Tracer method and tracer system

Abstract

The present application relates to a tracing method and a tracing system. Among them, the tracing method includes: using a tracer gas generating device to process two or more tracers to respectively form different tracer gases; the tracers are PLIF tracers; introducing each tracer gas into a wind tunnel through a dispensing device; the dispensing device is provided with two or more dispensing channels; each tracer gas is introduced into the wind tunnel through different dispensing channels; an imaging device excites each tracer gas to make each tracer gas radiate a fluorescence signal to generate a fluorescence image; a control device acquires the fluorescence image and determines the transition point of the turbulent flow field according to the fluorescence image. For the above tracing method, on the one hand, multiple tracer lines can be formed to expand the visualization range and obtain more flow field information; on the other hand, the relationship between the development and change of the turbulent flow field structure and the laminar flow field at a specific position can be analyzed, the visualization of the flow field structure during the transition process at different positions can be realized, and then the transition point of the turbulent flow field can be determined.

Description

Technical Field

[0001] This application relates to the field of flow field visualization, and particularly to a tracing method and a tracing system. Background Art

[0002] In aerospace engineering, wind tunnel experiments are an important means for verifying relevant aerodynamic models and evaluating the rationality of the aerodynamic layout of specific models. If the airflow changes from laminar flow to turbulent flow after passing through the model in the wind tunnel, that is, the transition phenomenon occurs, then the flight resistance and surface pressure received by the model will change. Obtaining information such as the change of the flow field structure and the transition position based on experimental data analysis is of great significance for the theoretical research verification of aerodynamics and the technical optimization of aerospace engineering.

[0003] For traditional low-speed flow field visualization techniques, due to the poor followability of tracer particles, it is difficult to visualize unsteady flows. The planar laser-induced fluorescence (PLIF) technique can be used to visualize the unsteady flow in the wind tunnel because the tracer particles are gas molecules and have excellent followability. However, for traditional tracing methods, the PLIF tracer gas is released into the wind tunnel flow field through the aircraft model, and only the visualization of the transition flow field structure at a single position can be achieved, and the visualization of the flow field structure during the transition process at different positions cannot be comprehensively obtained.

[0004] Therefore, traditional tracing methods have the problem of insufficient information. Summary of the Invention

[0005] It is necessary to provide a tracing method and a tracing system that can obtain more flow field information for the above technical problems.

[0006] In one embodiment, a tracing method is provided. In one embodiment, the tracing method includes:

[0007] Using a tracer gas generating device to process two or more tracers to respectively form different tracer gases; the tracers are PLIF tracers;

[0008] Introducing each tracer gas into the wind tunnel through a dispensing device; the dispensing device is provided with two or more dispensing channels; each tracer gas is introduced into the wind tunnel through different dispensing channels;

[0009] An imaging device excites each tracer gas to make each tracer gas emit a fluorescence signal and generate a fluorescence image;

[0010] A control device acquires the fluorescence image and determines the transition point of the turbulent flow field according to the fluorescence image.

[0011] In one of the embodiments, after the control device acquires the fluorescence image, it further includes:

[0012] The control device adjusts the parameters of the dispensing device according to the fluorescence image.

[0013] In one embodiment, the tracer gas generating device includes a bubbling tank. Processing the tracer to form the tracer gas by the tracer generating device includes:

[0014] Introducing the bubbling gas into the liquid tracer in the bubbling tank, mixing with the tracer vapor in the bubbling tank, and forming a tracer gas composed of the bubbling gas and the tracer vapor.

[0015] In one embodiment, the PLIF tracer is a ketone tracer, an aromatic tracer or an inorganic tracer.

[0016] In one embodiment, the dispensing device is a steel pipe. Introducing the respective tracer gases into the wind tunnel through the dispensing device includes:

[0017] Introducing the respective tracer gases into different dispensing channels inside the steel pipe through one end of the steel pipe; the other end of the steel pipe is closed, and at least one air outlet connected to the corresponding dispensing channel is correspondingly arranged on the leeward side of the steel pipe;

[0018] The respective tracer gases are respectively introduced into the wind tunnel through the corresponding air outlets.

