Method and system for synchronously measuring two-dimensional temperature field and velocity field of high-temperature airflow

Abstract

The invention discloses a high-temperature airflow two-dimensional temperature field and velocity field synchronous measurement system and method based on laser-induced phosphorescence, and the system comprises phosphorescence particles, a low-frequency double-pulse laser, an image collection device, a synchronous controller, and an image processing device. The image processing device analyzes the gray intensity ratio of different wave band images acquired by the two PIV cameras at the same time, and combines a temperature response function calibrated by an experiment to realize inversion of a temperature field; meanwhile, a double-frame time-resolved image acquired by any PIV camera is subjected to cross-correlation calculation, particle displacement is extracted, and then a velocity field is reconstructed. According to the invention, synchronous acquisition of temperature and speed based on the same data source is realized, and the system has the remarkable advantages of simple structure, high measurement precision and wide application environment.

Description

Technical Field

[0001] The present invention relates to the field of measurement technology, and specifically to a method for measuring the two-dimensional temperature field and velocity field of a high-temperature gas flow. Background Art

[0002] High-temperature gas flows widely exist in the fields of aerospace, energy, metallurgy, etc. The distribution characteristics of their temperature fields and velocity fields have important impacts on the efficiency, stability, and safety of system operation. Accurately obtaining the temperature and velocity information in the flow field not only helps to optimize the equipment structure and operating parameters but also provides experimental data support for complex fluid mechanics and numerical research. Measuring the temperature field or velocity field separately is difficult to comprehensively reveal the coupling mechanism of multiple physical quantity fields in high-temperature gas flows. Therefore, there is an urgent need to develop a method that can simultaneously measure the temperature field and velocity field of high-temperature gas flows.

[0003] Currently, temperature and velocity simultaneous measurement technologies are mostly based on the coupling of optical temperature measurement methods and particle image velocimetry (PIV) technologies. Usually, temperature-sensitive particles and tracer particles are introduced to jointly obtain temperature and velocity information. For example, Kearney S.P et al. combined planar laser-induced fluorescence (PLIF) with PIV technology, used a 248 nm laser to excite acetone tracer for temperature measurement, and cooperated with a 532 nm laser to illuminate hollow polystyrene particles for velocity measurement, achieving two-dimensional simultaneous measurement of unsteady laminar impinging jets. Bohlin A et al. combined coherent anti-Stokes Raman scattering (CARS) with PIV technology, used 800 nm and 532 nm lasers to excite nitrogen molecules for temperature measurement, and at the same time used a 532 nm laser to illuminate tracer particles for velocity measurement, successfully constructing a two-dimensional simultaneous measurement system for air jets. Salvi et al. combined tunable diode laser absorption spectroscopy (TDLAS) with PIV technology in the hypersonic wind tunnel of the German Aerospace Center (DLR), used a 266 nm laser to excite nitrogen molecules for temperature measurement, and used a 532 nm laser to illuminate magnesium oxide particles for velocity measurement, achieving simultaneous measurement of gas flows containing solid particles.

[0004] Although the above methods have made certain progress in simultaneous measurement, they still generally have the following problems: they require two laser systems and two types of particles, the system structure is complex, the optical path alignment requirements are high, the matching of temperature-sensitive particles and tracer particles is poor, etc. Especially in complex environments such as high temperature, high pressure, or combustion, they also face challenges such as weak signal intensity, large background interference, and difficult calibration.

[0005] To simplify the system structure and improve the feasibility of synchronous measurement, Yin Z et al. proposed a synchronous measurement method that combines the temperature measurement by the laser-induced phosphorescence intensity ratio method with the particle image velocimetry (PIV) technology. This scheme uses phosphorescent particles as both temperature-sensitive particles and tracer particles simultaneously. Under the excitation of a 355 nm pulsed laser, phosphorescence images are generated for temperature measurement, and under the irradiation of a 532 nm double-pulsed laser, scattering images are generated for velocity measurement. Although synchronous measurement is achieved, due to the need to use two sets of independent laser and imaging systems, the system structure is complex, the optical path adjustment is cumbersome, and the application scenario is limited. In addition, the reflected light of the phosphorescence by the 532 nm filter will interfere with the imaging of the phosphorescence imaging system and affect the measurement accuracy.

[0006] Currently, there is also a method that combines particle tracking velocimetry (PTV) technology with the phosphorescence lifetime decay method for synchronous measurement of the velocity field and temperature field. This method analyzes the motion trajectories and intensity changes of temperature-sensitive phosphorescent particles in the sequential images of particles, extracts the velocity and phosphorescence decay slope constant of the particles, and then calculates the temperature of the particles according to the preset calibration relationship, so as to achieve synchronous acquisition of temperature and velocity in the flow field. The main disadvantages of this method include:

[0007] (1) Particle matching needs to be carried out before calculating temperature and velocity, and the processing flow is cumbersome;

[0008] (2) The extraction of velocity and temperature depends on consecutive multiple frames of images (such as 10 frames mentioned in the invention), the data volume is large, the processing speed is slow, and it is difficult to achieve online measurement;

[0009] (3) High-speed cameras and high-frequency lasers need to be equipped, and the equipment cost is high;

[0010] (4) The physical properties of phosphorescent particles (such as luminescence lifetime, particle size, thermal conductivity, density) and image acquisition and processing parameters have a significant impact on the measurement applicability, but this scheme does not conduct a systematic evaluation and discussion on them. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a synchronous measurement system and method for the two-dimensional temperature field and velocity field of high-temperature airflow based on laser-induced phosphorescence, which has a simpler structure, lower cost and faster processing speed.

[0012] To solve the above technical problems, the technical solution adopted by the present invention is:

[0013] A synchronous measurement system for the two-dimensional temperature field and velocity field of high-temperature airflow based on laser-induced phosphorescence, comprising:

[0014] Phosphorescent particles, which are seeded into the high-temperature airflow field to be measured;

[0015] A low-frequency double-pulse laser, which is used to emit two excitation pulses with a time interval of Δt. The excitation pulses pass through a high-temperature gas flow with phosphorescent particles, and the phosphorescent particles are excited to generate phosphorescence.

[0016] An image acquisition device, which consists of a long-pass dichroic mirror and two synchronized PIV cameras. The long-pass dichroic mirror is used to split the phosphorescence into two beams of different bands. The two PIV cameras are equipped with optical band-pass filters with different central wavelengths to filter the split light signals, so as to select different spectral components of the phosphorescence.

