step, rotate and record. The angle of the rotatable half-wave plate and the average Rayleigh scattering signal intensity of the measured area are recorded at the same time. A curve of the average Rayleigh scattering intensity changing with the angle of the rotatable half-wave plate is plotted. The result is an approximate sine curve, with the peak position corresponding to the vertical polarization angle and the trough position corresponding to the horizontal polarization angle.

12. The method for measuring the two-dimensional Mach number distribution field of supersonic flow according to claim 9, characterized in that: If the area to be tested is located in the test section of the wind tunnel, the Rayleigh scattering calibration field signal acquisition uses a known gas as the test gas, the gas is left to stabilize, the pressure of the test section is maintained at the atmospheric pressure level, the temperature of the test section is collected by a thermocouple, and the calibration field Rayleigh scattering signal collects the results under the vertical polarization and horizontal polarization of the laser respectively to eliminate the influence of other interference signals; If the area to be tested is located in an open space, which is connected to the atmosphere, air is used as the test gas for Rayleigh scattering calibration field signal collection. The gas is left to stand still and the pressure in the open space is maintained at the atmospheric pressure level. The temperature in the open space is collected by a thermocouple. The calibration field Rayleigh scattering signal collects the results under vertical and horizontal polarization of the laser respectively to eliminate the influence of other interference signals.

13. The method for measuring the two-dimensional Mach number distribution field of supersonic flow according to claim 9, characterized in that: When determining the parameters of the first image signal acquisition device, after reducing the visible light interference in the area to be measured to the minimum, three specific processes of theoretical calculation, physical delay measurement and actual operation adjustment are adopted to complete the determination of the acquisition system parameters.

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