Operating method for double-window positioning of shock tube

Abstract

The present invention discloses an operation method for shock tube double-window positioning, including presetting the Mach number of the incident shock wave in the shock tube and the specific heat ratio of the driving gas as operating condition parameters; when the observation time at the first window observation position is at the maximum value, obtaining the first window observation position according to the specific heat ratio of region 4, the Mach number of region 3, and the length of the driving section of the shock tube in the known displacement-time image of the internal operation of the shock tube; obtaining the length of the driven section of the shock tube according to the airflow Mach number in region 2, the Mach number of the reflected shock wave, the Mach number of the incident shock wave, the first window observation position, and the sound speed ratio in regions 2 and 1 in the known displacement-time image; presetting the observation time at the second window observation position, and obtaining the second window observation position according to the sound speed and airflow velocity at regions 2 and 5, the Mach number of the reflected shock wave, the first window observation position, and the length of the driven section of the shock tube in the known displacement-time image; changing the operating condition parameters, and obtaining the range values of the first window observation position and the second window observation position under each operating condition parameter.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular, to an operation method for double-window positioning of a shock tube. Background Art

[0002] A shock tube is a reaction device that generates shock waves and uses shock waves to compress gases to simulate the required working conditions. It is one of the main reactors for studying fast or ultrafast gas-phase chemical reaction kinetics at high temperatures. Combining a variety of diagnostic techniques in shock tube experiments can qualitatively or quantitatively observe shock-induced flame autoignition and three-dimensional flame morphology.

[0003] Known single-use shock tubes are usually equipped with one type of experimental diagnostic technique, focusing on characterizing a specific combustion kinetic characteristic. Sidewall imaging and endwall imaging are common experimental diagnostic techniques. Among them, sidewall imaging usually adopts the method of planar windowing in a rectangular shock tube or designing the entire test section into a cylindrical lens windowing method, and endwall imaging usually adopts the method of an endoscope. However, planar windowing often generates unexpected pressures, rarefaction waves, and cold and hot spots during the transition from the circular cross-section to the square cross-section of the shock tube, and the windowing method using a cylindrical lens will cause a decrease in the overall pressure resistance, which has an adverse effect on the experiment. Therefore, the range of the window should be appropriate. However, both single sidewall imaging and endwall imaging have limitations. Conducting sidewall imaging and endwall imaging simultaneously and setting double windows on the shock tube can obtain more information and provide a detailed morphological data set. However, it is not easy to determine the opening position and range of the double windows of the shock tube. Summary of the Invention

[0004] Aiming at the existing technical problems, the present invention provides an operation method for double-window positioning of a shock tube, which is used to solve at least some of the above technical problems. By analyzing the length of the driver section of the shock tube, the length of the driven section of the shock tube, and the displacement-time images of the internal operation of the shock wave under different working condition parameters, the observation position and range of the first window and the observation position and range of the second window are obtained.

[0005] An embodiment of the present invention provides an operation method for double-window positioning of a shock tube, including the following steps:

[0006] S1. Preset the Mach number of the incident shock wave in the shock tube and the specific heat ratio of the driving gas as working condition parameters;

[0007] S2. When the observation time of the first window observation position is at the maximum value, obtain the first window observation position according to the specific heat ratio of region 4, the Mach number of region 3, and the length of the driver section of the shock tube in the known displacement-time image of the internal operation of the shock tube;

[0008] S3. Obtain the length of the driven section of the shock tube according to the Mach number of the air flow in region 2, the Mach number of the reflected shock wave, the Mach number of the incident shock wave, the observation position of the first window, and the sound speed ratio in regions 2 and 1 in the displacement-time image of the internal operation of the known shock tube;

[0009] S4. Preset the observation time of the second window observation position, and obtain the second window observation position according to the sound speed and air flow velocity at regions 2 and 5, the Mach number of the reflected shock wave, the observation position of the first window, and the length of the driven section of the shock tube in the displacement-time image of the internal operation of the known shock tube; and

[0010] S5. Change the working condition parameters, and obtain the range values of the first window observation position and the second window observation position under each of the working condition parameters.