[0017] A synchronization controller, which is respectively connected to the low-frequency double-pulse laser and the image acquisition device, and is used to ensure precise timing control between the laser excitation and the image acquisition device.

[0018] An image processing device, which realizes the inversion of the temperature field by analyzing the gray intensity ratio of different band images collected by the two PIV cameras at the same moment and combining the experimentally calibrated temperature response function. At the same time, the double-frame time-resolved images collected by any one of the PIV cameras are processed through cross-correlation calculation to extract the particle displacement and then reconstruct the velocity field.

[0019] The method for the image processing device to realize the inversion of the temperature field is as follows:

[0020] The calibration function f(T) of the gray intensity ratio of the image obtained by experimental calibration and the temperature.

[0021] Collect the gray intensity values of different band phosphorescence images at the same moment to obtain the gray intensity ratio of different band images at the same moment.

[0022] Substitute the obtained gray intensity ratio of different band images at the same moment into the calibration function f(T) of the gray intensity ratio of the image and the temperature to obtain the temperature at the current moment.

[0023] The method for the image processing device to realize the inversion of the velocity field is as follows:

[0024] Within the time interval of Δt, two laser pulses excite the phosphorescent particles to emit two frames of images. The two frames of images are divided into uniform rectangular interpretation windows, and the size of the rectangular interpretation window is M×N pixels. The correlation between the two frames of images is calculated through the cross-correlation algorithm within each rectangular interpretation window to identify the average displacement of the particles.

[0025] The cross-correlation function is defined as follows:

[0026]

[0027] Wherein, R(m,n) represents the cross-correlation function value of two interpretation windows at the displacement (m,n), f(k,l) and g(k,l) respectively represent the gray intensity value functions of the first frame image and the second frame image within the interpretation window area, 1≤k≤M, 1≤l≤N, m and n are displacement estimation parameters, -M≤m≤M, -N≤n≤N;

[0028] By performing cross-correlation matching on each interpretation window of the entire image, the displacement matrix of the entire image is obtained:

[0029]

[0030] Wherein, (i,j) represents the interpretation window in the i-th row and j-th column, ΔX and ΔY respectively represent the displacement matrices in the X direction and Y direction, m(i,j) and n(i,j) are the displacement parameters when the cross-correlation function R(m,n) reaches the maximum value, respectively representing the pixel displacements in the X direction and Y direction.

[0031] Combined with the time interval Δt, the two-dimensional velocity distribution can be reconstructed:

[0032]

[0033] Wherein, V x is the velocity matrix in the X direction; V y is the velocity matrix in the Y direction.

[0034] The method for selecting phosphorescent particles is:

[0035] Set the Reynolds number Re of the airflow on the particles to be <1; according to the set Reynolds number, determine the particle size of the phosphorescent particles; wherein the Reynolds number Re of the airflow on the particles is expressed as:

[0036]

[0037] Wherein, ρ g is the airflow density, ΔV is the relative velocity between the phosphorescent particles and the airflow, d p is the particle size of the phosphorescent particles, μ g is the gas dynamic viscosity;

[0038] Set the Strouhal number St <<1; according to the set Strouhal number, determine the density of the phosphorescent particles; wherein the Strouhal number St is:

[0039]

[0040] Wherein, ρ p is the density of the phosphorescent particles, L g is the characteristic length of the airflow;

[0041] Set the velocity relaxation time τ ΔV≤60 μs; Further optimize the particle size and density of the phosphorescent particles according to the set velocity relaxation time; The velocity relaxation time is:

[0042]

[0043] In the formula, ρ p is the density of the phosphorescent particles, d p is the particle size of the phosphorescent particles, μ g is the gas dynamic viscosity;

[0044] Set the Biot number Bi << 0.0333; Determine the thermal conductivity of the phosphorescent particles according to the set Biot number; The Biot number Bi is:

[0045]

[0046] In the formula, k g is the thermal conductivity of the air flow, d p is the particle size of the phosphorescent particles, k p is the thermal conductivity of the phosphorescent particles;

[0047] Set the temperature relaxation time τ ΔT ≤40 μs; Determine the specific heat capacity of the phosphorescent particles according to the set temperature relaxation time; The temperature relaxation time is:

[0048]

[0049] In the formula, ρ p is the density of the phosphorescent particles, C p,p is the specific heat capacity of the phosphorescent particles, k g is the thermal conductivity of the air flow, d p is the particle size of the phosphorescent particles.

[0050] The selected phosphorescent particles are BAM:Eu phosphorescent particles with a particle size of 2 μm.

[0051] The time interval Δt between the two excitation pulses emitted by the low-frequency double-pulse laser is:

[0052]

[0053] In the formula, N·L Pixel is the given spatial resolution, and V is the high-temperature air flow velocity.

[0054] The central wavelengths of the optical band-pass filters equipped with the two PIV cameras in the image acquisition device are 424 ± 13 nm and 463 ± 17 nm respectively.

[0055] The present invention also provides a method for synchronously measuring the two-dimensional temperature field and velocity field of a high-temperature air flow based on laser-induced phosphorescence, including:

[0056] Uniformly scatter phosphorescent particles into the flow field to be measured;

[0057] Use a low-frequency double-pulse laser to emit two excitation pulses with a time interval of Δt to excite the particles to generate phosphorescence;

[0058] The synchronization controller ensures precise timing control between the laser excitation and the image acquisition device;

[0059] The image acquisition device acquires the phosphorescence signal; the image acquisition device consists of a long-pass dichroic mirror and two synchronized PIV cameras; the two PIV cameras are equipped with optical band-pass filters with different central wavelengths to filter the spectral signals for selecting different spectral components of the phosphorescence;

[0060] Analyze the gray intensity ratio of the images in different bands acquired by the two PIV cameras at the same moment, and combine the experimentally calibrated temperature response function to realize the inversion of the temperature field; at the same time, the double-frame time-resolved images acquired by any one camera are processed by the cross-correlation algorithm to extract the particle displacement and then reconstruct the velocity field.

[0061] The present invention ingeniously combines the phosphorescence intensity ratio method with the phosphorescence PIV technology, uses the same phosphorescent particles to simultaneously obtain temperature and velocity information, extracts the flow field velocity information by processing the time series images of laser-induced phosphorescence through the cross-correlation algorithm, and at the same time uses the phosphorescence intensity ratio method to process the gray intensity ratio of the laser-induced phosphorescence spectral images to invert the temperature distribution, so as to realize the synchronous acquisition of temperature and velocity based on the same data source. This method has the remarkable advantages of simple system structure, high measurement accuracy, and wide applicable environment.

