A method for measuring two-dimensional wind speed in a heat flow field based on Moiré tomography

Abstract

This invention discloses a method for measuring two-dimensional wind speed in a thermal flow field based on moiré tomography, comprising: acquiring moiré fringe patterns with and without the measured thermal flow field; obtaining the phase information of the measured thermal flow field using a Fourier transform algorithm based on the moiré fringe patterns with and without the measured thermal flow field, and obtaining the deflection angle information of the measured thermal flow field based on the phase information; reconstructing the two-dimensional refractive index distribution of the measured thermal flow field using a filtered back projection algorithm based on the deflection angle information; and performing inversion based on the expression of the two-dimensional refractive index distribution and gas velocity to obtain the two-dimensional wind speed of the measured thermal flow field. This invention has strong anti-interference ability and better adaptability to complex flow field environments.

Description

Technical Field

[0001] This invention relates to a method for measuring two-dimensional wind speed in a thermal flow field based on Moiré tomography, belonging to the field of optical measurement technology. Background Technology

[0002] In existing technologies, the interference and holographic measurement techniques employed do not provide sufficient anti-interference capabilities for the measuring devices, resulting in low measurement reliability.

[0003] Moiré tomography is a branch of optical computational tomography, which has advantages such as real-time, stability and non-contact operation. Summary of the Invention

[0004] Objective: To overcome the shortcomings of existing technologies, this invention provides a method for measuring two-dimensional wind speed in a thermal flow field based on Moiré tomography, which has high measurement reliability.

[0005] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for measuring two-dimensional wind speed in a heat flow field based on Moiré tomography, comprising:

[0007] Obtain the moiré fringe patterns with and without the measured heat flow field;

[0008] Based on the moiré fringe patterns with and without the measured heat flow field, the phase information of the measured heat flow field is obtained by using a Fourier transform algorithm. Based on the phase information of the measured heat flow field, the deflection angle information of the measured heat flow field is obtained by using a multigrid Fourier transform algorithm.

[0009] Based on the deflection angle information of the measured thermal flow field, the two-dimensional refractive index distribution of the measured thermal flow field is reconstructed using a filtered back projection algorithm.

[0010] The two-dimensional wind speed of the measured thermal flow field is obtained by inversion based on the expression of the two-dimensional refractive index distribution and gas flow velocity.

[0011] In some embodiments, the expression for the gas flow rate includes:

[0012]

[0013] Where v is the wind speed of the measured thermal flow field, and P d R is the dynamic pressure of the flow field, A and B are constants related to the composition of the measured thermal flow field, λ is the detection wavelength, L is the Rochemitor constant, κ is the Boltzmann constant, M is the molar mass of the ideal gas, and n is the refractive index.

[0014] Furthermore,

[0015] Where A i B i and γ i These are the constants, particle number density, and molar coefficient of the i-th component in the measured heat flow field, respectively.

[0016] Furthermore, the dynamic pressure P of the flow field d Methods for obtaining [the information] include:

[0017] P d =P0-P′

[0018] Wherein, P0 and P' represent the pressures measured before and after the measured thermal flow field is placed into the optical path, respectively.

[0019] In some embodiments, the Fourier transform algorithm employs a multigrid Fourier transform algorithm.

[0020] In some embodiments, the moiré fringe patterns with and without the measured heat flow field are acquired using a CCD image sensor.

[0021] In some embodiments, obtaining the deflection angle information of the measured thermal flow field based on the phase information of the measured thermal flow field includes:

[0022] Under first-level filtering conditions, the phase caused by the disturbance of the measured thermal flow field Described as:

[0023]

[0024] Considering the deflection angle projection α(x,y) of Moiré tomography and the phase tomography projection The relationship between the deflection angle and the phase caused by the disturbance of the measured thermal flow field is expressed as follows:

[0025]

[0026] Where, α(x,y), denoted as the phase and deflection angle at (x,y) in the measured thermal flow field, respectively; d is the grating constant; n0 is the ambient reference refractive index during the actual experimental measurement; β is the grating angle; and Δ is the distance between the two gratings.

