A New Method For The PIV Image Processing

The velocimetry instruments or methods such as ultrasonic ADV and laser LDV adopted in hydrodynamic experiments and aerodynamic experiments generally can only measure single point of flow field, and most instruments must touch and come into flow field and cannot measure two-dimensional flow field. Touching single point measurement instruments cannot fulfill the measurement requirement when flow velocity changing is sensitive to exterior disturbance and in space, and when measurement of two-dimensional velocity distribution is needed. PIV technique is a kind of untouched flow field measurement, which can get the movement information of flow field by cross-correlation analysis of two flow field images. The great promising undisturbed flow field measurement technique gets over the limitation of the touching single point measurement instruments and can measure plane two-dimensional flow field. PIV technique has already been applied to two-dimensional flow field measurement of hydrodynamic experiments and aerodynamic experiments, and provides an effective way to study velocity distribution of flow field for scientific researchers.Many scholars have made a lot of research on PIV technique, but there is still much faultiness in theories and application of PIV technique, which most exist in quick algorithm and post-processing, including image recovery and enhancement, image denoising, deletion and correction of improper vectors, and the calculation of streamline, equal velocity line and vorticity. Systemic research on postprocessing of PIV technique has been made in this paper and will promote the application capability of PIV, which is the main purpose of this paper.Systemic research on post-processing of PIV is made based on experiments and computer application in this paper. Technical route based on theory deducing combined to experiments is adopted. Cross-correlation analysis and the implementation of PIV are researched, and quick calculation of PIV based on original algorithm is made, including real serial Fourier transform, complex serial Fourier transform and Hartley transform, and the best implementation is confirmed. In the research on particle image denoising, the theory and implementation of image denosing by wavelet analysis is established. In the research on improper vectors correction, the algorithm of vectors correction, namely the correction by filtering in frequency domain and the correction based on continuity equation, and the algorithm of flow field parameters is also researched. In the programming implementation of PIV, C++ libraries of PIV are developed, and multithreading is also implemented in PIV technique.