Temperature field and velocity field synchronous measurement device and method based on background schlieren method

Abstract

The present invention discloses a temperature field and velocity field synchronous measurement device and method based on the background schlieren method, which are used for quantitatively measuring the temperature field and velocity field of an incompressible flow field. The measurement device includes a reference beam generating component, a flow field, a first bilateral telecentric lens and a camera. The reference beam generating component generates a parallel beam containing a background image. The parallel beam containing the background image passes through the flow field and then is incident on the first bilateral telecentric lens, and then is captured by the camera after being transmitted by the first bilateral telecentric lens. The measurement device is used to capture static reference images and dynamic images, so as to reconstruct the temperature field and velocity field of the flow field to be measured. The present invention adopts a telecentric backlight light source to improve the contour contrast and spatial resolution of the background pattern, so that the light passes through the flow field parallel to the optical axis, so that quantitative data without correction can be obtained, which overcomes the disadvantage that the two-dimensional simplification of the refractive index of the light along the traditional centripetal background schlieren introduces a large error.

Description

Technical Field

[0001] The present invention relates to a temperature field and velocity field synchronous measurement device and method in the field of flow field visualization measurement, and in particular to a temperature field and velocity field synchronous measurement device and method of an incompressible flow field based on a background schlieren method. Background Art

[0002] There is a great demand for measuring the temporal and spatial non-uniform distribution of pressure, velocity, temperature, density, concentration and other factors in the flow process in the experimental and engineering fields. For example, in immersion lithography, the immersion flow field, as the internal fluid of the last "liquid lens", needs to be constantly updated, and the temperature stability and uniformity of the core flow field are one of the main factors affecting the exposure quality. Due to the complexity of the immersion flow field and the large number of thermal boundaries, it is difficult to obtain reliable flow field and temperature field distribution using simulation methods. Experiments generally use temperature sensors for single-point detection, and multiple sensors are arranged to obtain temperature distribution information in the mainstream field, but the spatial resolution is limited by the physical size and the influence of tooling installation. In addition, invasive measurements also have the risk of interfering with the flow field.

[0003] Existing flow display and detection technologies mainly target a single physical quantity. For example, conventional velocity field detection methods: Particle Image Velocimetry (PIV) uses the velocity of tracer particles to represent the velocity of the fluid microelement at the corresponding position of the flow field, and obtains the velocity field information of the flow field through the cross-correlation method; conventional temperature field detection methods: Schlieren method uses the irregular light and dark stripes formed by the illumination change of the image plane to represent the change of refractive index. Laser-Induced Fluorescence (LIF) uses the property of dyes to emit fluorescence after being irradiated to obtain the transmission and diffusion information of scalar fields (temperature fields, concentration fields) in fluid flow.

[0004] Background Oriented Schlieren Technique (BOS) is a relatively new flow detection technology, which was proposed by Meier et al. around 2000. BOS technology can overcome the difficulty of illumination change caused by self-luminescence in traditional Schlieren technology, and at the same time, the use of PIV algorithm eliminates the complex and expensive experimental equipment of traditional Schlieren technology. BOS technology was first used to quantitatively measure the density field in aerodynamic optics, and then expanded to the measurement of gas temperature field, random medium refractive index field and fluid free surface.

[0005] Existing synchronous detection technologies for temperature and velocity fields usually require two systems, for example, PIV combined with PLIF technology to simultaneously measure fluid velocity field and scalar field; LIF combined with BOS to synchronously measure concentration and density fields (see patent: CN111458533 A for details); PIV combined with BOS to synchronously measure fluid velocity field and temperature field. The LIF method can obtain the concentration distribution and velocity field of the flow field through the scalar image inversion method. However, in fields with high cleanliness requirements such as semiconductors, biomedicine, and electronic-grade chemicals, ultra-clean flow control needs to strictly prevent contamination and wear caused by pollutants such as particulate matter. Therefore, traditional LIF and PIV methods are not applicable. At present, it is urgent to carry out research on a non-contact and pollution-free temperature field-velocity field synchronous measurement and display method. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a temperature field-velocity field synchronous measurement device and method based on background schlieren to achieve synchronous measurement of the temperature field and velocity field of incompressible fluids, which can obtain the temperature field and velocity field information within the field of view, reduce the complexity of the system, and reduce the cost of building multiple systems. The use of a bilateral telecentric arrangement overcomes the contradiction between the resolution and sensitivity of the traditional BOS system and improves the spatial resolution; a high-speed camera is used as an image receiving device to ensure the temporal resolution.