[0027] In some embodiments, based on the deflection angle information of the measured thermal flow field, a filtered back-projection algorithm is used to reconstruct the two-dimensional refractive index distribution of the measured thermal flow field, including:

[0028] The filtered back projection theorem for phase tomography is expressed as:

[0029]

[0030] in, For phase tomography projection, θ is the deflection angle, and n(x,y) = n0 - n c (x,y),n(x,y) represents the refractive index at (x,y) in the measured thermal flow field, n0 represents the environmental reference refractive index, and n c (x,y) represents the refractive index distribution of the measured thermal flow field, G(Y′) is the corresponding window function, and k(y′) is the inverse Fourier transform of |Y′|G(Y′).

[0031] Phase tomography projection The relationship with the deflection tomography projection α is as follows:

[0032]

[0033] Then we have:

[0034]

[0035] The airspace form is:

[0036]

[0037] Δy′ is the sampling interval in each direction, then the filtering back projection algorithm for deflection tomography is:

[0038] n(x,y)=∫0 π [α(y′,θ)*h(y′) y′＝ycosθ-xsinθ dθ

[0039] in, Let α(y′,θ) be the deflection tomographic projection along the y′ direction at a deflection angle θ, sgny′ be the sgn function of y′, and h(y′) be the phase tomographic projection along the y′ direction at a deflection angle θ. The form of airspace;

[0040] Then the refractive index distribution n of the measured thermal flow field c (x,y) is: n c (x,y)=n0-n(x,y).

[0041] Secondly, the present invention provides a device for measuring two-dimensional wind speed in a thermal flow field based on Moiré tomography, including a processor and a storage medium;

[0042] The storage medium is used to store instructions;

[0043] The processor is configured to operate according to the instructions to execute the method according to the first aspect.

[0044] Thirdly, the present invention provides an apparatus comprising,

[0045] Memory;

[0046] processor;

[0047] as well as

[0048] Computer programs;

[0049] The computer program is stored in the memory and configured to be executed by the processor to implement the method described in the first aspect above.

[0050] Fourthly, the present invention provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in the first aspect.

[0051] Beneficial Effects: The method for measuring two-dimensional wind speed in a thermal flow field based on moiré tomography provided by this invention has the following advantages: Compared with interferometric and holographic measurement techniques, moiré tomography has a simpler measurement device, stronger anti-interference ability, and better adaptability to complex flow field environments, exhibiting unique potential advantages in wind speed field measurement. Therefore, the method and device for measuring two-dimensional wind speed in a thermal flow field based on moiré tomography provided by this invention are of great significance in practical atmospheric measurement research, and also expand the application field of moiré tomography. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the experimental apparatus according to an embodiment of the present invention;

[0053] Figure 2 This is a schematic diagram of a moiré fringe pattern without a measured thermal flow field according to an embodiment of the present invention;

[0054] Figure 3 This is a schematic diagram of a partial moiré fringe pattern when there is a measured thermal flow field according to an embodiment of the present invention;

[0055] Figure 4 This is a schematic diagram of the thermal flow field deflection angle information according to an embodiment of the present invention;

[0056] Figure 5 This is a schematic diagram of the refractive index distribution of the thermal flow field according to an embodiment of the present invention;

[0057] Figure 6 This is a schematic diagram of the two-dimensional wind speed distribution in the heat flow field according to an embodiment of the present invention;

[0058] Figure 1 In the middle: 1-Laser; 2, 3-Beam expanding and collimating system; 4-Measured thermal flow field; 5, 6-Ronchi grating; 7, 9-Imaging lens; 8-Filter; 10-Receiving screen; 11-Hot air blower. Detailed Implementation

[0059] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be used to limit the scope of protection of the present invention.