[0019] In a second aspect of the present application, a tracer system is provided. In one embodiment, the tracer system includes a tracer gas generating device, a dispensing device, an imaging device and a control device;

[0020] The tracer gas generating device is used to process two or more tracers to respectively form different tracer gases; the tracer is a PLIF tracer;

[0021] The dispensing device is used to introduce the respective tracer gases into the wind tunnel; the dispensing device is provided with two or more dispensing channels; the respective tracer gases are respectively introduced into the wind tunnel through different dispensing channels;

[0022] The imaging device is used to excite the respective tracer gases to make the respective tracer gases radiate fluorescence signals and generate a fluorescence image;

[0023] The control device is used to acquire the fluorescence image and determine the transition point of the turbulent flow field according to the fluorescence image.

[0024] In one embodiment, the tracer gas generating device includes a high-pressure gas cylinder, a gas mass flowmeter and a bubbling tank connected in sequence; the gas mass flowmeter is connected to the control device, and the bubbling tank is connected to the dispensing device.

[0025] In one embodiment, the imaging device includes an excitation device and a detection device.

[0026] In one embodiment, the excitation device includes a laser light source and a beam delivery device.

[0027] In one embodiment, the detection device includes a beam splitter, and more than two filters and detectors; the filters and the detectors are correspondingly arranged for detecting fluorescence images of different PLIF tracers respectively.

[0028] In the above-mentioned tracer method, more than two PLIF tracers are introduced into the wind tunnel using different injection channels. On the one hand, multiple tracer lines can be formed to expand the visualization range and obtain more flow field information. On the other hand, since the laminar flow fields at various positions represented by different tracers influence each other during the transition process, by simultaneously obtaining the turbulent flow field structure images after the transition of the laminar flow fields at different positions, the relationship between the development and change of the turbulent flow field structure and the laminar flow field at a specific position can be analyzed, realizing the visualization of the flow field structure during the transition process at different positions, and further determining the transition points of the turbulent flow field. Description of the Drawings

[0029] Figure 1 is a schematic flow chart of the tracer method in one embodiment;

[0030] Figure 2 is a schematic diagram of the tracer process in one embodiment;

[0031] Figure 3 is a schematic flow chart of using a tracer gas generation device to process more than two tracers to form different tracer gases respectively in one embodiment;

[0032] Figure 4 is a schematic flow chart of introducing each tracer gas into the wind tunnel through an injection device in one embodiment;

[0033] Figure 5 is a block diagram of the composition of the tracer system in one embodiment;

[0034] Figure 6 is a schematic structural diagram of the tracer gas generation device in one embodiment;

[0035] Figure 7 is the fluorescence absorption spectra of acetone and toluene;

[0036] Figure 8 is a schematic structural diagram of the detection device in one embodiment. Detailed Embodiments

[0037] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application with reference to the relevant accompanying drawings. Embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of this application more thorough and comprehensive.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0039] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" or "having" etc. specify the presence of the stated features, wholes, steps, operations, components, parts or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the related listed items.

[0040] In the first aspect of this application, a tracing method is provided, which can be used for the study of the range of the laminar flow influence area in aerodynamics and can also be applied to establish the relationship between the development and change of the turbulent flow field structure and the laminar flow field at a specific position. In one embodiment, please refer to Figure 1 , this tracing method includes steps S100 to step S700.

[0041] Step S100: Use a tracer gas generating device to process more than two tracers to form different tracer gases respectively.

[0042] Among them, a tracer refers to a marker added to observe, study, and measure the behavior or properties of a certain substance in a specified process. As a tracer, its properties or behavior should be exactly the same or have very little difference from the substance being traced in this process; its addition amount should be very small, have no significant impact on the system, and must be easily detectable. A tracer gas refers to a gas containing a tracer. Further, the tracer used in this application is a PLIF (Planer Laser Induced Fluorescence) tracer. A PLIF tracer is a tracer that can emit fluorescence under laser irradiation. Specifically, under the irradiation of a laser, the tracer particles in the PLIF tracer are excited. The electrons in the tracer particles transition from the ground state to the excited state, and then return to the ground state through spontaneous emission and emit fluorescence. By using a camera to record the intensity and position distribution of the fluorescence, the parameter information of the flow field can be analyzed. Since the fluorescence lifetime is on the order of nanoseconds and the pixel of the camera can also reach the million level, the biggest feature of PLIF is that it has high temporal resolution and spatial resolution. In addition, compared with other detection methods, PLIF is a non-contact measurement method, which can meet the measurement requirements while ensuring that it does not interfere with the original state of the flow field. The PLIF tracer can be a ketone tracer such as acetone or 3-pentanone, an aromatic tracer such as toluene or naphthalene, or an inorganic tracer such as NO or Kr. In one embodiment, among two or more tracers, the distance between the peak regions of the fluorescence spectra of any two tracers is greater than a preset distance, so as to distinguish the fluorescence image information of different tracers.