[0007] The technical solution adopted by the present invention comprises the following steps:

[0008] 1. A synchronous measurement device for temperature field and velocity field based on background schlieren method

[0009] The measuring device includes a reference beam generating component, a flow field, a first bilateral telecentric lens and a camera. The reference beam generating component generates a parallel beam containing a background image. The parallel beam containing the background image passes through the flow field and then is incident on the first bilateral telecentric lens, and then is collected by the camera after being transmitted by the first bilateral telecentric lens.

[0010] A reference beam generating assembly and a first double-sided telecentric lens are respectively arranged at intervals on both sides of the flow field. The parallel beam containing the background image generated by the reference beam generating assembly is directly incident on the first double-sided telecentric lens after being transmitted through the flow field.

[0011] The flow field includes two pieces of flat glass and a fluid. The two pieces of flat glass are arranged in parallel and at intervals, and the space between the two pieces of flat glass is filled with the fluid.

[0012] One of the flat glass sheets in the flow field is replaced with a reflector, and a reference beam generating assembly and a first double-sided telecentric lens are placed on a side close to the other flat glass sheet. An angle is set between the parallel light beam containing a background image generated by the reference beam generating assembly and the side surface of the flow field, and an angle is set between the optical axis of the first double-sided telecentric lens and the side surface of the flow field. The parallel light beam containing the background image is incident on the first double-sided telecentric lens after being transmitted through the flow field, reflected by the reflector, and re-transmitted through the flow field.

[0013] The reference beam generating assembly comprises a background pattern plate, a light source and a second double-sided telecentric lens; the light beam emitted from the light source passes through the second double-sided telecentric lens and then passes through the background pattern plate to obtain a parallel light beam containing a background image.

[0014] 1. A method for synchronously measuring temperature field and velocity field based on background schlieren method

[0015] Step 1: Build a synchronous measurement device for temperature field and velocity field based on background schlieren;

[0016] Step 2: Use the temperature field and velocity field synchronous measurement device to collect the reference image I filled with air in the flow field in sequence air (x, y, t0), reference image I filled with static liquid static (x, y, t0), reference image I with fluid without temperature gradient flow (x, y, t0) and dynamic images of fluid with temperature gradient;

[0017] Step 3: Based on the reference image I filled with air air (x, y, t0), reference image I filled with static liquid static (x, y, t0), reference image I with fluid without temperature gradient flow (x, y, t0), reconstruct the refractive index field of the dynamic image of the fluid with temperature gradient, and obtain the refractive index field of the current flow field to be measured;

[0018] Step 4: Calculate and obtain the temperature field of the current flow field to be measured according to the refractive index field of the current flow field to be measured;

[0019] Step 5: Obtain the corresponding velocity field based on the temperature field inversion of the current flow field to be measured.

[0020] The temperature field and velocity field synchronization device based on background schlieren includes a reference beam generating component, a flow field, a first bilateral telecentric lens and a camera. The reference beam generating component generates a parallel beam containing a background image. The parallel beam containing the background image passes through the flow field and then is incident on the first bilateral telecentric lens, and then is collected by the camera after being transmitted by the first bilateral telecentric lens.

[0021] In step 2, when the fluid in the flow field is air, the camera captures a reference image I filled with air. air (x, y, t0); when the fluid in the flow field is a static liquid, the camera acquires a reference image I filled with static liquid static (x, y, t0); when the fluid in the flow field is a fluid without temperature gradient, the camera acquires a reference image I of the fluid without temperature gradient. flow (x, y, t0); when the fluid in the flow field is a fluid with a temperature gradient, the camera captures a dynamic image of the fluid with a temperature gradient.

[0022] The step 3 is specifically as follows:

[0023] 3.1) For the reference image I filled with air air (x, y, t0) and the reference image I filled with static liquid static After convolution of (x, y, t0), the background pattern offset is obtained;

[0024] 3.2) Based on the background pattern offset, the reference image I of the fluid without temperature gradient is passed through flow (x, y, t0) is remapped to obtain the reference background image I remapping (x, y, t0);

[0025] 3.3) According to the reference background image I remapping (x, y, t0) and the dynamic image of the fluid with a temperature gradient are used to calculate the background displacement; based on the background displacement, geometric optics and Fermat's principle are used to establish the relationship between the background pattern displacement and the deflection angle ε and the deflection angle ε and the refractive index gradient in the dynamic image of the fluid with a temperature gradient, and the refractive index field of the current flow field to be measured is obtained.

