Method for measuring ablation retreat rate of workpiece surface in arc wind tunnel

Abstract

The invention discloses a method for measuring the ablation retreat rate of the surface of a workpiece in an arc wind tunnel, which is a measurement method based on an emission spectrum, and can realize the measurement of the ablation retreat rate of different types of workpieces under the condition of different enthalpy values by extracting the position of the surface of the workpiece at each moment through a high space-time resolution emission spectrum of an area near the workpiece. A high-frequency non-contact emission spectrum measurement technology is adopted, the spatial position of the surface of the workpiece can be identified by indirectly utilizing emission spectrums of the workpiece and a boundary layer, and the problems of direct measurement failure and the like caused by high temperature and intense radiation in a traditional method are solved. According to the method, a double-grating cooperative measurement strategy (pre-scanning and accurate measurement) is combined with a boundary layer radiation peak to position the surface position of the workpiece, a measurement wavelength range with a high signal-to-noise ratio can be selected, and better accuracy and measurement precision are achieved.

Description

Technical Field

[0001] The present invention relates to a method for measuring dynamic parameters of an arc wind tunnel, and more particularly to a method for measuring the ablation recession rate of a workpiece surface in an arc wind tunnel. Background Art

[0002] When an aircraft flies at hypersonic speed in a high-altitude environment, the combined action of shock compression and viscous effects will cause sharp changes in the flow field temperature and density, making its surface actually in a non-equilibrium state. Moreover, when the thermal protection material of the aircraft interacts with the surrounding flow field, more complex high-temperature phenomena will occur, such as surface catalysis, oxidation, ablation pyrolysis, and ablation product effects. The occurrence of these phenomena will significantly affect the thermal protection system of the aircraft. Due to its advantages of persistence, stability, and the ability to provide high-temperature and high-enthalpy plasma jets, the arc wind tunnel has become the most ideal experimental device in ground-based simulation facilities for such aerospace environments. As a non-invasive diagnostic technique, optical emission spectroscopy (OES) does not affect the flow field and the test workpiece, and has the advantages of sensitive response and convenient operation, and is widely used for the assessment of thermal protection materials and the characterization of non-equilibrium flow fields in arc wind tunnels.

[0003] When performing high-spatiotemporal-resolution non-equilibrium flow field spectral measurements in an arc wind tunnel, the surface of the test workpiece model is constantly changing, with local oxidation, ablation recession, etc. This will seriously affect the accuracy of the non-equilibrium flow field characterization in the spatial dimension. Moreover, the ablation rate can be used as an evaluation parameter for the ablation assessment test of thermal protection materials, and can assist in analyzing the gas-surface interaction between thermal protection materials and high-enthalpy non-equilibrium flow fields. Therefore, there is an urgent need to propose a method for measuring the ablation rate of a test workpiece in an arc wind tunnel. Summary of the Invention

[0004] The present invention provides a method for measuring the ablation recession rate of a workpiece surface in an arc wind tunnel. This method is based on high-spatiotemporal-resolution emission spectroscopy to identify the spatial position of the test workpiece in the arc wind tunnel and then obtain the ablation recession rate of the test workpiece.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A method for measuring the ablation recession rate of a workpiece surface in an arc wind tunnel includes the following steps:

[0007] Step 1: Arrange the test workpiece in the test area of the high-enthalpy gas flow and align the central axis of the test workpiece with the central axis of the arc wind tunnel chamber;

[0008] Step 2: Set up a 500 Hz emission spectrum measurement system. The system includes an ultraviolet fixed-focus lens, a spectrometer, a timing controller, a CMOS camera, and an image intensifier. The timing controller generates a test signal with a 500 Hz repetition frequency. The CMOS camera and the image intensifier, as the imaging system, collect and record the spectral signals. The ultraviolet fixed-focus lens collects the radiation light and images it onto the spectrometer slit. After the radiation light is dispersed by the spectrometer, it enters the imaging system. The central wavelength of the spectrometer is set to 0 nm. Adjust the ultraviolet fixed-focus lens to ensure that the field of view in the spatial dimension completely covers the test workpiece and part of the high-enthalpy gas flow field and can be clearly imaged on the COMS camera.

