Non-intrusive velocity measurement system for rarefied gas directional flow

Abstract

The present application relates to the technical field of aerospace metrology, and in particular to a non-intrusive velocity measurement system for a rarefied gas directional flow, comprising a fast-acting pulsed valve, a test chamber, a computer, a laser, a beam splitter, and a wavemeter. The fast-acting pulsed valve is disposed on the outer wall of the front end of the test chamber; the front end inside the test chamber is provided with a first reflector group, and the rear end inside the test chamber is provided with a second reflector group; the computer is connected to the laser by means of a laser controller; the laser is connected to the beam splitter, and the beam splitter splits laser light into three beams: a first laser beam entering the wavemeter, a second laser beam entering the first reflector group, and a third laser beam entering the second reflector group; and the computer is further connected to the fast-acting pulsed valve. The present application uses a non-intrusive measurement method based on time-of-flight combined with laser absorption spectroscopy, without introducing an additional electromagnetic field, thereby not affecting the composition, state and movement direction of a molecular flow under test, and achieving accurate velocity measurement of the rarefied gas directional flow.

Description

A non-invasive directional flow velocity measurement system for rarefied gases Technical Field

[0001] This application relates to the field of aerospace metrology technology, and more specifically, to a non-invasive system for measuring the directional flow velocity of rarefied gases. Background Technology

[0002] Spacecraft travel at very high speeds in orbit. For example, a spacecraft orbiting the Earth typically reaches the first cosmic velocity of 7.8 km / s. This speed is much greater than the thermal motion speed of the gas in the orbital environment. In other words, the spacecraft is in an environment of high-speed directional molecular flow. The directional molecular flow environment is very different from the static molecular environment. Under this environment, the question of whether various types of measuring instruments can accurately measure or even quantify characteristic parameters requires a lot of theoretical and experimental research. Therefore, it is necessary to establish an experimental device on the ground to simulate the high-speed directional molecular flow environment in orbit.

[0003] For the generated high-speed rarefied gas directional flow, its key parameters such as velocity and density must first be accurately measured before they can be used as input conditions for subsequent instrument experiments and calibrations.

[0004] Because neutral molecules are uncharged, conventional electromagnetic-based measurement methods are difficult to directly detect and measure them, especially in vacuum environments (<10). -5 Pa) at high speed (>5km / s) rarefied gas (flux <10 20 / m 2 The velocity measurement of directional molecular flows is particularly challenging. While electromagnetic measurement methods are employed, other methods are needed to charge the gas molecules before detection. However, this method is invasive and may interfere with the state of the gas molecules, leading to distorted measurement results. Summary of the Invention

[0005] This application provides a non-invasive system for measuring the directional flow velocity of rarefied gases, which combines time-of-flight measurement and laser absorption spectroscopy to achieve non-invasive, high-precision measurement of the directional flow velocity of rarefied gases.

[0006] To achieve the above objectives, this application provides a non-invasive rarefied gas directional flow velocity measurement system, including a quick-opening valve, a test chamber, a computer, a laser, a beam splitter, and a wavelength meter. The quick-opening valve is located on the outer front wall of the test chamber, through which the directional molecular flow to be measured enters the test chamber. A first set of reflectors is located at the front end of the test chamber, and a second set of reflectors is located at the rear end. The first and second sets of reflectors are positioned along the movement path of the directional molecular flow. The computer is connected to the laser via a laser controller. The laser is connected to the beam splitter, which divides the laser into three beams: the first beam enters the wavelength meter, the second beam enters the first set of reflectors, and the third beam enters the second set of reflectors. The computer is also connected to the quick-opening valve to control its opening and closing.

[0007] Furthermore, it also includes photodetectors, which include a first photodetector and a second photodetector. The first photodetector is located at the laser emission position of the first reflector group, and the second photodetector is located at the laser emission position of the second reflector group.

[0008] Furthermore, it also includes a signal acquisition and data processing unit, which is connected to the first photodetector, the second photodetector, and the computer, respectively.