[0026] The step 5 is specifically as follows:

[0027] According to the temperature field of the current flow field to be measured, the temperature parameters in the temperature convection-diffusion equation corresponding to the temperature field are calculated and analyzed using the second-order central difference method, and then the velocity field u is inverted and calculated based on the temperature parameters.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a synchronous measurement device for the temperature field and velocity field of an incompressible flow field based on the telecentric arrangement of background schlieren technology. The device replaces the illumination method of the traditional background schlieren method by the telecentric lens parallel light projection method, and can obtain quantitative data without correction, which overcomes the disadvantage that the two-dimensional simplification of the refractive index along the light of the traditional centripetal background schlieren introduces a large error; the present invention uses the scalar image velocimetry principle combined with the BOS method to achieve synchronous measurement of the temperature field and velocity field in the flow field. If the flow field is a compressible fluid, the density field of the flow field can be obtained using the Lorentz-Lorentz formula to achieve synchronous measurement of multiple physical fields; compared with the existing BOS and PIV combined temperature field and velocity field measurement method, the present invention reduces the system complexity and reduces the cost of building multiple systems. The present invention can be used to measure the temperature field and velocity field of ultra-clean flow fields, or other flow fields with high cleanliness requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the transmission-type solution of telecentric lenses arranged on both sides of Example 1 of the measuring device of the present invention.

[0031] Figure 2 This is a schematic diagram of a transmission-type solution in which telecentric lenses are arranged on both sides in Example I of the measuring device of the present invention.

[0032] Figure 3 It is a schematic diagram of the laser speckle transmission scheme arranged on both sides of Example II of the measuring device of the present invention.

[0033] Figure 4 This is a schematic diagram of a reflective solution in which a telecentric lens is arranged on the same side of Example III of the measuring device of the present invention.

[0034] Figure 5 It is a schematic diagram of the flow of the measurement method in the present invention.

[0035] In the figure, 1: background pattern plate; 2: flow field; 3: first double-sided telecentric lens; 31: first positive lens; 32: aperture; 33: second positive lens; 4: light source; 5: camera; 6: data processor; 7: flat glass; 8: reflector; 9: laser; 10: holographic beam expander; 11: hole; 12: third positive lens; 13: fluid; 14: second double-sided telecentric lens. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and implementation modes.

[0037] like Figure 1As shown, the measuring device includes a reference beam generating component, a first bilateral telecentric lens 3 and a camera 5. The reference beam generating component generates a parallel beam containing a background image. The parallel beam containing the background image passes through the flow field 2 and then is incident on the first bilateral telecentric lens 3. Then, it is transmitted through the first bilateral telecentric lens 3 and then collected by the camera 5. The camera 5 is connected to a data processor 6. The first bilateral telecentric lens 3 and the camera 5 are arranged on the same optical axis. The light beam incident on the first bilateral telecentric lens 3 may have an angle with the optical axis.

[0038] The flow field 2 includes two pieces of flat glass 7 and a fluid 13 . The two pieces of flat glass 7 are arranged in parallel and at an interval, and the space between the two pieces of flat glass 7 is filled with the fluid 13 .

[0039] A reference beam generating assembly and a first bilateral telecentric lens 3 are arranged at intervals on both sides of the flow field 2 . A parallel beam containing a background image generated by the reference beam generating assembly is directly incident on the first bilateral telecentric lens 3 after being deflected by the flow field 2 .

[0040] One of the flat glass sheets 7 in the flow field 2 is replaced with a reflector 8, and the reference beam generating assembly and the first double-sided telecentric lens 3 are placed on the side close to the flat glass sheet 7. The reflector 8 is used to ensure that the optical axis of the camera coincides with the optical axis of the first double-sided telecentric lens 3, so as to measure the temperature distribution of the single-sided transparent flow field. The reference beam generating assembly and the first double-sided telecentric lens 3 are arranged at another flat glass sheet 7 of the flow field 2. The reference beam generating assembly and the first double-sided telecentric lens 3 are arranged at intervals from the flow field 2, and the reference beam generating assembly and the first double-sided telecentric lens 3 are also arranged at intervals. An angle is set between the parallel beam containing the background image generated by the reference beam generating assembly and the side of the flow field 2, and an angle is set between the optical axis of the first double-sided telecentric lens 3 and the side of the flow field 2. The parallel beam containing the background image is incident on the first double-sided telecentric lens 3 after being transmitted by the flow field 2, reflected by the reflector 8, and re-transmitted by the flow field 2.

