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

Abstract

The invention belongs to the technical field of wind tunnel measurement, and discloses a method and system for visualization of a large-scale high-enthalpy wind tunnel flow field structure. The method comprises the following steps: generating sheet light of which the width is greater than or equal to 300mm by using continuous laser of which the wavelength is 811.5 nm, and irradiating a wind tunnel flow field to excite naturally existing metastable state argon atoms and generate a fluorescence signal; collecting the fluorescence signal through a narrow-band filter with the central wavelength of 910nm and the bandwidth of less than or equal to 5nm in a direction perpendicular to a sheet light plane; performing synchronous scanning and displacement measurement on the sheet light and the signal acquisition device to obtain three-dimensional flow field data; and based on the three-dimensional flow field data, reconstructing a hypersonic speed wind tunnel flow field structure with the total enthalpy being greater than or equal to 10MJ / kg and the wind tunnel caliber being greater than or equal to 500mm. According to the invention, the problem that the prior art cannot satisfy the visualization of the fine flow field of the large-scale high-enthalpy wind tunnel is effectively solved, the tracing-free and wide-range measurement capability suitable for the extreme environment and the high model near wall surface is realized, and a new powerful tool is provided for the hypersonic velocity 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 diameter is usually more than 500mm, and the test model size is usually more 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 methods of self-radiation imaging, schlieren measurement and laser-induced fluorescence (PLIF) imaging are mainly used for large-scale high-enthalpy wind tunnel flow field visualization. The self-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-of-sight integration, 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, the measurement cross-sectional size of this method is narrow, usually within 50mm, which is difficult to apply to large-size model wind tunnel measurement test. 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, which leads to strong self-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 is difficult to meet the needs of fine visualization of large-scale high-enthalpy wind tunnel flow field structure.

[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: The method for large-scale high-enthalpy wind tunnel flow field structure visualization comprises: 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 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 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. The sheet light and the signal collection device are synchronously scanned and moved to obtain three-dimensional flow field data. Based on the three-dimensional flow field data, 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 is reconstructed.

[0007] Preferably, the thickness of the sheet light is less than or equal to 1 mm.

[0008] Preferably, the signal collection device is an infrared high-speed camera.

[0009] Preferably, the synchronous scanning and moving is realized through an electric displacement table or a galvanometer.

[0010] Preferably, the method further comprises the steps of synchronizing the timing of the wind tunnel operation, the laser irradiation and the signal collection.

[0011] Preferably, the original PLIF signal data obtained through the synchronous scanning and moving is filtered and feature-extracted to obtain the three-dimensional flow field data.

[0012] Preferably, the filtering method comprises median filtering or adaptive filtering, and the feature extraction method comprises Fourier frequency statistics or intensity probability density statistics.

[0013] The second technical solution adopted by the present application is: The system for large-scale high-enthalpy wind tunnel flow field structure visualization comprises: A signal generation module is configured 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 to irradiate a wind tunnel flow field to excite naturally existing metastable argon atoms and generate a fluorescent signal. A signal collection module is configured 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. A scanning and moving module is configured to synchronously scan and move the sheet light and the signal collection device to obtain three-dimensional flow field data. A reconstruction module 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.

[0014] Compared with the prior art, the present application has the following beneficial effects: The 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 an interference-free 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 facilities due to the addition of the tracer, and realizes truly "interference-free and tracer-free" measurement.

[0015] The application innovatively designs and realizes a super-large size laser sheet light of >300 mm; specifically proposes a key scheme of using a 910 nm narrow-band (≤5 nm) filter to suppress strong background noise; can effectively suppress extremely strong spontaneous radiation background light in an extreme environment with total enthalpy ≥10 MJ / kg, successfully extract weak effective fluorescence signals, and obtain flow field images with excellent signal-to-noise ratio, thereby breaking through the signal-to-noise ratio bottleneck of fluorescence imaging in a high-enthalpy strong noise environment.

[0016] The application first realizes wide-range (≥300 mm) and high-spatial-resolution three-dimensional fine structure imaging of the flow field around a model with a size ≥200 mm in a large-caliber (≥500 mm) wind tunnel, and solves the problem of full-area and fine visualization of large-scale flow fields. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A flowchart of a method for large-scale high-enthalpy wind tunnel flow field structure visualization is provided for the embodiments of the application; Figure 2 A structural schematic diagram of a system for large-scale high-enthalpy wind tunnel flow field structure visualization is provided for the embodiments of the application; Figure 3 A structural schematic diagram of a system for large-scale high-enthalpy wind tunnel flow field structure visualization is provided for one specific embodiment of the application; Figure 3 In the figure, 1 is a near-infrared continuous laser, 2 is a laser, 3 is a mirror, 4 is a first galvanometer, 5 is a second galvanometer, 6 is a directional coordinate system, 7 is a movable outgoing laser, 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 light, 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 table, 21 is a time sequence control line of the three-dimensional displacement table, 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

[0018] 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 those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0019] 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: S101, generating a sheet light with a width of ≥300mm by using a continuous laser with a wavelength of 811.5nm, and irradiating the wind tunnel flow field to excite naturally existing metastable argon atoms and generate a fluorescence signal; S102, collecting the fluorescence signal by a narrow-band filter with a center wavelength of 910nm and a bandwidth of ≤5nm in a direction perpendicular to the plane of the sheet light; S103, synchronously scanning and moving the sheet light and the signal collection device to obtain three-dimensional flow field data; S104, reconstructing the high-enthalpy wind tunnel flow field structure with a total enthalpy of ≥10MJ / kg and a wind tunnel aperture of ≥500mm based on the three-dimensional flow field data.

