Method for measuring the recession rate of a workpiece surface after ablation in an arc tunnel

Abstract

The application discloses a kind of methods for measuring the recession rate of workpiece surface ablation in arc wind tunnel, the method is based on the measurement method of emission spectrum, the position of workpiece surface at each moment is extracted by high space-time resolution emission spectrum of the region near workpiece, the recession rate of ablation of different types of workpieces under different enthalpy conditions can be measured.The application uses high-frequency non-contact emission spectrum measurement technology, which can indirectly identify the spatial position of the workpiece surface using the emission spectrum of the workpiece and the boundary layer, avoiding the problems of direct measurement failure caused by high temperature and strong radiation in traditional methods.The application uses a double-grating cooperative measurement strategy (pre-scanning + fine measurement) combined with the method of positioning 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

TECHNICAL FIELD

[0001] The present application relates to an arc tunnel dynamic parameter measurement method, in particular to an arc tunnel workpiece surface ablation recession rate measurement method. BACKGROUND

[0002] When the aircraft is in a high-altitude environment at hypersonic speed, the combined effect of shock compression and viscosity will cause a sharp change in the temperature and density of the flow field, so that the surface is actually in a non-equilibrium state, and when the aircraft thermal protection material 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. The arc tunnel, with its durability, stability, and ability to provide high-temperature, high-enthalpy plasma jets, has become the most ideal experimental device in ground simulation of such space environment facilities. Optical emission spectroscopy (OES) as a non-invasive diagnostic technique will not affect the flow field and test workpiece, and has the advantages of sensitive response and easy operation, and is widely used in thermal protection material evaluation and non-equilibrium flow field characterization in arc tunnels.

[0003] When performing high-spatial and temporal resolution non-equilibrium flow field spectral measurements in an arc tunnel, the surface of the test workpiece model is constantly changing, with local oxidation, ablation recession, and other phenomena, which can seriously affect the accuracy of the spatial characterization of the non-equilibrium flow field. Moreover, the ablation rate can be used as an evaluation parameter for ablation tests of thermal protection materials, to 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 develop an arc tunnel test workpiece ablation rate measurement method. SUMMARY

[0004] The present application provides an arc tunnel workpiece surface ablation recession rate measurement method, which is based on high-spatial and temporal resolution emission spectroscopy to identify the spatial position of the test workpiece in the arc tunnel and then obtain the ablation recession rate of the test workpiece.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] An arc tunnel workpiece surface ablation recession rate measurement method, comprising the following steps:

[0007] 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 tunnel chamber;

[0008] Step two, build a 500Hz emission spectrum measurement system, the system includes a UV focusing lens, a spectrometer, a time controller, a CMOS camera and an image intensifier, the time controller generates a 500Hz frequency test signal, the CMOS camera and the image intensifier collect and record the spectral signal as an imaging system, the UV focusing lens collects the radiation and images to the slit of the spectrometer, and the radiation enters the imaging system after being dispersed by the spectrometer; the center wavelength of the spectrometer is set to 0nm, the UV focusing lens is adjusted to ensure that the spatial dimension field of view 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 three, adjust the spatial position of the spectrometer so that the slit is on the same horizontal plane as the central axis of the test workpiece and is parallel, when moving the scale paper back and forth along the surface of the test workpiece, if the intersection line in the COMS camera does not move, it means that the slit is parallel to the central axis of the test workpiece;

[0010] Step four, determine the relevant parameters according to the enthalpy value, 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, the above parameters should be kept constant under the same enthalpy value;

[0011] Step five, select a grating with 600l / mm of line number and set the center wavelength to 500nm, perform emission spectrum prediction measurement on the test workpiece in the high-enthalpy gas flow field environment, and obtain a wide spectral coverage prediction spectrum; according to the prediction spectrum, select a wavelength range that only exists continuous radiation of the workpiece surface boundary layer and radiation of the workpiece material without other types of radiation (n is the number of wavelength ranges), and calculate the center wavelength and n is the number of wavelength ranges), and calculate the center wavelength

[0012] Step six, select a grating with 1800l / mm of line number, rotate the grating so that the center wavelength of the grating is perform high spatial and temporal resolution spectrum measurement on the test workpiece in the high-enthalpy gas flow field environment; sum the spatial resolution spectrum at a certain time 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, and take the average value as the signal quality evaluation index corresponding to the wavelength range;

[0013] Step seven, repeat step six, select the radiation intensity-spatial position curve with the maximum signal-to-noise ratio to calculate the ablation recession rate of the workpiece surface;

[0014] Step eight, since the boundary layer radiation is continuous, the peak value of its radiation intensity after summation along the wavelength dimension is often greater than that of the workpiece material, and its half-width is narrower, so 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, identifying the workpiece surface position at each moment, obtaining the workpiece surface position-time curve through polynomial fitting and deriving the time, that is, obtaining the workpiece surface ablation recession rate.

