Optical method and system for detecting local circulation of flow field

Abstract

The invention discloses an optical method and system for detecting local circulation of a flow field. The system comprises a first laser used for emitting a first light beam, and a second laser used for emitting a second light beam; the first beam splitter is used for splitting the first light beam, and the second beam splitter is used for splitting the second light beam; the first lens is used for converging the light split by the first beam splitter at a measured point of a flow field; the second lens is used for converging the light split by the second beam splitter at a measured point of the flow field; the third lens is used for converging scattered light of the measured point; the fourth lens is used for converging scattered light of the measured point; the first photoelectric detector is used for detecting light converged by the third lens and converting the light into a first electric signal, and the first spectrum analyzer is used for analyzing the first electric signal; the second photoelectric detector is used for detecting light dispersed by the fourth lens and converting the light into a second electric signal, and the second spectrum analyzer is used for analyzing the second electric signal. According to the invention, the process of calculating the local circulation of the measured point of the flow field can be simplified.

Description

Technical Field

[0001] The present invention belongs to the technical field of flow field characteristic detection, and in particular relates to an optical method and a system for detecting local circulation of a flow field. Background Art

[0002] In the 19th century, the study of fluid mechanics led to the invention of aviation and spacecraft. Circulation, a fundamental physical quantity in fluid mechanics that reflects the rotational properties of fluid motion, has played a key role in the design of aerospace vehicles such as ships, airships, and aircraft. Furthermore, circulation is present in a variety of natural phenomena, including tornadoes and oceans. Its study helps us better understand and predict these phenomena. With the advancement of science and technology, the importance of circulation research in engineering applications and scientific exploration has become increasingly prominent.

[0003] Existing methods for detecting circulation mainly include thermal methods, acoustic methods and optical methods. Among them, the thermal method obtains the velocity field of the fluid and then the circulation by measuring the temperature change of a hot wire in the fluid; however, the measurement range of the thermal method is limited and is affected by temperature. The acoustic method measures the velocity of the fluid through the Doppler effect of ultrasound to calculate the circulation; the acoustic method is only suitable for the measurement of high-temperature and high-pressure fluids. Commonly used optical methods include particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The former calculates the velocity of the flow field by capturing the motion trajectory of tiny particles in the flow field with a high-speed camera; the latter calculates the velocity of the flow field based on the laser frequency shift by using the laser Doppler effect, and finally integrates the velocity along the specified path to obtain the flow field circulation.

[0004] In summary, existing methods for measuring circulation generally require measuring the velocity distribution along a specific path in the flow field and then integrating the velocity at each location to obtain the vorticity. This makes measuring circulation complex and expensive. Therefore, there is an urgent need for an optical method and system for detecting local circulation in a flow field to address these shortcomings. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] In a first aspect, the present invention provides an optical system for detecting local circulation of a flow field, comprising:

[0007] A first laser and a second laser, the first laser is used to emit a first light beam, and the second laser is used to emit a second light beam; wherein the first light beam and the second light beam are perpendicular to each other;

[0008] a first beam splitter and a second beam splitter, the first beam splitter is used to split the first light beam, and the second beam splitter is used to split the second light beam;

[0009] a first lens and a second lens, wherein the first lens is used to converge the light split by the first beam splitter to the measured point of the flow field; and the second lens is used to converge the light split by the second beam splitter to the measured point of the flow field;

[0010] A third lens and a fourth lens, the third lens is used to converge the light passing through the measured point; the fourth lens is used to converge the light passing through the measured point;

[0011] a first photodetector and a first spectrum analyzer, wherein the first photodetector is used to detect the light converged by the third lens and convert it into a first electrical signal, and the first spectrum analyzer is used to analyze the first electrical signal;

[0012] a second photodetector and a second spectrum analyzer, wherein the second photodetector is used to detect the light converged by the fourth lens and convert the light into a second electrical signal, and the second spectrum analyzer is used to analyze the second electrical signal.