[0043] Specifically, the tracer gas can be directly introduced into the flow field, or the method of using other gases to carry the tracer vapor can be used to form a tracer gas for flow field measurement. Correspondingly, the tracer gas generating device can be a heating device or a bubbling device. In short, this embodiment does not limit the specific generation method of the tracer gas and the specific type of the tracer gas generating device.

[0044] Step S300: Introduce each tracer gas into the wind tunnel through a delivery device.

[0045] Among them, the delivery device refers to a device that introduces the tracer gas into the wind tunnel. The windward surface of this delivery device is provided with an air outlet connected to the delivery channel to ensure that the air outlet direction of the delivery device is consistent with the air flow direction of the main fluid. The tracer gas introduced from these air outlets can form multiple tracer lines, more comprehensively reflecting the air flow state of the wind tunnel. The wind tunnel refers to the specific scenario where a tracer experiment needs to be carried out. This wind tunnel is not a wind tunnel in the traditional sense, but a general term for a space with gas disturbance. For example, when the application scenario is a mine roadway, the "wind tunnel" refers to the mine roadway; when the application scenario is an indoor environment for detecting the fresh air volume index, the "wind tunnel" refers to the gas flow channel starting from the fresh air system outlet.

[0046] Specifically, after the tracer gas generating device generates the tracer gas, the tracer gas is introduced into the dispensing device, and then the gas is introduced into the wind tunnel through the dispensing device. Further, the dispensing device is provided with more than two dispensing channels, so that each tracer gas can be introduced into the wind tunnel through different dispensing channels. It can be understood that when the number of dispensing channels of the dispensing device is equal to the number of tracers, the dispensing channels and the tracers can be in one-to-one correspondence, and each dispensing channel corresponds to dispensing a tracer gas containing a different tracer; when the number of dispensing channels of the dispensing device is greater than the number of tracers, the redundant dispensing channels can be left idle, or multiple dispensing channels can be set to dispense the same tracer gas.

[0047] Step S500: The imaging device excites each tracer gas to make each tracer gas radiate a fluorescence signal and generate a fluorescence image.

[0048] As described above, after the PLIF tracer in the tracer gas absorbs energy, it will radiate a fluorescence signal and generate a fluorescence image. Specifically, since the PLIF tracers in each tracer gas are different, the finally generated fluorescence image is a superposition of fluorescence images of multiple PLIF tracers.

[0049] Step S700: The control device acquires the fluorescence image and determines the transition point of the turbulent flow field according to the fluorescence image.

[0050] Among them, the transition point refers to the point in the flow field where the laminar flow changes into turbulent flow. Specifically, the turbulent flow field structure downstream of the model is formed by the transition coupling of the laminar flow fields at different upstream positions. By decoupling the turbulent flow field structure and then analyzing the influence of the laminar flow fields at different positions on the turbulent flow field structure, the analysis and measurement of the turbulent flow field structure can be realized and the transition point of the turbulent flow field can be determined. Different tracers are put into the laminar flow field of the wind tunnel at specific positions. The air flow undergoes transition after passing through the model, and the laminar air flows at each position become turbulent and mix with each other during the downstream flow. Using more than two PLIF tracers, the PLIF technology can be used to simultaneously acquire the fluorescence images of various tracers in the turbulent flow field. According to the flow field structure shown in the fluorescence image of each tracer, the specific position of the upstream laminar region can be determined. Based on this, the relationship between the development and change of the turbulent flow field structure and the laminar flow field at a specific position can be established according to the fluorescence images of different tracers, and the transition point of the turbulent flow field can be determined.

[0051] As Figure 2As shown, the acetone tracer line is solid, and the toluene tracer line is dashed. When two adjacent PLIF tracer lines in the flow field pass through the model under test, both tracer lines remain in laminar flow. This indicates that the area where these two lines are located is not affected by the model under test, which is the upstream laminar region. When both lines undergo transition to turbulent flow, it means that the areas where they are located are all regions affected by the model under test, which is the downstream turbulent region. The two tracer lines transition from the upstream separated state to the mixed turbulent state and mix together in the downstream region. Point O in the figure is the transition point.