[0009] Step 3: Adjust the spatial position of the spectrometer so that the slit is on the same horizontal plane and parallel to the central axis of the test workpiece. When moving the scale paper back and forth along the surface of the test workpiece, if the intersection line between the two in the COMS camera does not move, it indicates that the slit is parallel to the central axis of the test workpiece.

[0010] Step 4: Determine the relevant parameters according to the enthalpy conditions, including the integration time and the number of accumulations of the COMS camera, the gain coefficient of the image intensifier, the camera trigger delay, and the intensifier trigger delay. Under the same enthalpy value, ensure that the above parameters remain unchanged.

[0011] Step 5: Select a grating with 600 l / mm ruling density and set the central wavelength to 500 nm. Perform an emission spectrum pre-measurement on the test workpiece in the high-enthalpy gas flow field environment to obtain a pre-measured spectrum with a wide spectral coverage range. According to the pre-measured spectrum, select the wavelength range where there is only the continuous radiation of the workpiece surface boundary layer and the radiation of the workpiece material and no other types of radiation ( and n is the number of wavelength ranges), and calculate the central wavelength

[0012] Step 6: Select a grating with 1800 l / mm ruling density and rotate the grating so that the central wavelength of the grating is Perform high-spatiotemporal resolution spectral measurement on the test workpiece in the high-enthalpy gas flow field environment. Sum the spatial resolution spectra at a certain moment along the wavelength dimension to obtain a radiation intensity - spatial position curve. Calculate the signal-to-noise ratio of the radiation intensity at different moments in the wavelength range of and use the average value as the signal quality evaluation index corresponding to this wavelength range.

[0013] Step 7: Repeat Step 6, and select a set of radiation intensity - spatial position curves with the maximum signal-to-noise ratio to calculate the ablation recession rate of the workpiece surface.

[0014] Step 8: Since the boundary layer radiation is continuous radiation, after summing along the wavelength dimension, the peak value of its radiation intensity is often greater than the radiation peak value of the workpiece material, and its full width at half maximum is narrower. Then, the first trough near the maximum value in the radiation intensity - spatial position curve is the position of the test workpiece surface.

[0015] Step Nine: Identify the workpiece surface position at each moment, obtain the workpiece surface position-time curve through polynomial fitting, and take the derivative with respect to time to obtain the ablation recession rate of the workpiece surface.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The method for measuring the ablation recession rate of the workpiece in the arc wind tunnel test provided by the present invention is a measurement method based on emission spectroscopy. By extracting the workpiece surface position at each moment from the high spatio-temporal resolution emission spectroscopy in the area near the workpiece, the measurement of the ablation recession rate of workpieces under different enthalpy conditions and different types of workpieces can be realized.

[0018] 2. The present invention adopts a high-frequency non-contact emission spectroscopy measurement technology, which can indirectly identify the spatial position of the workpiece surface by using the emission spectroscopy of the workpiece and the boundary layer, avoiding problems such as the failure of direct measurement caused by high temperature and strong radiation in the traditional method.

[0019] 3. The present invention uses a double-grating collaborative measurement strategy (pre-scanning + fine measurement) combined with a method of locating the workpiece surface position by the boundary layer radiation peak, which can select a measurement wavelength range with high signal-to-noise ratio and has better accuracy and measurement precision. Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of a 500Hz emission spectroscopy measurement system in the area near the workpiece surface in the arc wind tunnel of the present invention.

[0021] Figure 2 is the radiation intensity-spatial position curve of the present invention;

[0022] Figure 3 is the ablation recession rate of the workpiece surface when the enthalpy value is 25MJ. Detailed Embodiments

[0023] The technical solution of the present invention will be further described below in conjunction with the drawings, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.

