Optical test system and test method for measuring total temperature of supersonic flow field

Abstract

The invention discloses an optical test system and test method for measuring the total temperature of a supersonic flow field, and relates to the field of supersonic flow field measurement, and the optical test system comprises a static temperature measurement system, a speed measurement system and a time schedule controller. The static temperature measuring system is used for generating narrow-band pump light, probe light and broadband Stokes light, converging the narrow-band pump light, the probe light and the broadband Stokes light, emitting the converged light into a measured position of a flow field to generate anti-Stokes light, and acquiring the filtered anti-Stokes light to obtain the static temperature of the measured position; the speed measuring system is used for generating laser, focusing the laser into the flow field, acquiring motion information of the marked substance, and calculating the airflow speed of the measured position based on the motion information of the marked substance; the time schedule controller is used for controlling the static temperature measuring system and the speed measuring system to work synchronously to obtain the static temperature at the measured position and the airflow speed at the measured position at the same moment; the calculation unit is used for calculating the total temperature of the corresponding area of the measured position based on the static temperature of the measured position and the airflow velocity of the measured position; according to the invention, the problems that the flow field structure is invaded and damaged and the invading piece is ablated and invalid under the condition of high total temperature in the current contact measurement can be solved.

Description

Technical Field

[0001] The invention relates to the field of supersonic flow field measurement, and in particular to an optical test system and a test method for measuring the total temperature of a supersonic flow field. Background Art

[0002] Under supersonic flow conditions, the total parameters of the airflow (such as total temperature, total pressure, and Mach number) are important physical quantities that characterize its characteristics. For ground supersonic tests, the acquisition of total parameters of supersonic flow is very important for determining the test state and analyzing the test results. The total temperature acquisition of supersonic combustion flow fields and supersonic cold flow fields (without combustion chemical reactions) is basically based on contact-type total temperature probe measurement technology. According to reports on the optimization design of the total temperature measurement structure, it can be seen that users are still optimizing the structure of the total temperature probe to improve its anti-damage performance and improve the airflow stagnation efficiency. For detailed information, see the literature Zhang Zhuoli, Wang Jiawei, Dong Weichao, Huang Kaifang. Optimization design of the thermocouple structure of a total temperature and total pressure sensor [J], China Testing, 2023, 49(12): 73-78. However, the contact-type total temperature measurement method has two obvious disadvantages. First, the flow structure of the supersonic flow field will be destroyed by the invading probe, thereby affecting various flow field parameters at the probe's location and downstream. Second, for the measured object with a very high total temperature of the incoming flow, the contact-type structure body will face the problem of ablation and failure. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the current contact measurement may invade and destroy the flow field structure and the intruding parts may be ablated and fail under high total temperature conditions.

[0004] To achieve the above-mentioned object of the invention, the present invention provides an optical test system for measuring the total temperature of a supersonic flow field, the system comprising:

[0005] Static temperature measurement system, speed measurement system and timing controller;

[0006] The static temperature measurement system is used to generate narrowband pump light, detection light and broadband Stokes light, and converge the narrowband pump light, detection light and broadband Stokes light into the measured position of the flow field to generate anti-Stokes light, collect the anti-Stokes light after filtering, and process it to obtain the static temperature at the measured position;

[0007] The velocity measurement system is used to generate laser focus into the flow field, collect the motion information of the marked substance, and calculate the airflow velocity at the measured position based on the motion information of the marked substance;

[0008] The timing controller is used to control the static temperature measurement system and the speed measurement system to work synchronously, so as to obtain the static temperature at the measured position and the airflow speed at the measured position at the same time;

[0009] The calculation unit is used to calculate the total temperature of the area corresponding to the measured position based on the static temperature at the measured position and the airflow velocity at the measured position.