[0052] In the above tracer method, more than two PLIF tracers are introduced into the wind tunnel using different injection channels. On the one hand, multiple tracer lines can be formed to expand the visualization range and obtain more flow field information. On the other hand, since the laminar flow fields at various positions represented by different tracers interact with each other during the transition process, by obtaining the turbulent flow field structure images after the transition of the laminar flow fields at different positions simultaneously, the relationship between the development and change of the turbulent flow field structure and the laminar flow field at specific positions can be analyzed, realizing the visualization of the flow field structure during the transition process at different positions, and then determining the transition point of the turbulent flow field.

[0053] In one embodiment, after the control device acquires the fluorescence image, it further includes: the control device adjusts the parameters of the injection device according to the fluorescence image.

[0054] Among them, the parameters of the injection device include the distance between the injection device and the model under test, the relative positions of different tracer lines, and the injection speed, etc. Specifically, the parameters of the injection device will affect the quality of the fluorescence image. For example, if the distance between the injection device and the model under test is too far, the laminar section of the fluorescence image will be too long, increasing the data volume and being unfavorable for improving efficiency. If the distance is too small, it may result in tracer lines that are all in the turbulent state, making it impossible to determine the transition point. If the distance between the air outlets of different channels is too far, it will lead to too large a measurement error in the boundary range of the fluorescence image. If they are too close, it may result in the same change trend for both, making it difficult to determine the transition point. Whether the injection speed is too fast or too slow may affect the main flow field of the wind tunnel, and then lead to disorder in the fluorescence image.

[0055] Furthermore, the way for the control device to adjust the parameters of the injection device is not unique. For example, different parameters can be adjusted one by one, or related different parameters can be combined and adjusted simultaneously. It can be adjusted according to the preset layout distance, or continuous adjustment of the parameters can be carried out, and then the parameters of the injection device are determined based on the best fluorescence image obtained during the continuous adjustment process. In short, this embodiment does not limit the specific way for the control device to adjust the parameters of the injection device according to the fluorescence image.

[0056] In the above embodiment, after the control device acquires the fluorescence image and adjusts the parameters of the injection device according to the fluorescence image, it is beneficial to improve the tracer effect.

[0057] In one embodiment, the tracer gas generating device comprises a bubbling tank, such as Figure 3 As shown, step S100 includes step S120: introducing the bubbling gas into the liquid tracer in the bubbling tank, mixing with the tracer vapor in the bubbling tank, and forming a tracer gas composed of the bubbling gas and the tracer vapor.

[0058] It can be understood that, since the types of tracers in different tracer gases are different, different bubbling bottles need to be used to prepare the tracer gases.

[0059] Specifically, most PLIF tracers are liquid at room temperature. If the liquid PLIF tracer is placed in a bubbling tank, some of the liquid PLIF tracer will evaporate to form PLIF tracer vapor. At this time, injecting bubbling gas into the bubbling tank for bubbling can accelerate the evaporation rate of the liquid PLIF tracer, and allow the bubbling gas and the PLIF tracer vapor in the bubbling tank to have sufficient time and space to mix to form tracer gas. The tracer gas is then introduced into the wind tunnel by the delivery device. When the bubbling gas flow rate used for bubbling is constant, and the tracer delivery device has been working for a long time, the reduction rate of the PLIF tracer vapor caused by the introduction of the tracer gas into the wind tunnel and the evaporation rate of the liquid PLIF tracer reach a dynamic balance, that is, in the tracer gas delivered into the mainstream field of the wind tunnel, the concentration ratio of the bubbling gas to the PLIF tracer vapor is certain. Furthermore, the bubbling gas should be consistent with the gas in the wind tunnel flow field, or as consistent as possible, to reduce the interference of other gas components in the tracer gas on the mainstream field of the wind tunnel. For example, when the gas in the mainstream of the wind tunnel is air, air is used as the bubbling gas.

[0060] Further, in one embodiment, please continue to refer to Figure 3 , before step S120, step S110 is also included: controlling the flow rate of the introduced bubbling gas. The flow rate of the bubbling gas reflects the flow rate of the bubbling gas introduced into the liquid PLIF tracer per unit time, and further determines the speed at which the tracer gas is introduced into the delivery device. If no speed limiting device is provided in the delivery device, the flow rate of the bubbling gas directly determines the speed at which the tracer gas is introduced into the wind tunnel. Therefore, before injecting the bubbling gas into the liquid PLIF tracer, controlling the flow rate of the bubbling gas is beneficial to effectively controlling the delivery speed of the tracer gas. The flow control device of the bubbling gas may be a flow meter or a pressure valve. In short, the present embodiment does not limit the specific type of the flow control device of the bubbling gas.