[0062] Innovatively designed a spectroscopic phosphorescence image acquisition device, which uses a 445nm long-pass dichroic mirror and a dual-band band-pass filter to separate the phosphorescence signal, and acquires the λ 424 and λ 463 band images through two synchronized PIV cameras respectively, and combines the full-target calibration method to significantly improve the accuracy and spatial consistency of temperature inversion.

[0063] The present invention systematically established a parameter selection model around the velocity following ability, temperature response ability and luminescence characteristics of the particles, and finally selected BAM:Eu phosphorescent particles. Combining the particle lifetime, key parameters such as the laser pulse interval, camera exposure time, cross-correlation window size, and particle concentration in the cross-correlation window were optimized to achieve reliable synchronous measurement in high-temperature and high-speed environments.

[0064] Compared with the prior art, the beneficial effects of the present invention are:

[0065] (1) The system structure is simpler and more adaptable

[0066] The present invention uses a single laser source and a single type of phosphorescent particles, and can realize the synchronous measurement of the temperature field and velocity field in a high-temperature gas flow without introducing additional scattering particles or a complex dual-laser system. This design effectively avoids the optical path interference problem caused by multi-system coupling, and is especially suitable for measurement environments with limited space or limited optical windows, such as narrow areas inside burners and nozzle outlets.

[0067] (2) Low equipment configuration requirements and relatively low system cost

[0068] The proposed measurement system only needs to configure a low-frequency laser and a conventional PIV camera to complete the synchronous measurement task. Compared with the existing solutions that require high-frequency lasers and high-speed cameras, it significantly reduces the system cost and equipment requirements, and improves the engineering feasibility.

[0069] (3) Low image data requirements and high processing efficiency

[0070] Traditional technologies usually rely on multiple frames of images (such as more than 10 frames) for synchronous measurement, with a large amount of data and slow processing speed, making it difficult to meet the on-line measurement requirements. The present invention only needs three frames of images (i.e., two sequential images collected by PIV camera 1 + a single frame image collected by camera 2) to realize the synchronous extraction of temperature and velocity information, greatly reducing the amount of image data and improving the processing speed, providing the possibility for real-time on-line measurement.

[0071] (4) No particle matching is required, and the algorithm is simple and efficient

[0072] Existing technologies usually calculate temperature and velocity through particle matching algorithms, with high matching difficulty and complex processing. The present invention extracts the intensity ratio and particle displacement based on the intensity information of image regions respectively, without performing particle-level matching operations, significantly improving the image processing efficiency and reliability.

[0073] (5) There is a clear guiding basis for parameter selection, and it has strong adaptability

[0074] The present invention systematically proposes the principle of selecting physical property parameters of phosphorescent particles, and establishes a selection model for synchronous measurement parameters based on physical quantities such as velocity / temperature relaxation time, particle size, and luminescence lifetime, so as to be applied to different application scenarios.

[0075] (6) Low requirement for particle concentration, and broadens the applicable range of particle concentration

[0076] Unlike traditional PIV, which requires high particle concentrations (e.g., ≥10 particles / window), this method achieves high-quality image acquisition and analysis with a lower particle concentration (approximately 6 particles / window) while maintaining measurement accuracy. This feature is particularly suitable for measurement scenarios with limited particle dispersion or poor particle stability in high-temperature environments, expanding the applicable particle concentration range by approximately 40%, significantly improving the technology's practicality and environmental adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 Schematic diagram of the synchronous measurement system structure of phosphorescence intensity ratio method coupled with phosphorescence PIV;

[0078] Figure 2 It is the principle diagram of image processing;

[0079] Figure 3 is the thermal quenching characteristic curve of phosphorescence spectrum intensity;

[0080] Figure 4 This is a temperature measurement principle diagram based on the phosphorescence intensity ratio method;

[0081] Figure 5 This is a schematic diagram of the calculation principle of phosphorescent particle displacement based on the cross-correlation algorithm;

[0082] Figure 6 It is a timing relationship diagram between laser pulse time interval, pulse width, particle luminescence lifetime and camera exposure time;

[0083] Figure 7 The emission spectrum intensity curve of BAM:Eu phosphor particles at 300-800K; (a) absolute intensity, (b) normalized intensity;

[0084] Figure 8 This is the luminescence lifetime measurement result of BAM:Eu phosphor particles in the temperature range of 300-800K;

[0085] Figure 9 It is a graph of intensity ratios for different wavelength pairs in the temperature range of 300-800K;

[0086] Figure 10 Images of tracer particles in a laminar flow field with a central velocity of 30 m / s; (a) scattering PIV particle image, (b) phosphorescent PIV particle image;

[0087] Figure 11 is the velocity reconstruction result on the central axis of the flow field under different particle concentrations;

[0088] Figure 12 This is a structural diagram of a spectroscopic laser-induced phosphorescence image acquisition device;

[0089] Figure 13It is a temperature calibration experimental platform for the full-target phosphorescence intensity ratio method of a phosphorescent image acquisition device;

[0090] Figure 14 It is the full-target phosphorescence spectral image of the phosphorescent image acquisition device under the condition of 300K; (a) λ 424 band, (b) λ 463 band;

[0091] Figure 15 It is the calibration result of the full-target gray intensity ratio - temperature of the phosphorescent image acquisition device;

[0092] Figure 16 It is an experimental system for synchronous measurement of the two-dimensional velocity field and temperature field of high-temperature air circular pipe free jet;

[0093] Figure 17 It is the phosphorescent particle spectral image under Case 3 working condition; (a) λ 424 band, (b) λ 463 band;

[0094] Figure 18 It is the synchronous measurement results under three working conditions (the left is instantaneous and the right is time-averaged);

[0095] Figure 19 It is the experimental measurement results of the repeatability of the centerline position under three working conditions. Specific implementation mode

[0096] This embodiment provides a synchronous measurement system for the two-dimensional temperature field and velocity field of high-temperature airflow based on laser-induced phosphorescence, as Figure 1 shown, including:

[0097] A 355nm low-frequency double-pulse laser, which emits two excitation pulses with a time interval of Δt to excite particles to generate phosphorescence.

[0098] An image acquisition device, which consists of a long-pass dichroic mirror and two synchronous PIV cameras. The long-pass dichroic mirror is used to divide the phosphorescence into two-band light beams, and each camera is equipped with band-pass filters with different central wavelengths (λ 424 and λ 463 ) to select different spectral components of the phosphorescence.

[0099] A synchronous controller, which is respectively connected to the 355nm low-frequency double-pulse laser and the image acquisition device, and is used to ensure the precise timing control between the laser excitation and the image acquisition device.

