Method and system for large scale high enthalpy wind tunnel flow field structure visualization

Abstract

The present application belongs to the technical field of wind tunnel measurement, and discloses a method and system for large-scale high-enthalpy wind tunnel flow field structure visualization. The method comprises: generating a sheet light with a width of greater than or equal to 300 mm by using a continuous laser with a wavelength of 811.5 nm, irradiating the wind tunnel flow field to excite naturally occurring metastable argon atoms and generate a fluorescent signal; in a direction perpendicular to the sheet light plane, the fluorescent signal is collected by a narrow-band filter with a center wavelength of 910 nm and a bandwidth of less than or equal to 5 nm; the sheet light and the signal collection device are synchronously scanned and moved to obtain three-dimensional flow field data; and the high-supersonic wind tunnel flow field structure with a total enthalpy of greater than or equal to 10 MJ / kg and a wind tunnel aperture of greater than or equal to 500 mm is reconstructed based on the three-dimensional flow field data. The present application effectively solves the problem that the prior art cannot meet the fine flow field visualization of large-scale high-enthalpy wind tunnels, realizes the measurement capability of tracer-free, wide range, and being suitable for extreme environments and high model near-wall surfaces, and provides a new powerful tool for high-supersonic research.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wind tunnel measurement, in particular to a method and system for large-scale high-enthalpy wind tunnel flow field structure visualization. BACKGROUND

[0002] The large-scale high-enthalpy wind tunnel is a key facility for simulating extreme hypersonic flight environment and testing high-speed aircraft material performance. However, the total temperature of the incoming flow of the wind tunnel is usually higher than 3000K, the total enthalpy is as high as 10MJ / kg, and the test wind tunnel aperture is usually larger than 500mm, and the test model size is usually larger than 200mm, which brings great difficulties to the evaluation of aircraft aerodynamic thermal performance and the study of high-temperature non-equilibrium flow characteristics near the wall.

[0003] At present, the flow field visualization of large-scale high-enthalpy wind tunnels mainly adopts spontaneous radiation imaging, schlieren measurement and laser-induced fluorescence (PLIF) imaging methods. Spontaneous radiation imaging mainly uses passive measurement to obtain the macroscopic characteristics of the flow field in front of the hypersonic aircraft. The schlieren measurement technology can obtain the refractive index and density gradient distribution of the flow field to be measured, and is widely used for observing the boundary layer, shock wave and hypersonic flow measurement. However, these two methods are limited by the effect of line integral, and it is difficult to obtain the fine features of the complex flow structure of the aircraft. The laser-induced fluorescence imaging method based on gas tracer combines gas tracer and laser sheet imaging, which can analyze the structural characteristics of complex turbulent flow field with high temporal and spatial resolution. At present, domestic and foreign research teams have realized the display of complex flow in the near-field region of the aircraft by using NO, NO2 and other gas tracers. The sampling frequency of NO-PLIF has reached the order of 100kHz. However, this method has a narrow measurement cross-sectional size, usually within 50mm, which is difficult to apply to large-size model wind tunnel measurement tests. At the same time, the total enthalpy of the flow field to be measured is high, and most of the gas molecules are in the excited state, resulting in strong spontaneous radiation interference of the flow field to be measured, weak PLIF signal intensity, and low signal-to-noise ratio of the PLIF measurement image, which cannot meet the needs of fine visualization of the flow field structure of large-scale high-enthalpy wind tunnels.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] To solve the technical problems in the background art, the present application provides a method and system for large-scale high-enthalpy wind tunnel flow field structure visualization.

[0006] To achieve the above purpose, the first technical solution adopted by the present application is:

[0007] The method for large-scale high-enthalpy wind tunnel flow field structure visualization comprises:

[0008] The continuous laser with a wavelength of 811.5 nm is used to generate a sheet light with a width of greater than or equal to 300 mm, and the flow field of the wind tunnel is irradiated to excite naturally existing metastable argon atoms and generate a fluorescent signal;

[0009] The fluorescent signal is collected in a direction perpendicular to the plane of the sheet light through a narrow-band filter with a center wavelength of 910 nm and a bandwidth of less than or equal to 5 nm;

[0010] The sheet light and the signal collection device are synchronously scanned and moved to obtain three-dimensional flow field data;

[0011] Based on the three-dimensional flow field data, the flow field structure of a hypersonic wind tunnel with a total enthalpy of greater than or equal to 10 MJ / kg and a wind tunnel aperture of greater than or equal to 500 mm is reconstructed.