[0013] In a second aspect, the present invention further provides an optical method for detecting local circulation of a flow field, which is applied to the optical system for detecting local circulation of a flow field provided in the above embodiment, comprising:

[0014] S101, acquiring a first light beam and a second light beam having orthogonal transmission directions;

[0015] S102, splitting the first light beam and the second light beam to generate a first coherent light beam and a second coherent light beam respectively;

[0016] S103, converging the first coherent light beam and the second coherent light beam at a measured point in the flow field to generate light carrying flow field velocity information;

[0017] S104, converging the scattered light carrying flow field velocity information to form a first converging light beam and a second converging light beam;

[0018] S105, converting the first converging light beam into a first electrical signal, an echo signal carrying partial flow field velocity information; converting the second converging light beam into a second electrical signal, an echo signal carrying partial flow field velocity information;

[0019] S106. Performing Fourier transform on the first electrical signal and the second electrical signal to obtain a Doppler spectrum of the first electrical signal; performing Fourier transform on the second electrical signal to obtain a Doppler spectrum of the second electrical signal;

[0020] S107 , calculating two velocity values ​​in orthogonal directions of the measured point in the flow field based on the Doppler spectrum of the first electrical signal and the Doppler spectrum of the second electrical signal, and calculating the local circulation of the measured point based on the two velocity values.

[0021] Beneficial effects of the present invention:

[0022] The present invention provides an optical method and system for detecting the local circulation of a flow field. Based on a dual-beam-dual-scattering system, a composite dual-beam-dual-scattering system with orthogonal measurement directions is constructed. First, two lasers generate two laser beams with orthogonal transmission directions. Each laser beam passes through a beam splitter to generate two coherent light beams. After passing through a lens, each coherent light beam intersects at the measured point and produces scattered light carrying flow field velocity information. Two detectors receive intensity signals carrying the velocity components in the two orthogonal directions. A spectrum analyzer then performs a Fourier transform on the echo signal to obtain its Doppler spectrum, thereby determining the velocity at the measured point. To eliminate the situation where the circulation is zero but the component velocities are not zero when the flow field moves in a fixed direction, the optical system is rotated around the measured point until it reaches its initial position. This prevents the situation where the velocity detected by any detector at a certain angle is zero, thus preventing the local circulation at that measured point from being zero. Otherwise, the velocities in the orthogonal directions measured at the initial detection angle are used to calculate the local circulation of the flow field.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of a dual-beam-dual-scattering system provided by an embodiment of the present invention;

[0025] Figure 2 1 is a schematic diagram of an optical system for detecting local circulation of a flow field provided by an embodiment of the present invention;

[0026] Figure 3 is another schematic diagram of an optical system for detecting local circulation of a flow field provided by an embodiment of the present invention;

[0027] Figure 4 This is a flow chart of an optical method for detecting local circulation of a flow field provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0029] The purpose of the present invention is to use two sets of dual-beam-dual-scattering light paths to measure two velocity values ​​in the orthogonal directions of a moving flow field respectively, and to propose a method for approximately calculating the local circulation of the flow field, and to obtain the circulation at the minimum position of the flow field by adding the velocities in the orthogonal directions.

[0030] Based on a dual-beam-dual-scattering test system, this invention proposes a method for measuring the circulation at a local minimum position in a flow field. By utilizing the Doppler effect of lasers, an optical system for measuring local circulation in a flow field is proposed. Using this optical system, a composite dual-beam-dual-scattering system based on the dual-beam-dual-scattering system is proposed to implement a method for measuring local circulation in a flow field, providing a simple, low-cost, and non-contact flow field detection method.

[0031] See Figure 1 , Figure 1 This is a schematic diagram of a dual-beam-dual-scattering system provided by an embodiment of the present invention. Two laser beams in different directions are incident on the measured flow field. They pass through the measured flow field and scatter scattered light with Doppler frequency shift. A photoelectric detector is used to collect the scattered light at the same position and perform frequency mixing processing. Finally, the one-dimensional velocity of the measured object can be obtained through Fourier transform.

[0032] Based on the dual-beam-dual-scattering system, a dual-beam-dual-scattering velocimetry system with two detection directions perpendicular to each other can realize the detection of the velocity of the fluid in two orthogonal directions in the plane.