[0100] The image processing device realizes the inversion of the temperature field by analyzing the gray intensity ratio of images in different bands collected by two cameras at the same time and combining the experimentally calibrated temperature response function. At the same time, the double-frame time-resolved images collected by any one camera are processed by cross-correlation calculation to extract the particle displacement and then reconstruct the velocity field.

[0101] The measurement system provided in this embodiment uses phosphorescent particles as the only temperature and tracer medium. The flow field velocity information is extracted by processing the time series images of laser-induced phosphorescence through the cross-correlation algorithm. At the same time, the temperature distribution is inverted by using the phosphorescence intensity ratio method to process the gray intensity ratio of the laser-induced phosphorescence spectral images, so as to realize the synchronous acquisition of temperature and velocity based on the same data source.

[0102] The measurement method of the measurement system of the present invention is as follows:

[0103] First, the BAM:Eu phosphorescent particles are evenly scattered into the flow field to be measured.

[0104] A 355nm low-frequency double-pulse laser is used to emit two excitation pulses with a time interval of Δt to excite the particles to generate phosphorescence.

[0105] The synchronous controller ensures the precise timing control between the laser excitation and the image acquisition device.

[0106] The image acquisition device acquires the phosphorescence signal; the image acquisition device consists of a long-pass dichroic mirror and two synchronous PIV cameras. The long-pass dichroic mirror is used to divide the phosphorescence into two beams of light in different bands, and each camera is equipped with band-pass filters with different central wavelengths (λ1 and λ2) to select different spectral components of the phosphorescence.

[0107] In the image processing stage, the inversion of the temperature field is realized by analyzing the gray intensity ratio of images in different bands collected by two cameras at the same time and combining the experimentally calibrated temperature response function. At the same time, the double-frame time-resolved images collected by any one camera can be used for the cross-correlation algorithm to extract the particle displacement and then reconstruct the velocity field.

[0108] The inversion of the temperature field uses the phosphorescence intensity ratio method for temperature measurement. The phosphorescence intensity ratio method for temperature measurement is based on the thermal quenching characteristics of phosphorescent materials: as the temperature increases, the phosphorescence emission intensity weakens, and the spectral peak undergoes a blue shift (shifts towards the short-wave direction), as Figure 3 shown.

[0109] By selecting appropriate phosphorescence emission bands, a monotonic function relationship between the phosphorescence intensity ratio and the temperature can be established,

[0110] R = I λ1 / I λ2 = f(T)(1)

[0111] In the formula, I λ1 and Iλ2 They are the gray intensity values of the phosphorescence images in the λ1 and λ2 bands respectively, and f(T) is the calibration function of the intensity ratio and temperature obtained through experimental calibration. By calculating the gray intensity ratio of each region in the image and substituting it into the function f(T), two-dimensional reconstruction of the temperature field can be achieved, as Figure 4 shown.

[0112] To improve the measurement sensitivity and accuracy, it is necessary to select spectral bands that are highly sensitive to temperature and less affected by background noise. Therefore, it is necessary to systematically study the emission characteristics of phosphorescent particles to optimize the band selection and improve the reliability of temperature measurement.

[0113] The reconstruction of the velocity field is based on the principle of phosphorescent PIV velocity measurement. As Figure 5 shown, within the time interval Δt, two laser pulses excite the phosphorescent particles to emit two frames of images, and the PIV camera records them in double-exposure mode. The image is divided into uniform rectangular interrogation windows (M×N pixels). The correlation between the two frames of images is calculated through the cross-correlation algorithm within each window to identify the average displacement of the particles.

[0114] The cross-correlation function is defined as follows:

[0115]

[0116] In the formula, R(m,n) represents the cross-correlation function value of the two interrogation windows at the displacement (m,n), f(k,l) and g(k,l) respectively represent the gray intensity value functions of the first frame of image and the second frame of image within the interrogation window area, 1≤k≤M, 1≤l≤N, m and n are displacement estimation parameters, -M≤m≤M, -N≤n≤N. By performing cross-correlation matching on each interrogation window of the entire image, the displacement matrix of the entire image is obtained:

[0117]

[0118] In the formula, (i,j) represents the interrogation window in the i-th row and j-th column, ΔX and ΔY respectively represent the displacement matrices in the X direction and Y direction, m(i,j) and n(i,j) are the displacement parameters when the cross-correlation function R(m,n) reaches the maximum value, and respectively represent the pixel displacements in the X direction and Y direction. Combining the time interval Δt, the two-dimensional velocity distribution can be reconstructed:

[0119]

[0120] In the formula, V x is the velocity matrix in the X direction; V y is the velocity matrix in the Y direction.

[0121] Due to the long emission lifetime of phosphorescent particles, streak-like structures may appear in the image, reducing image clarity and thus affecting the velocity measurement accuracy. Therefore, it is necessary to study the influence of phosphorescence lifetime on PIV measurement through theoretical analysis and simulation to optimize system parameters and improve measurement accuracy.

[0122] Selection of phosphorescent particles and choice of synchronous measurement parameters:

[0123] In the present invention, phosphorescent particles serve as both temperature and tracer media in the airflow. Their response characteristics (including velocity followability and temperature response ability) and luminescence and imaging characteristics in a high-temperature and high-speed environment directly determine the accuracy of the measurement. Through theoretical analysis, the present invention clarifies the principles for particle selection (type, particle size, density, specific heat capacity, thermal conductivity, luminescence lifetime), determines the final selection of phosphorescent particles based on the characteristics of the flow field to be measured, and then systematically analyzes the luminescence characteristics of phosphorescent particles and their influence on the selection of PIV measurement parameters to determine the optimal phosphorescence band selection and PIV measurement parameters for the phosphorescence intensity ratio method.

[0124] The selection criteria for phosphorescent particles include velocity followability and temperature followability:

[0125] (1) Velocity followability:

[0126] In PIV measurement, the particles should closely follow the changes in the airflow. The Reynolds number (Re) of the airflow acting on the particles is expressed as:

[0127]

[0128] where ρ g is the airflow density, ΔV is the relative velocity between the phosphorescent particle and the airflow, d p is the particle size of the phosphorescent particle, and μ g is the dynamic viscosity of the gas.

[0129] When Re < 1, it indicates that the Stokes flow condition is satisfied. The Strouhal number (St) is further introduced to evaluate the velocity responsiveness:

[0130]

[0131] where ρ p is the density of the phosphorescent particle, and L g is the characteristic length of the airflow.