[0060] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0061] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] Example 1

[0063] Firstly, this embodiment provides a method for measuring two-dimensional wind speed in a heat flow field based on Moiré tomography, including:

[0064] Obtain the moiré fringe patterns with and without the measured heat flow field;

[0065] Based on the moiré fringe patterns with and without the measured heat flow field, the phase information of the measured heat flow field is obtained by using the Fourier transform algorithm, and the deflection angle information of the measured heat flow field is obtained based on the phase information of the measured heat flow field.

[0066] Based on the deflection angle information of the measured thermal flow field, the two-dimensional refractive index distribution of the measured thermal flow field is reconstructed using a filtered back projection algorithm.

[0067] The two-dimensional wind speed of the measured thermal flow field is obtained by inversion based on the expression of the two-dimensional refractive index distribution and gas flow velocity.

[0068] In some embodiments, the expression for the gas flow rate includes:

[0069]

[0070] Where v is the wind speed of the measured thermal flow field, and P dR is the dynamic pressure of the flow field, A and B are constants related to the composition of the measured thermal flow field, λ is the detection wavelength, L is the Rochemitor constant, κ is the Boltzmann constant, M is the molar mass of the ideal gas, and n is the refractive index.

[0071] Furthermore, the method for obtaining the expression for the gas flow velocity includes: firstly, obtaining the dynamic pressure P by measuring the pressure in the absence of the measured thermal flow field and with the measured thermal flow field, respectively. d The dynamic pressure P of the flow field is obtained. d The relationship between the gas flow rate and the gas velocity v is obtained, and the expression for the gas density ρ is derived from the ideal gas law, which in turn leads to the expression for the gas flow rate.

[0072] Generally, the refractive index of a mixed gas flow field can be expressed as:

[0073]

[0074] Wherein, L is the Rochemitor constant (2.687 × 10⁻⁶). 19 cm -3 ), A i B i N ni and γ i Let be the constants, particle number density, and molar coefficient of the i-th component in the measured heat flow field, respectively, and λ be the detection wavelength. N t The total particle number density is the measured thermal flow field.

[0075] Considering the relationship between the total particle number density in the gas flow field and the temperature T and total pressure P of the measured thermal flow field. The relationship between the refractive index of the measured thermal flow field and temperature and pressure can be obtained as follows:

[0076]

[0077] Where κ is the Boltzmann constant (1.38 × 10⁻⁶). -23 J / K).

[0078] For an ideal gas with a Mach number less than 1, we have [4] :

[0079]

[0080] Among them, P d Here, ρ is the gas dynamic pressure, γ is the gas density, and γ is the isentropic coefficient. (where v is the flow velocity) (where M is the local speed of sound) is the Mach number. a When <0.1, from equation (3) we get:

[0081]

[0082] The above equation describes the dynamic pressure P of the gas flow. a The relationship between flow rate v and velocity v.

[0083] From the ideal gas law PM = ρRT and equation (2), the gas density ρ satisfies:

[0084]

[0085] Where M is the molar mass of the ideal gas.

[0086] From equations (4) and (5), we can obtain the expression for the gas flow velocity under the condition of a very small Mach number:

[0087]

[0088] The above formula reflects the wind speed v and the dynamic pressure P of the measured thermal flow field. d The relationship between P and the refractive index n. It is worth noting that in this invention, P... d =P0-P', where P0 and P' represent the pressures measured before and after the measured thermal flow field is placed into the optical path during the experiment.

[0089] In some embodiments, the Fourier transform algorithm employs a multigrid Fourier transform algorithm. The multigrid Fourier transform algorithm is existing technology; for details, please refer to the literature "Improved Multigrid Method for Reconstructing Interference Wavefronts with Obstructions," which will not be elaborated upon in this application.

[0090] In some embodiments, obtaining the deflection angle information of the measured thermal flow field based on the phase information of the measured thermal flow field includes:

[0091] Under first-level filtering conditions, the phase caused by the disturbance of the measured thermal flow field They are described as follows:

[0092]

[0093] Considering the deflection angle projection α(x,y) of Moiré tomography and the phase tomography projection The relationship between the deflection angle and the phase caused by the disturbance of the measured thermal flow field is expressed as follows:

[0094]

[0095] n0 is the refractive index of the surrounding environment during the actual experimental measurement.