[0011] According to an embodiment of the present disclosure, in S2, the first formula for calculating the observation position (200) of the first window is:

[0012] ,

[0013] where, is the observation position of the first window; L is the length of the driving section of the shock tube; is the Mach number of region 3; is the specific heat ratio of region 4.

[0014] According to an embodiment of the present disclosure, in S3, the second formula for calculating the length of the driven section of the shock tube is:

[0015] ,

[0016] where, is the length of the driven section of the shock tube; is the Mach number of the reflected shock wave; is the Mach number of region 2; is the Mach number of the incident shock wave; is the sound speed ratio in regions 2 and 1; is the observation position of the first window.

[0017] According to an embodiment of the present disclosure, in S4, the third formula for calculating the second window observation position is:

[0018] ,

[0019] where, is the observation time of the second window observation position; is the observation position of the first window; is the observation position of the second window; is the length of the driven section of the shock tube; and are the sound speeds in regions 2 and 5, respectively; and are the gas flow velocities in regions 2 and 5, respectively; is the Mach number of the reflected shock wave; is the Mach number of the incident shock wave.

[0020] According to an embodiment of the present disclosure, in S2, according to the displacement-time image of the internal operation of the shock tube, analyze the law between the length of the driver section of the shock tube, the length of the driven section of the shock tube, the observation time of the first window observation position, and the observation time of the second window observation position. When the reflected rarefaction wave, the contact surface, and the reflected shock wave intersect, that is, at the first window observation position, the observation time of the first window observation position is at the maximum value. The relevant calculation formula four:

[0021] ,

[0022] wherein, is the observation time of the first window observation position; is the first window observation position; is the Mach number of the incident shock wave; is the specific heat ratio of region 1; is the sound speed in region 1.

[0023] According to an embodiment of the present disclosure, it further includes that the position of the sampling port is the same as that of the second window observation position.

[0024] According to the disclosed operation method for shock tube double-window positioning, by analyzing the displacement-time image of the internal operation of the shock wave under different working condition parameters, the first window observation position, range, the second window observation position, and range are obtained according to the length of the driver section of the shock tube and the length of the driven section of the shock tube, so that the opening positions of the double windows on the shock tube are convenient for observation and information collection, the range is appropriate, while reducing the influence on the experiment, more information can be obtained, and a detailed morphological data set is provided. Brief Description of the Drawings

[0025] Figure 1 is a cross-sectional view of the shock tube according to an embodiment of the present invention;

[0026] Figure 2 is the displacement-time image of the internal operation of the shock tube according to an embodiment of the present invention.

[0027] Reference Signs

[0028] 100. Shock tube;

[0029] 101. End arm;

[0030] 102. Diaphragm;

[0031] 103. Driver section;

[0032] 104. Driven section;

[0033] 200. First window observation position;

[0034] 300. Second window observation position. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0036] The structural embodiments and method descriptions of the present invention are disclosed herein. It should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and the present invention can be implemented by using other features, elements, methods and embodiments. Similar elements in different embodiments are usually labeled with similar numbers.

[0037] In the related art, sidewall imaging is usually carried out by making a planar window in a rectangular shock tube 100 or designing the entire test section into a cylindrical lens windowing method, and endwall imaging is usually carried out by means of an endoscope. However, the planar window often generates unexpected pressure, rarefaction waves and cold and hot spots in the transition from the circular cross-section to the square cross-section of the shock tube 100, and the windowing method using a cylindrical lens will cause a decrease in the overall pressure resistance, which has an adverse effect on the experiment. Therefore, the range of the window should be moderate. However, both single sidewall imaging and endwall imaging have limitations. Conducting sidewall imaging and endwall imaging simultaneously and setting double windows on the shock tube 100 can obtain more information and provide a detailed morphological data set. However, it is not easy to determine the opening position and range of the double windows of the shock tube 100. The window setting is very dependent on experience and extremely lacks theoretical support and guidance.