[0132] When St << 1, it indicates that the particles have good velocity followability. The formula for the velocity relaxation time is as follows:

[0133]

[0134] where ρ p is the density of the phosphorescent particle, and dp is the particle size of the phosphorescent particles, μm g is the dynamic viscosity of the air flow.

[0135] (2), Temperature tracking performance

[0136] When the movement of the particles relative to the flow field can be ignored, the heat transfer process between the air flow and the phosphorescent particles can be simplified to a pure heat conduction process. The Biot number (Bi) is introduced to evaluate whether the temperature distribution inside the particles is uniform:

[0137]

[0138] In the formula, h is the heat transfer coefficient between the fluid and the particles (here, take the thermal conductivity k of the air flow g ), l is the characteristic length of the particles (take d p / 6), and k p is the thermal conductivity of the phosphorescent particles.

[0139] When Bi << 0.0333, it indicates that the temperature distribution inside the particles is uniform and can be regarded as a lumped parameter system. Further introduce the temperature relaxation time:

[0140]

[0141] In the formula, ρ p is the density of the phosphorescent particles, C p,p is the specific heat capacity of the phosphorescent particles, k g is the thermal conductivity of the air flow, and d p is the particle size of the phosphorescent particles.

[0142] Influence of phosphorescence lifetime on phosphorescence PIV:

[0143] Phosphorescence PIV is different from traditional scattering PIV because the tracer particles continuously emit light on the microsecond time scale. This extended emission will cause particle streaks, reduce image clarity, and introduce uncertainties in cross-correlation-based velocity measurements. The streak length of a particle moving at velocity V is approximately 3τV, and it is necessary to systematically evaluate its impact on the velocity field measurement and optimize the system parameters.

[0144] Laser pulse time interval and camera exposure time:

[0145] Figure 6 shows the timing relationship between the laser pulse interval Δt, the laser pulse width t laser , the phosphorescence lifetime t LIP (T) and the camera exposure time t. Due to the extended emission duration, compared with traditional PIV, phosphorescence PIV requires a longer pulse interval and camera exposure time. According to the "quarter window" criterion, for a cross-correlation window of M×M pixels, an imaging magnification of 1 / N, and a pixel size L PixelFor a given mainstream velocity V, the optimal pulse interval is given by:

[0146]

[0147] For a given N·L Pixel The spatial resolution, the maximum measurable velocity constrained by the phosphorescence lifetime, is expressed as:

[0148]

[0149] After determining the laser pulse time interval Δt according to the requirements of the flow field to be measured, the value range of the camera exposure time is also determined. For laser-induced phosphorescence imaging, the phosphorescence lifetime of the tracer particles is relatively long. Therefore, in laser-induced phosphorescence tracer particle imaging, the exposure time t of the camera needs to satisfy:

[0150] t LIP (T) ≤ t ≤ Δt(12)

[0151] After determining the relevant parameters for the acquisition of phosphorescent tracer particle images, the values of the relevant parameters for image processing can be further determined.

[0152] Particle image characteristics:

[0153] The PIV measurement accuracy depends on the number of particles in each interrogation window and the image clarity. Since the phosphorescent particles have a long lifetime, they will produce streaks during the luminescence period, increasing the number of luminescent pixels of a single particle, and the measurement accuracy can be maintained even at low particle concentrations.

[0154] The streak length of a particle moving at a velocity (V) within its emission period (3τ) can be expressed as:

[0155]

[0156] where Δx and Δy represent the streak lengths of the particle in the x and y directions during the phosphorescence emission. Considering the flow direction, the number of luminescent pixels of a single phosphorescent particle can be expressed as:

[0157]

[0158] where μ is the velocity direction correction factor (usually between 1 and 2), L Pixel is the pixel size, M is the cross-correlation window size, and 1 / N is the imaging magnification. The ceil() function represents the ceiling function.

[0159] The total number of illuminated pixels in each window is:

[0160]

[0161] In the formula, N particleIt is to inquire about the number of particles within the interrogation window.

[0162] Selection of Phosphorescent Particles and Analysis of Their Synchronous Measurement Characteristics

[0163] Physical Property Parameters of Phosphorescent Particles

[0164] Based on the foregoing analysis of the high-temperature gas flow following characteristics of phosphorescent particles, the analysis of the influence of phosphorescence lifetime on PIV image characteristics, and the guiding formula for the selection of physical property parameters (density, thermal conductivity, specific heat capacity, and particle size), the present invention selects BaMgAl 10 O 17 :Eu 2+ (BAM:Eu) as the phosphorescent material for tracer and temperature indication. BAM:Eu has excellent thermal stability, a relatively high quantum efficiency, a short phosphorescence lifetime (about 1.67 μs at room temperature), an obvious thermal quenching effect, and an emission wavelength in the visible light range. Tables 1 and 2 list the key physical parameters of BAM:Eu particles and the flowing working fluid (air) respectively:

[0165] Table 1 Physical Property Parameters of BAM:Eu Phosphorescent Particles

[0166]

[0167] Table 2 Physical Property Parameters of Air

[0168]

[0169] The emission spectrum of BAM:Eu particles and its normalization results are as Figure 7 shown:

[0170] As Figure 7 (a) shows, the phosphorescence emission is mainly distributed in the spectral range of 400 - 500 nm. At different temperatures, the emission intensity shows a typical single-peak distribution, initially increasing with the wavelength and then decreasing. As the temperature increases, the overall emission intensity decreases, accompanied by a blue shift of the peak wavelength towards shorter wavelengths. Figure 7 (b) gives the normalized spectral intensity, further revealing the variation trend of the intensity ratio in different wavelength bands with temperature. In the regions of 400 - 437 nm and 480 - 500 nm, the proportion of phosphorescence intensity in the total emission increases with the increase in temperature. On the contrary, in the range of 445 - 480 nm, this proportion decreases with the increase in temperature. In the intermediate region of 437 - 445 nm, no obvious monotonic trend is observed. These temperature-related emission characteristics indicate that when using the intensity ratio method for temperature measurement, appropriate spectral channels (λ1 and λ2) should be carefully selected to improve the sensitivity and accuracy of the measurement.

[0171] As Figure 8As shown, the lifetime of the phosphorescent particles decreases with increasing temperature: from 1.67 μs at 300 K to 1.05 μs at 800 K. This decrease is mainly attributed to the enhanced molecular vibration at high temperatures, which leads to an increased probability of non-radiative transitions. In addition, when the temperature exceeds 723 K, the oxidation effect becomes significant, further accelerating the decay of the phosphorescence lifetime. These results indicate that when using phosphorescent PIV technology for flow velocity measurement, the characteristics of the lifetime variation with temperature must be fully considered to achieve reasonable optimization of the parameters.

