Optical flow velocity measurement method based on PIV technology

Abstract

The invention discloses an optical flow velocity measurement method, and relates to the interdisciplinary fields of fluid mechanics, optics and the like. According to the technical scheme, a laser, a measured object, a cylindrical mirror, a laser beam polarizer (galvanometer), a sound wave emitter, a control module and a high-speed camera are involved in the related measurement method. A laser beam enters the laser beam polarizer to enable the angle of the laser beam polarizer to be changed through a signal, then the laser beam passes through the cylindrical mirror to form sheet-shaped light, the sheet-shaped light irradiates a flow field in the fluid speed direction, and the sheet-shaped light moves continuously. At the moment, the flow field velocity can be obtained through vertical shooting of the camera and calculation of a cross-correlation algorithm. Through the control module and the sound wave emitter, the device can stably move at a high speed, and the measurement precision and efficiency are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the interdisciplinary fields of fluid mechanics, optics, etc., and particularly relates to an optical flow velocity measurement method. Background Art

[0002] Particle Image Velocimetry is also called PIV. Tracer particles are added to the fluid, and the motion images of the particles are recorded by a high-speed imaging system. Image processing algorithms are used to calculate the position changes of the particles at different time intervals, so as to infer the velocity distribution of the flow field.

[0003] The three-dimensional stereoscopic velocity measurement of the flow field is one of the research focuses. At present, most of the measurements of the optical flow field velocity are mainly carried out by fixing a laser and a high-speed camera on a stepping motor or a rotating gear, and forming a cylindrical light through a cylindrical lens to irradiate the flow field. The stepping motor or the rotating gear drives the laser and the camera to move together. With the development of image processing technology, the two-dimensional velocity distribution on the cross-section can basically be obtained quickly.

[0004] Due to the inherent inertia and dynamic response limitations of the mechanical system, it is difficult to achieve real-time acquisition and three-dimensional reconstruction of high-frequency and high-dynamic cross-sections, which seriously restricts the measurement efficiency. At the same time, the long-term operation of the mechanical structure is prone to wear, resulting in the attenuation of the system accuracy over time, and even the image will be distorted, greatly affecting the experimental reliability. Summary of the Invention

[0005] In view of the above problems and technical requirements, the present invention proposes an optical flow velocity measurement method based on PIV technology.

[0006] The technical solution of the present invention is as follows: An optical flow velocity measurement method based on PIV technology, characterized in that the device includes a laser emission device, a flow field, and a detection device.

[0007] The laser emission device includes a laser emitter, a cylindrical lens, an acoustic wave emitter, and a laser beam deflector; the laser emitter emits a laser beam, which forms a laser sheet light through the cylindrical lens; the outside of the flow field is wrapped by a transparent medium and contains PIV tracer particles inside; the laser sheet light enters the laser beam deflector along the same direction as the optical path of the flow field and illuminates the PIV tracer particles in the flow field. The laser beam deflector is used to control the moving distance and frequency of the laser sheet light; the acoustic wave emitter emits longitudinal waves with a stable frequency. The detection device includes a high-speed camera and a computer; the high-speed camera is used to photograph the PIV tracer particles and collect images; the computer is used to process the images to obtain the two-dimensional velocity distribution and then reconstruct the three-dimensional flow field velocity distribution. A further technical solution thereof is that the laser beam deflector can control the moving distance and frequency of the laser sheet light, and its angle remains unchanged; The acoustic wave emitter emits longitudinal waves with stable frequency to control the movement of the laser sheet light passing through the laser beam deflector; The frequency of the camera for collecting images is the same as that of the acoustic wave emitter; The above description is only an overview of the method of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specific embodiments are given, and in conjunction with the accompanying drawings, the details are described as follows. Description of the Drawings

[0008] Figure 1 It is a schematic diagram of the measuring device provided by the embodiment of the present invention. Marking description: S1, laser emitter; S2, flow field; S3, cylindrical mirror; S4, laser beam deflector; S5, acoustic wave emitter; S6, high-speed camera; Figure 2 is Figure 1 a sectional view of. Detailed Embodiments

[0009] To make the objectives, technical solutions and advantages of the present invention clearer, the following will further describe the embodiments of the present invention in detail in conjunction with the accompanying drawings.