[0012] Preferably, the thickness of the sheet light is less than or equal to 1 mm.

[0013] Preferably, the signal collection device is an infrared high-speed camera.

[0014] Preferably, the synchronous scanning and movement is realized through an electric displacement table or a galvanometer.

[0015] Preferably, the method further comprises the steps of synchronizing the timing of the wind tunnel operation, the laser irradiation and the signal collection.

[0016] Preferably, the original PLIF signal data obtained by the synchronous scanning and movement is filtered and feature-extracted to obtain the three-dimensional flow field data.

[0017] Preferably, the filtering method comprises median filtering or adaptive filtering; and the feature extraction method comprises Fourier frequency statistics or intensity probability density statistics.

[0018] The second technical solution adopted by the present application is:

[0019] The system for large-scale high-enthalpy wind tunnel flow field structure visualization comprises:

[0020] The signal generation module is used to generate a sheet light with a width of greater than or equal to 300 mm by using a continuous laser with a wavelength of 811.5 nm, and the flow field of the wind tunnel is irradiated to excite naturally existing metastable argon atoms and generate a fluorescent signal;

[0021] The signal collection module is used to collect the fluorescent signal in a direction perpendicular to the plane of the sheet light through a narrow-band filter with a center wavelength of 910 nm and a bandwidth of less than or equal to 5 nm;

[0022] The scanning and movement module is used to synchronously scan and move the sheet light and the signal collection device to obtain three-dimensional flow field data.

[0023] Reconstruction module, for reconstructing the hypersonic wind tunnel flow field structure with total enthalpy >= 10 MJ / kg and wind tunnel caliber >= 500 mm based on the three-dimensional flow field data.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The present application creatively transplants Ar*-PLIF from the field of plasma diagnosis to the extreme high-enthalpy wind tunnel environment, ingeniously uses the naturally existing Ar* in the wind tunnel as a non-interference tracer, does not need to inject any external tracer (such as NO, NO2, solid particles, etc.) into the flow field, completely avoids the risk of changing the chemical reaction process, thermodynamic state or polluting the experimental facility due to the addition of the tracer, and realizes truly "non-interference, tracer-free" measurement.

[0026] The present application innovatively designs and realizes the super-large size laser sheet light of >300 mm, specifically proposes the key scheme of using a 910 nm narrow-band (<=5 nm) filter to suppress strong background noise, can effectively suppress the extremely strong spontaneous radiation background light in the extreme environment with total enthalpy >= 10 MJ / kg, successfully extract the weak effective fluorescent signal, obtain the flow field image with excellent signal-to-noise ratio, and break through the signal-to-noise ratio bottleneck of fluorescent imaging in the high-enthalpy strong noise environment.

[0027] The present application first realizes the wide-range (>=300 mm), high spatial resolution three-dimensional fine structure imaging of the model periphery flow field with a size of >=200 mm in a large-scale wind tunnel with a caliber of >=500 mm, and solves the problem of global and fine visualization of large-scale flow field. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The flowchart of the method for large-scale high-enthalpy wind tunnel flow field structure visualization provided for the embodiments of the present application;

[0029] Figure 2 The structure diagram of the system for large-scale high-enthalpy wind tunnel flow field structure visualization provided for the embodiments of the present application;

[0030] Figure 3 The structure diagram of the system for large-scale high-enthalpy wind tunnel flow field structure visualization provided for one specific embodiment of the present application;

[0031] Figure 3Fig. 1 is a schematic diagram of a laser system according to the present application, wherein 1 is a continuous near-infrared laser, 2 is a laser beam, 3 is a mirror, 4 is a first galvanometer, 5 is a second galvanometer, 6 is a direction coordinate system, 7 is a movable outgoing laser beam, 8 is a concave cylindrical mirror, 9 is a short-focus convex cylindrical mirror, 10 is a long-focus convex cylindrical mirror, 11 is a large-size laser sheet, 12 is a large-scale high-enthalpy wind tunnel, 13 is a top test window, 14 is a first time sequence controller, 15 is a time sequence control line of the first galvanometer, 16 is a time sequence control line of the second galvanometer, 17 is a front test window, 18 is a high-frame-rate fast-response infrared camera, 19 is a narrow-band filter, 20 is a three-dimensional displacement stage, 21 is a time sequence control line of the three-dimensional displacement stage, 22 is a second time sequence controller, 23 is a high-enthalpy wind tunnel start time sequence control line, 24 is a laser time sequence control line, 25 is a high-speed camera time sequence control line, and 26 is a computer. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0033] Reference Figure 1 The first embodiment of the present application provides a method for large-scale high-enthalpy wind tunnel flow field structure visualization, comprising:

[0034] S101, a continuous laser with a wavelength of 811.5 nm is used to generate a sheet light with a width of ≥300 mm, which irradiates the wind tunnel flow field to excite naturally existing metastable argon atoms and generate a fluorescence signal;

[0035] S102, in the direction perpendicular to the plane of the sheet light, the fluorescence signal is collected by a narrow-band filter with a center wavelength of 910 nm and a bandwidth of ≤5 nm;

[0036] S103, the sheet light and the signal collection device are synchronously scanned and moved to obtain three-dimensional flow field data;

[0037] S104, based on the three-dimensional flow field data, the flow field structure of a hypersonic wind tunnel with a total enthalpy of ≥10 MJ / kg and a wind tunnel aperture of ≥500 mm is reconstructed.

[0038] Argon is a kind of test gas commonly used in high-enthalpy wind tunnel simulation test, which is inert gas and does not react with components in the flow field, so that the problem of reaction of NO, OH radical and other conventional tracers with the flow field can be avoided, and it is suitable for high-temperature, high-pressure or reaction system. The argon content in the wind tunnel flow field is relatively high, and the atom is easily excited to metastable state level in high-enthalpy environment. The argon atom in metastable state has long life, is easy to be excited by laser, and has high fluorescence yield. At the same time, the pumping laser of metastable argon atom can be near-infrared laser. Compared with the traditional PLIF ultraviolet laser pumping method, the near-infrared laser is easy to produce, has high energy, and the equipment is relatively cheap, so it has broad application prospect in extremely harsh large-scale high-enthalpy wind tunnel measurement.

[0039] The traditional NO-PLIF needs to inject NO gas, which may interfere with the chemical reaction; the PIV technology needs to inject solid particles, which has the problems of poor following, pollution of equipment, and unsuitability for high-temperature flow field. The present application realizes that there is enough concentration of Ar naturally existing under the high-temperature condition of high-enthalpy wind tunnel, and gives up external tracer, and instead uses this characteristic, which is a clever idea for high-enthalpy wind tunnel environment (especially for hypersonic clean air / nitrogen wind tunnel), and creatively uses the metastable argon atom Ar* naturally produced by argon naturally existing in high-enthalpy wind tunnel working medium (air) at high temperature as an intrinsic tracer particle, so that any external tracer (such as NO, NO2, solid particles, etc.) does not need to be injected into the flow field, and the risk of changing the chemical reaction process, thermodynamic state or polluting the experimental facility due to the addition of the tracer is completely avoided.

[0040] The embodiment of the present application adopts innovative optical design to generate super-large size laser sheet light with a width of ≥300mm, which is enough to completely cover the large-size test model and its complex flow field structure. Combined with high-precision synchronous scanning technology, three-dimensional global scanning measurement of the region of interest is realized, and for the first time, the flow field region with a size of more than 300mm*300mm*100mm is finely three-dimensionally imaged, which completely changes the limitation of traditional methods that can only obtain local, two-dimensional or integrated information.

[0041] The embodiment of the present application also adopts a highly targeted 910nm narrowband (≤5nm) filter scheme. This design can extremely accurately transmit the characteristic fluorescence of metastable argon atom, and almost completely filter out the strong spontaneous emission background interference with a wide spectral range generated by high-temperature gas in high-enthalpy flow field. In the strong noise background with total enthalpy ≥10MJ / kg, the fluorescence image with excellent signal-to-noise ratio can still be obtained, which can be used for quantitative analysis, and provides reliable data for high-temperature non-equilibrium flow field research.

[0042] The embodiment of the present application combines large-size sheet light generation, accurate strong background filtering, three-dimensional scanning synchronization, high-speed imaging and other means, and cooperates with each other, to form a complete and systematic solution to the problem of fine visualization of large-scale high-enthalpy wind tunnel.

[0043] For the super large size sheet light, the application is realized by the following scheme:

[0044] 1) The continuous laser emitted laser is expanded into a large size laser sheet light by a cylindrical lens combination;

[0045] 2) The measurement position of the wind tunnel flow field to be measured is determined, and the laser sheet light is arranged in the measurement area for exciting the metastable argon atoms.

