A high-dynamic in-situ online measurement system for dew point in a low-temperature wind tunnel test section

Abstract

This invention discloses a high-dynamic in-situ online dew point measurement system for a low-temperature wind tunnel test section in the field of wind tunnel dew point testing. It includes a first chamber and a second chamber, each located within one of the two chambers of the wind tunnel. The first chamber houses an optical emission unit, and the second chamber houses an optical reflection unit. An environmental monitoring module is installed within the wind tunnel. The optical emission unit, optical reflection unit, and laser drive unit are connected to a laser drive unit, which in turn is connected to a communication control unit. Both the first and second chambers are connected to a nitrogen unit and a vacuum unit via pipelines, with valve groups installed on the pipelines to control their operation. This invention enables high-frequency response, real-time, and high-precision dew point monitoring, providing criteria for wind tunnel cooling procedures and gas state parameters for detecting water vapor concentration and changes, and calculating Reynolds numbers during testing.

Description

Technical Field

[0001] This invention relates to the field of wind tunnel testing, specifically a high-dynamic in-situ online measurement system for dew point in a low-temperature wind tunnel test section. Background Technology

[0002] Low-temperature, high-Reynolds-number wind tunnels are essential equipment for conducting complex viscous flow field performance tests during the development of large aircraft, advanced fighter jets, and spacecraft operating in atmospheric reentry. Unlike ambient-temperature wind tunnels, low-temperature wind tunnels operate at extremely low temperatures to generate high Reynolds-number conditions. Low-temperature operation places stringent requirements on the control of water vapor concentration within the wind tunnel, necessitating the prevention of frost / ice formation on the surface of scaled-down test models, which would affect the accuracy of model tests. Therefore, during the cleaning and drying process before cooling the low-temperature transonic wind tunnel, water vapor levels must be reduced to a sufficiently low level. Dew point, also known as dew temperature, is the temperature at which water vapor in a gas condenses into dew or frost under constant pressure. It can be used to characterize the water vapor content in a gas. According to the design requirements of low-temperature wind tunnels, online monitoring of the gas dew point is necessary during the cleaning and cooling process, with a measurement range of -100℃ to +20℃.

[0003] Currently, wind tunnel dew point measurements primarily employ cold mirror dew point meters for gas extraction-based measurements. In extraction-based dew point measurements, the results are affected by the adsorption and desorption effects of water vapor in the pipeline, leading to errors or even erroneous readings. Furthermore, the mirror of the cold mirror dew point meter is easily contaminated, affecting measurement accuracy. Additionally, cold mirror dew point meters have long response times under extremely low dew point conditions; for example, at dew point temperatures below -80°C, the response time can reach approximately 10 minutes.

[0004] In summary, low-temperature high Reynolds number wind tunnels have the following testing requirements:

[0005] 1) High dynamic demand: The partial pressure of water vapor at a dew point of -100℃ is 1.4 × 10⁻⁶. -3 Pa, the partial pressure of water vapor at the dew point of 20℃ is 2.34 Pa × 10⁻¹⁰. 3 Pa spans six orders of magnitude, thus providing a wide dynamic range for dew point measurement.

[0006] 2) In-situ measurement requirements: In order to accurately monitor the dew point of the wind tunnel test section and to avoid the impact of pipeline desorption on measurement accuracy, in-situ measurement is required.

[0007] 3) Online measurement requirements: Cold mirror dew point meters have a slow response time at extremely low dew points, making it difficult to monitor rapid changes in water vapor concentration in the test section. Therefore, online rapid measurement is required.

[0008] Therefore, a high-dynamic dew point in-situ online measurement system is needed to overcome the above-mentioned existing problems and meet measurement requirements. Summary of the Invention

[0009] The purpose of this invention is to provide a high-dynamic in-situ online measurement system for dew point in a low-temperature wind tunnel test section, so as to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A high-dynamic in-situ online measurement system for dew point in a low-temperature wind tunnel test section includes a first chamber and a second chamber respectively located in two chambers of the wind tunnel. The first chamber is equipped with an optical emission unit, and the second chamber is equipped with an optical reflection unit. An environmental monitoring module is installed inside the wind tunnel. The optical emission unit, the optical reflection unit, and the laser driving unit are connected to a laser driving unit. The laser driving unit and the environmental monitoring module are connected to a communication control unit. Both the first chamber and the second chamber are connected to a nitrogen unit and a vacuum unit through pipelines, and valve groups for controlling their on / off states are installed on the pipelines.