[0041] like Figure 2 and Figure 4As shown, the reference beam generating assembly includes a background pattern plate 1, a light source 4 and a second double-sided telecentric lens 14; the light source 4 provides light with stable irradiation intensity to image the background pattern 1 in the high-speed camera 5; the light source 4 and the second double-sided telecentric lens 14 constitute a telecentric light source, and the light is incident on the background pattern plate 1 approximately in parallel. The first double-sided telecentric lens 3 and the camera 5 ensure that the background image is incident on the imaging plane approximately in parallel. The magnification of the assembly composed of the first double-sided telecentric lens 3 and the camera 5 is related to the focal length of the two thin lenses in the first double-sided telecentric lens, and has nothing to do with the relative distance between the schlieren object and the background and the camera. The light beam emitted from the light source 4 passes through the second double-sided telecentric lens 14 and then passes through the background pattern plate 1 to obtain a parallel light beam containing the background image. In a specific implementation, the background pattern plate 1 is a transparent screen with random dot matrix scattered on it. The imaging size of the transparent screen with random dot matrix and the spots generated by laser speckle on the camera photosensitive element should be 3 to 5 pixels. The optical system of the present invention is in a microenvironment where the ambient temperature, humidity and noise can be controlled, and the integral effect of the refractive index change caused by temperature fluctuation along the optical path mainly comes from the flow field 2.

[0042] The structure of the first double-sided telecentric lens 3 or the second double-sided telecentric lens 14 consists of a first positive lens 31, a second positive lens 33 and an aperture 32 which are sequentially arranged along the optical axis, and the aperture 32 is located at the focus of the first positive lens 31 and the focus of the second positive lens 33. The first positive lens 31 and the second positive lens 33 are positive thin lenses with focal lengths of f1 and f2 respectively.

[0043] like Figure 3 As shown, the reference beam generating assembly includes a laser 9, a holographic beam expander 10, a third positive lens 12 and a hole 11; the aperture of the hole 11 can be calculated by a formula, which is related to the focal length of the third positive lens, the laser wavelength and a constant parameter, and the hole 11 is located exactly at the focus of the third positive lens. The light beam emitted from the laser 9 passes through the holographic beam expander 10 and then emits from the hole 11. The light beam emitted from the hole 11 is transmitted through the third positive lens 12 to obtain a parallel speckle pattern as a background pattern.

[0044] In a specific implementation, the camera 5 is a high-speed camera. The spatial resolution of the high-speed camera 5 must be smaller than the molecular diffusion scale λ in the local flow field. D , that is, in the flow field captured by the camera at a certain moment, the distance between two adjacent pixels in the background pattern is smaller than the molecular diffusion scale. The time resolution of the fluid is smaller than the molecular diffusion time λ of the local flow field. D / U, U represents the average velocity of the fluid;

[0045] The data processor 6 is used to receive and store the background pattern output by the high-speed camera and perform post-processing calculations, including: background displacement estimation, refractive index field reconstruction, refractive index field conversion to temperature field and scalar image velocimetry of temperature field.

[0046] The measurement method relies on the temperature field information measured by the high spatiotemporal resolution measurement device based on the background schlieren, and uses the convection-diffusion equation of the direct inversion temperature field or the integral minimization scalar image velocimetry principle to obtain the flow field velocity field information, such as Figure 5 As shown, the specific steps include:

[0047] Step 1: Build a temperature field and velocity field synchronization device based on background schlieren;

[0048] Step 2: Use the temperature field and velocity field synchronization device to collect the reference image I filled with air in the flow field in sequence air (x, y, t0), reference image I filled with static liquid static (x, y, t0), reference image I with fluid without temperature gradient flow (x, y, t0) and dynamic images of fluid with temperature gradient;

[0049] In step 2, when the fluid 13 in the flow field 2 is air, the camera 5 acquires a reference image I filled with air. air (x, y, t0); when the fluid 13 in the flow field 2 is a stationary liquid, the camera 5 acquires a reference image I filled with stationary liquid static (x, y, t0); when the fluid 13 in the flow field 2 is a fluid without a temperature gradient, the camera 5 acquires a reference image I of the fluid without a temperature gradient. flow (x, y, t0); when the fluid 13 in the flow field 2 is a fluid with a temperature gradient, water with a temperature gradient is introduced as a schlieren object. Due to the uneven temperature distribution, light is deflected, and the camera 5 collects and obtains a dynamic image of the fluid with a temperature gradient.