[0033] See Figure 2 , Figure 2 Schematic diagram of an optical system for detecting local circulation of a flow field provided by an embodiment of the present invention. Figure 3 is another schematic diagram of an optical system for detecting local circulation of a flow field provided by an embodiment of the present invention. The optical system for detecting local circulation of a flow field provided by the present invention includes:

[0034] A first laser and a second laser, wherein the first laser is used to emit a first light beam, and the second laser is used to emit a second light beam; wherein the first light beam and the second light beam are perpendicular to each other;

[0035] a first beam splitter and a second beam splitter, the first beam splitter being used to split the first light beam, and the second beam splitter being used to split the second light beam;

[0036] a first lens and a second lens, wherein the first lens is used to converge the light split by the first beam splitter to a measured point in the flow field; and the second lens is used to converge the light split by the second beam splitter to a measured point in the flow field;

[0037] a third lens and a fourth lens, wherein the third lens is used to converge the light passing through the measured point; and the fourth lens is used to converge the light passing through the measured point;

[0038] a first photodetector and a first spectrum analyzer, wherein the first photodetector is used to detect the light converged by the third lens and convert it into a first electrical signal, and the first spectrum analyzer is used to analyze the first electrical signal;

[0039] a second photodetector and a second spectrum analyzer, wherein the second photodetector is used to detect the light converged by the fourth lens and convert it into a second electrical signal, and the second spectrum analyzer is used to analyze the second electrical signal.

[0040] In an optional embodiment of the present invention, the light converged by the first lens and the light converged by the second lens are perpendicular to each other.

[0041] like Figure 3 As shown, the horizontal incident laser 1 measures the vertical component v of the velocity of the fluid at the measured point y , the vertical incident laser 2 measures the horizontal component v of the velocity of the fluid at the measured point x In the extremely small area of ​​the fluid measured point, the velocity of the flow field can be considered to be approximately the horizontal component v x and the vertical component v y The circulation Γ refers to the path integral of the flow field velocity along a closed curve. The flow field circulation at the measured point can be obtained by integrating the flow field velocity around a very small closed path, which is expressed as:

[0042]

[0043] The horizontal component of the flow velocity in the closed area is v x , the vertical component is v y , assuming that the spot diameters in the x and y directions are ρ x and ρ y , f dx and f dy For v x and v y The corresponding Doppler frequency shift, considering the Doppler frequency shift relationship, formula (1) is converted to:

[0044]

[0045] It should be noted that when the horizontal velocity component and the vertical velocity component are both along the positive or negative direction of the x-axis and y-axis, the local circulation of the measured point in the flow field is positive; otherwise, the local circulation of the measured point in the flow field is negative.

[0046] Optionally, the first photodetector and the second photodetector are photomultiplier tubes.

[0047] Based on the same inventive concept, see Figure 4 , Figure 4 : is a flow chart of an optical method for detecting local circulation of a flow field according to an embodiment of the present invention. The present invention further provides an optical method for detecting local circulation of a flow field, which is applied to an optical system for detecting local circulation of a flow field according to the above embodiment of the present invention. The embodiment of the optical system is described above and will not be described in detail here. The optical method comprises:

[0048] S101, acquiring a first light beam and a second light beam having orthogonal transmission directions;

[0049] S102, splitting the first light beam and the second light beam to generate a first coherent light beam and a second coherent light beam respectively;

[0050] S103, converging the first coherent light beam and the second coherent light beam at a measured point in the flow field to generate light carrying flow field velocity information;

[0051] S104, converging the light carrying the flow field velocity information to form a first converging light beam and a second converging light beam;

[0052] S105, converting the first converging light beam into a first electrical signal, an echo signal carrying partial flow field velocity information; converting the second converging light beam into a second electrical signal, an echo signal carrying partial flow field velocity information;

[0053] S106. Performing Fourier transform on the first electrical signal and the second electrical signal to obtain a Doppler spectrum of the first electrical signal; performing Fourier transform on the second electrical signal to obtain a Doppler spectrum of the second electrical signal;

[0054] S107 , calculating two velocity values ​​in orthogonal directions of the measured point in the flow field based on the Doppler spectrum of the first electrical signal and the Doppler spectrum of the second electrical signal, and calculating the local circulation of the measured point based on the two velocity values.