[0012] The communication control unit includes a data receiving module, a dew point calculation module, an H2O background feedback control module, and a temperature control module. The data receiving module is connected to the laser driving unit. The dew point calculation module receives detection data from the data receiving module and the environmental monitoring module and calculates the wind tunnel dew point parameters. The temperature control module is used to control the temperature inside the first chamber and the second chamber. The H2O background feedback control module is connected to the valve group.

[0013] In some embodiments, a purifier is connected before the nitrogen unit is connected to the first chamber and the second chamber.

[0014] In some embodiments, the optical emitting unit includes a laser source module, a laser detector module, and an integrated emitting and receiving module, and the optical reflecting unit includes a reflecting device module. The laser source module emits a measurement beam and a reference beam through the integrated emitting and receiving module. The measurement beam is received and collected by the laser detector module after being reflected multiple times by the reflecting device module, and the reference beam is received and collected by the laser detector module after being reflected by the integrated emitting and receiving module.

[0015] In some embodiments, the laser driving unit is disposed in the third chamber and installed on one side of the laser source module; the laser driving unit includes a laser control module, a laser modulation signal module, a photoelectric signal amplification module, and a data acquisition and transmission module; the laser control module is used to control the operating temperature and driving current of the laser source module; the laser modulation signal module is connected to the laser control module and is used to generate a laser modulation signal and send it to the laser source module; the photoelectric signal amplification module is used to convert the photoelectric signal of the laser detector module into a voltage signal; the data acquisition and transmission module is connected to the output terminal of the photoelectric signal amplification module and also connected to the communication control unit.

[0016] In some embodiments, the optical reflection unit further includes an automatic optical path alignment adjustment device module, and a fourth chamber is provided on one side of the second chamber. An optical path adjustment drive unit is installed in the fourth chamber. The optical path adjustment drive unit includes an electric adjustment device controller, which is connected to the automatic optical path alignment adjustment device module and the communication control unit.

[0017] In some embodiments, the communication control unit further includes an optical path adjustment module and a measurement and control system communication and control module. The optical path adjustment module controls the electric adjustment device controller through data from the data receiving module, and the measurement and control system communication and control module is connected to the temperature control module.

[0018] In some embodiments, the first chamber and the second chamber are both cryogenic protective shells with a double-layer vacuum structure.

[0019] In some embodiments, the windows on the first chamber and the second chamber are arranged on the optical observation window on the wall of the wind tunnel test section.

[0020] Beneficial effects: This invention can be used for online dew point measurement in low-temperature transonic wind tunnel test sections and stable sections, enabling high-frequency response and real-time high-precision dew point monitoring, providing criteria for wind tunnel cooling procedures, and providing gas state parameters for detecting water vapor concentration and changes and calculating Reynolds number during the test. Attached Figure Description

[0021] Figure 1 This is an overall schematic diagram of the present invention;

[0022] Figure 2 This is a schematic diagram of the basic structure of Embodiment 1 of the present invention;

[0023] Figure 3 This is a schematic diagram of measuring 10 reflections of the light beam in Embodiment 1 of the present invention;

[0024] Figure 4 This is a complete schematic diagram of Embodiment 1 of the present invention;

[0025] Figure 5 This is a schematic diagram of Embodiment 2 of the present invention.