[0050] Step 3: Based on the reference image I filled with air air (x, y, t0), reference image I filled with static liquid static (x, y, t0), reference image I with fluid without temperature gradient flow (x, y, t0), reconstruct the refractive index field of the dynamic image of the fluid with temperature gradient, and obtain the refractive index field of the current flow field to be measured;

[0051] Step 3 is as follows:

[0052] 3.1) For the reference image I filled with air air (x, y, t0) and the reference image I filled with static liquid staticAfter convolution of (x, y, t0), the background pattern offset (Δx, Δy) caused by the transparent glass plate 7 is obtained;

[0053] 3.2) Based on the background pattern offset (Δx, Δy) caused by the transparent glass plate 7, the reference image I flow (x, y, t0) is remapped to obtain the reference background image I remapping (x, y, t0);

[0054] 3.3) According to the reference background image I remapping The background displacement, i.e., (Δx′, Δy′), is calculated by using a cross-correlation algorithm, an optical flow method or a point tracking algorithm for the dynamic image of a fluid with a temperature gradient (x, y, t0). Based on the background displacement, the relationship between the background pattern displacement and the deflection angle ε and the deflection angle ε and the refractive index gradient in the dynamic image of a fluid with a temperature gradient is established by using geometric optics and Fermat's principle to obtain the refractive index field of the current flow field to be measured.

[0055] Step 4: Calculate and obtain the temperature field of the current flow field to be measured according to the refractive index field of the current flow field to be measured;

[0056] Step 4 is as follows:

[0057] The refractive index field of the current flow field to be measured is converted into a temperature field using the thermo-optic coefficient dn / dT.

[0058] Step 5: Obtain the corresponding velocity field based on the temperature field inversion of the current flow field to be measured.

[0059] Step 5 is as follows:

[0060] According to the temperature field of the current flow field to be measured, the second-order central difference method is used to calculate and analyze the temperature parameters in the temperature convection-diffusion equation corresponding to the temperature field, namely the time differential term, gradient term and Laplace term of the temperature, and then the velocity field u is inverted and calculated based on the temperature parameters.

[0061] The scalar diffusion equation for temperature is:

[0062]

[0063] in, is the partial derivative of temperature with respect to time, is the temperature gradient in space, κ is the temperature diffusion coefficient, is the Laplace term.

[0064] In a specific implementation, the principle of integral minimization scalar image velocimetry may be used instead of the direct inversion method.

[0065] Embodiment 1

[0066] A double-sided telecentric lens transmission background schlieren system, reference Figure 2 , including a background pattern plate 1, a fluid 13, a flat glass 7, a first double-sided telecentric lens 3, a light source 4, a high-speed camera 5, a data processor 6, and a second double-sided telecentric lens 14. The optical axes of the light source 4, the first double-sided telecentric lens 3, and the high-speed camera 5 coincide; the flat glass 7 is used as an observation window for the flow field; and the background pattern plate 1 is a transparent screen with random dot matrix scattered on it.

[0067] The light source 4 emits a spherical incident light of a certain wavelength, which becomes a plane incident light after passing through the first double-sided telecentric lens 3. It passes through the background pattern plate 1 screen and then penetrates the flow field 2. Due to the uneven refractive index distribution in the flow to be measured, the deflected light is filtered by the first double-sided telecentric lens 3 and is parallel to the main optical axis again and converges on the photosensitive element of the camera 5, so that the camera can take pictures to obtain continuous images, and the images are output to the data processor for post-processing.

[0068] A method for synchronously measuring temperature field and velocity field is applied to a double-sided telecentric lens transmission background schlieren system provided in Example I. The method comprises: first obtaining a reference image I filled with air in a flow channel air (x, y, t0), and then obtain the reference image I of the channel filled with static liquid static (x, y, t0), perform convolution operation on the two images to obtain the background pattern offset (Δx, Δy) caused by the transparent glass plate, and then take a reference image I with fluid (no temperature gradient) flow (x, y, t0), and remap I remapping (x, y, t0) is used as the final reference background pattern without optical distortion field, and then a fluid with a temperature gradient is introduced and a dynamic background pattern with an optical distortion field is photographed.