[0038] An operation method for double-window positioning of a shock tube 100 according to an embodiment of the present invention includes the following steps:

[0039] Step S1, preset the Mach number of the incident shock wave in the shock tube 100 and the specific heat ratio of the driving gas as working condition parameters;

[0040] Step S2, when the observation time of the first window observation position 200 is at the maximum value, obtain the first window observation position 200 according to the specific heat ratio of region 4, the Mach number of region 3 in the known displacement-time (x-t) image of the internal operation of the shock tube 100, and the length of the driver section 103 of the shock tube 100;

[0041] Step S3. Obtain the length of the driven section 104 of the shock tube 100 according to the air flow Mach number, the Mach number of the reflected shock wave, the Mach number of the incident shock wave in region 2 in the displacement-time image of the internal operation of the known shock tube 100, the first window observation position 200, and the sound speed ratio in regions 2 and 1.

[0042] Step S4. Preset the observation time of the second window observation position 300. Obtain the second window observation position 300 according to the sound speed and air flow speed at regions 2 and 5 in the displacement-time image of the internal operation of the known shock tube 100, the Mach number of the reflected shock wave, the first window observation position 200, and the length of the driven section 104 of the shock tube 100; and

[0043] Step S5. Change the working condition parameters, and obtain the range values of the first window observation position 200 and the second window observation position 300 under each of the working condition parameters.

[0044] According to the disclosed operation method for double-window positioning of the shock tube 100, preset the Mach number of the incident shock wave in the shock tube 100 and the specific heat ratio of the driving gas as the working condition parameters. Based on the shock dynamics theory model, by determining the maximum observation time after the incident shock wave and the test time after the reflected shock wave, obtain the first window observation position 200 according to the specific heat ratio in region 4 and the Mach number in region 3 in the displacement-time (x-t) image of the internal operation of the known shock tube 100 and the length of the driving section 103 of the shock tube 100. Obtain the length of the driven section 104 of the shock tube 100 according to the air flow Mach number, the Mach number of the reflected shock wave, the Mach number of the incident shock wave in region 2 in the displacement-time image of the internal operation of the known shock tube 100, the first window observation position 200, and the sound speed ratio in regions 2 and 1. Preset the observation time of the second window observation position 300 according to the experimental requirements, obtain the second window observation position 300, change the working condition parameters, and obtain the range values of the first window observation position 200 and the second window observation position 300 under each of the working condition parameters, so as to be able to determine the first window observation position 200, the range, the second window observation position 300, and the range, make the double-window opening positions on the shock tube 100 convenient for observation and information collection, with a moderate range, reduce the influence on the experiment, and at the same time be able to obtain more information and provide a detailed morphological data set.

[0045] In an exemplary embodiment, the shock tube 100 is a hollow pipe with closed end walls on both sides. A diaphragm 102 is disposed inside the shock tube 100. The diaphragm 102 divides the shock tube 100 into two sections. High-pressure gas and low-pressure gas are respectively introduced into the two sections of the shock tube 100 to form a driver section 103 and a driven section 104. During the experiment, the driven section 104 is filled with a mixed test gas, and the driver section 103 is filled with an inert gas to a high pressure until the diaphragm 102 ruptures. When the diaphragm 102 ruptures, a huge pressure difference causes a series of compression waves to propagate from the high-pressure side of the driver section 103 to the low-pressure side of the driven section 104. These compression waves are superimposed to form an incident shock wave. The incident shock wave rapidly propagates along the shock tube 100 towards the end wall of the driven section 104 and is reflected from the end wall to form a reflected shock wave. The test gas is rapidly compressed and heated to a high temperature by the incident and reflected shock waves. At the same time, the incident rarefaction wave hits the left end wall to form a reflected rarefaction wave, which propagates into the high-pressure gas to reduce the gas pressure and cool the gas.