[0026] In the picture:

[0027] 1-Optical transmitting unit; 101-First chamber; 102-Laser source module; 103-Laser detector module; 104-Integrated transmitting and receiving module;

[0028] 2-Optical reflection unit; 201-Second chamber; 202-Reflection device module; 203-Automatic optical path alignment adjustment device module;

[0029] 3-Laser drive unit; 301-Third chamber; 302-Laser control module; 303-Laser modulation signal module; 304-Photoelectric signal amplification module; 305-Data acquisition and transmission module;

[0030] 4-Optical path adjustment drive unit; 401-Fourth chamber; 402-Electric adjustment device controller;

[0031] 51 - First light window, 52 - Second light window;

[0032] 6-Control cabinet;

[0033] 7-Communication control unit; 71-Data receiving module; 72-Dew point calculation module; 73-H2O background feedback control module; 74-Optical path adjustment module; 75-Measurement and control system communication and control module;

[0034] 9-Power supply module;

[0035] 10-Temperature and pressure transmitter;

[0036] 11, 12 - Temperature control module;

[0037] 13, 14, 16, 17 - Solenoid valves;

[0038] 15-Purifier;

[0039] 18, 19 - Nitrogen Units;

[0040] 20 - Ambient temperature and pressure sensor; Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1, see Figure 2A high-dynamic dew point in-situ online measurement system for a low-temperature wind tunnel test section includes a first chamber 101 and a second chamber 201, which are respectively located in two chambers on opposite sides of the wind tunnel test section. Window panes are provided on the opposite surfaces of the first chamber 101 and the second chamber 201. A first optical window 51 is provided on the wall of the test section near the first chamber 101, and a second optical window 52 is provided on the wall of the test section near the second chamber 201. The first optical window 51 and the second optical window 52 are used to allow laser light to pass through. Preferably, the window panes of the first chamber 101 and the second chamber 201 coincide with the first optical window 51 and the second optical window 52, ​​respectively, that is, they are combined into a single window pane, which can eliminate the optical etalon effect that may be introduced by multiple optical planes.

[0043] In this embodiment, the first chamber 101 and the second chamber 201 are ordinary instrument chambers. The first chamber 101 is provided with an optical emission unit 1, which includes a laser source module 102, a laser detector module 103 and an integrated transmission and reception module 104. The second chamber 201 is provided with an optical reflection unit 2, which includes a reflection device module 202.

[0044] The laser source module 102 generates laser light of the target wavelength, which is collimated by the integrated transmitter-receiver module 104. Then, spatial beam combining is used to combine the laser beams; part of the combined laser beam serves as the measurement beam, and the other part serves as the reference beam. The measurement beam passes through the flow field of the test section multiple times via the measurement optical path and returns to the optical transmitter unit 1, where it is received by the laser detector module 103. Simultaneously, the reference beam, after being reflected by the integrated transmitter-receiver module 104 within the optical transmitter unit 1, directly reaches the laser detector module 103. The laser detector module 103 receives the laser signal and performs the conversion from laser detection to an electrical signal.

[0045] Specifically, in order to achieve dew point measurement with a wide dynamic range, the laser source module 102 is configured to emit multiple lasers with different wavelengths. The laser detector module 103 needs to receive the measurement beam and the reference beam. Therefore, the laser detector module 103 includes a first detector and a second detector, wherein the first detector is used to receive information of the reference beam and the second detector is used to receive information of the measurement beam.

[0046] The integrated transmitter and receiver module 104 is used to perform multiplexing of different wavelengths, laser collimated transmission, and laser collection. It includes multiple transmitter reflectors, an off-axis parabolic mirror, a laser beam splitter and synthesizer, a wavelength division multiplexer, a collimator, and an optical isolator. In this embodiment, the transmitter reflectors include a first transmitter reflector, a second transmitter reflector, a third transmitter reflector, a fourth transmitter reflector, and a fifth transmitter reflector. The reflection device module 202 includes multiple reflector reflectors and a hollow cone retroreflector. Specifically, the reflector reflectors include a first reflector reflector and a second reflector reflector.

[0047] The lasers emitted by the second and third lasers are combined by a wavelength division multiplexer and then collimated by a collimator before being emitted. The laser emitted by the first laser after collimation by an optical isolator is combined with the light emitted from the collimator by a laser beam splitter and combiner. 90% of the combined laser energy is used as the measurement beam, and the remaining 10% of the combined laser energy is used as the reference beam. This ensures that both the reference and measurement optical paths have sufficient signal-to-noise ratios and will not affect the accuracy of low dew point measurements.