[0069] According to Fermat's principle, the background pattern displacement Δy′ and the deflection angle ε are established, and the deflection angle ε and the refractive index gradient are established. , solve the Poisson equation to obtain the refractive index field, specifically:

[0070] Δy′=Z D tan ε

[0071]

[0072]

[0073]

[0074] The temperature field is calculated based on the refractive index field, specifically:

[0075]

[0076] Where n0 is the initial refractive index of the environment, T0 is the initial temperature of the environment, and dn / dT is the thermo-optic coefficient of the fluid.

[0077] Calculate the velocity field from the temperature field.

[0078]

[0079] in is the partial derivative of temperature with respect to time, is the temperature gradient in space, κ is the temperature diffusion coefficient, is the Laplace term. The time differential term, gradient term, and Laplace term can be obtained by the second-order central difference method, and then the velocity field u(x, t) can be inverted. Furthermore, the principle of integral minimization scalar image velocimetry can be used instead of the direct inversion method.

[0080] Embodiment 2

[0081] A double-sided laser speckle transmission background schlieren system, reference Figure 3 , including a laser 9, a holographic beam expansion device 10, a pinhole 11, a lens 12, a fluid 13, a flat glass 7, a first double-sided telecentric lens 3, a high-speed camera 5, and a data processor 6.

[0082] Embodiment II and Embodiment I have the same arrangement method of some optical systems and the same devices, and the difference lies in another way of generating a background image, which is characterized in that a continuous laser beam is generated by a laser 9 and passes through a holographic diffuser 10, a small hole 11 and a lens 12 to generate a collimated background image. The background image is directly projected through a fluid 13 onto an image sensor of a high-speed camera 5. On the cross section of the same beam path, the speckle pattern remains consistent, which is suitable for situations requiring a low signal-to-noise ratio.

[0083] Embodiment 3

[0084] A background schlieren system with telecentric lenses arranged on the same side, reference Figure 4, including a background pattern plate 1, a fluid 13, a flat glass 7, a reflector 8, a first double-sided telecentric lens 3, a second double-sided telecentric lens 14, a light source 4, a high-speed camera 5, and a data processor 6. Embodiment III is the same as Embodiment I in the optical system, except that the high-speed camera and the background plate are arranged on the same side, and the collimated light generated by the telecentric light source first enters the flat glass 7 and the fluid 13, and then is reflected by the reflector 8 and emitted again through the fluid 13 and the flat glass 7. From geometric optics, it can be known that the flat glass will only cause the light to displace along the axial direction without changing its direction; because BOS studies the integral effect of the refractive index change along the optical path, the integral length (flow field thickness) of Embodiment III is twice the original one, which is conducive to detecting small temperature gradients and is suitable for the measurement of unilateral opaque flow fields.

[0085] In the description of the positional relationship of the present invention, the terms such as "inside", "outside", "up", "down", "left", "right", etc. that indicate the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "parallel", "vertical", etc. do not mean that the components are required to be absolutely parallel or vertical, but are allowed to be slightly tilted. At the same time, although the steps shown in the flowchart of the accompanying drawings show a logical order in the flowchart, in some cases, the steps shown or described may be performed in an order different from that here.

[0086] The above content and structure describe the basic principle, main features and advantages of the product of the present invention, which should be understood by those skilled in the art. The above examples and descriptions are only for explaining the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which are within the scope of the present invention. The scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A temperature field and velocity field synchronous measurement device based on background schlieren method, characterized in that: The invention comprises a reference beam generating component, a flow field (2), a first double-sided telecentric lens (3) and a camera (5), wherein the reference beam generating component generates a parallel beam containing a background image, and the parallel beam containing the background image passes through the flow field (2) and then is incident on the first double-sided telecentric lens (3), and then is collected by the camera (5) after being transmitted by the first double-sided telecentric lens (3); A reference beam generating assembly and a first double-sided telecentric lens (3) are respectively arranged at intervals on both sides of the flow field (2); a parallel beam containing a background image generated by the reference beam generating assembly is directly incident on the first double-sided telecentric lens (3) after being transmitted through the flow field (2); The flow field (2) comprises two pieces of flat glass (7) and a fluid (13); the two pieces of flat glass (7) are arranged in parallel and at an interval, and the space between the two pieces of flat glass (7) is filled with the fluid (13); One of the flat glass sheets (7) in the flow field (2) is replaced with a reflector (8), a reference beam generating assembly and a first double-sided telecentric lens (3) are placed on a side close to the other flat glass sheet (7), an angle is set between a parallel beam containing a background image generated by the reference beam generating assembly and a side surface of the flow field (2), an angle is set between an optical axis of the first double-sided telecentric lens (3) and a side surface of the flow field (2), and the parallel beam containing the background image is incident on the first double-sided telecentric lens (3) after being transmitted through the flow field (2), reflected by the reflector (8), and re-transmitted through the flow field (2).