[0010] The present invention is based on non-contact optical testing technology. Without intruding into the flow field, the flow field velocity is obtained by marking the nitrogen in the flow field, the static temperature of the measurement position is obtained by using the coherent anti-Stokes Raman scattering principle and the nitrogen in the flow field, and the total temperature of the flow field is obtained by synchronous speed measurement and static temperature measurement. In order to provide an experimental measurement method for evaluating the flow parameters of the flow field, the present invention fundamentally solves the problem of intrusive destruction of the flow field and ablation of the intruding parts under high total temperature conditions.

[0011] In some embodiments, the static temperature measurement system includes:

[0012] Nd:YAG laser, first laser beam splitter M1, fuel laser, first total reflection mirror M2, laser beam expansion system, second total reflection mirror M5, oblique reflection mirror M6, first focusing mirror M7, second focusing mirror M8, second laser beam splitter M9, light shielding plate, filtering system, third focusing mirror M10, collection end, optical fiber, spectrometer, first ICCD and first computer;

[0013] The Nd:YAG laser is used as a pump light source to emit a first laser, which is split by the first laser beam splitter M1 to obtain a second laser and a third laser; the second laser is injected into the fuel laser, which is used as a Stokes light source, and the second laser outputs broadband Stokes light after passing through the fuel laser and is injected into the oblique reflector M6; the third laser is a narrow-band pump light and a detection light, which is reflected by the first total reflection mirror M2 and then enters the laser beam expansion system for beam expansion processing to obtain a fourth laser, which is reflected by the second total reflection mirror M5 and then injected into the oblique reflector M6, which is used to transmit the broadband Stokes light and reflect the narrow-band pump light and the detection light; the fourth laser reflected by the oblique reflector M6 and the fourth laser reflected by the oblique reflector M6 are The broadband Stokes light transmitted by the mirror M6 passes through the first focusing mirror M7 and converges at the measured position of the flow field to generate anti-Stokes light; the light beam containing the anti-Stokes light is emitted from the flow field and enters the second focusing mirror M8, and the second focusing mirror M8 converges the light beam on the second laser beam splitter M9; the second laser beam splitter M9 reflects the non-anti-Stokes light in the light beam to the shading plate, and transmits the anti-Stokes light in the light beam to the filtering system, and the laser processed by the filtering system is focused on the collection end through the third focusing mirror M10, and the collection end transmits the laser to the spectrometer through the optical fiber signal, and the spectrometer images the laser signal through the first ICCD, and the first computer calculates the static temperature at the measured position based on the imaging result of the first ICCD.

[0014] In some embodiments, the speed measurement system includes:

[0015] Femtosecond laser, third total reflection mirror M11, fourth focusing mirror M12, second ICCD and second computer;

[0016] The laser output by the femtosecond laser is emitted into the third total reflection mirror M11. After being reflected by the third total reflection mirror M11, the laser is emitted into the fourth focusing mirror M12. The fourth focusing mirror M12 focuses the laser into the flow field. The second ICCD collects and obtains the motion information of the marked substance. The second computer calculates and obtains the airflow velocity at the measured position based on the motion information of the marked substance.

[0017] In some embodiments, the timing controller controls the femtosecond laser to emit laser light first, and after a preset time period, the timing controller controls the second ICCD to capture an image.

[0018] In some embodiments, the second computer calculates the airflow velocity at the measured position based on the starting position, movement time and end position of the marked substance.

[0019] In some embodiments, the laser beam expansion system includes: a concave lens M3 and a fifth focusing lens M4, the concave lens M3 is used to diverge the third laser, and the fifth focusing lens M4 is used to converge the diverged laser.

[0020] In some embodiments, the flow field contains nitrogen, and the airflow in the flow field is a supersonic airflow.

[0021] In some embodiments, the timing controller is used to control the Nd:YAG laser at t o The first ICCD is turned on at t1. o The femtosecond laser is controlled to be turned on in the time period from t1 to t2, and the second ICCD is controlled to be turned on in the time period from t3 to t4, so that the displacement of the material marked by the femtosecond laser in the flow field is recorded by the detector after a certain period of time, thereby calculating the speed.