[0048] The measurement beam is emitted through an off-axis parabolic mirror, passes through the first optical window 51 and the second optical window 52, ​​and is reflected 10 times back and forth through the incoming gas medium in the test section in the measurement optical path composed of the fourth transmitting end reflector, the fifth transmitting end reflector, the first reflecting end reflector, the second reflecting end reflector and the hollow corner cone retroreflector, thereby increasing the measurement optical path. Finally, the off-axis parabolic mirror receives and focuses the beam onto the second detector, realizing a compact optical system design that integrates transmission and reception.

[0049] The reference beam is mainly increased in optical path by multiple reflections through the first, second, and third transmitter mirrors before being received by the first detector.

[0050] Because the measuring beam has a certain optical path length within the two optical emitting units 1 and optical reflecting units 2, to reduce the impact of water vapor absorption along this optical path on the accuracy of dew point measurement, the water vapor absorption along the reference optical path can be measured as background subtraction. The two units are cascaded and purged, and background subtraction is performed according to the ratio of the optical path length within the two units to the optical path length of the reference beam. The ratio of the optical path lengths of the two units is controlled within 1:5 to 5:1. If the optical path lengths of the two units are approximately equal at a ratio of 1:1, the subtraction effect is better within an error range of ±5%.

[0051] A laser driving unit 3 is installed outside the wind tunnel. The optical emitting unit 1 and the optical reflecting unit 2 are connected to the laser driving unit 3. The laser driving unit 3 can control the laser in the laser source module 102 to emit light. In this embodiment, an environmental monitoring module is also installed inside the wind tunnel. The environmental monitoring module can be configured as an environmental temperature and pressure sensor 20. The detection values ​​of the environmental temperature and pressure sensor 20 can be converted into static temperature and static pressure values ​​of the test section by the temperature and pressure converter 10 and sent to the communication control unit 7 for data processing.

[0052] The principle of the in-situ online dew point measurement technology in this embodiment is as follows:

[0053] Based on the principle of laser absorption spectroscopy, the measurement beam passes through the test section, directly acquiring the accumulated absorption signal along the optical path. After intensity normalization and wavelength calibration, the transmittance or absorbance signal is obtained. The integrated absorbance signal A = S(T)PXL of the water vapor target absorption line is obtained through spectral model fitting. Combined with the static temperature T of the flow field collected by the environmental monitoring module, the upper limit intensity S(T) at the current temperature can be calculated to obtain the water vapor partial pressure. Corresponding dew point temperature T d The lower saturated vapor pressure; if atmospheric dew point needs to be calculated, it is converted using the environmental static pressure P collected by the environmental monitoring module, keeping the water vapor partial pressure ratio / volume ratio concentration constant during the conversion, as shown in the following formula:

[0054]

[0055] The conversion from saturated vapor pressure to dew point temperature is obtained by using the empirical formula given in WSO ITS-90 or by referring to tables in GB / T5832.2-2016 Determination of Trace Moisture in Gases Part II: Dew Point Method.

[0056] The principle of high dynamic range dew point measurement in this embodiment is as follows:

[0057] The partial pressure of water vapor at a dew point of -100℃ is approximately 1.4 × 10⁻⁶. -3 Pa, the partial pressure of water vapor at the dew point of 20℃ is approximately 2.34 Pa × 10⁻¹⁰. 3 Pa spans six orders of magnitude. A single wavelength cannot cover the water vapor volume ratio concentration corresponding to the dew point range of -100℃ to 20℃. Therefore, this invention employs a multi-wavelength measurement system, with stronger absorption lines used for detecting lower dew point temperatures and weaker absorption lines used for detecting higher dew point temperatures. In this embodiment, 1383nm and 2626nm lasers are selected to achieve coverage of multiple absorption wavelengths, allowing the dew point measurement system to detect a dew point temperature range of -100℃ to +20℃. Specifically, the 2626nm laser covers the low dew point range of -100℃ to -40℃, and the 1383nm laser covers the dew point range of -60℃ to +20℃. The overlapping coverage areas can be used for mutual verification.

