An improved method for enhancing the resolution of conventional double-exposure single-frame particle image velocimetry

An improved hybrid particle image velocimetry (PIV)/particle tracking veloc imetry technique is presented. The method uses a conventional autocorrelati on for a predictor step followed by local cross-correlations of individual particles to obtain individual particle pair displacements within a double- exposed single-frame image. Simulated particle fields are used to demonstra te the improved tracking success (better than 90%, even in very dense parti cle fields) and accuracy of the technique as compared to an existing single -frame hybrid method. In addition, the number of erroneous measured pairs i s reduced. The improved success is attributed to the ability of the algorit hm to differentiate between overlapped particles and the criteria for corre ctly identifying overlapped particles are presented. As a check on the effe ct on derived quantities, computed values before and after resolution enhan cement from a real image with constant vorticity and dilatation are present ed. Application of this method to a turbulent non-premixed flame shows abou t a factor of six increase in the resolution over conventional PIV.