[0046] The displacement-time image of the internal operation of the shock tube 100 is an image in which the displacement of the contact surface CS (the plane where the high-pressure gas in the driver section 103 contacts the low-pressure gas in the driven section 104), the incident shock wave S, the reflected shock wave Sr, the incident rarefaction wave R, and the reflected rarefaction wave Rr changes with time inside the shock tube 100. The horizontal axis is the displacement and the vertical axis is the time. The displacement-time (x-t) image of the internal operation of the shock tube 100 is divided into five regions, namely regions R1-R5. Region R1 (region 1) is the region of the low-pressure gas in the initial driven section 104, which is composed of the incident shock wave, the positive direction of the horizontal axis, and the wall surface of the driven section 104; Region R2 (region 2) is the low-pressure gas in the driver section 103 after the action of the incident shock wave, which is composed of the incident shock wave, the contact surface, and the reflected shock wave; Region R3 (region 3) is the high-pressure gas in the driver section 103 after the action of the incident rarefaction wave beam, which is composed of the incident rarefaction wave (i.e., Figure 2 the line beam in) the contact surface, and the reflected rarefaction wave; Region R4 (region 4) is the high-pressure gas in the initial driver section 103, which is composed of the incident rarefaction wave, the negative direction of the horizontal axis, and the wall surface of the end wall of the driver section 103; Region R5 (region 5) is the low-pressure gas in the driven section 104 after the action of the reflected shock wave, which is composed of the reflected shock wave, the reflected rarefaction wave, and the wall surface of the end wall of the driven section 104.

[0047] The incident shock wave increases the temperature and pressure in region 2. A first window observation position 200 is set in region 2, and laser schlieren and / or high-speed imaging techniques are used to observe reactive or non-reactive flows; the reflected shock wave forms a high-temperature and high-pressure reactive flow in region 5. A second window observation position 300 is set in region 5, and by combining laser absorption spectroscopy and / or gas chromatography (GC) sampling diagnostic techniques, basic chemical reactions or fuel ignition characteristics can be tested and observed. Regions 2 and 5 inside the shock tube 100 where displacement-time images are run are of great significance for fundamental combustion research. For time-resolved optical techniques (such as schlieren and laser diagnostics), the observation time in region 2 is from the appearance of the incident shock wave until the appearance of the reflected rarefaction wave or the contact surface. For example, at the observation time in region 2 is , and at the observation time in region 2 is ; the observation time in region 5 is from the appearance of the reflected shock wave until the appearance of the reflected rarefaction wave. Appropriate observation time or test time is crucial. For GC sampling diagnostics, it is necessary to ensure a rapid quenching rate of the reaction sample. The positioning of the first window observation position 200, range in regions 2 and 5, and the second window observation position 300, range is crucial for test observations.

[0048] In an exemplary embodiment, in step S1, the Mach number of the incident shock wave in the shock tube 100 and the specific heat ratio of the driver gas are preset as operating parameters; S2, when the observation time at the first window observation position 200 is at the maximum value, based on the specific heat ratio in region 4, the Mach number in region 3, and the length of the driver section 103 of the shock tube 100 in the known displacement-time image of the internal operation of the shock tube 100, the first window observation position 200 is obtained; S3, based on the airflow Mach number in region 2, the Mach number of the reflected shock wave, the Mach number of the incident shock wave, the first window observation position 200, and the sound speed ratio in regions 2 and 1 in the known displacement-time image of the internal operation of the shock tube 100, the length of the driven section 104 of the shock tube 100 is obtained.

[0049] Among them, in step S2, based on the displacement-time image of the internal operation of the shock tube 100, the laws among the length of the driver section 103 of the shock tube 100, the length of the driven section 104 of the shock tube 100, the observation time at the first window observation position 200, and the observation time at the second window observation position 300 are analyzed. When the reflected rarefaction wave, the contact surface, and the reflected shock wave intersect, that is, at the first window observation position 200, the observation time at the first window observation position 200 is at the maximum value. Related calculation formula four:

[0050]

[0051] Among them, is the observation time at the first window observation position; is the first window observation position; is the Mach number of the incident shock wave; is the specific heat ratio of region 1; is the speed of sound in region 1.

[0052] In step S2, the first calculation formula for the first window observation position 200 is:

[0053] ,

[0054] where, is the first window observation position; L is the length of the driver section of the shock tube; is the Mach number of region 3; is the specific heat ratio of region 4.

[0055] In step S3, the second calculation formula for the length of the driven section of the shock tube is:

[0056] ,

[0057] where, is the length of the driven section of the shock tube; is the Mach number of the reflected shock wave; is the Mach number of region 2; is the Mach number of the incident shock wave; is the ratio of the speed of sound in region 2 and region 1; is the first window observation position 200.