[0046] Wherein, the laser is a near-infrared continuous laser, and the emitted laser wavelength is 811.5nm; the emitted laser can be expanded into a large size laser sheet light by a cylindrical lens combination, and the sheet light size reaches more than 300mm, and the sheet light thickness is not more than 1mm. The minimum size of the flow field three-dimensional measurement range of the application is more than 300mm*300mm*100mm.

[0047] The cylindrical lens combination used in the embodiment of the application is a device commonly used in the art to obtain large size laser polarization, which generally includes a concave cylindrical mirror with a focal length of-5mm, a short-focus convex cylindrical mirror with a focal length of 400mm, and a long-focus convex cylindrical mirror with a focal length of 1000mm. In some preferred embodiments, an infrared high-speed camera is used to collect the fluorescent signal, such as a high-frame-rate fast-response infrared camera.

[0048] In some preferred embodiments, the synchronous scanning displacement is realized by a motorized displacement stage or a galvanometer. Specifically, a three-dimensional displacement stage can be used to synchronously move the high-speed camera and the displacement device, and the camera imaging surface is confocal with the laser sheet light.

[0049] In some preferred embodiments, the step of synchronizing the timing of the high-enthalpy wind tunnel start, the laser trigger and the camera shooting trigger is further included. Specifically, a timing controller can be used to synchronize the timing of the high-enthalpy wind tunnel start, the laser trigger and the camera shooting trigger, so as to ensure that the high-speed camera can clearly obtain the laser-induced fluorescence image of the metastable argon atoms in the flow field in the high-enthalpy wind tunnel.

[0050] In some preferred embodiments, during data processing and analysis, the original PLIF signal data obtained by the synchronous scanning displacement is filtered and feature extracted to obtain the three-dimensional flow field data. For example, median filtering or adaptive filtering can be used for filtering, and Fourier frequency statistics or intensity probability density statistics can be used for feature extraction.

[0051] The second embodiment of the application provides a system 200 for large-scale high-enthalpy wind tunnel flow field structure visualization, which includes a signal generation module 201, a signal acquisition module 202, a scanning displacement module 203, and a reconstruction module 204, and the specific functions of each module are as follows:

[0052] The signal generation module 201 is configured to generate a sheet light with a width of greater than or equal to 300 mm by using continuous laser with a wavelength of 811.5 nm, and irradiate the flow field of the wind tunnel to excite naturally occurring metastable argon atoms and generate a fluorescent signal;

[0053] The signal acquisition module 202 is configured to acquire the fluorescent signal by using a narrow-band filter with a center wavelength of 910 nm and a bandwidth of less than or equal to 5 nm in a direction perpendicular to the plane of the sheet light;

[0054] The scanning and moving module 203 is configured to synchronously scan and move the sheet light and the signal acquisition device to obtain three-dimensional flow field data;

[0055] The reconstruction module 204 is configured to reconstruct a hypersonic wind tunnel flow field structure with a total enthalpy of greater than or equal to 10 MJ / kg and a wind tunnel aperture of greater than or equal to 500 mm based on the three-dimensional flow field data.

[0056] The following provides specific implementations to specifically illustrate the implementation and effects of the method for visualizing the flow field structure of a large-scale high-enthalpy wind tunnel.

[0057] Embodiment

[0058] Reference Figure 3 The method for visualizing the flow field structure of a large-scale high-enthalpy wind tunnel is implemented as follows:

[0059] (1) The laser 2 (wavelength of 811.5 nm, spot diameter of 5 mm) emitted by the near-infrared continuous laser 1 is irradiated on the first galvanometer mirror 4 (x-direction scanning) and the second galvanometer mirror 5 (z-direction scanning) after being reflected by the mirror 3, and can be finely moved in two directions, as shown in the direction coordinate system 6;

[0060] (2) The movable emitted laser 7 is expanded into a large-size laser sheet light 11 (width of 400 mm, thickness of about 1 mm) after passing through the concave cylindrical lens 8 (focal length of about -5 mm), the short-focus convex cylindrical lens 9 (focal length of 400 mm), and the long-focus convex cylindrical lens 10 (focal length of about 1000 mm);

[0061] (3) The measurement position of the large-scale high-enthalpy wind tunnel 12 to be measured is determined, and the large-size laser sheet light 11 is introduced into the to-be-measured area through the top test window 13 for exciting metastable argon atoms;