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

[0017] 1. The arc tunnel test workpiece ablation recession rate measurement method provided by the present application is a measurement method based on emission spectrum, the workpiece surface position at each moment is extracted through high space-time resolution emission spectrum of the workpiece vicinity, and the ablation recession rate of different types of workpieces under different enthalpy conditions can be measured.

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

[0019] 3. The present application uses a double-grating cooperative measurement strategy (pre-scanning + precision measurement) combined with the method of positioning the workpiece surface position by the boundary layer radiation peak, can select a measurement wavelength range with high signal-to-noise ratio, and has better accuracy and measurement precision. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a structural schematic diagram of a 500Hz emission spectrum measurement system of a workpiece surface vicinity in an arc tunnel of the present application.

[0021] Figure 2 is a radiation intensity-space position curve of the present application;

[0022] Figure 3 is a workpiece surface ablation recession rate when the enthalpy is 25MJ. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be further described below in conjunction with the drawings, but are not limited thereto, and any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and scope of the present application shall be covered in the protection scope of the present application.

[0024] The present application provides a workpiece surface ablation recession rate measurement method in an arc tunnel, which comprises the following steps:

[0025] Step one, arranging the test workpiece in the test area of high-enthalpy gas flow, and aligning the central axis of the test workpiece with the central axis of the arc tunnel chamber.

[0026] Step two, build a 500Hz emission spectrum measurement system, the center wavelength of the spectrometer is set to 0nm, adjust the fixed focus lens to ensure that the spatial dimension of the field of view completely covers the test workpiece and part of the high-enthalpy gas flow field and can be clearly imaged on the COMS camera.

[0027] Under high-enthalpy conditions, the surface of the workpiece undergoes severe ablation, surface catalysis, oxidation and other processes, resulting in a very fast ablation recession rate of the surface of the workpiece, which requires the system to be capable of high-repetition-rate measurement. The high-frequency 500Hz emission spectrum measurement system near the surface of the workpiece in the arc wind tunnel built in the present application is shown in FIG. 1. Figure 1 In order to reduce optical loss and improve collection efficiency, a high-flux ultraviolet fixed focus lens is used to collect and image the radiation to the spectrometer slit; after the radiation passes through the spectrometer, it enters the imaging system; since the measurement repetition rate of the traditional CMOS camera can only reach 20-30Hz, in the present application, 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 500Hz; wherein the 500Hz repetition rate test signal is generated by a time sequence controller.

[0028] Step three, adjust the spatial position of the spectrometer so that the slit and the central axis of the test workpiece are in the same horizontal plane and parallel, and when moving the scale paper back and forth along the surface of the workpiece, if the intersection line of the two in the COMS camera does not move, it means that the slit is parallel to the central axis of the test workpiece.

[0029] Step four, determine the relevant parameters according to the enthalpy value, such as camera integration time and accumulation times, image intensifier gain coefficient, camera trigger delay and intensifier trigger delay, and the above parameters should be kept constant under the same enthalpy value.

[0030] Step five, select a grating with fewer lines (600l / mm) and set the center wavelength to 500nm, perform emission spectrum pre-measurement on the test workpiece under the high-enthalpy gas flow field environment, and obtain a pre-measurement spectrum with a wide spectral coverage; according to the pre-measurement spectrum, select a wavelength range in which only the continuous radiation of the boundary layer of the workpiece surface and the radiation of the workpiece material exist and no other types of radiation exist (λ1 and ), and calculate the center wavelength.

