Reconstruction of large coherent structures from SPIV measurements in a forced turbulent mixing layer

A procedure is suggested here for reconstructing the time variation of a three-dimensional (3D) coherent velocity field, based on applying Least Square Method to a very limited number of phase-locked measurements. The measurements are performed in a spanwise plane of a forced turbulent mixing layer by employing the stereo particle image velocimetry system. The forcing is produced by oscillating two- and three-dimensional (3D) flappers placed at the edge of the splitter plate. The feasibility and validity of the procedure for velocity field reconstruction are checked by using Hot Wire Measurements. Very clear patterns are observed of two types of coherent structures: spanwise K-H billows (rolls) and streamwise vortices. These are due to primary and secondary instabilities and their time evolution is presented.