[0009] Furthermore, both the first and second mirror groups consist of two symmetrically distributed plano-concave lenses.

[0010] Furthermore, the background pressure in the test chamber is more than an order of magnitude lower than the pressure of the molecular flow being measured.

[0011] The non-invasive directional flow velocity measurement system for rarefied gases provided in this application has the following advantages:

[0012] This application employs a non-invasive measurement method combining time-of-flight and laser absorption spectroscopy. It does not introduce additional electromagnetic fields and does not affect the composition, state, or direction of motion of the molecular flow being measured. This enables accurate measurement of the directional flow velocity of rarefied gases and can provide accurate input parameters for directional flow-related experimental equipment and space load testing. Attached Figure Description

[0013] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings:

[0014] Figure 1 is a schematic diagram of a non-invasive rarefied gas directional flow velocity measurement system according to an embodiment of this application;

[0015] Figure 2 is a graph showing the relationship between light intensity and time during the measurement in an embodiment of this application;

[0016] In the figure: 1-The molecular flow to be measured, 2-Quick-opening valve, 3-Test chamber, 4-First reflector group, 5-Second reflector group, 6-Computer, 7-Laser controller, 8-Laser, 9-Beam splitter, 10-Wavemeter, 11-First photodetector, 12-Second photodetector, 13-Signal acquisition and data processing unit. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0018] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0019] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0020] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0021] In addition, the term "multiple" should mean two or more.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] As shown in Figure 1, this application provides a non-invasive rarefied gas directional flow velocity measurement system, including a quick-opening valve 2, a test chamber 3, a computer 6, a laser 8, a beam splitter 9, and a wavelength meter 10. The quick-opening valve 2 is located on the outer wall of the front end of the test chamber 3, through which the molecular flow 1 to be measured enters the test chamber 3. A first reflector group 4 is located at the front end of the test chamber 3, and a second reflector group 5 is located at the rear end. The first reflector group 4 and the second reflector group 5 are positioned along the movement path of the molecular flow 1 to be measured. The computer 6 is connected to the laser 8 via a laser controller 7. The laser 8 is connected to the beam splitter 9, which splits the laser into three beams: the first beam enters the wavelength meter 10, the second beam enters the first reflector group 4, and the third beam enters the second reflector group 5. The computer 6 is also connected to the quick-opening valve 2 to control its opening and closing.

[0024] Specifically, the non-invasive rarefied gas directional flow velocity measurement system provided in this application embodiment is mainly for measuring the directional flow velocity of high-speed rarefied gases. A computer 6 controls a quick-opening valve 2 to open and close at a certain frequency, causing the molecular flow 1 to be measured to change from a continuous flow to a pulsed flow of a certain frequency before entering the test chamber 3. Two sets of reflectors are placed at a certain distance along the path of the molecular flow 1 within the test chamber 3. By measuring the time it takes for the molecular flow to pass sequentially through the first reflector group 4 and the second reflector group 5, and combining this with the distance between the two reflector groups, the flight velocity of the molecular flow can be obtained. The computer 6 is connected to the laser 8 via a laser controller 7 to control the laser 8 so that it can output laser light of a specific wavelength. The laser light emitted by the laser 8 is split into three beams by a beam splitter 9. The first beam enters a wavelength meter 10 for real-time wavelength measurement; the second beam enters the first reflector group 4, and the third beam enters the second reflector group 5 for subsequent light intensity signal acquisition. When the laser frequency equals the molecular transition frequency, the molecules absorb photon energy and transition to a higher energy level, causing the output light intensity to decrease.

[0025] Furthermore, it also includes photodetectors, which include a first photodetector 11 and a second photodetector 12. The first photodetector 11 is located at the laser emission position of the first reflector group 4, and the second photodetector 12 is located at the laser emission position of the second reflector group 5.

[0026] Furthermore, it also includes a signal acquisition and data processing unit 13, which is connected to the first photodetector 11, the second photodetector 12, and the computer 6.