[0020] Argon is a commonly used test gas in high-enthalpy wind tunnel simulation tests. It is an inert gas and does not react with components in the flow field, which can avoid the problem of reaction of conventional tracers such as NO and OH radicals with the flow field, and is suitable for high-temperature, high-pressure or reaction systems. The content of argon in the wind tunnel flow field is relatively high, and the atom is easily excited to a metastable state under high-enthalpy environment. The argon atom in the metastable state has a long lifetime, is easily excited by laser, and has a high fluorescence yield. At the same time, the metastable argon atom pump laser 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 inexpensive, and has broad application prospects in extremely harsh large-scale high-enthalpy wind tunnel measurement.

[0021] 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 application realizes that there is enough concentration of Ar under the high-enthalpy wind tunnel high-temperature condition, and discards the added tracer, and instead uses this feature, which is a clever idea for the high-enthalpy wind tunnel environment (especially the hypersonic pure air / nitrogen wind tunnel), and creatively uses the metastable argon atoms Ar* generated by the naturally existing argon in the high-enthalpy wind tunnel working medium (air) at high temperature as the intrinsic tracer particles, 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 flow field chemical reaction process, thermodynamic state or polluting the experimental facilities due to the addition of the tracer is completely avoided.

[0022] The embodiment of the application adopts an innovative optical design to generate super-large-size laser sheet light with a width of ≥300mm, which is sufficient to completely cover the large-size test model and the complex flow field structure thereof. 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 the traditional method that can only obtain local, two-dimensional or integrated information.

[0023] The embodiment of the application also adopts a highly targeted 910nm narrowband (≤5nm) filter scheme. This design can extremely accurately transmit the characteristic fluorescence of metastable argon atoms, and almost completely filter out the strong spontaneous emission background interference with a wide spectral range generated by high-temperature gas in the high-enthalpy flow field, and under the strong noise background of total enthalpy ≥10MJ / kg, still can obtain fluorescence images with excellent signal-to-noise ratio and can be used for quantitative analysis, and provides reliable data for high-temperature non-equilibrium flow field research.

[0024] The embodiment of the application combines and cooperates large-size sheet light generation, accurate strong background filtering, three-dimensional scanning synchronization, high-speed imaging and other means to form a complete and systematic solution to the problem of fine visualization of large-scale high-enthalpy wind tunnels.

[0025] For super-large-size sheet light, the application specifically realizes the following schemes: 1) The continuous laser emitted light is expanded into large-size laser sheet light through a combination of cylindrical lenses; 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 metastable argon atoms.

[0026] The laser is a near-infrared continuous laser, and the wavelength of the emitted laser is 811.5 nm; the emitted laser can be expanded into a large-size laser sheet light through a column lens combination, the size of the sheet light is more than 300 mm, and the thickness of the sheet light is not more than 1 mm. The minimum size of the flow field three-dimensional measurement range of the application is more than 300 mm*300 mm*100 mm.

[0027] The column lens combination used in the embodiments of the application is a device commonly used in the art to obtain a large-size laser polarized light, which generally comprises a concave cylindrical mirror with a focal length of-5 mm, a short-focus convex cylindrical mirror with a focal length of 400 mm, and a long-focus convex cylindrical mirror with a focal length of 1000 mm. In some preferred embodiments, the fluorescent signal is collected by using an infrared high-speed camera, such as a high-frame-rate fast-response infrared camera.

[0028] In some preferred embodiments, the synchronous scanning and moving is realized by using a motorized displacement table or a galvanometer. Specifically, the high-speed camera and the moving device can be synchronously moved by using a three-dimensional displacement table, and the imaging surface of the camera is coaxial with the sheet light.

[0029] 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, the timing of the high-enthalpy wind tunnel start, the laser trigger and the camera shooting trigger can be synchronized by using a timing controller, so 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.

[0030] In some preferred embodiments, the original PLIF signal data obtained by the synchronous scanning and moving is filtered and feature-extracted to obtain the three-dimensional flow field data during data processing and analysis. For example, the filtering can be performed by using median filtering or adaptive filtering, and the feature extraction can be performed by using Fourier frequency statistics or intensity probability density statistics.

