Non-intrusive rarefied gas directional flow velocity measurement system

Abstract

The invention relates to the technical field of spaceflight space metering, in particular to a non-intrusive rarefied gas directional flow velocity measurement system which comprises a quick-opening valve, a test chamber, a computer, a laser, a beam splitter and a wavemeter, and the quick-opening valve is arranged on the outer wall of the front end of the test chamber; a first reflector group is arranged at the front end in the test chamber, and a second reflector group is arranged at the rear end in the test chamber; the computer is connected with the laser through the laser controller; the laser is connected with the beam splitter, the beam splitter divides laser into three beams, the first beam of laser enters the wavelength meter, the second beam of laser enters the first reflector group, and the third beam of laser enters the second reflector group; and the computer is also connected with the quick-opening valve. The non-intrusive measurement method combining the flight time with the laser absorption spectrum is adopted, an additional electromagnetic field is not introduced, the components, the state and the movement direction of the measured molecular flow are not influenced, and accurate measurement of the directional flow velocity of the rarefied gas is achieved.

Description

Technical Field

[0001] The present application relates to the field of aerospace metrology technology, and in particular to a non-invasive rarefied gas directional flow velocity measurement system. Background Art

[0002] When a spacecraft is in orbit, it flies very fast. For example, a spacecraft orbiting the earth generally reaches the first cosmic velocity of 7.8km / s, which is much faster than the thermal motion speed of the orbital environment gas. That is, 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. In this environment, a lot of theoretical and experimental research is needed to determine whether various types of measuring instruments can achieve accurate characteristic parameter measurement or even metrology. Therefore, it is necessary to establish an experimental device on the ground to simulate the orbital high-speed directional molecular flow environment.

[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 various instrument experiments and calibrations.

[0004] Since neutral molecules are not charged, conventional electromagnetic measurement methods are difficult to detect and measure them directly. -5 Pa) at high speed (>5km / s) rarefied gas (flux <10 20 / m 2 .s) Directed molecular flow, its velocity measurement is even more difficult. If electromagnetic measurement is used, other methods must be used to charge gas molecules and then detect them, but this method is an invasive measurement and may interfere with the state of gas molecules, thereby distorting the measurement results. Summary of the invention

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

[0006] In order to achieve the above-mentioned purpose, the present 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, wherein: the quick-opening valve is arranged on the front end outer wall of the test chamber, and the directional molecular flow to be measured enters the test chamber through the quick-opening valve; a first reflector group is arranged at the front end of the test chamber, and a second reflector group is arranged at the rear end, and the first reflector group and the second reflector group are arranged on the moving path of the directional molecular flow to be measured; the computer is connected to the laser through a laser controller; the laser is connected to the beam splitter, and the beam splitter divides 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 to control the opening and closing of the quick-opening valve.

[0007] Furthermore, it also includes a photoelectric detector, which includes a first photoelectric detector and a second photoelectric detector. The first photoelectric detector is arranged at the laser emission position of the first reflector group, and the second photoelectric detector is arranged 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, the first reflector group and the second reflector group are both composed of two symmetrically distributed plano-concave lenses.

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

[0011] The present application provides a non-invasive rarefied gas directional flow velocity measurement system, which has the following beneficial effects:

[0012] This application adopts a non-invasive measurement method combining time of flight with laser absorption spectroscopy, which does not introduce additional electromagnetic fields and does not affect the composition, state and movement direction of the molecular flow being measured. It can achieve accurate measurement of the velocity of rarefied gas directional flow and provide accurate input parameters for directional flow-related test equipment and space load testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings constituting a part of this application are used to provide a further understanding of this application, so that other features, purposes and advantages of this application become more obvious. The schematic embodiment drawings and their descriptions of this application are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

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

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

[0016] In the figure: 1-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-wavelength meter, 11-first photodetector, 12-second photodetector, 13-signal acquisition and data processing unit. DETAILED DESCRIPTION

[0017] In order 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 in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0018] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0019] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0020] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0021] In addition, the term "plurality" shall mean two or more.