[0058] Because the range and accuracy of dew point measurement are related not only to the intensity of the selected wavelength but also to the optical path length of the measurement optical path, a longer optical path results in a larger absorbance signal. In this embodiment, an optical path length better than 20m is required to achieve dew point measurement within the range of -100℃ to +20℃. Figure 3 As shown, assuming the test section length is 2.6m, and based on 10 round trip reflections, the test optical path is no less than 26m. The laser source module 102 emits light containing laser beams from 1383nm and 2626nm wavelength lasers combined and propagating along the same optical path.

[0059] In this embodiment, the window materials of the first chamber 101, the second chamber 201, the first optical window 51, and the second optical window 52 can all be configured as infrared quartz JGS3, which can meet the penetration requirements of 1383nm and 2626nm lasers. The beam emitted by the first laser is in the 2626nm band, the beam emitted by the second laser is in the 650nm band, and the beam emitted by the third laser is in the 1383nm band.

[0060] Since the optical emitting unit 1 and the optical reflecting unit 2 are located in the wind tunnel's occupancy chamber, in a low-temperature and variable-pressure environment, both the first chamber 101 and the second chamber 201 are configured as low-temperature protective shells with a double-layer vacuum structure to protect the equipment inside the optical emitting unit 1 and the optical reflecting unit 2.

[0061] Both the first chamber 101 and the second chamber 201 have pressure-bearing capacity in their cryogenic protective shells, and the cryogenic protection temperature control structures of the two chambers are identical.

[0062] Both chambers are equipped with temperature sensors and heating modules, and each is connected to two external pipelines. One pipeline connects to a nitrogen unit 18, with a solenoid valve 16 installed on it. A purifier 15 is installed between the nitrogen unit 18 and the solenoid valve 16 to remove moisture from the nitrogen, reducing the moisture content to the level of 0.1–1 ppb. This significantly reduces the moisture background in the optical emission unit 1 and optical reflection unit 2, effectively controlling the moisture background in these units to below -100°C dew point or 14 ppb. The other pipeline is equipped with a solenoid valve 17 and connects to a vacuum unit (not shown in the figure). The temperature sensor detects temperature changes inside the cryogenic protective shell, and the reference optical path in the first chamber 101 detects the moisture content inside the cryogenic protective shell. The temperature sensor, heating module, and solenoid valve 16 are all connected to a temperature control module 11, which controls the temperature inside the first chamber 101.

[0063] When necessary, the vacuum unit evacuates the first chamber 101 and the second chamber 201 to test for leaks. Initial moisture background treatment of the first chamber 101 and the second chamber 201 is performed using a series purging method. During nitrogen purging, solenoid valves 16 and 17 on the connecting pipes of the first chamber 101 and the second chamber 201 are opened to vent gas and force heat exchange to prevent excessive temperature inside the cryogenic protective housing. Solenoid valves 16 and 17 are both connected to the H2O background feedback control module 73 and the power module 9 in the communication control unit 7. The H2O background feedback control module 73, based on the moisture background monitoring data in the two chambers, uses ultra-high purity N2 series purging feedback to control the moisture background in the first chamber 101 and the second chamber 201 to below the threshold level. The power module 9 includes a UPS module and a DC power conversion module, providing the required DC voltage for the communication control power supply of the dew point measurement system and the optical and electronic units.

[0064] Through heating modules and nitrogen purging, the internal temperature of the first chamber 101 and the second chamber 201 is controlled and maintained between 15℃ and 35℃, and the equipment is kept in a dry gas environment, which is suitable for the operation of the optical emission unit 1 and the optical reflection unit 2.

[0065] Example 2, as Figure 5 As shown, unlike the above embodiments, in this embodiment, the laser driving unit 3 is located in the third chamber 301 and installed on one side of the laser source module 102, that is, installed close to the laser source module 102, at a distance of no more than 0.5m. The laser driving unit 3 includes a laser control module 302, a laser modulation signal module 303, a photoelectric signal amplification module 304, and a data acquisition and transmission module 305. The laser control module 302 is used to control the operating temperature and driving current of the laser source module 102; the laser modulation signal module 303 is connected to the laser control module 302, used to generate a laser modulation signal and send it to the laser source module 102, and provide a unified clock signal for the data acquisition and transmission module 305; the laser control module 302, the laser modulation signal module 303 and the laser source module 102 are installed close to each other, which can eliminate the possible electromagnetic interference of long-distance transmission on the laser operating temperature and current, stabilize the laser output wavelength, and reduce wavelength drift and intensity fluctuation noise.