[0055] In an optional embodiment of the present invention, calculating the circulation of the measured point according to the two velocity values ​​includes:

[0056] If at least one of the two velocity values ​​is zero, the local circulation at the measured point is zero; if both velocities are not zero, the optical system is rotated in a preset direction and at a preset angle, and S101 to S107 are repeated until the optical system rotates to the initial position, and the local circulation of the measured point is calculated.

[0057] It should be noted that when the measured v x and vy are all non-zero values, but when the flow field moves in a fixed direction, there is obviously no circulation in the flow field; therefore, before calculating the circulation, the entire composite dual-beam-dual-scattering system is rotated around the measured point in the flow field motion plane, and the velocity components in two directions of the flow field are detected at different angles. Only when the two velocity components at each angle are not zero, the velocity components measured at the selected position are calculated to obtain the flow field circulation at the measured point.

[0058] In an optional embodiment of the present invention, the preset angle is 10° to 40°.

[0059] Optionally, the preset direction may be clockwise or counterclockwise, and the preset angle may be 10°, 20°, 30° or 40°.

[0060] In an optional embodiment of the present invention, the expression for calculating the local circulation of the measured point is:

[0061]

[0062] Where v represents the composite velocity of the horizontal and vertical directions;

[0063] The expression of the local circulation of the measured point is transformed and updated as follows:

[0064]

[0065] Among them, v x represents the horizontal velocity component, v y represents the vertical velocity component, ρ x Indicates the horizontal spot diameter, ρ y Indicates the vertical spot diameter, f dx Indicates the Doppler frequency shift corresponding to the horizontal velocity component, f dy represents the Doppler frequency shift corresponding to the vertical velocity component, λ x The wavelength of the light wave (second detection beam) that detects the x-direction velocity of the flow field, λ y The wavelength of the light wave (first detection beam) used to detect the velocity in the y direction of the flow field, α x The angle between the two beams of light (the second detection beam) that detect the velocity in the x direction of the flow field, α y Represents the angle between the two beams of light (the second detection beam) used to detect the velocity in the y direction of the flow field.

[0066] In an optional embodiment of the present invention, when the horizontal velocity component and the vertical velocity component are both along the positive or negative direction of the x-axis and the y-axis, the local circulation of the measured point of the flow field is positive; otherwise, the local circulation of the measured point of the flow field is negative.

[0067] In summary, the optical method and system for detecting local circulation in a flow field provided in this embodiment builds on a dual-beam dual-scattering system to construct a composite dual-beam dual-scattering system with orthogonal measurement directions. First, two lasers generate two laser beams with orthogonal transmission directions. Each laser beam passes through a beam splitter to generate two coherent beams. After passing through a lens, each coherent beam intersects at the measured point and produces scattered light carrying flow field velocity information. Two detectors receive intensity signals carrying velocity components in two orthogonal directions. A spectrum analyzer then performs a Fourier transform on the echo signal to obtain its Doppler spectrum, thereby determining the velocity at the measured point. To eliminate the situation where the circulation is zero but the component velocities are not zero when the flow field moves in a fixed direction, the optical system is rotated 360° around the measured point to prevent the situation where the velocity detected by any detector at a certain angle is zero, thus assuming the local circulation at that measured point is zero. Otherwise, the velocities in the orthogonal directions measured at the initial detection angle are used to calculate the local circulation of the flow field.

[0068] It should be noted that, in this document, relational terms such as first and second are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not explicitly listed. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or device comprising the element. Terms such as "connected" or "connected" are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. References to orientations or positional relationships, such as "upper," "lower," "left," and "right," are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate description and simplify the description of the present invention. They do not indicate or imply that the device or element referred to must have, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention.