[0022] In some embodiments, the total temperature of the area corresponding to the measured position is calculated as follows:

[0023]

[0024] T * =T·(1+0.2·Ma 2 );

[0025] Where c is the speed of sound, T is the static temperature, Ma is the Mach number, V is the speed, T * is the total temperature.

[0026] The present invention also provides a test method for the optical test system for measuring the total temperature of a supersonic flow field, the method comprising:

[0027] Step 1: Build an optical test system;

[0028] Step 2: Turn on the static temperature measurement system and confirm the temperature measurement position at the measured position through the fluorescence generated by the laser on the positioning paper;

[0029] Step 3: Turn off the static temperature measurement system and turn on the speed measurement system. Confirm the speed measurement position by the fluorescence generated by the laser on the positioning paper at the measured position;

[0030] Step 4: Adjust and fix the frames of the lenses of the static temperature measurement system and the frames of the lenses of the speed measurement system so that the measuring points of the static temperature measurement system and the speed measurement system coincide with each other;

[0031] Step 5: Set the static temperature measurement system and speed measurement system to standby mode;

[0032] Step 6: Open the flow field;

[0033] Step 7: Turn on the optical test system;

[0034] Step 8: After a period of time, turn off the optical test system and flow field in turn;

[0035] Step 9: Result processing, respectively calculating the static temperature at the measured position and the airflow velocity at the measured position, and calculating the total temperature of the area corresponding to the measured position.

[0036] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0037] The present invention adopts non-contact measurement. Under the premise of not invading the flow field, the present invention can fundamentally solve the problems of intrusive destruction of the flow field and ablation of the intruding parts under high total temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of the present invention, and do not constitute a limitation on the embodiments of the present invention;

[0039] Figure 1 The figure is a schematic diagram of the composition of an optical test system for measuring the total temperature of a supersonic flow field;

[0040] Figure 2 It is a schematic diagram of the timing relationship of each component in the system;

[0041] Figure 3 This is a schematic diagram of the measurement location of the test site;

[0042] Figure 4 It is a schematic diagram of the velocity distribution at the measured position;

[0043] Figure 5 Schematic diagram of Stokes light intensity distribution at the measured position. DETAILED DESCRIPTION

[0044] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0045] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those within the scope of this description. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0046] Embodiment 1;

[0047] The schematic diagram of the composition of the total temperature measurement test system in the embodiment of the present invention is as follows Figure 1 As shown, M1 / M9 are the first and second laser beam splitters, respectively, M2 / M5 / M11 are the first, second and third total reflection mirrors, respectively, M3 is a concave lens, M4 / M7 / M8 / M10 / M12 are the fifth, first, second, third and fourth focusing mirrors, respectively, M6 is an oblique reflection mirror, LBES is a laser beam expansion system, EDS is a beam expansion and delay system, SP is a light shielding plate, and FS is a filtering system.

[0048] The present invention generally comprises a static temperature measurement system and a speed measurement system. The working time of the two systems is controlled by a timing controller so that they work synchronously, thereby obtaining the static temperature and speed at the same time. The optical path system is adjusted so that the focal points of the optical paths of the two systems are basically located in the same area in space, thereby ensuring that the measurement positions of the two systems basically coincide.

[0049] The static temperature measurement system includes an excitation light source, an optical path system, data acquisition and timing control. The excitation light source includes a narrowband Nd:YAG laser and a broadband dye fuel laser, which serve as a pump light source and a Stokes light source, respectively. The laser of the pump light source is a narrowband laser with a central wavelength of 532nm. After passing through the M1 laser beam splitter, a part of the laser enters the fuel laser, and after being acted on by the fuel, it outputs broadband Stokes light, and the other part of the narrowband laser serves as pump light and detection light. After beam expansion and reflection, the pump light and the detection light reach the M6 ​​oblique reflector, which is characterized by being able to transmit broadband Stokes light and reflect narrowband pump light / detection light. The two laser beams reaching M6 converge at the measured position of the flow field after passing through the M7 focusing lens. At this position, the two focused laser beams interact in an environment containing N2 to generate a beam of anti-Stokes light. The spectrum of this optical signal is strongly related to the local temperature, and the temperature can be inverted and calculated from this. The light passing through the flow field reflects the rest of the light except the anti-Stokes light through the M9 laser beam splitter, while transmitting the anti-Stokes light. The transmitted anti-Stokes light may be mixed with stray light from other bands. The stray light is filtered out by the filtering system, and the clean anti-Stokes light is collected through the M10 focusing lens. The collection end transmits the light into the spectrometer through the optical fiber, and the spectrometer expands the light and forms an image through the first ICCD. The imaging result of the first ICCD is fitted with the theoretical calculated spectrum by multi-parameters to obtain the temperature at the focal position. For specific methods, see the reference Yang Wenbin, Qi Xinhua, Li Meng, et al. CARS measurement of the temperature field distribution at the outlet of the scramjet combustion chamber [J]. Propulsion Technology, 2022, 43(9): 210190.