[0061] In the above embodiment, the same gas as that in the mainstream field of the wind tunnel is used as the bubbling gas, and the bubbling method is used to form a tracer gas composed of the bubbling gas and tracer vapor, which is beneficial to reduce the interference of the tracer gas on the mainstream field of the wind tunnel.

[0062] In one embodiment, the dispensing device is a steel pipe, such as Figure 4 shown, step S300 includes step S310 and step S320.

[0063] Step S310: Introduce each tracer gas into different dispensing channels inside the steel pipe through one end of the steel pipe; the other end of the steel pipe is closed, and at least one air outlet connected to the corresponding dispensing channel is correspondingly arranged on the leeward side of the steel pipe.

[0064] Step S320: Each tracer gas is introduced into the wind tunnel through the corresponding air outlet respectively.

[0065] Specifically, the steel pipe is arranged at the air outlet of the wind tunnel and is perpendicular to the air flow direction of the wind tunnel. One end of the steel pipe is connected to the tracer gas generating device, and the other end is closed. At least one air outlet connected to the corresponding dispensing channel is arranged on the leeward side of the steel pipe. After the tracer gas is introduced into the steel pipe from the tracer gas sending device, it enters the wind tunnel from the air outlet. The central connection line of these air outlets is perpendicular to the air flow direction of the wind tunnel. After the tracer gas enters the wind tunnel from the air outlet, it moves along the air flow direction of the wind tunnel with the mainstream fluid in the wind tunnel, and multiple tracer lines can be formed.

[0066] Furthermore, a steel pipe fixing member can be arranged on the steel pipe to facilitate fixing the steel pipe to the outer frame of the wind tunnel. The steel pipe fixing member for fixing the steel pipe to the wind tunnel frame can move up and down, thereby changing the relative position of the air outlet in the wind tunnel and adjusting the coverage area of different tracer lines. It can be understood that the relative position of the air outlet is determined by the position of the model to be measured.

[0067] In one embodiment, the inner diameter of the steel pipe is 4 mm, the outer diameter is 6 mm, and the distance between the air outlets on the leeward side can be adjusted. According to the aerodynamic principle, the area and shape of the air holes are designed into a combination that is more likely to generate laminar flow. For example, the cross-section of the steel pipe is designed as an airfoil to reduce the influence of the steel pipe on the mainstream field of the wind tunnel.

[0068] Such as Figure 2 shown, the steel pipe includes two relatively independent dispensing channels, and each dispensing channel is correspondingly provided with an air outlet. The two selected tracers are toluene and acetone. The two tracers enter the corresponding dispensing channels in the copper pipe from different inlets respectively, and enter the wind tunnel from the corresponding air outlets connected to the dispensing channels, forming a toluene tracer line and an acetone tracer line.

[0069] In addition, if the distances between the air outlets of different channels on the steel pipe are too far apart, it will lead to excessive measurement errors in the boundary range of the fluorescence image. If they are too close, it may cause the change trends of the two to be the same, making it difficult to determine the transition point. Therefore, it is necessary to adjust the distances between the air outlets of different injection channels according to the obtained fluorescence image to improve the tracer effect. The method of adjusting the distances between the air outlets of different injection channels is not unique. For example, several steel pipes with different air outlet distances can be customized in combination with the actual situation of the wind tunnel and the model to be measured, and tracer experiments can be carried out as needed. Then, according to the fluorescence images obtained in the tracer experiments, steel pipes of appropriate specifications can be selected. Alternatively, the steel pipe can be designed into a mechanical structure with at least one adjustable injection channel, and the position of the air outlet of the adjustable injection channel can be correspondingly adjusted according to the fluorescence images obtained in the tracer experiments.

[0070] It should be understood that although the steps in the respective flowcharts involved in the above embodiments are displayed in sequence according to the indications of the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover, at least some of the steps in the respective flowcharts involved in the above embodiments may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential either, but can be executed alternately or in turn with at least some of the other steps or sub-steps or stages of the other steps.

[0071] In the second aspect of the present application, a tracer system is provided, as Figure 5 shown. The tracer system includes a tracer gas generating device 100, a dispensing device 200, an imaging device 300, and a control device 400. The tracer gas generating device 100 is used to process more than two types of tracers to respectively form different tracer gases; the tracer is a PLIF tracer. The dispensing device 200 is used to introduce each tracer gas into the wind tunnel; the dispensing device 200 is provided with more than two dispensing channels, and each tracer gas is introduced into the wind tunnel through different dispensing channels. The imaging device 300 is used to excite each tracer gas to make each tracer gas radiate fluorescence signals and generate fluorescence images. The control device 400 is used to acquire the fluorescence images and determine the transition point of the turbulent flow field according to the fluorescence images.

