Lagrangian and Eulerian investigation of the flow over periodic hills using advanced PIV and 4D-PTV "Shake-the-box"

Abstract

In a joint experiment within the FP7 project AFDAR several advanced particle image velocimetry (PIV) and particle tracking velocimetry (PTV) methods have been successively applied to measure the flow within the the ERCOFTAC test case Nr. 81 “Periodic hill” water tunnel at TU Munich. Snapshot and time-resolved PIV, using an evaluation scheme based on single-pixel ensemble-correlation, as well as the newly developed high resolution 4D-PTV technique “Shake-the-box” (STB) have been applied. The results of the STB evaluation technique are dense, ghostless, highly accurate and nearly complete reconstructions of all particle positions per time step within relatively long Lagrangian tracks. The examination of the mean velocity, turbulence levels and Reynolds stress distributions indicate that with advanced measurement equipment and sophisticated evaluation techniques all flow features can be resolved. Single-pixel ensemble-correlation on a large number of 2D-PIV data provides the necessary spatial resolution to characterize the flow in a time averaged sense. The newly developed 4D-PTV measurement technique Shake-the-box enables the investigation of spatial and temporal dynamics of coherent structures and Lagrangian particle tracks.