[0062] (4) The first timing controller 14, the timing control line 15 of the first galvanometer mirror, and the timing control line 16 of the second galvanometer mirror are used to control the first galvanometer mirror 4 and the second galvanometer mirror 5 to scan and move the laser sheet light, so as to realize three-dimensional measurement of the to-be-measured flow field;

[0063] (5) In the direction of 90 degrees with the laser sheet light, through the front test window 17 of the wind tunnel, the metastable argon atom laser-induced fluorescence signal is collected by using a high-frame-rate fast-response infrared camera 18, and a narrow-band filter 19 is arranged in front of the high-speed camera to eliminate the interference of spontaneous radiation of other components;

[0064] (6) The high-frame-rate fast-response infrared camera is arranged on a three-dimensional displacement table 20 for fine and fast movement, and then the first time sequence controller 14 and the three-dimensional displacement table time sequence control line 21 are used to realize the synchronous movement of the high-speed camera and the galvanometer displacement device, and the imaging surface of the camera and the confocal surface of the laser sheet light;

[0065] (7) The second time sequence controller 22, the high-enthalpy wind tunnel start time sequence control line 23, the laser time sequence control line 24 and the high-speed camera time sequence control line 25 are used to synchronize the time sequence of the high-enthalpy wind tunnel start, the laser triggering and the camera shooting triggering, so that the high-speed camera can clearly obtain the metastable argon atom PLIF image in the flow field in the high-enthalpy wind tunnel, and the measurement result is input into the computer 26 for processing and analysis;

[0066] (8) Data processing and analysis: the PLIF image is filtered (median filtering, adaptive filtering) and the features (Fourier frequency statistics, intensity probability density statistics) are extracted by using Matlab software, so as to obtain the large-scale high-enthalpy wind tunnel flow field structure feature information.

[0067] The above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for large scale hypersonic wind tunnel flow field structure visualization, characterized in that, The application relates to a method for reconstructing a hypersonic wind tunnel flow field structure. The method comprises the following steps: a continuous laser with a wavelength of 811.5 nm is used to generate a sheet light with a width of greater than or equal to 300 mm and a thickness of less than or equal to 1 mm, and the sheet light is used to irradiate a wind tunnel flow field to excite naturally existing metastable argon atoms and generate a fluorescent signal; the fluorescent signal is collected through a narrow-band filter with a central wavelength of 910 nm and a bandwidth of less than or equal to 5 nm in a direction perpendicular to the plane of the sheet light; original PLIF signal data obtained through synchronous scanning and displacement of the sheet light and a signal collection device are filtered and feature-extracted to obtain three-dimensional flow field data; and a high-speed hypersonic wind tunnel flow field structure with a total enthalpy of greater than or equal to 10 MJ / kg and a wind tunnel caliber of greater than or equal to 500 mm is reconstructed based on the three-dimensional flow field data. The signal collection device is an infrared high-speed camera. The synchronous scanning and displacement is realized through an electric displacement table or a galvanometer. The method further comprises a step of synchronizing a wind tunnel operation, laser irradiation and signal collection timing.

2. The method for large-scale high-enthalpy wind tunnel flow field structure visualization according to claim 1, characterized in that, The filtering method comprises median filtering or adaptive filtering, and the feature extraction method comprises Fourier frequency statistics or intensity probability density statistics.

3. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The application relates to a method for reconstructing a hypersonic wind tunnel flow field structure.

4. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The signal generation module is used for generating a sheet light with a width of greater than or equal to 300 mm and a thickness of less than or equal to 1 mm through a continuous laser with a wavelength of 811.5 nm, and irradiating a wind tunnel flow field to excite naturally existing metastable argon atoms and generate a fluorescent signal; 5. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The signal collection module is used for collecting the fluorescent signal through a narrow-band filter with a central wavelength of 910 nm and a bandwidth of less than or equal to 5 nm in a direction perpendicular to the plane of the sheet light; 6. System for large scale hypersonic wind tunnel flow field structure visualization, characterized by, The scanning and displacement module is used for filtering and feature-extracting original PLIF signal data obtained through synchronous scanning and displacement of the sheet light and a signal collection device to obtain three-dimensional flow field data; The reconstruction module is used for reconstructing a high-speed hypersonic wind tunnel flow field structure with a total enthalpy of greater than or equal to 10 MJ / kg and a wind tunnel caliber of greater than or equal to 500 mm based on the three-dimensional flow field data. ​ ​ ​

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