[0024] The present invention provides a method for measuring the ablation recession rate of the workpiece surface in an arc wind tunnel. The method includes the following steps:

[0025] Step One: Arrange the test workpiece in the test area of the high-enthalpy gas flow, and align the central axis of the test workpiece with the central axis of the arc wind tunnel chamber.

[0026] Step 2: Set up a 500 Hz emission spectrum measurement system. Set the central wavelength of the spectrometer to 0 nm. Adjust the fixed-focus lens to ensure that the field of view in the spatial dimension completely covers the test workpiece and part of the high-enthalpy gas flow field and can be clearly imaged on the CMOS camera.

[0027] Under high-enthalpy conditions, intense ablation, surface catalysis, oxidation, etc. occur on the workpiece surface, resulting in an extremely fast ablation recession rate on the workpiece surface. This requires the system to achieve high-repetition-rate measurement. The high-frequency 500 Hz emission spectrum measurement system in the area near the workpiece surface in the arc wind tunnel built in the present invention is as Figure 1 shown. To reduce optical loss and improve the collection efficiency, a high-throughput ultraviolet fixed-focus lens is used to collect and image the radiation light onto the spectrometer slit; after the radiation light is dispersed by the spectrometer, it enters the imaging system; since the measurement repetition rate of the traditional CMOS camera can only reach 20 - 30 Hz, in the present invention, the CMOS camera and the image intensifier are used as the imaging system to collect and record the spectral signal, and the measurement repetition rate can be increased to 500 Hz; among them, the test signal with a repetition rate of 500 Hz is generated by the timing controller.

[0028] Step 3: Adjust the spatial position of the spectrometer so that the slit is in the same horizontal plane as the central axis of the test workpiece and parallel. When the scale paper is moved back and forth along the workpiece surface, if the intersection line of the two in the CMOS camera does not move, it indicates that the slit is parallel to the central axis of the test workpiece.

[0029] Step 4: Determine relevant parameters according to the enthalpy conditions, such as the camera integration time and the number of accumulations, the gain coefficient of the image intensifier, the camera trigger delay and the intensifier trigger delay. The above parameters should be kept unchanged under the same enthalpy value.

[0030] Step 5: Select a grating with a smaller number of rulings (600 l / mm), set the central wavelength to 500 nm, and perform pre-measurement of the emission spectrum on the test workpiece in the high-enthalpy gas flow field environment to obtain a pre-measured spectrum with a wide spectral coverage range; according to the pre-measured spectrum, select a wavelength range ([[]] and ) where there is only continuous radiation in the boundary layer of the workpiece surface and radiation of the workpiece material and no other types of radiation, and calculate the central wavelength.

[0031] Assume the wavelength range is The central wavelength calculation formula is as follows:

[0032]

[0033] Step 6: Select a grating with a larger number of rulings (1800 l / mm, spectral coverage range is about 15 nm), rotate the grating so that the central wavelength of the grating is Perform high-spatial and high-temporal resolution spectral measurement on the test workpiece in the high-enthalpy gas flow field environment; sum the spatial resolution spectra at a certain moment obtained along the wavelength dimension to obtainFigure 2 The shown radiation intensity - spatial position curve, where the two peaks, one corresponds to the radiation of the boundary layer and the other corresponds to the radiation of the workpiece material; the calculated wavelength range is The signal - to - noise ratio of the radiation intensity at different times, and the average value is used as the signal quality evaluation index corresponding to this wavelength range.

[0034] Step Seven: Repeat Step Six (i = 1, 2, 3..., n), and select the set of radiation intensity - spatial position curves with the largest signal - to - noise ratio to calculate the ablation recession rate of the workpiece surface.

[0035] Step Eight: Since the boundary layer radiation is continuous radiation, after summing along the wavelength dimension, the peak value of its radiation intensity often exceeds the radiation peak value of the workpiece material, and its full width at half maximum is narrower. Then, the first wave trough near the maximum value in the radiation intensity - spatial position curve is the position of the tested workpiece surface.