[0066] The laser modulation signal module 303 generates a laser modulation signal, which is then loaded onto the laser source module 102 via the laser control module 302 to perform periodic scanning of the laser wavelength. The laser control module 302 is connected to the laser source module 102 via a cable, enabling attitude control of the laser source module 102 and allowing the laser source to periodically and repeatedly scan the selected water vapor absorption spectrum measurement band. The photoelectric signal amplification module 304 is connected to the laser detector module 103. The photoelectric signal amplification module 304 converts the detector's photoelectric signal into a voltage signal suitable for acquisition, including two channels: measurement and reference. The data acquisition and transmission module 305 performs AD conversion on the output voltage of the photoelectric signal amplification module 304, acquires spectral signals from the measurement and reference channels, laser operating status parameters, and other signals, and transmits the acquired data to the data receiving unit 71 within the communication control unit 7 (typically configurable as an industrial computer) outside the wind tunnel via the Ethernet UDP protocol.

[0067] In this embodiment, the optical reflection unit 2 further includes an automatic optical path alignment adjustment device module 203. The automatic optical path alignment adjustment device module 203 is mainly configured as a piezoelectric control adjustment unit 206, which can be used to compensate for optical path deflection and misalignment effects that may be caused by wind tunnel deformation, vibration, etc. A fourth chamber 401 is provided on one side of the second chamber 201. An optical path adjustment drive unit 4 is installed in the fourth chamber 401. The optical path adjustment drive unit 4 includes an electric adjustment device controller 402. The electric adjustment device controller 402 converts the adjustment command issued by the communication control unit 7 into an action requirement and transmits it to the automatic optical path alignment adjustment device module 203 in the form of voltage through the connection port of the second chamber 201.

[0068] In this embodiment, the communication control unit 7 is located in the control cabinet 6, enabling communication with the laser driver unit 1, the optical path alignment automatic adjustment device driver unit 1, and the wind tunnel measurement and control system, thereby transmitting data signals and control signals. The communication control unit 7 includes a data receiving module 71, a dew point calculation module 72, an H2O background feedback control module 73, an optical path adjustment module 74, and a measurement and control system communication and control module 75.

[0069] In this embodiment, the third chamber 301 and the fourth chamber 401 are located in the occupancy chamber of the wind tunnel, and are therefore also configured as low-temperature protective shells to protect the internal equipment. Since laser emission is not required, no light window is needed. The control cabinet 6 is also equipped with a temperature control module for controlling the temperature of the third chamber 301 and the fourth chamber 401.

[0070] The cryogenic control structure of the fourth chamber 401 is the same as that of the third chamber 301. Taking the third chamber 301 as an example, the third chamber 301 is connected to two external pipelines. One pipeline connects to the vacuum unit and a solenoid valve 14 is installed on the pipeline. The other pipeline connects to the nitrogen unit 19 and a solenoid valve 13 is installed on the pipeline. Both solenoid valves 13 and 14 are connected to the temperature control module 12.

[0071] The H2O background feedback control module 73 is connected to the solenoid valves on the connecting pipes of each chamber, and the measurement and control system communication and control module 75 is connected to the temperature control module corresponding to each chamber.

[0072] The data receiving module 71 is used to receive laser spectral signals, laser operating status parameters, and electric adjustment devices. The dew point calculation module 72 determines the test system status composed of optical emission unit 1 and optical unit 2 in the TDLAS dew point measurement system based on the received data signals, and processes the spectral signals to obtain the dew point value by combining the static temperature and static pressure data of the wind tunnel flow field measured by the ambient temperature and pressure sensor 20 and output by the temperature and pressure transmitter 10.