[0072] Among them, the number of the tracer gas generating devices 100 is not unique and is determined by the types of tracers used. The tracer gas generating device 100 can be a heating device or a bubbling device. The dispensing device 200 can be a mechanical device including a hollow housing and a dispensing channel inside the housing. The material of the housing can be steel, ceramic, plastic, etc., and the shape of the housing can be cylindrical, cubic, annular, etc. The imaging device 300 can be an integrated device with both excitation and detection functions or a discrete device composed of an excitation device and a detection device. The control device 400 can be various controllers or control chips. The control chip can be a single-chip microcomputer chip, a programmable logic array chip, etc.

[0073] Specifically, after the tracer gas generating device 100 processes two or more tracers to form different tracer gases respectively, the dispensing device 200 introduces each tracer gas into the wind tunnel through different dispensing channels, and then the imaging device 300 excites each tracer gas to make each tracer gas radiate fluorescence signals to generate a fluorescence image. Finally, the control device 400 acquires the fluorescence image and determines the transition point of the turbulent flow field according to the fluorescence image.

[0074] Furthermore, the tracer gas generating device 100 is mechanically connected to the dispensing device 200, and the tracer gas generated by the tracer gas generating device 100 can be introduced into the wind tunnel through the dispensing device 200. The control device 400 is electrically connected to the tracer gas generating device 100, the dispensing device 200 and the imaging device 300. The control device 400 can adjust the working parameters of the tracer gas generating device 100, the dispensing device 200 and the imaging device 300 according to the acquired fluorescence image.

[0075] In the above tracer system, two or more PLIF tracers are introduced into the wind tunnel using different dispensing channels. On the one hand, multiple tracer lines can be formed to expand the visualization range and obtain more flow field information; on the other hand, since the laminar flow fields at each position represented by different tracers affect each other during the transition process, by simultaneously obtaining the turbulent flow field structure images after the transition of the laminar flow fields at different positions, the relationship between the development and change of the turbulent flow field structure and the laminar flow field at a specific position can be analyzed, realizing the visualization of the flow field structure during the transition process at different positions, and then determining the transition point of the turbulent flow field.

[0076] In one embodiment, as Figure 6 shown, the tracer gas generating device 100 includes a high-pressure gas cylinder 110, a gas mass flowmeter 120 and a bubbling tank 130 connected in sequence; the gas mass flowmeter 120 is connected to the control device 400, and the bubbling tank 130 is connected to the dispensing device 200.

[0077] Among them, the above-mentioned various devices are connected by air ducts, and sealing rings and valves are provided at the joints to prevent air leakage. Specifically, the bubbling gas in the high-pressure gas cylinder 110 reaches the bubbling tank 130 after passing through the gas mass flowmeter 120. The bubbling gas is directly introduced into the tracer liquid in the bubbling tank 130, which can accelerate the evaporation rate of the tracer liquid. The bubbling gas is mixed with the tracer vapor in the bubbling tank 130 to form a tracer gas composed of the bubbling gas and the tracer vapor, and is introduced into the dispensing device 200 through the air duct. Then, the tracer gas is introduced into the wind tunnel through the dispensing device 200. The gas mass flowmeter 120 is used to control the flow rate of the bubbling gas in the high-pressure gas cylinder 110 to achieve the purpose of controlling the dispensing speed of the tracer gas.

[0078] Furthermore, in one embodiment, the bubbling tank 130 is placed in a constant temperature environment. This constant temperature environment can be realized by a constant temperature water bath 140; alternatively, a temperature control device can be provided on the side wall of the bubbling tank 130, and this temperature control device is connected to the control device 400, and the control device 400 performs feedback control according to the temperature collected by the temperature control device. In short, the specific implementation method of the constant temperature environment in this embodiment is not limited. Placing the bubbling tank 130 in a constant temperature environment can keep the temperature in the bubbling tank 130 unchanged, and further keep the evaporation rate of the liquid tracer in the bubbling tank 130 constant, which is beneficial to maintaining the stability of the proportion of the tracer vapor in the tracer gas in a short time and improving the stability of the tracer effect.

[0079] In one embodiment, the imaging device 300 includes an excitation device and a detection device. Among them, the excitation device is used to excite each tracer gas to make each tracer gas radiate a fluorescence signal, and the detection device is used to detect the fluorescence signal radiated by each tracer gas to obtain a fluorescence image.