[0010] The present invention discloses an optical flow velocity measurement method based on PIV technology. This device is used for measuring the fluid velocity distribution of a high-precision, high-frequency, and high-dynamic cross-sectional flow field.

[0011] When the PIV tracer particle laser stereoscopic velocity measurement device is in use, both the laser emission device and the detection device are located outside the flow field. For example, Figure 1 , the laser sheet light is perpendicular to the camera.

[0012] Please refer to Figure 2 , which shows a PIV tracer particle laser stereoscopic velocity measurement device and method according to an exemplary embodiment of the present invention. This device includes a laser emission device (S1, S3, S4, S5), a flow field (S2), and a detection device (S6).

[0013] The centers of the laser emitter (S1), the cylindrical mirror (S3), the laser beam deflector (S4), and the flow field (S2) are on the same vertical line.

[0014] Please refer to Figure 1 , which shows that the laser passes through the cylindrical mirror to form a laser sheet light, and then irradiates into the flow field through the laser beam deflector.

[0015] The high-speed camera (S6) is connected to a computer, which is used to process the images and reconstruct them into a three-dimensional velocity distribution and display it thereon.

[0016] The acoustic wave emitter (S5) is used to control the moving frequency of the laser beam deflector (S4).

[0017] Both the moving distance of the laser beam deflector (S4) and the frequency of the acoustic wave emitter (S5) need to be set and changed on the computer.

[0018] The tracer particles in the flow field are fully mixed with the fluid, and the outer shell is a transparent medium for convenient detection by us.

[0019] The working principle of the PIV tracer particle laser stereo velocimetry device disclosed in this application is as follows: Before the experiment starts, the PIV tracer particles are fully mixed with the flow field fluid. The frequency of the acoustic wave emitter (S5) and the moving distance of the laser beam deflector (S4) each time are set on the computer, and the laser emitter (S1) is turned on. The laser enters the cylindrical lens (S3). Under the control of the acoustic wave emitter (S5), the laser beam deflector (S4) starts to move according to the frequency, and the high-speed camera (S6) starts to collect images and transmit them to the computer. Thereafter, the computer starts to display the real-time three-dimensional velocity distribution image.

Claims

1. An optical flow velocity measurement method based on PIV technology, characterized in that: The device includes a laser emitting device, a measured object S2 and a detection device.

2. The laser emitting device includes a laser emitter S1, a cylindrical mirror S3, a laser beam deflector S4, and an acoustic wave emitter S5; The detection device includes a high-speed camera S6 and a computer; When in use, the laser deflector is controlled by the control module, and the sound wave transmitter emits a longitudinal wave with a stable frequency. After receiving the signal, the control module controls the laser deflector to deflect at the same frequency. The laser emitted by the laser is incident on the laser deflector and deflected, and then forms a sheet of light through a cylindrical mirror and irradiates the flow field along the direction of the flow field, and produces a high-frequency offset. The high-speed camera collects images perpendicular to the flow field, and the frequency of taking pictures is the same as the frequency of the sound wave; the angle of the sheet of light formed by the laser does not change at all, and after collecting the photos, the cross-correlation algorithm is used for processing and analysis, and each slice is reconstructed and superimposed to obtain the flow conditions of the entire flow field.

3. The optical flow velocity measurement method based on PIV technology according to claim 1 is characterized in that: The laser enters the laser beam deflector through an optical path.

4. The optical flow velocity measurement method based on PIV technology according to claim 1 is characterized in that: The laser beam deflector forms a sheet of light moving in a vertical flow field, which is controlled by longitudinal waves, and the angle of the deflected light will not be deflected.

5. An optical flow velocity measurement method based on PIV technology according to claim 1, characterized in that: The high-speed camera and the laser beam deflector have the same deflection frequency.

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