[0036] Step Nine: Identify the workpiece surface position at each moment, obtain the workpiece surface position - time curve through polynomial fitting and take the derivative with respect to time, then the ablation recession rate of the workpiece surface can be obtained. When the enthalpy value is 25 MJ, the ablation recession rate of the workpiece surface is as Figure 3 shown.

Claims

1. A method for measuring the ablation recession rate of the surface of a workpiece in an arc wind tunnel, characterized in that The method includes the following steps: Step 1: Arrange the test workpiece in the test area of the high-enthalpy gas flow, and align the central axis of the test workpiece with the central axis of the arc wind tunnel chamber; Step 2: Set up a 500Hz emission spectrum measurement system, set the central wavelength of the spectrometer to 0nm, adjust the ultraviolet fixed-focus lens to ensure that the field of view in the spatial dimension completely covers the test workpiece and part of the high-enthalpy gas flow field and can be clearly imaged on the COMS camera; Step 3: Adjust the spatial position of the spectrometer so that the slit is in the same horizontal plane as the central axis of the test workpiece and parallel. When moving the scale paper back and forth along the surface of the test workpiece, if the intersection line of the two does not move in the COMS camera, it means that the slit is parallel to the central axis of the test workpiece; Step 4: Determine the relevant parameters according to the enthalpy value conditions; Step 5: Select a grating with 600l / mm ruling density, set the central wavelength to 500nm, and perform pre-measurement of the emission spectrum of the test workpiece in the high-enthalpy gas flow field environment to obtain a pre-measured spectrum with a wide spectral coverage range; According to the predicted spectral quantity, select the wavelength range where there is only the continuous radiation of the workpiece surface boundary layer and the radiation of the workpiece material and no other types of radiation, and calculate the central wavelength Step 6: Select a grating with 1800 l / mm ruling density and rotate the grating so that its central wavelength is Perform high-spatiotemporal-resolution spectral measurement on the test workpiece in the high-enthalpy gas flow field environment; sum the spatial resolution spectra at a certain moment along the wavelength dimension to obtain the radiation intensity - spatial position curve; Calculate the signal-to-noise ratio of the radiation intensity at different times within the wavelength range, and use the average value as the signal quality evaluation index corresponding to this wavelength range; Step 7: Repeat Step 6, and select a set of radiation intensity - spatial position curves with the maximum signal-to-noise ratio to calculate the ablation recession rate of the workpiece surface; Step 8: Since the boundary layer radiation is continuous radiation, after summing along the wavelength dimension, the first trough near the maximum value in the radiation intensity - spatial position curve is the position of the test workpiece surface; Step 9: Identify the workpiece surface position at each moment, obtain the workpiece surface position - time curve through polynomial fitting and take the derivative with respect to time, that is, obtain the ablation recession rate of the workpiece surface.

2. The method for measuring the ablation recession rate of the workpiece surface in an arc wind tunnel according to claim 1, characterized in that In the above Step 2, the 500Hz emission spectrum measurement system includes an ultraviolet fixed-focus lens, a spectrometer, a timing controller, a CMOS camera, and an image intensifier. The timing controller generates a test signal with a 500Hz repetition frequency. The CMOS camera and the image intensifier act as an imaging system to collect and record the spectral signal. The ultraviolet fixed-focus lens collects the radiation light and images it onto the spectrometer slit, and the radiation light enters the imaging system after being dispersed by the spectrometer.

3. The method for measuring the ablation recession rate of the workpiece surface in the arc wind tunnel according to claim 1, characterized in that In the above Step 4, the relevant parameters include the integration time and accumulation times of the COMS camera, the gain coefficient of the image intensifier, the camera trigger delay, and the intensifier trigger delay. Under the same enthalpy value, the above parameters should be kept unchanged.

4. The method for measuring the ablation recession rate of the workpiece surface in the arc wind tunnel according to claim 1, wherein In the fifth step, the wavelength range is: and where n is the number of wavelength ranges, and the central wavelength is calculated as follows:

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