[0050] The speed measurement system includes a femtosecond laser, an optical path system, an imaging system and a timing control. The femtosecond laser outputs a laser with a central wavelength of 800nm, which is reflected by the M11 total reflection mirror and focused by the M12 focusing mirror to form an area with higher energy density in the flow field. The focusing lens has a fixed focus, and the energy density of the laser is the highest at the intersection. However, in the speed measurement system introduced in the present invention, the energy density of the laser in a certain area near the focus may be marked N2 and further calculated by the spatial displacement of the marked material recorded by the second ICCD. The working time of the second ICCD and the femtosecond laser is controlled by the timing controller, so that the femtosecond laser emits light first, and then is recorded by the second ICCD after a certain period of time. In this way, the three information of the starting position, movement time and end position of the marked material are all known, and the speed of the measured position can be obtained through the simple relationship between displacement, time and speed.

[0051] The system calculates the total temperature of the area corresponding to the measured position based on the static temperature at the measured position and the airflow velocity at the measured position by a calculation unit. The calculation unit can be a computer or a calculator or a processor or a chip, etc., which is not specifically limited in the embodiment of the present invention.

[0052] The main steps of the test are as follows:

[0053] Step 1: Follow Figure 1 The test system is built as shown;

[0054] Step 2: Turn on the static temperature measurement system and confirm the temperature measurement position at the measured position through the fluorescence generated by the laser on the positioning paper;

[0055] Step 3: Turn off the static temperature measurement system and turn on the speed measurement system. Confirm the speed measurement position by the fluorescence generated by the laser on the positioning paper at the measured position;

[0056] Step 4: Adjust the frames of the lenses of the static temperature measurement system and the frames of the lenses of the speed measurement system so that the measuring points of the two systems are basically overlapped;

[0057] Step 5: Set the static temperature and speed measurement system to standby mode;

[0058] Step 6: Open the flow field;

[0059] Step 7: Start the measurement system;

[0060] Step 8: After a period of time, turn off the measurement system and flow field in turn;

[0061] Step 9: Result processing, calculate static temperature, speed and total temperature respectively.

[0062] Please refer to Figure 2 , Figure 2 The timing controller is a timing control schematic diagram. The timing controller is connected to the Nd:YAG laser, the first ICCD, the femtosecond laser and the second ICCD respectively. The timing controller is used to control the Nd:YAG laser at t o The first ICCD is turned on at t1. o The femtosecond laser is controlled to be turned on in the time period from t1 to t1, the femtosecond laser is controlled to be turned on in the time period from t1 to t2, and the second ICCD is controlled to be turned on in the time period from t3 to t4.

[0063] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the measurement location of the test site. Figure 3 a is the original image, b is a diagram with coordinate origin and specific measurement position diagram, the present invention Figure 3 The measurement points shown realize the synchronous measurement of velocity and static temperature, and then the sound speed (c), static temperature (T), Mach number (Ma) and total temperature (T * ) to obtain the total temperature.