[0031] Assuming the wavelength range is The center wavelength calculation formula is as follows:

[0032]

[0033] Step six, select a grating with more lines (1800l / mm, spectral coverage about 15nm), rotate the grating so that the center wavelength of the grating is Perform high-temporal-spatial-resolution spectrum measurement on the test workpiece under the high-enthalpy gas flow field environment; sum the spatial resolution spectrum at a certain time along the wavelength dimension to obtain​Figure 2 two peaks in the radiation intensity-space position curve, one corresponding to the radiation of the boundary layer and the other corresponding to the radiation of the workpiece material; calculate the wavelength range the signal-to-noise ratio of the radiation intensity at different times, and take the average value as the signal quality evaluation index corresponding to the wavelength range.

[0034] Step seven, repeat step six (i = 1, 2, 3..., n), select the group of radiation intensity-space position curves with the maximum 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 summation along the wavelength dimension, the peak value of its radiation intensity is often greater than that of the workpiece material, and its half-width is narrower, so the first valley near the maximum value in the radiation intensity-space position curve is the test workpiece surface position.

[0036] Step nine, identify the workpiece surface position at each time, obtain the workpiece surface position-time curve by polynomial fitting, and derive the time to obtain the ablation recession rate of the workpiece surface. When the enthalpy is 25 MJ, the ablation recession rate of the workpiece surface is as shown in Figure 3 .

Claims

1. A method for measuring the recession rate of a workpiece surface after ablation in an arc tunnel, characterized in that The method comprises the following steps: Step one, arrange the test workpiece in the test area of high-enthalpy gas flow, and align the central axis of the test workpiece with the central axis of the arc wind tunnel chamber; Step two, build a 500Hz emission spectrum measurement system, set the central wavelength of the spectrometer to 0nm, adjust the ultraviolet focusing lens to ensure that the spatial dimension field of view completely covers the test workpiece and part of the high-enthalpy gas flow field and can be clearly imaged on the COMS camera; Step three, 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 is parallel to it. When moving the scale paper back and forth along the surface of the test workpiece, if the intersection line of the two in the COMS camera does not move, it means that the slit is parallel to the central axis of the test workpiece; Step four, determine the relevant parameters according to the enthalpy value; Step five, select a grating with 600l / mm of scale line number and set the central wavelength to 500nm, and perform emission spectrum prediction measurement on the test workpiece in the high-enthalpy gas flow field environment to obtain a wide-spectrum coverage prediction spectrum; According to the predicted spectrum, a wavelength range in which only the continuous radiation of the boundary layer of the workpiece surface and the radiation of the workpiece material exist and no other type of radiation exists is selected, and a center wavelength is calculated Step six, select the grating with 1800 l / mm, rotate the grating to make the center wavelength of the grating The high spatial and temporal resolution spectrum of the test workpiece in the high-enthalpy airflow flow field environment is measured; the spatial resolution spectrum at a certain time is summed along the wavelength dimension to obtain a radiation intensity-space position curve; The wavelength range is calculated The signal-to-noise ratio of the radiation intensity at different times is calculated, and the average value is taken as the signal quality evaluation index corresponding to the wavelength range. Step seven, repeat step six, select a group of radiation intensity-spatial position curves with the maximum signal-to-noise ratio to calculate the ablation recession rate of the workpiece surface; Step eight, since the boundary layer radiation is continuous radiation, after summing along the wavelength dimension, the first valley near the maximum value in the radiation intensity-spatial position curve is the test workpiece surface position; Step nine, identify the workpiece surface position at each time, obtain the workpiece surface position-time curve by polynomial fitting, and derive the time to obtain the ablation recession rate of the workpiece surface.

2. The method of claim 1, wherein In step two, the 500Hz emission spectrum measurement system includes an ultraviolet focusing lens, a spectrometer, a time sequence controller, a CMOS camera and an image intensifier. The time sequence controller generates a 500Hz frequency test signal. The CMOS camera and the image intensifier collect and record the spectrum signal as an imaging system. The ultraviolet focusing lens collects the radiation and images it to the spectrometer slit. The radiation enters the imaging system after being spectrally dispersed by the spectrometer.

3. The method of claim 1, wherein In step four, the relevant parameters include the COMS camera integration time and the cumulative number, the image intensifier gain coefficient, the camera trigger delay, the intensifier trigger delay, and the same enthalpy value should ensure that the above parameters remain unchanged.

4. The method of claim 1, wherein In the fifth step, the wavelength range is: and n is the number of wavelength ranges, the center wavelength The calculation formula is as follows:

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