[0058] Specifically, during the positioning operation of the double windows of the shock tube 100, changing the temperature and pressure inside the shock tube 100 will change the Mach number of the incident shock wave inside the shock tube 100, and changing the gas type inside the shock tube 100, that is, changing the specific heat ratio of the driving gas will change the running speed of the shock wave inside the shock tube 100. By changing the temperature, pressure or gas type inside the shock tube 100, thereby changing the Mach number of the incident shock wave inside the shock tube 100 and the specific heat ratio of the driving gas as different working condition parameters, and then obtaining displacement-time images of the internal operation of multiple shock tubes 100 under different working condition parameters. After analyzing the displacement-time images of the internal operation of multiple shock tubes 100, it is concluded that when the contact surface, the reflected shock wave and the reflected rarefaction wave intersect, the observation time of region 2 reaches the maximum value, which can ensure that there is enough observation time in region 2, that is, it is determined that the first window observation position 200 is .

[0059] When the observation time in region 2 reaches the maximum value, analyze and deduce the relationship formula between the length of the first window observation position 200, the length of the driver section 103, and the length of the driven section 104, and obtain Formula 1 and Formula 2. Preset the Mach number of the incident shock wave and the specific heat ratio of the driver gas in the shock tube 100 as operating parameters. According to the specific heat ratio in region 4, the Mach number in region 3, and the length of the driver section 103 of the shock tube 100 in the known displacement-time image of the internal operation of the shock tube 100, obtain the first window observation position 200 through Formula 1; according to the Mach number of the air flow in region 2, the Mach number of the reflected shock wave, the Mach number of the incident shock wave, the first window observation position 200, and the sound speed ratio in regions 2 and 1 in the known displacement-time image of the internal operation of the shock tube 100, obtain the length of the driven section 104 of the shock tube 100 through Formula 2. Or obtain the first window observation position 200 through Formula 2 according to the known length of the driven section 104 of the shock tube 100, and then obtain the length of the driver section 103 of the shock tube 100 through Formula 1 according to the first window observation position 200.

[0060] In an exemplary embodiment, in step S4, preset the observation time of the second window observation position 300. According to the sound speeds and air flow speeds at regions 2 and 5, the Mach number of the reflected shock wave, the first window observation position 200, and the length of the driven section 104 of the shock tube 100 in the known displacement-time image of the internal operation of the shock tube 100, obtain the second window observation position 300. 。

[0061] In step S4, the calculation formula 3 for the second window observation position 300 is:

[0062] ,

[0063] where, is the observation time of the second window observation position (300); is the first window observation position (200); is the second window observation position (300); is the length of the driven section (104) of the shock tube (100); and are the sound speeds in regions 2 and 5 respectively; and are the air flow speeds in regions 2 and 5 respectively; is the Mach number of the reflected shock wave; is the Mach number of the incident shock wave.

[0064] Specifically, preset the observation time of the second window observation position 300 that meets the experimental requirements. According to the sound speed and air flow speed at regions 2 and 5 in the displacement-time image of the internal operation of the known shock tube 100, the Mach number of the reflected shock wave, the first window observation position 200, and the length of the driven section 104 of the shock tube 100, the second window observation position 300 is obtained through Formula 3.

[0065] In an exemplary embodiment, in step S5, change the operating parameters, and obtain the range values of the first window observation position 200 and the second window observation position 300 under each of the operating parameters.

[0066] Specifically, after obtaining the first window observation position 200 and the second window observation position 300 under this operating parameter, change the operating parameters to obtain different first window observation positions 200 and second window observation positions 300, so as to obtain the range values of the first window observation position 200 and the second window observation position 300 under all operating parameters.

[0067] In an exemplary embodiment, the operation method for double-window positioning of the shock tube 100 further includes that the position of the sampling port is the same as the second window observation position 300, which is convenient for the gas chromatography-mass spectrometry to perform sampling processing at the second window observation position 300.