[0064] For ease of presentation, Figure 3 The Schlieren test results of the measured flow field are given. As shown in the figure: the supersonic airflow flows from left to right in the confined space, the center of the flow field is a structure, the upstream of the flow field is connected to the supersonic nozzle with a designed Mach number of 2.0, the origin of the flow field is the center of the end of the central structure, and the measurement position of this test is located at 88.9mm in the flow direction and 10mm in the longitudinal direction. From the Schlieren results, it can be seen that the measured flow field is a supersonic flow state (because there are flow fields and shock waves).

[0065] Figure 4 A schematic diagram of the velocity distribution of the measured position is given. As shown in the figure, the velocity distribution is recorded in the area from 9.25mm to 10.51mm in the y direction and the total length is 1.26mm, indicating that the femtosecond laser successfully marked N2 in this area and was recorded by the second ICCD. The velocity range in this area is 515m / s to 534m / s, and the average velocity is 527.8m / s.

[0066] Figure 5 A schematic diagram of the Stokes intensity distribution at the measured position is given. The scattered points are the measured light intensity, and the solid line is the result of multi-parameter fitting based on the spectrum calculated by the scattered point theory. The fitting temperature is 172K, which is the static temperature at the measured position.

[0067] According to the calculation formula of the gas speed of sound, the calculation formula of the Mach number, and the relationship between the total temperature and the static temperature, the total temperature calculation process of the measured area is as follows:

[0068]

[0069] T * =T·(1+0.2·Ma 2 )=172·(1+0.2·2.01 2 )=311K(3)

[0070] In formula (1), c is the speed of sound, T is the static temperature, in formula (2), Ma is the Mach number, V is the speed, and in formula (3), T * The total temperature is calculated to be about 311K in the area of ​​about 2mm. When the air at room temperature is accelerated to supersonic speed, its total temperature should be close to the room temperature. The difference between the total temperature obtained in this test and the room temperature 298K is about 4%, which proves that the results of the present invention are highly credible.

[0071] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0072] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An optical test system for measuring total temperature in a supersonic flow field, characterized in that: The system comprises: Static temperature measurement system, speed measurement system and timing controller; The static temperature measurement system is used to generate narrowband pump light, detection light and broadband Stokes light, and converge the narrowband pump light, detection light and broadband Stokes light into the measured position of the flow field to generate anti-Stokes light, collect the anti-Stokes light after filtering, and process it to obtain the static temperature at the measured position; The velocity measurement system is used to generate laser focus into the flow field, collect the motion information of the marked substance, and calculate the airflow velocity at the measured position based on the motion information of the marked substance; The timing controller is used to control the static temperature measurement system and the speed measurement system to work synchronously, so as to obtain the static temperature at the measured position and the airflow speed at the measured position at the same time; The calculation unit is used to calculate the total temperature of the area corresponding to the measured position based on the static temperature at the measured position and the airflow velocity at the measured position.

2. The optical test system for measuring total temperature of a supersonic flow field according to claim 1, characterized in that: The static temperature measurement system includes: Nd:YAG laser, first laser beam splitter M1, fuel laser, first total reflection mirror M2, laser beam expansion system, second total reflection mirror M5, oblique reflection mirror M6, first focusing mirror M7, second focusing mirror M8, second laser beam splitter M9, light shielding plate, filtering system, third focusing mirror M10, collection end, optical fiber, spectrometer, first ICCD and first computer; The Nd:YAG laser is used as a pump light source to emit a first laser, which is split by the first laser beam splitter M1 to obtain a second laser and a third laser; the second laser is injected into the fuel laser, which is used as a Stokes light source, and the second laser outputs broadband Stokes light after passing through the fuel laser and is injected into the oblique reflector M6; the third laser is a narrow-band pump light and a detection light, which is reflected by the first total reflection mirror M2 and then enters the laser beam expansion system for beam expansion processing to obtain a fourth laser, which is reflected by the second total reflection mirror M5 and then injected into the oblique reflector M6, which is used to transmit the broadband Stokes light and reflect the narrow-band pump light and the detection light; the fourth laser reflected by the oblique reflector M6 and the fourth laser reflected by the oblique reflector M6 are The broadband Stokes light transmitted by the mirror M6 passes through the first focusing mirror M7 and converges at the measured position of the flow field to generate anti-Stokes light; the light beam containing the anti-Stokes light is emitted from the flow field and enters the second focusing mirror M8, and the second focusing mirror M8 converges the light beam on the second laser beam splitter M9; the second laser beam splitter M9 reflects the non-anti-Stokes light in the light beam to the shading plate, and transmits the anti-Stokes light in the light beam to the filtering system, and the laser processed by the filtering system is focused on the collection end through the third focusing mirror M10, and the collection end transmits the laser to the spectrometer through the optical fiber signal, and the spectrometer images the laser signal through the first ICCD, and the first computer calculates the static temperature at the measured position based on the imaging result of the first ICCD.

