PARTICLE IMAGE VELOCIMETRY VIA WAVELET ANALYSIS

Novel analytical and image processing methods derived as part of the d evelopment of a digital particle image velocimetry system, based on mu ltiresolution analysis, are presented. The derivation of wavelet-based multiresolution methods for velocity field reconstruction is addresse d, and the experimental setup used for validation of results is descri bed. New techniques are proposed with improved spatial resolution and reliability over some existing methods. The techniques are based on wa velet-based representations of digital particle image data that are us ed to calculate spatially localized and frequency localized filtered c orrelations of successive images. An essential feature of the method i s the development of windowed cross-correlation expressions for wavele t-based expansions that are not orthogonal (or biorthogonal) over the cross-correlation window. The methodology makes use of recently introd uced refinable functions and generalized connection coefficients deriv ed in wavelet-based finite element methods. A conventional charge-coup led device camera is used with a frame rate of 30 frames/s and pixel r esolution of 512 x 480 per frame. The images are acquired in pairs at 30 frames/s, with a user-defined time def ay between image pairs, to c apture the flowfield structure evolution. The dow illumination was ach ieved using a 5-W, argon-ion laser. Finally, hardware and algorithm pe rformance is demonstrated via sample water-tunnel experiments.