Measurement Technology On Three-Dimensional Flow Field With Multi-camera

The Particle Image Velocimetry (PIV) is a n ewly de veloped fluid field measurement technology w hich has be en w idely used as a n important e xperiment method in hy drodynamic, aerodynamics, vortex and turbulence and other r esearch areas. S tereo-PIV s ystem ba sed on Mu lti-camera e mploys co mputer s tereo vision theory and image processing means. It can measure 3D velocity vectors in a cer tain volume of the fluid field. However, in the traditional shooting system, the lens and image planes of camera are parallel, and the plane of focus (POF) is parallel to the lens and image planes. If the subject plane is not parallel to the image plane, it will be in focus only along a line where it intersects the POF. As the rest of the subject is out of focus in t he image p lane, the image becomes blurred and distorted. T his paper based on Scheimpflug principle (The lens plane and the object plane and the image plane for each camera have to intersect in a co mmon line) which makes the image plane of m ulti-camera three-dimensional flow field measurement system as a pure focal p lane. T he ca libration system is more acc urate by r educing the d istortion to minimum, which provided a more accurate and effective method for the measurement of flow field.In t his pa per, a mu lti-camera three-dimensional flow f ield measurement hardware system was designed, which included multiple camera, three-dimensional movement,rotating coordinate system, three-dimensional calibration device, the laser light source and multi-block of high-performance image acquisition cards. Based on the principle of particle image velocimetry, the mathematical model which serviced for the improved camera and Multi-camera system was established. The mathematical process of calibration and reconstruction was clearly given. The Multi-camera model and image pr ocessing such as ca mera ca libration, f eature ex traction, 3D reconstructions were described in de tail. The improved MATLAB t oolbox a nd the OPENCV software package were applied for system calibration. The corresponding speed signal was obtained by applying cross-correlation algorithm to the reconstruct signals o f ad jacent time. T he ke y a lgorithms of t he above were imp lemented by making use of MATLAB programming. The results showed that flow measurement method and the Multi-camera model us ed in t his pa per were effective,the measurement accuracy could basically meet the requirements of users.This paper also did s ome appropriate research on t he experimental da ta processing methods, an integrated data processing techniques was proposed to analyze experimental da ta, which is a combination o f Hilbert Huang transform (HHT), wavelet transform and other methods. By analyzing experimental data, the features, advantages a nd disadvantages o f the Fourier t ransform, wavelet transform a nd Hilbert-Huang Transform have a more comprehensive analysis, which would provide a more efficient processing method of flow measurement data.