3. The optical test system for measuring total temperature of a supersonic flow field according to claim 1, characterized in that: The speed measurement system includes: Femtosecond laser, third total reflection mirror M11, fourth focusing mirror M12, second ICCD and second computer; The output laser of the femtosecond laser is emitted into the third total reflection mirror M11. The laser is reflected by the third total reflection mirror M11 and then emitted into the fourth focusing mirror M12. The fourth focusing mirror M12 focuses the laser to the measured position in the flow field. The second ICCD collects and obtains the motion information of the marked substance. The second computer calculates and obtains the airflow velocity at the measured position based on the motion information of the marked substance.

4. The optical test system for measuring total temperature of a supersonic flow field according to claim 3, characterized in that: The timing controller controls the femtosecond laser to emit laser light first, and after a preset time period, the timing controller controls the second ICCD to capture an image.

5. The optical test system for measuring total temperature of a supersonic flow field according to claim 3, characterized in that: The second computer calculates the air flow velocity at the measured position based on the starting position, movement time and end position of the marked substance.

6. The optical test system for measuring total temperature of a supersonic flow field according to claim 2, characterized in that: The laser beam expansion system includes: a concave lens M3 and a fifth focusing lens M4. The concave lens M3 is used to diverge the third laser, and the fifth focusing lens M4 is used to converge the diverged laser.

7. The optical test system for measuring total temperature of a supersonic flow field according to claim 1, characterized in that: The flow field contains nitrogen, and the airflow in the flow field is a supersonic airflow.

8. The optical test system for measuring total temperature of a supersonic flow field according to claim 1, characterized in that: The timing controller is used to control the Nd:YAG laser at t o The first ICCD is turned on at t1. o The femtosecond laser is controlled to be turned on in the time period from t1 to t1, the femtosecond laser is controlled to be turned on in the time period from t1 to t2, and the second ICCD is controlled to be turned on in the time period from t2 to t3.

9. The optical test system for measuring total temperature of a supersonic flow field according to claim 1, characterized in that: The total temperature of the area corresponding to the measured position is calculated as follows: T * =T·(1+0.2·Ma 2 ); Where c is the speed of sound, T is the static temperature, Ma is the Mach number, V is the speed, T * is the total temperature.

10. A test method for an optical test system for measuring total temperature of a supersonic flow field according to any one of claims 1 to 9, characterized in that: The method comprises: Step 1: Build an optical test system; Step 2: Turn on the static temperature measurement system and confirm the temperature measurement position at the measured position through the fluorescence generated by the laser on the positioning paper; Step 3: Turn off the static temperature measurement system and turn on the speed measurement system. Confirm the speed measurement position by the fluorescence generated by the laser on the positioning paper at the measured position; Step 4: Adjust and fix the frames of the lenses of the static temperature measurement system and the frames of the lenses of the speed measurement system so that the measuring points of the static temperature measurement system and the speed measurement system coincide with each other; Step 5: Set the static temperature measurement system and speed measurement system to standby mode; Step 6: Open the flow field; Step 7: Turn on the optical test system; Step 8: After a period of time, turn off the optical test system and flow field in turn; Step 9: Result processing, respectively calculating the static temperature at the measured position and the airflow velocity at the measured position, and calculating the total temperature of the area corresponding to the measured position.

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