[0172] Temperature and velocity relaxation times of phosphorescent particles

[0173] Calculated from Equation (6), the velocity relaxation time of the BAM:Eu phosphorescent particles selected in the present invention is 45.1 μs, which is significantly lower than that of the commonly used TiO2 and Al2O3 particles (53–65 μs) in the literature. This is attributed to their lower density. The results show that BAM:Eu has good velocity followability and meets the requirements for velocity field measurement in high-temperature and high-speed airflows.

[0174] In addition, calculated from Equation (8), the temperature relaxation time of the BAM:Eu phosphorescent particles selected in the present invention is 29.6 μs, which is less than its velocity relaxation time, indicating that it responds more rapidly to temperature changes and can quickly reflect the temperature changes in the airflow. It is an ideal high-temperature temperature-indicating material.

[0175] Band selection for intensity ratio method

[0176] To determine the optimal wavelength combination for temperature measurement based on intensity ratio, the present invention evaluated multiple emission bands in terms of both signal-to-noise ratio (SNR) and temperature sensitivity. The first band is selected from the region where the proportion of the normalized phosphorescent spectral radiation intensity in the total radiation intensity increases with increasing temperature, including 400 - 410 nm (denoted as λ 405 ), 410 - 437 nm (denoted as λ 424 ), and 480 - 500 nm (denoted as λ 490 ); the second band is selected from the region where this proportion decreases with increasing temperature, i.e., 445–480 nm (denoted as λ 463 ).

[0177] Figure 9 shows the variation of the intensity ratio of different wavelength pairs in the temperature range of 300–800 K. For all three sets of wavelength pairs, the intensity ratio increases with increasing temperature. However, the absolute ratio of λ 405 / λ 463 is relatively low (0.06–0.21), resulting in a poor signal-to-noise ratio and a high measurement uncertainty. In contrast, λ 490 / λ 463The ratio ranges from 0.21 to 0.27, and the signal-to-noise ratio is improved, but the temperature sensitivity is insufficient. After comprehensive comparison, λ 424 / λ 463 exhibits high temperature sensitivity and good signal-to-noise ratio across the entire temperature range, making it the optimal wavelength combination for achieving high-precision temperature measurement.

[0178] Cross-correlation window phosphorescent particle concentration

[0179] To quantitatively analyze the influence of the phosphorescent particle emission stripes on the particle concentration within the cross-correlation window, this application conducted numerical simulations on a laminar flow field with a centerline velocity of 10–100 m / s, assuming a gas temperature of 300 K. The configuration of the image acquisition system includes: a pixel size of 4.54 μm, an optical magnification of 1 / 6.58, and the cross-correlation window sizes are set to 16×16, 32×32, and 64×64 pixels respectively. Simulated images at different particle concentrations (2–16 particles per window) were generated in MATLAB. Figure 10 Shows particle images at a typical flow velocity of 30 m / s and compares traditional scattering PIV (a) with phosphorescent PIV (b). The results show that, due to the fact that scattering PIV is based on a nearly instantaneous scattering process, the particles in the obtained images appear as compact near-spherical shapes; while in phosphorescent PIV, due to the long emission lifetime of phosphorescence, the particle images exhibit an obviously stretched stripe structure.

[0180] Subsequently, by applying a two-dimensional cross-correlation algorithm to the sequential images, the velocity distribution along the flow centerline was extracted. Figure 11 Shows the velocity distribution results reconstructed under different particle concentration conditions.

[0181] The results indicate that: under the condition of using a 32×32 pixel cross-correlation window, phosphorescent PIV can achieve accurate and stable velocity measurement with only 6 particles per window; in contrast, traditional scattering PIV requires at least 10 particles to achieve the same measurement accuracy. This shows that, on the premise of ensuring measurement accuracy, phosphorescent PIV can operate under the condition of a particle concentration reduction of approximately 40%, demonstrating significant advantages in high-temperature environments. Since particle seeding is often limited by material properties and flow characteristics under high-temperature conditions, this characteristic is particularly crucial. Table 3 summarizes the minimum particle concentrations required to achieve accurate velocity reconstruction at different flow velocities and cross-correlation window sizes.

[0182] Table 3 Minimum particle concentrations required for phosphorescent PIV and scattering PIV under different cross-correlation window sizes (unit: number of particles per window)

[0183]

[0184] Note: "\ " indicates that at the specified window size and flow rate, the particle displacement exceeds the one - quarter window criterion, and velocity measurement is not feasible.

[0185] Laser - induced Phosphorescence Measurement System and Temperature Calibration

[0186] Phosphorescence Spectrum Image Acquisition Module

[0187] Figure 12 Shows a schematic diagram of the phosphorescence spectrum image acquisition system designed in this application to achieve high - precision and time - synchronized phosphorescence measurement. Based on the determined optimal wavelength combination (λ 424 / λ 463 ), the system uses a 445 - nm long - pass dichroic mirror to separate the excited phosphorescence into two different bands. Subsequently, optical band - pass filters with central wavelengths of 424 nm (±13 nm) and 463 nm (±17 nm) are used to filter the spectral signals respectively, and the transmittance of both filters exceeds 90%. Finally, images of two channels are simultaneously acquired by two synchronized PIV cameras to achieve synchronous acquisition of temperature field and velocity field data.

[0188] Since the spectroscopic laser - induced phosphorescence imaging system has non - uniformity in spatial response, it may have a greater impact on the temperature measurement accuracy. Although the traditional correction matrix method can be used to correct this problem, its operation process is rather cumbersome and prone to introducing cumulative errors. To simplify the calibration process and improve the measurement accuracy, the present invention proposes and implements a "full - target - surface direct calibration method" and builds a temperature calibration experimental platform as shown in Figure 13 . During the calibration process, a glass slide coated with BAM:Eu phosphorescent particles is placed in a high - precision temperature - controlled box (temperature control range is 300 K to 800 K, temperature control accuracy is ±0.1 K), 355 - nm pulsed laser is used to excite phosphorescence, and signal images in the λ 424 and λ 463 bands are synchronously acquired by the imaging system. To avoid damage to the imaging system caused by high temperature, the glass slide is quickly moved out of the high - temperature area by an electric displacement stage after each calibration. The imaging target surface is divided into several small areas of 4×4 pixels, and the calibration relationship between the image gray - scale intensity ratio and temperature within each area is established respectively. Finally, a complete phosphorescence intensity ratio image is obtained through image stitching, as shown in Figure 14 .