2. The device for synchronously measuring temperature field and velocity field based on background schlieren method according to claim 1, characterized in that: The reference beam generating assembly comprises a background pattern plate (1), a light source (4) and a second double-sided telecentric lens (14); a light beam emitted from the light source (4) passes through the second double-sided telecentric lens (14) and then passes through the background pattern plate (1) to obtain a parallel light beam containing a background image.

3. A method for synchronously measuring temperature field and velocity field based on background schlieren method using the synchronous measuring device for temperature field and velocity field based on background schlieren method according to claim 1, characterized in that: The following steps are involved: Step 1: Build a synchronous measurement device for temperature field and velocity field based on background schlieren; Step 2: Use the temperature field and velocity field synchronous measurement device to collect reference images filled with air in the flow field in sequence , reference image filled with static liquid , Reference image of fluid without temperature gradient and dynamic images of fluids with temperature gradients being introduced; Step 3: Based on the reference image filled with air , reference image filled with static liquid , Reference image of fluid without temperature gradient , reconstruct the refractive index field of the dynamic image of the fluid with temperature gradient, and obtain the refractive index field of the current flow field to be measured; Step 4: Calculate and obtain the temperature field of the current flow field to be measured according to the refractive index field of the current flow field to be measured; Step 5: Obtain the corresponding velocity field based on the temperature field inversion of the current flow field to be measured; In step 2, when the fluid (13) in the flow field (2) is air, the camera (5) acquires a reference image filled with air. ; When the fluid (13) in the flow field (2) is a stationary liquid, the camera (5) acquires a reference image filled with the stationary liquid. ; When the fluid (13) in the flow field (2) is a fluid without a temperature gradient, the camera (5) acquires a reference image of the fluid without a temperature gradient. When the fluid (13) in the flow field (2) is a fluid with a temperature gradient, the camera (5) acquires a dynamic image of the fluid with a temperature gradient; The step 3 is specifically as follows: 3.1) Reference image filled with air and a reference image filled with static liquid After convolution, the background pattern offset is obtained; 3.2) Based on the background pattern offset, the reference image of the fluid without temperature gradient is Remap to obtain the reference background image ; 3.3) Based on the reference background image and the background displacement is obtained by calculating the dynamic image of the fluid with temperature gradient; Based on the background displacement, geometric optics and Fermat's principle are used to establish the background pattern displacement and deflection angle in the dynamic image of the temperature gradient fluid. and deflection angle The relationship between the refractive index gradient and the refractive index field of the current flow field to be measured is obtained; The background displacement includes the displacement of the background on the x-axis. and the background displacement on the y-axis , for the displacement of the background on the y-axis , based on Fermat's principle, the background pattern displacement is established Deflection Angle , deflection angle With refractive index gradient , solve the Poisson equation to obtain the refractive index field, specifically: The temperature field is calculated based on the refractive index field, specifically: in, is the distance between the flow field to be measured and the background pattern plate, is the initial refractive index of the environment, is the initial ambient temperature, is the thermo-optical coefficient of the fluid; are respectively the focal lengths corresponding to the first positive lens (31) and the second positive lens (33) in the first double-sided telecentric lens (3); is the fluid temperature, is the thickness of the flow field to be measured, is the Laplace operator, refers to the gradient operator, is the displacement of the background pattern plate A collection of; is the refractive index of the fluid at temperature T; The step 5 is specifically as follows: According to the temperature field of the current flow field to be measured, the temperature parameters in the temperature convection-diffusion equation corresponding to the temperature field are calculated and analyzed using the second-order central difference method, and then the velocity field is inverted and calculated based on the temperature parameters; Calculate velocity field based on temperature field , the formula is as follows: in, is the partial derivative of temperature with respect to time, is the temperature gradient in space, is the diffusion coefficient of temperature, is the Laplace term.

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