[0080] In one embodiment, the excitation device includes a laser light source and a beam transmission device. Among them, the laser light source can be a tunable laser, and the beam transmission device includes a cylindrical lens, a collimating mirror, a condenser lens, etc. According to the excitation wavelengths required by different tracers, at least two groups of laser light sources and beam transmission devices can be correspondingly set. Specifically, the laser emitted by the tunable laser is expanded and collimated into a planar sheet beam that meets the requirements through the beam transmission device, and irradiates the PLIF tracer particles in the tracer gas, so that the corresponding electrons in the tracer particles are excited and transition from the ground state to the excited state. The electrons in the excited state then return to the ground state through spontaneous emission and emit fluorescence, forming a fluorescence image.

[0081] In one embodiment, the detection device includes a beam splitter, and more than two filter plates and detectors; the filter plates and detectors are correspondingly arranged to detect the fluorescence images of different PLIF tracers respectively.

[0082] Among them, the types of the beam splitter and the filter depend on the wavelength corresponding to the absorption peak of the tracer. The principle for selecting the beam splitter is to ensure that the fluorescence signals corresponding to different tracer gases can be separated, and the principle for selecting the filter is to ensure that while the detector captures the fluorescence signal of one tracer, the fluorescence signals of the remaining tracers and the laser scattered light are shielded. Since the beam splitter has the characteristic of achieving high transmission of the laser at some wavelengths and high reflection of the laser at the remaining wavelengths with a specific wavelength as the boundary, one beam splitter can be used to separate the fluorescence signals of two tracer gases. Then, according to the types of the tracer gases, the number of beam splitters can be correspondingly determined to separate the fluorescence signals of different tracer gases.

[0083] As Figure 7 shown, when acetone and toluene are selected as the tracers, the wavelength corresponding to the absorption peak of toluene is about 265 nm, and the wavelength corresponding to the absorption peak of acetone is about 535 nm. At this time, a beam splitter with high reflection in the wavelength band below 400 nm and high transmission in the wavelength band above 400 nm can be selected, and the Semrock BP280 filter is selected to obtain the fluorescence signal of toluene, and a combination of the Semrock LP430 and Andover FL450 filters is selected to obtain the fluorescence signal of acetone, which can ensure that the peak signal of the acetone fluorescence spectrum is captured while filtering out the toluene fluorescence signal and other laser scattered light.

[0084] Specifically, first, the same region is photographed to simultaneously obtain the fluorescence signals of multiple different tracers. According to the fluorescence spectral characteristics of these tracers, the corresponding filters can be selected for signal screening: the beam splitter is used to separate the fluorescence signals of different tracer gases, and appropriate filters are selected to extract the fluorescence signals of different tracer gases, and the transition point of the turbulent flow field is determined according to the fluorescence images of different tracer gases.

[0085] For easy understanding, the following combines Figure 7 and Figure 8 to illustrate the image detection process using two PLIF tracers, acetone and toluene.

[0086] As Figure 7As shown, the two PLIF tracers, acetone and toluene, have fluorescence spectral peak regions that are far apart. First, the observation surface of the same region is photographed to obtain the fluorescence signals of acetone and toluene respectively. The mixed fluorescence signal emitted by acetone and toluene passes through the beam splitter 321, which has the characteristics of high reflectivity in the wavelength band below 400 nm and high transmittance in the wavelength band above 400 nm. The first filter 322-1 and the first detector 323-1 are located on the transmission optical path of the beam splitter 321; the second filter 322-2 and the second detector 323-2 are located on the reflection optical path of the beam splitter 321. According to the above fluorescence spectral differences, the first filter 322-1 selects a combination of two filters, Semrock LP430 and Andover FL450, which can ensure capturing the peak signal of the acetone fluorescence spectrum while filtering out the toluene fluorescence signal and other laser scattered light. The second filter 322-2 selects the Semrock BP280 filter, which can retain most of the toluene fluorescence signal while shielding the acetone fluorescence signal and various laser scattered light. In addition, since the toluene fluorescence spectral region is mainly in the ultraviolet range, the lens of the second detector 323-2 used to photograph the toluene fluorescence signal selects an ultraviolet lens.