[0189] Based on the intensity ratios of the two - band images at different temperatures, a full - target - surface image gray - scale intensity ratio - temperature calibration database covering 300 K to 800 K is established (see Figure 15)。The results show that within the entire temperature range, the gray intensity ratio of the same imaging area has a good monotonic increasing relationship with temperature, providing a reliable basis for the subsequent inversion of the temperature field. At the same time, as the temperature increases, the growth rate of the intensity ratio gradually slows down, showing typical non-linear characteristics. It is worth noting that under the same temperature conditions, there are obvious differences in the gray intensity ratios of different target surface areas, further verifying the importance of the full target surface calibration method in eliminating the non-uniformity of the system's spatial response. In addition, the research also shows that when the optical parameters of the imaging system change, the full target surface spectral calibration should be carried out again to ensure the accuracy and consistency of the temperature measurement results.

[0190] Two-dimensional Flow Field and Temperature Field Synchronous Measurement Experiment of High-temperature Air Round Tube Free Jet

[0191] Experimental System and Setup

[0192] To verify the feasibility and effectiveness of the proposed method for synchronous measurement of two-dimensional temperature field and velocity field of high-temperature airflows based on laser-induced phosphorescence in this invention, an experimental platform for high-temperature air round tube free jet is designed and built in this invention, and its system composition is as Figure 16 shown. The platform consists of six subsystems: gas source supply, particle seeding, temperature control, laser illumination, optical imaging, and synchronous control.

[0193] In the experiment, compressed air is provided by an air compressor. To accurately control the seeding concentration of phosphorescent particles, the compressed air is divided into two paths by a flow controller: one path enters the particle generator to fluidize the BAM:Eu phosphorescent particles, and the other path serves as the main gas. The two airflows are mixed and then enter an electric heater for temperature increase treatment, and finally are ejected vertically upward through a nozzle with an inner diameter of 18 mm to form a free jet. A 355 nm double-pulse Nd:YAG laser (single-pulse energy 60 mJ, frequency 5 Hz) is used as the excitation light source, and after passing through a beam expander, a laser sheet with a thickness of 0.4 mm is formed, which vertically irradiates the jet center plane to excite the phosphorescent particles to emit light. The phosphorescence signal is collected by two synchronous PIV cameras through a spectroscopic image acquisition device at λ 424 / λ 463Phosphorescence images in the wavelength bands. The timing control of the system is completed by a high-precision synchronous controller to ensure the precise coordination of laser emission and camera exposure. To monitor the jet outlet temperature in real time, a K-type thermocouple (accuracy ±0.1K) is arranged at the center of the nozzle. The parameters of the imaging system are: pixel size 5.4μm, magnification 1 / 6.58, and camera exposure time 6μs (triggered 1μs before the laser pulse). Early triggering can ensure that the camera starts to expose before the laser pulse arrives, thus completely capturing the rising edge and decay process of the phosphorescence signal, avoiding laser scattering interference, and at the same time ensuring sufficient exposure time to improve the signal-to-noise ratio. Synchronous measurements are carried out under three typical working conditions, with the outlet center temperature set at 373K, 573K, and 773K, and the flow rate is 200 standard liters per minute (slpm). The experimental ambient temperature is 300K, and the ambient pressure is 101.3kPa. The Reynolds number (Re) range at the nozzle outlet is 7000 - 13000, indicating that the jet is in a turbulent state. The experimental working condition parameters are shown in Table 4.

[0194] Table 4 Working condition parameters of the verification experiment

[0195]

[0196] Experimental results and analysis

[0197] Figure 17 Shows the collected λ in the Case 3 working condition 424 and λ 463 Phosphorescence images in two wavelength bands. The images show that the phosphorescent particles are evenly distributed and the signal-to-noise ratio is good, meeting the requirements of the intensity ratio method and PIV analysis.

[0198] During the image processing, by calculating the gray intensity ratio of the dual-wavelength images and combining with the temperature calibration database, the two-dimensional temperature field distribution was reconstructed. At the same time, using the time series images in the λ 463 wavelength band, the cross-correlation algorithm was used to extract the particle displacement to obtain the two-dimensional velocity field information. To balance the spatial resolution and signal-to-noise ratio, a 16×16 pixel window was used for temperature field reconstruction, and a 32×32 pixel window with a 50% overlap rate was used for the velocity field, and finally the unified spatial resolution was 0.47mm.

[0199] Figure 18 Shows the synchronous measurement results of the instantaneous and time-averaged temperature fields and velocity fields under three typical working conditions. The results show that: there is a significant coupling characteristic between the temperature field and the velocity field in the core region of the free jet, and the high-temperature region corresponds to the high-speed region; in the boundary region, the asymmetry of the temperature gradient and the velocity gradient reflects the turbulent mixing effect; the instantaneous images reveal the vortex structure and temperature perturbation at the flow field boundary, while the time-averaged images show a smooth and symmetric distribution.

[0200] Figure 19The repetitive experimental results of the centerline position under three working conditions are presented. The experimental data show that within the temperature range of 373 - 773 K and the velocity range of 15 - 40 m / s, the relative error of temperature measurement by this method is less than 0.98%, and the relative standard deviation is less than 1.17%; the relative error of velocity measurement is less than 1.89%, and the relative standard deviation is less than 2.84%. These results fully demonstrate that the synchronous measurement method based on thermographic phosphorescent particles has good measurement accuracy and stability in high-temperature gas flows and can simultaneously obtain accurate temperature field and velocity field information.

Claims

1. A two-dimensional temperature field and velocity field synchronous measurement system for high-temperature airflows based on laser-induced phosphorescence, characterized in that, Including: Phosphorescent particles, which are scattered into the high-temperature gas flow field to be measured; A low-frequency double-pulse laser, which is used to emit two excitation pulses with a time interval of Δt. The excitation pulses pass through the high-temperature gas flow with phosphorescent particles, exciting the phosphorescent particles to generate phosphorescence; An image acquisition device, which consists of a long-pass dichroic mirror and two synchronized PIV cameras; the long-pass dichroic mirror is used to divide the phosphorescence into two beams of different bands; the two PIV cameras are equipped with optical band-pass filters with different central wavelengths to filter the spectroscopic signals, so as to select different spectral components of the phosphorescence; A synchronization controller, which is respectively connected to the low-frequency double-pulse laser and the image acquisition device, and is used to ensure the precise timing control between the laser excitation and the image acquisition device; An image processing device, which realizes the inversion of the temperature field by analyzing the gray intensity ratio of different-band images collected by the two PIV cameras at the same moment and combining the experimentally calibrated temperature response function; meanwhile, the double-frame time-resolved images collected by any one of the PIV cameras are calculated by cross-correlation to extract the particle displacement and then reconstruct the velocity field.