[0069] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0070] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. An optical system for detecting local circulation of a flow field, characterized in that: include: A first laser and a second laser, wherein the first laser is used to emit a first light beam, and the second laser is used to emit a second light beam; wherein the first light beam and the second light beam are perpendicular to each other; a first beam splitter and a second beam splitter, the first beam splitter being used to split the first light beam, and the second beam splitter being used to split the second light beam; a first lens and a second lens, wherein the first lens is used to converge the light split by the first beam splitter to a measured point in the flow field; and the second lens is used to converge the light split by the second beam splitter to a measured point in the flow field; a third lens and a fourth lens, wherein the third lens is used to converge the light passing through the measured point; and the fourth lens is used to converge the light passing through the measured point; a first photodetector and a first spectrum analyzer, wherein the first photodetector is used to detect the light converged by the third lens and convert it into a first electrical signal, and the first spectrum analyzer is used to analyze the first electrical signal; a second photodetector and a second spectrum analyzer, wherein the second photodetector is used to detect the light converged by the fourth lens and convert it into a second electrical signal, and the second spectrum analyzer is used to analyze the second electrical signal.

2. The optical system for detecting local circulation of a flow field according to claim 1, characterized in that: The light converged by the first lens and the light converged by the second lens are perpendicular to each other.

3. An optical method for detecting local circulation of a flow field, applied to the optical system for detecting local circulation of a flow field as claimed in any one of claims 1 to 2 for detection, characterized in that: include: S101, acquiring a first light beam and a second light beam having orthogonal transmission directions; S102, splitting the first light beam and the second light beam to generate a first coherent light beam and a second coherent light beam respectively; S103, converging the first coherent light beam and the second coherent light beam at a measured point in the flow field to generate light carrying flow field velocity information; S104, converging the scattered light carrying the flow field velocity information to form a first converging light beam and a second converging light beam respectively; S105, converting the first converging light beam into a first electrical signal, an echo signal carrying partial flow field velocity information; converting the second converging light beam into a second electrical signal, an echo signal carrying partial flow field velocity information; S106. Perform a Fourier transform on the first electrical signal to obtain a Doppler spectrum of the first electrical signal; perform a Fourier transform on the second electrical signal to obtain a Doppler spectrum of the second electrical signal; S107 , calculating two velocity values ​​in orthogonal directions of the measured point in the flow field based on the Doppler spectrum of the first electrical signal and the Doppler spectrum of the second electrical signal, and calculating the local circulation of the measured point based on the two velocity values.

4. The optical method for detecting local circulation of a flow field according to claim 3, characterized in that: The calculating the circulation amount of the measured point according to the two speed values ​​includes: If at least one of the two velocity values ​​is zero, the local circulation at the measured point is zero; if both velocities are not zero, the optical system is rotated in a preset direction and at a preset angle, and S101 to S107 are repeated until the optical system rotates to the initial position, and the local circulation of the measured point is calculated.

5. The optical method for detecting local circulation of a flow field according to claim 4, characterized in that: The preset angle is 10° to 40°.

6. The optical method for detecting local circulation of a flow field according to claim 3, characterized in that: The expression for calculating the local circulation of the measured point is: Where v represents the composite velocity of the horizontal and vertical directions; The expression of the local circulation of the measured point is transformed and updated as follows: Among them, v x represents the horizontal velocity component, v y represents the vertical velocity component, ρ x Indicates the horizontal spot diameter, ρ y Indicates the vertical spot diameter, f dx Indicates the Doppler frequency shift corresponding to the horizontal velocity component, f dy represents the Doppler frequency shift corresponding to the vertical velocity component, λ x The wavelength of the light wave that detects the velocity in the x direction of the flow field, λ y Indicates the wavelength of the light wave used to detect the velocity in the y direction of the flow field, α x Represents the angle between the two beams of light used to detect the velocity in the x direction of the flow field, α y Represents the angle between the two beams of light used to detect the velocity in the y direction of the flow field.

7. The optical method for detecting local circulation of a flow field according to claim 6, characterized in that: When the horizontal velocity component and the vertical velocity component are both along the positive or negative direction of the x-axis and the y-axis, the local circulation of the measured point of the flow field is positive; otherwise, the local circulation of the measured point of the flow field is negative.

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