[0073] The H2O background feedback control module 73 performs H2O background concentration feedback control based on the monitoring data of water vapor background in the chamber, determining whether to use high-purity nitrogen, which has been further filtered by the purifier 15 to purge the first chamber 101 with nitrogen. Ultra-high-purity N2 purging feedback control keeps the water vapor background in the first chamber below the threshold level. Meanwhile, each temperature control module uses the temperature monitoring values ​​from the temperature sensors inside the four chambers 101, 201, 301, and 401 to control the heating power of the heating module, and uses high-purity nitrogen purging for forced convection heat transfer to maintain the temperature in each chamber between 15℃ and 35℃. Figure 1 The gas and electrical connection cables of the second chamber 201 and the fourth chamber 401 are not shown. The first chamber 101, the second chamber 201, the third chamber 301 and the fourth chamber 401 are all connected to the purifier through pipes to achieve further water vapor removal from the nitrogen unit.

[0074] The optical path control module 74 generates a control strategy based on the intensity of the spectral signal received by the data receiving module 71, and feeds back the control strategy to the automatic optical path alignment adjustment module 203 via the electric adjustment device controller 402 to achieve automatic optical path adjustment and alignment. The measurement and control system communication and control module 75 is used to realize communication with the measurement and control system for full data management of the wind tunnel, and to complete the transmission of dew point data, temperature, pressure, system health status information, and control commands.

[0075] In this embodiment, the optical emission unit, optical reflection unit, and laser drive unit inside the wind tunnel are connected to the control unit 6 outside the wind tunnel via cables. More specifically, the laser source module 102 and laser detector module 103 in the optical emission unit 1 are directly connected to the laser drive unit 3, with the connection being an analog signal; the laser drive unit 3 is connected to the communication control unit 7 outside the wind tunnel, with the connection being a digital signal, including spectral signals and laser status parameters, transmitted via Ethernet and serial ports. Furthermore, the communication control unit 7 provides DC power and temperature control signals connected to the optical emission unit 1 and the laser drive unit 3.

[0076] The automatic optical path alignment adjustment device 203 in the optical reflection unit 2 inside the wind tunnel is connected to the electric adjustment device controller 402 in the optical path adjustment drive unit 4 via an analog signal. The optical path adjustment drive unit 4 is connected to the communication control unit 7 via a digital signal to control the adjustment parameters of the automatic optical path alignment adjustment device 203. In addition, the communication control unit 7 provides DC power and temperature control signals to the optical reflection unit 2 and the optical path adjustment drive unit 4. The communication control unit 7 in the control cabinet 6 can be connected to the overall wind tunnel measurement and control system via a network port.

[0077] The present invention has at least the following advantages:

[0078] (1) Compared with the cold mirror dew point meter, the TDLAS dew point measurement system provided in this application has the advantages of non-contact and in-situ online measurement. It can directly measure the dew point in-situ without extracting gas, thereby eliminating the uncertain measurement error caused by the desorption effect of the extraction pipeline.

[0079] (2) The dew point measurement system shown in this invention maintains consistent spectral measurement and dew point calculation time regardless of water vapor content or dew point level, and can output dew point measurement values ​​with a frequency response exceeding 1 Hz. In contrast, due to limitations in its measurement principle, the cold mirror dew point meter requires a long time to determine the frost temperature at low dew points, and a response time on the order of 10 minutes is needed for dew points below -80℃.

[0080] (3) The present invention can achieve accurate measurement of dew point temperature from -100℃ to 20℃, covering a water vapor concentration range of more than 6 orders of magnitude.

[0081] This invention can be used for online dew point measurement in low-temperature transonic wind tunnel test sections and stable sections. It can implement high-frequency response and real-time high-precision dew point monitoring, provide criteria for wind tunnel cooling procedures, and provide gas state parameters for detecting water vapor concentration and changes and calculating Reynolds number during the test.