[0031] The second embodiment of the application provides a system 200 for large-scale high-enthalpy wind tunnel flow field structure visualization, which comprises a signal generation module 201, a signal acquisition module 202, a scanning and moving module 203, and a reconstruction module 204, and the specific functions of each module are as follows: The signal generation module 201 is used for generating a sheet light with a width of ≥300 mm by using a continuous laser with a wavelength of 811.5 nm, and irradiating the flow field of the wind tunnel to excite the metastable argon atoms and generate a fluorescent signal; The signal acquisition module 202 is used for acquiring the fluorescent signal by using a narrow-band filter with a center wavelength of 910 nm and a bandwidth of ≤5 nm in the direction perpendicular to the plane of the sheet light; The scanning and moving module 203 is used for synchronously scanning and moving the sheet light and the signal acquisition device to obtain three-dimensional flow field data; The reconstruction module 204 is used for reconstructing a hypersonic wind tunnel flow field structure with a total enthalpy ≥10 MJ / kg and a wind tunnel caliber ≥500 mm based on the three-dimensional flow field data.

[0032] The following provides specific implementations to specifically illustrate the implementation and effects of the method for large-scale high-enthalpy wind tunnel flow field structure visualization.

[0033] Embodiment Reference Figure 3 The method for large-scale high-enthalpy wind tunnel flow field structure visualization is specifically implemented as follows: (1) The laser 2 (wavelength: 811.5 nm, spot diameter: 5 mm) emitted by the near-infrared continuous laser 1 is irradiated on the first galvanometer 4 (x-direction scanning) and the second galvanometer 5 (z-direction scanning) after the reflection mirror 3, and can be finely moved in two directions, as shown in the direction coordinate system 6; (2) The movable emitted laser 7 passes through the concave cylindrical lens 8 (focal length: about -5 mm), the short-focus convex cylindrical lens 9 (focal length: 400 mm), and the long-focus convex cylindrical lens 10 (focal length: about 1000 mm), and is expanded into a large-size laser sheet light 11 (width: 400 mm, thickness: about 1 mm); (3) The measurement position of the large-scale high-enthalpy wind tunnel 12 flow field 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; (4) The first time sequence controller 14, the time sequence control line 15 of the first galvanometer, and the time sequence control line 16 of the second galvanometer are used to control the scanning movement of the first galvanometer 4 and the second galvanometer 5 laser sheet light, so that the three-dimensional displacement measurement of the to-be-measured flow field can be realized; (5) In the direction at a 90-degree angle with the laser sheet light, the metastable argon atom laser-induced fluorescence signal is collected by the high-frame-rate fast-response infrared camera 18 through the front test window 17 of the wind tunnel, and the narrow-band filter 19 is arranged in front of the high-speed camera to eliminate the interference of spontaneous radiation of other components; (6) The high-frame-rate fast-response infrared camera is arranged on the three-dimensional displacement table 20 for fine and fast movement, and 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 measurement device, and the imaging surface of the camera is confocal with the laser sheet light; (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 sequences 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; (8) Data processing analysis, using Matlab software to filter (median filter, adaptive filter) and feature (Fourier frequency statistics, intensity probability density statistics) extraction of PLIF images to obtain large-scale high-enthalpy wind tunnel flow field structure characteristic information.

[0034] 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 high enthalpy wind tunnel flow field structure visualization, characterized by, The application relates to a method for reconstructing a hypersonic wind tunnel flow field structure. The method comprises the following steps: generating 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, irradiating a wind tunnel flow field to excite naturally existing 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 central wavelength of 910 nm and a bandwidth of less than or equal to 5 nm; Synchronous scanning and displacement measurement are performed on the sheet light and the signal collection device to obtain three-dimensional flow field data; Based on the three-dimensional flow field data, a 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.

2. The method for large-scale high-enthalpy wind tunnel flow field structure visualization according to claim 1, characterized in that, The sheet light thickness is less than or equal to 1 mm.

3. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The signal collection device is an infrared high-speed camera.

4. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The synchronous scanning and displacement measurement is realized by an electric displacement table or a galvanometer.

5. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The method further comprises the steps of synchronizing the timing of the wind tunnel operation, the laser irradiation and the signal collection.

6. The method for large-scale high-enthalpy wind tunnel flow field structure visualization of claim 1, wherein, The original PLIF signal data obtained by the synchronous scanning and displacement measurement are filtered and feature-extracted to obtain the three-dimensional flow field data.

7. The method for large-scale high-enthalpy wind tunnel flow field structure visualization according to claim 6, 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.

8. System for large scale hypersonic wind tunnel flow field structure visualization, characterized by, The application relates to a method for reconstructing a hypersonic wind tunnel flow field structure. The method comprises the following steps: a signal generation module is used 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, irradiate a wind tunnel flow field to excite naturally existing metastable argon atoms and generate a fluorescent signal; A signal collection module is used to collect the fluorescent signal in a direction perpendicular to the sheet light plane by using a narrow-band filter with a central wavelength of 910 nm and a bandwidth of less than or equal to 5 nm; A scanning and displacement measurement module is used to perform synchronous scanning and displacement measurement on the sheet light and the signal collection device to obtain three-dimensional flow field data; A reconstruction module is used 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 caliber of greater than or equal to 500 mm based on the three-dimensional flow field data.

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