[0096] In some embodiments, based on the deflection angle information of the measured thermal flow field, a filtered back-projection algorithm is used to reconstruct the two-dimensional refractive index distribution of the measured thermal flow field, including:

[0097] The filtered back projection theorem for phase tomography is expressed as:

[0098]

[0099] in, For phase tomography projection, θ is the deflection angle, and n(x,y) = n0 - n c (x,y),n c (x,y) represents the refractive index distribution of the measured thermal flow field, G(Y′) is the corresponding window function, and k(y′) is the inverse Fourier transform of |Y′|G(Y′).

[0100] Phase tomography projection The relationship with the deflection tomography projection α is as follows:

[0101]

[0102] Then we have:

[0103]

[0104] The airspace form is:

[0105]

[0106] Δy′ is the sampling interval in each direction; then the filtering back projection algorithm for deflection tomography is:

[0107] n(x,y)=∫0 π [α(y′,θ)*h(y′) y′＝ycosθ-xsinθ dθ.#(13)

[0108] Furthermore, in some embodiments, the moiré fringe patterns with and without the measured heat flow field are acquired using a CCD image sensor.

[0109] In some embodiments, a method for measuring two-dimensional wind speed in a heat flow field based on Moiré tomography includes:

[0110] The experimental apparatus used in this embodiment follows the principle as follows: Figure 1 As shown in the diagram. Laser 1 uses a 532nm wavelength laser; 2 and 3 form a beam expander and collimator system; and the measured thermal flow field 4 is generated using a hot air blower 11. Ronchi gratings 5 ​​and 6 are two Ronchi gratings, each with an effective size of 50mm × 50mm and a grating constant d of 0.02mm. To obtain a high-contrast fringe image, the distance Δ between the two gratings must be an integer multiple of the Talbot distance. Imaging lenses 7 and 9 are two identical imaging lenses with a focal length of 300mm; 8 is a filter. A CCD is used to acquire and receive the moiré fringe pattern presented on the receiving screen 10.

[0111] In this example experiment, the distance Δ between the two gratings was maintained at 26 mm, and a single-stage filter was used. The hot air inlet size was 73 mm × 28 mm, its distance from the edge of the optical path was 30 mm, and the distance from the outlet to the center of the optical path was 55 mm. The CCD was set to acquire one frame of moiré fringe image per second, and a total of 600 frames were acquired and stored in the computer for later phase information extraction to obtain the refractive index of the flow field. During the experiment, the indoor temperature in the laboratory was 27.5℃, the static pressure at room temperature without wind disturbance was 100.36 kPa, the pressure with the measured hot flow field was 100.45 kPa, and the temperature in the flow field was 39.4℃ (312.5 K).

[0112] In the experiment, CCD was first used to acquire moiré fringe patterns without the measured thermal flow field, such as... Figure 2 As shown.

[0113] In the optical path, there is a partial moiré pattern of the measured thermal flow field, as shown below. Figure 3 As shown.

[0114] Next, the phase information of the measured thermal flow field recorded in the above images was obtained based on the Fourier transform algorithm. Taking a cross-section 44.5 mm from the outlet of the hot air blower as an example, its deflection angle information was further obtained, as shown in the following figures. Figure 4 As shown.

[0115] Based on the aforementioned deflection angle information, a filtered back-projection algorithm is used to reconstruct the two-dimensional refractive index distribution of the measured thermal flux field. The results are as follows: Figure 5 As shown.

[0116] Based on the two-dimensional refractive index distribution of the measured thermal flow field and the above expression for gas velocity (6), the two-dimensional wind velocity of the measured thermal flow field is inverted, and the results are as follows: Figure 6 As shown.

[0117] Example 2

[0118] Secondly, based on Embodiment 1, this embodiment provides a device for measuring two-dimensional wind speed in a thermal flow field based on Moiré tomography, including a processor and a storage medium;

[0119] The storage medium is used to store instructions;

[0120] The processor is configured to operate according to the instructions to execute the method according to Embodiment 1.