[0082] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0083] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A high-dynamic dew point in-situ online measurement system for a low-temperature wind tunnel test section, comprising a first chamber (101) and a second chamber (201) respectively located in two chambers of the wind tunnel, wherein the first chamber (101) is provided with an optical emission unit (1) and the second chamber (201) is provided with an optical reflection unit (2); an environmental monitoring module is installed in the wind tunnel, characterized in that, The optical emission unit (1), optical reflection unit (2) are connected to the laser drive unit (3), and the laser drive unit (3) and environmental monitoring module are connected to the communication control unit (7); the first chamber (101) and the second chamber (201) are both connected to a nitrogen unit and a vacuum unit through pipes, and valve groups that control their opening and closing are installed on the pipes; The communication control unit (7) includes a data receiving module (71), a dew point calculation module (72), an H2O background feedback control module (73), and a temperature control module. The data receiving module (71) is connected to the laser driving unit (3). The detection data from the data receiving module (71), the dew point calculation module (72), and the environmental monitoring module are used to calculate the wind tunnel dew point parameters. The temperature control module is used to control the temperature inside the first chamber (101) and the second chamber (201). The H2O background feedback control module (73) is connected to the valve group. The H2O background feedback control module (73) is used to purge the water vapor background in the first chamber (101) and the second chamber (201) using ultra-high purity N2 from the nitrogen unit in series, based on the water vapor background monitoring data in the first chamber (101) and the second chamber (201), so that the water vapor background in the chamber is lower than the threshold.

2. The high-dynamic in-situ online measurement system for dew point in a low-temperature wind tunnel test section according to claim 1, characterized in that, The nitrogen unit is connected to a purifier (15) before entering the first chamber (101) and the second chamber (102).

3. The high-dynamic in-situ online measurement system for dew point in a low-temperature wind tunnel test section according to claim 1, characterized in that, The optical emission unit (1) includes a laser source module (102), a laser detector module (103), and an integrated transmission and reception module (104). The optical reflection unit (2) includes a reflection device module (202). The laser source module (102) emits a measurement beam and a reference beam through the integrated transmission and reception module (104). The measurement beam is received and collected by the laser detector module (103) after being reflected multiple times by the reflection device module (202). The reference beam is received and collected by the laser detector module (103) after being reflected by the integrated transmission and reception module (104).

4. The in-situ online high-dynamic dew point measurement system for a low-temperature wind tunnel test section according to claim 3, characterized in that, The laser driving unit (3) is located in the third chamber (301) and installed on one side of the laser source module (102). The laser driving unit (3) includes a laser control module (302), a laser modulation signal module (303), a photoelectric signal amplification module (304), and a data acquisition and transmission module (305). The laser control module (302) is used to control the operating temperature and driving current of the laser source module (102). The laser modulation signal module (303) is connected to the laser control module (302) and is used to generate a laser modulation signal and send it to the laser source module (102). The photoelectric signal amplification module (304) is used to convert the photoelectric signal of the laser detector module (103) into a voltage signal. The data acquisition and transmission module (305) is connected to the output end of the photoelectric signal amplification module (304) and is also connected to the communication control unit (7).

5. The high dynamic dew point in-situ online measurement system for a low-temperature wind tunnel test section according to claim 1, characterized in that, The optical reflection unit (2) further includes an automatic optical path alignment adjustment device module (203). A fourth chamber (401) is provided on one side of the second chamber (201). An optical path adjustment drive unit (4) is installed in the fourth chamber (401). The optical path adjustment drive unit (4) includes an electric adjustment device controller (402). The electric adjustment device controller (402) is connected to the automatic optical path alignment adjustment device module (203) and the communication control unit (7).

6. The high dynamic dew point in-situ online measurement system for a low-temperature wind tunnel test section according to claim 5, characterized in that, The communication control unit (7) further includes an optical path control module (74) and a measurement and control system communication and control module (75). The optical path control module (74) controls the electric adjustment device controller (402) through the data received by the data receiving module (71). The measurement and control system communication and control module (75) is connected to the temperature control module.

7. The in-situ online high-dynamic dew point measurement system for a low-temperature wind tunnel test section according to claim 1, characterized in that, Both the first chamber (101) and the second chamber (201) are low-temperature protective shells with a double-layer vacuum structure.

8. The high dynamic dew point in-situ online measurement system for a low-temperature wind tunnel test section according to claim 1, characterized in that, The windows on the first chamber (101) and the second chamber (201) are both set on the optical observation windows on the wall of the wind tunnel test section.

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