[0027] Specifically, the photodetector receives the emitted laser light from the two mirror groups respectively, and the light intensity signal is converted into an electrical signal by the signal acquisition and data processing unit 13. The computer 6 identifies the falling edge time of the two signals, which is the time when the molecular flow passes through the two mirror groups in sequence.

[0028] Furthermore, both the first reflector group 4 and the second reflector group 5 are composed of two symmetrically distributed plano-concave lenses. After being split by the beam splitter 9, the laser beam enters the first reflector group 4 and the second reflector group 5 respectively. The laser beam will be reflected multiple times between the two plano-concave lenses to extend the transmission path. The longer the transmission path, the more photon energy the molecules absorb, and the more significant the decrease in the intensity of the emitted laser beam.

[0029] Furthermore, the background pressure in test chamber 3 is more than an order of magnitude lower than the pressure of the molecular flow 1 being measured.

[0030] Specifically, in this embodiment, the background pressure of the test chamber 3 is preferably one order of magnitude lower than the pressure of the measured molecular flow 1. During measurement, the laser of the laser 8 is first adjusted to the required wavelength by the computer 6 and the laser controller 7, and the laser 8 is turned on so that the laser is continuously output to the first reflector group 4 and the second reflector group 5. The first photodetector 11 and the second photodetector 12 continuously collect the emitted laser. The signal acquisition and data processing unit 13 processes the signal of the photodetector to obtain the waveform of light intensity changing with time. As shown in Figure 2, at time T0, the quick-opening valve 2 is opened by the computer 6, and the measured molecular flow 1 enters the test chamber 3 in the form of pulsed airflow. When the measured molecular flow 1 enters the area where the first reflector group 4 is located, the light intensity waveform shows a falling edge. This time is T1. When the measured molecular flow 1 enters the area where the second reflector group 5 is located, the light intensity waveform shows a falling edge. This time is T2. The time difference between T1 and T2 is the flight time of the measured molecular flow 1 through the two reflector groups. Combined with the distance between the two reflector groups, the flight speed of the measured molecular flow 1 can be obtained. The non-invasive rarefied gas directional flow velocity measurement system provided in this application embodiment is simple and practical. It does not introduce additional electromagnetic fields and does not affect the composition, state, and direction of motion of the measured molecular flow, thus realizing the accurate measurement of high-speed rarefied gas directional flow velocity.

[0031] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A non-invasive directional flow velocity measurement system for rarefied gases, characterized in that, Includes quick-opening valves, a test chamber, a computer, a laser, a beam splitter, and a wavelength meter, among which: The quick-opening valve is located on the front outer wall of the test chamber, and the molecular flow to be measured enters the test chamber through the quick-opening valve; The front end of the test chamber is provided with a first set of reflectors, and the rear end is provided with a second set of reflectors. The first set of reflectors and the second set of reflectors are positioned on the movement path of the molecular flow being measured. The computer is connected to the laser via a laser controller; The laser is connected to the beam splitter, which splits the laser into three beams. The first laser beam enters the wavelength meter, the second laser beam enters the first reflector group, and the third laser beam enters the second reflector group. The computer is also connected to the quick-opening valve and is used to control the opening and closing of the quick-opening valve.

2. The non-invasive rarefied gas directional flow velocity measurement system according to claim 1, characterized in that, It also includes photodetectors, which include a first photodetector and a second photodetector. The first photodetector is located at the laser emission position of the first reflector group, and the second photodetector is located at the laser emission position of the second reflector group.

3. The non-invasive rarefied gas directional flow velocity measurement system according to claim 2, characterized in that, It also includes a signal acquisition and data processing unit, which is connected to the first photodetector, the second photodetector, and the computer, respectively.

4. The non-invasive rarefied gas directional flow velocity measurement system according to claim 3, characterized in that, Both the first and second mirror groups consist of two symmetrically distributed plano-concave lenses.

5. The non-invasive rarefied gas directional flow velocity measurement system according to claim 4, characterized in that, The background pressure in the test chamber is more than an order of magnitude lower than the pressure of the molecular flow being measured.

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