2. The two-dimensional temperature field and velocity field synchronous measurement system for high-temperature gas flow according to claim 1, characterized in that The method for the image processing device to realize the temperature field inversion is: The calibration function f(T) of the gray intensity ratio of the image obtained by experimental calibration and the temperature; Collect the gray intensity values of the phosphorescence images of different bands at the same moment, and obtain the gray intensity ratio of the images of different bands at the same moment; Substitute the obtained gray intensity ratio of the images of different bands at the same moment into the calibration function f(T) of the gray intensity ratio of the image and the temperature to obtain the temperature at the current moment.

3. The two-dimensional temperature field and velocity field synchronous measurement system for high-temperature gas flow according to claim 1, characterized in that, The method for the image processing device to realize the velocity field inversion is: Within the time interval of Δt, two laser pulses excite the phosphorescent particles to emit two frames of images. The two frames of images are divided into uniform rectangular interpretation windows, and the size of the rectangular interpretation window is M×N pixels; within each rectangular interpretation window, the correlation between the two frames of images is calculated by the cross-correlation algorithm to identify the average displacement of the particles; The cross-correlation function is defined as follows: In the formula, R(m,n) represents the cross-correlation function value of the two interpretation windows at the displacement (m,n), f(k,l) and g(k,l) respectively represent the gray intensity value functions of the first frame of image and the second frame of image within the interpretation window area, 1≤k≤M, 1≤l≤N, m and n are displacement estimation parameters, -M≤m≤M, -N≤n≤N; By performing cross-correlation matching on each interpretation window of the entire image, the displacement matrix of the entire image is obtained: In the formula, (i,j) represents the interpretation window in the i-th row and j-th column, ΔX and ΔY respectively represent the displacement matrices in the X direction and the Y direction, and m(i,j) and n(i,j) are the displacement parameters when the cross-correlation function R(m,n) reaches the maximum value, respectively representing the pixel displacements in the X direction and the Y direction. Combined with the time interval Δt, the two-dimensional velocity distribution can be reconstructed: Wherein, V x is the velocity matrix in the X direction; V y is the velocity matrix in the Y direction.

4. The two-dimensional temperature field and velocity field synchronous measurement system for high-temperature gas flow according to claim 1, characterized in that The method for selecting phosphorescent particles is: Set the Reynolds number Re of the gas flow on the particles <1; according to the set Reynolds number, determine the particle size of the phosphorescent particles; where the Reynolds number Re of the gas flow on the particles is expressed as: where ρ g is the air flow density, ΔV is the relative velocity between the phosphorescent particles and the air flow, and d p is the particle size of the phosphorescent particles, and μ g is the dynamic viscosity of the gas; Set the Strouhal number St <<1; according to the set Strouhal number, determine the density of the phosphorescent particles; where the Strouhal number St is: Where ρ p is the density of phosphorescent particles, and L g is the characteristic length of the air flow; Set the velocity relaxation time τ ΔV ≤60 μs; further optimize the particle size and density of the phosphorescent particles according to the set velocity relaxation time; Where the velocity relaxation time is: Where ρ p is the density of phosphorescent particles, d p is the particle size of phosphorescent particles, and μ g is the dynamic viscosity of the gas; Set the Biot number Bi << 0.0333; determine the thermal conductivity of the phosphorescent particles according to the set Biot number. The Biot number Bi is: where k g is the thermal conductivity of the gas flow, d p is the particle size of the phosphorescent particles, and k p is the thermal conductivity of the phosphorescent particles; Set the temperature relaxation time τ ΔT ≤40 μs; Determine the specific heat capacity of the phosphorescent particles according to the set temperature relaxation time; where the temperature relaxation time is: where ρ p is the density of the phosphorescent particles, C p,p is the specific heat capacity of the phosphorescent particles, k g is the thermal conductivity of the air flow, d p is the particle size of the phosphorescent particles.

5. The two-dimensional temperature field and velocity field synchronous measurement system for high-temperature gas flow according to claim 4, characterized in that, The selected phosphorescent particles are BAM:Eu phosphorescent particles with a particle size of 2 μm.

6. The high-temperature gas flow two-dimensional temperature field and velocity field synchronous measurement system according to claim 5, characterized in that The time interval Δt between the two excitation pulses emitted by the low-frequency double-pulse laser is: Where N·L Pixel is the given spatial resolution and V is the high-temperature gas flow velocity.

7. The two-dimensional temperature field and velocity field synchronous measurement system for high-temperature airflow according to claim 6, characterized in that, The central wavelengths of the optical band-pass filters equipped on the two PIV cameras in the image acquisition device are 424 ± 13 nm and 463 ± 17 nm respectively.

8. A method for synchronously measuring the two-dimensional temperature field and velocity field of a high-temperature gas flow based on laser-induced phosphorescence, characterized in that, Including: Uniformly disperse the phosphorescent particles into the flow field to be measured; Use a low-frequency double-pulse laser to emit two excitation pulses with a time interval of Δt to excite the particles to generate phosphorescence; The synchronization controller ensures precise timing control between the laser excitation and the image acquisition device; The image acquisition device acquires the phosphorescence signal; the image acquisition device consists of a long-pass dichroic mirror and two synchronized PIV cameras; the two PIV cameras are equipped with optical band-pass filters with different central wavelengths to filter the spectral signals for selecting different spectral components of the phosphorescence; Analyze the gray intensity ratio of the images in different bands acquired by the two PIV cameras at the same moment, and combine the experimentally calibrated temperature response function to realize the inversion of the temperature field; at the same time, the double-frame time-resolved images acquired by any camera are processed by the cross-correlation algorithm to extract the particle displacement and then reconstruct the velocity field.

9. The method for synchronously measuring the two-dimensional temperature field and velocity field of a high-temperature gas flow by laser-induced phosphorescence according to claim 8, characterized in that, The phosphorescent particles are BAM:Eu phosphorescent particles with a particle size of 2 μm.

10. The method for synchronously measuring the two-dimensional temperature field and velocity field of a high-temperature gas flow by laser-induced phosphorescence according to claim 8, characterized in that The image acquisition device acquires signals of two wavelength bands λ 424 and λ 463 to obtain signal images of two wavelength bands

Images