[0121] Example 3

[0122] Thirdly, based on Embodiment 1, this embodiment provides a device, including,

[0123] Memory;

[0124] processor;

[0125] as well as

[0126] Computer programs;

[0127] The computer program is stored in the memory and configured to be executed by the processor to implement the method described in Embodiment 1.

[0128] Example 4

[0129] Fourthly, based on Embodiment 1, this embodiment provides a storage medium on which a computer program is stored, and when the computer program is executed by a processor, it implements the method described in Embodiment 1.

[0130] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0131] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0132] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0133] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0134] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for measuring two-dimensional wind speed in a heat flux field based on Moiré tomography, characterized in that, The method includes: Obtain the moiré fringe patterns with and without the measured heat flow field; Based on the moiré fringe patterns with and without the measured heat flow field, the phase information of the measured heat flow field is obtained by using a Fourier transform algorithm. Based on the phase information of the measured heat flow field, the deflection angle information of the measured heat flow field is obtained by using a multigrid Fourier transform algorithm. Based on the deflection angle information of the measured thermal flow field, the two-dimensional refractive index distribution of the measured thermal flow field is reconstructed using a filtered back projection algorithm. The two-dimensional wind speed of the measured thermal flow field is obtained by inversion based on the expression of the two-dimensional refractive index distribution and gas flow velocity. The expression for the gas flow rate includes: ； in, The wind speed in the measured thermal flow field is... For the dynamic pressure of the flow field, It is a thermodynamic constant. , It is a constant related to the composition of the measured heat flow field. It is the detection wavelength. Let be the Rochemitor constant. Boltzmann constant, For the molar mass of an ideal gas, The refractive index; ； in, and These represent the pressures measured before and after the measured thermal flow field is placed into the optical path, respectively.

2. The method according to claim 1, characterized in that, ， ， in , and The measured heat flow field and the first The constants related to the component, the particle number density, and the molar coefficient of the component in the measured thermal flow field.

3. The method according to claim 1, characterized in that, The deflection angle information of the measured thermal flow field is obtained based on the phase information of the measured thermal flow field, including: The relationship between the deflection angle and the phase caused by the disturbance of the measured thermal flow field is expressed as: ； in, , The measured heat flow field The deflection angle and phase at the location, The grating constant is The refractive index is the environmental reference index used in the actual experimental measurement. The angle between the gratings, The distance between the two gratings.

4. The method according to claim 1, characterized in that, Based on the deflection angle information of the measured thermal flow field, a filtered back projection algorithm is used to reconstruct the two-dimensional refractive index distribution of the measured thermal flow field, including: The filtered back projection theorem for phase tomography is expressed as: ； in, For phase tomography projection, It is a deflection angle. = - , In the measured heat flow field The refractive index at that point, For environmental reference refractive index, The refractive index distribution of the measured heat flow field is shown. It is the corresponding window function. for The inverse Fourier transform; Phase tomography projection With deflection tomography projection The relationship is: ； Then we have: ； The airspace form is: ； Given the sampling interval in each direction, the filtering back-projection algorithm for deflection tomography is as follows: ； in, For deflection angle hour Directional deflection tomographic projection, For deflection angle hour Phase tomographic projection of the direction, yes of function, yes The form of airspace; The refractive index distribution of the measured thermal flow field for: .

5. The method according to any one of claims 1-4, characterized in that, Moiré fringe patterns with and without the measured thermal flow field were acquired using a CCD image sensor.

6. A device for measuring two-dimensional wind speed in a heat flux field based on Moiré tomography, characterized in that, Including processor and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the method according to any one of claims 1 to 5.

7. A computer device, characterized in that, include: Memory; processor; as well as Computer programs; The computer program is stored in the memory and configured to be executed by the processor to implement the method as described in any one of claims 1 to 5.

8. A storage medium, characterized in that, It stores a computer program thereon, which, when executed by a processor, implements the method described in any one of claims 1 to 5.

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