[0068] According to the disclosed operation method for double-window positioning of the shock tube 100, preset the Mach number of the incident shock wave in the shock tube 100 and the specific heat ratio of the driving gas as operating parameters. Based on the shock dynamics theory model, by determining the maximum observation time after the incident shock wave and the test time after the reflected shock wave, according to the specific heat ratio in region 4 and the Mach number in region 3 in the displacement-time image of the internal operation of the known shock tube 100 and the length of the driving section 103 of the shock tube 100, the first window observation position 200 is obtained. According to the air flow Mach number in region 2, the Mach number of the reflected shock wave, the Mach number of the incident shock wave, the first window observation position 200, and the sound speed ratio in regions 2 and 1 in the displacement-time image of the internal operation of the shock tube 100, the length of the driven section 104 of the shock tube 100 is obtained. Preset the observation time of the second window observation position 300 according to the experimental requirements, and obtain the second window observation position 300. Change the operating parameters, and obtain the range values of the first window observation position 200 and the second window observation position 300 under each of the operating parameters, so as to be able to determine the first window observation position 200, the range, and the second window observation position 300, the range, making the double-window opening positions on the shock tube 100 convenient for observation and information collection, with a moderate range, reducing the impact on the experiment while being able to obtain more information and providing a detailed morphological data set.

[0069] In the above specific embodiments, the objectives, technical solutions and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An operation method for the double-window positioning of a shock tube, comprising the following steps: S1. Preset the Mach number of the incident shock wave and the specific heat ratio of the driving gas in the shock tube (100) as operating condition parameters; S2. When the observation time of the first window observation position (200) is at the maximum value, obtain the first window observation position (200) according to the specific heat ratio of region 4, the Mach number of region 3, and the length of the driving section (103) of the shock tube (100) in the known displacement-time image of the internal operation of the shock tube (100); S3. Obtain the length of the driven section (104) of the shock tube (100) according to the airflow Mach number in region 2, the Mach number of the reflected shock wave, the Mach number of the incident shock wave, the first window observation position (200), and the sound speed ratio in regions 2 and 1 in the known displacement-time image of the internal operation of the shock tube (100); S4. Preset the observation time of the second window observation position (300), and obtain the second window observation position (300) according to the sound speed and airflow velocity at regions 2 and 5, the Mach number of the reflected shock wave, the first window observation position (200), and the length of the driven section (104) of the shock tube (100) in the known displacement-time image of the internal operation of the shock tube (100); and S5. Change the operating condition parameters, and obtain the range values of the first window observation position (200) and the second window observation position (300) under each of the operating condition parameters.

2. The operating method according to claim 1, characterized in that, In S2, the first calculation formula for the first window observation position (200) is: ， Among them, is the first window observation position (200); L is the length of the driver section (103) of the shock tube (100); is the Mach number of region 3; is the specific heat ratio of region 4.

3. The operating method according to claim 1, characterized in that, In S3, the second calculation formula for the length of the driven section (104) of the shock tube (100) is: ， Wherein, is the length of the driven section (104) of the shock tube (100); is the Mach number of the reflected shock wave; is the Mach number of Region 2; is the Mach number of the incident shock wave; is the ratio of the speed of sound in Region 2 and Region 1; is the first window observation position (200).

4. The operating method according to claim 1, wherein In S4, the third calculation formula for the second window observation position (300) is: ， wherein, is the observation time of the second window observation position (300); is the first window observation position (200); is the second window observation position (300); is the length of the driven section (104) of the shock tube (100); and are the sound speeds in region 2 and region 5 respectively; and are the gas flow velocities in region 2 and 5 respectively; is the Mach number of the reflected shock wave; is the Mach number of the incident shock wave.

5. The operating method according to claim 1, characterized in that In S2, according to the displacement-time image of the internal operation of the shock tube (100), analyze the law among the length of the driving section (103) of the shock tube (100), the length of the driven section (104) of the shock tube (100), the observation time of the first window observation position (200), and the observation time of the second window observation position (300). When the reflected rarefaction wave, the contact surface, and the reflected shock wave intersect, i.e., at the first window observation position (200), the observation time of the first window observation position (200) is at the maximum value, and the relevant fourth calculation formula is: ， wherein, is the observation time of the first window observation position (200); is the first window observation position (200); is the Mach number of the incident shock wave; is the specific heat ratio of region 1; is the speed of sound in region 1.

6. The operating method according to claim 4, wherein It also includes that the position of the sampling port is the same as the second window observation position (300).

Images