[0087] In this way, the main fluorescence signal of acetone will pass through the beam splitter 321 and reach the first detector 323-1; most of the toluene fluorescence signal will be reflected into the second detector 323-2. By photographing the fluorescence images of acetone and toluene in this way, the image visualization of the fluorescence signals of acetone and toluene is completed, and the fluorescence images are obtained. The control device 400 can determine the tracer line of the gas from which the fluorescence signal that becomes turbulent comes based on the fluorescence images, and then determine the transition point of the turbulent flow field.

[0088] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0089] The above embodiments only represent several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A tracing method, characterized in that, Including: Using a tracer gas generating device to process two or more tracers to respectively form different tracer gases; the tracer is a PLIF tracer; Introducing each of the tracer gases into different delivery channels inside the steel pipe through one end of the steel pipe, so that each of the tracer gases respectively passes through the air outlet corresponding to each delivery channel and is introduced into the laminar flow field of the wind tunnel; the other end of the steel pipe is closed, and at least one air outlet connected to the corresponding delivery channel is correspondingly arranged on the leeward side of the steel pipe; the central connecting line of each air outlet is perpendicular to the air flow direction of the wind tunnel; the steel pipe is fixed to the outer frame of the wind tunnel by a movable fixing member to change the relative position of each air outlet in the wind tunnel; at least one of the delivery channels includes an adjustable delivery channel; The imaging device excites each of the tracer gases to make each of the tracer gases radiate fluorescence signals to generate a fluorescence image; The control device acquires the fluorescence images of each of the tracer gases and adjusts the position of the air outlet of the adjustable delivery channel according to the fluorescence images; The control device also determines the position where the tracer lines respectively characterized by each of the fluorescence images change from laminar flow transition to turbulent flow as the transition point between the laminar flow field and the downstream turbulent flow field; the transition point refers to the point in the flow field where the flow changes from laminar flow to turbulent flow.

2. The tracing method according to claim 1, wherein After the control device acquires the fluorescence images of each of the tracer gases, it further includes: The control device adjusts the delivery parameters of each of the tracer gases according to the fluorescence images.

3. The tracer method according to claim 1, characterized in that The tracer gas generating device includes a bubbling tank, and the use of the tracer generating device to process the tracer to form the tracer gas includes: Introducing the bubbling gas into the liquid tracer in the bubbling tank and mixing it with the tracer vapor in the bubbling tank to form a tracer gas composed of the bubbling gas and the tracer vapor.

4. The tracing method according to claim 1, characterized in that, The PLIF tracer is a ketone tracer, an aromatic tracer or an inorganic tracer.

5. A tracing system, characterized in that, Including a tracer gas generating device, a delivery device, an imaging device and a control device; The tracer gas generating device is used to process two or more tracers to respectively form different tracer gases; the tracer is a PLIF tracer; The delivery device is a steel pipe; each of the tracer gases is introduced into different delivery channels inside the steel pipe through one end of the steel pipe, so that each of the tracer gases respectively passes through the air outlet corresponding to each delivery channel and is introduced into the laminar flow field of the wind tunnel; the other end of the steel pipe is closed, and at least one air outlet connected to the corresponding delivery channel is correspondingly arranged on the leeward side of the steel pipe; the central connecting line of each air outlet is perpendicular to the air flow direction of the wind tunnel; the steel pipe is fixed to the outer frame of the wind tunnel by a movable fixing member to change the relative position of each air outlet in the wind tunnel; at least one of the delivery channels includes an adjustable delivery channel; The imaging device is used to excite each of the tracer gases to make each of the tracer gases radiate fluorescence signals to generate a fluorescence image; The control device is used to obtain the fluorescence images of each of the tracer gases, adjust the outlet position of the adjustable delivery channel according to the fluorescence images, and determine the position where the tracer lines characterized by each of the fluorescence images change from laminar flow transition to turbulent flow as the transition point between the laminar flow field and the downstream turbulent flow field; the transition point refers to the point in the flow field where the laminar flow changes into turbulent flow.

6. The tracer system according to claim 5, wherein The tracer gas generating device includes a high-pressure gas cylinder, a gas mass flowmeter, and a bubbling tank connected in sequence; the gas mass flowmeter is connected to the control device, and the bubbling tank is connected to the delivery device.

7. The tracer system according to claim 5, wherein The imaging device includes an excitation device and a detection device.

8. The tracer system according to claim 7, wherein The excitation device includes a laser light source and a beam delivery device.

9. The tracer system according to claim 7, characterized in that, The detection device includes a beam splitter, and more than two filters and detectors; the filters and the detectors are correspondingly arranged for detecting the fluorescence images of different PLIF tracers respectively.

Images