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] like Figure 1 As shown, the present 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, wherein: the quick-opening valve 2 is arranged on the front end outer wall of the test chamber 3, and the measured directional molecular flow 1 enters the test chamber 3 through the quick-opening valve 2; a first reflector group 4 is arranged at the front end inside the test chamber 3, and a second reflector group 5 is arranged at the rear end, and the first reflector group 4 and the second reflector group 5 are arranged on the moving path of the measured directional molecular flow 1; the computer 6 is connected to the laser 8 through a laser controller 7; the laser 8 is connected to the beam splitter 9, and the beam splitter 9 divides the laser into three beams, the first laser beam enters the wavelength meter 10, the second laser beam enters the first reflector group 4, and the third laser beam enters the second reflector group 5; the computer 6 is also connected to the quick-opening valve 2 for controlling the opening and closing of the quick-opening valve 2.

[0024] Specifically, the non-invasive rarefied gas directional flow velocity measurement system provided in the embodiment of the present application is mainly for measuring the velocity of high-speed rarefied gas directional flow. The computer 6 controls the quick-opening valve 2 to open and close at a certain frequency, so that the measured directional molecular flow 1 is transformed from a continuous form to a pulsed gas flow form with a certain frequency and enters the test chamber 3. Two groups of reflectors are set at a certain distance on the path of the measured directional molecular flow 1 in the test chamber 3. By measuring the time when the molecular flow passes through the first reflector group 4 and the second reflector group 5 in sequence, and combining the distance between the two reflector groups, the flight speed of the molecular flow can be obtained. Among them, the computer 6 is connected to the laser 8 through the laser controller 7, which is used to control the laser 8 so that it can output a laser of a specific wavelength; the laser emitted by the laser 8 is divided into three laser beams through the beam splitter 9, and the first laser beam enters the wavelength meter 10 to measure the wavelength in real time; the second laser beam enters the first reflector group 4, and the third laser beam enters the second reflector group 5, which is used for the subsequent collection of light intensity signals. When the laser frequency is equal to the molecular transition frequency, the molecule absorbs the photon energy and transitions to a high energy level, so that the output light intensity is weakened.

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

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

[0027] Specifically, the photoelectric detector receives the emitted lasers of the two reflector groups respectively, and converts the light intensity signals into electrical signals through the signal acquisition and data processing unit 13. The computer 6 identifies the falling edge moments of the two signals, which are the moments when the molecular flow passes through the two reflector groups in sequence.

[0028] Furthermore, the first reflector group 4 and the second reflector group 5 are both composed of two symmetrically distributed plano-concave lenses. The laser beams split by the beam splitter 9 enter the first reflector group 4 and the second reflector group 5 respectively. The laser beams are 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 obvious the decrease in the laser output light intensity.

[0029] Furthermore, the background pressure of the test chamber 3 is more than one order of magnitude lower than the pressure of the molecular flow 1 to be measured.

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

[0031] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A non-invasive rarefied gas directional flow velocity measurement system, characterized in that: It includes a quick-opening valve, a test chamber, a computer, a laser, a beam splitter, and a wavelength meter, wherein: The quick-opening valve is arranged on the front outer wall of the test chamber, and the molecules to be measured flow into the test chamber through the quick-opening valve; A first reflector group is disposed at the front end of the test chamber, and a second reflector group is disposed at the rear end, wherein the first reflector group and the second reflector group are disposed on the moving path of the molecular flow to be measured; The computer is connected to the laser through a laser controller; The laser is connected to the beam splitter, and the beam splitter 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 a photodetector, which includes a first photodetector and a second photodetector. The first photodetector is arranged at the laser emission position of the first reflector group, and the second photodetector is arranged 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 a computer respectively.

4. The non-invasive rarefied gas directional flow velocity measurement system according to claim 3, characterized in that: The first reflector group and the second reflector group are both composed 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 of the test chamber is more than one order of magnitude lower than the pressure of the measured molecular flow.

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