Vortex identification schemes and its application to PIV data

Abstract

The dynamics of vortical structures in turbulent flow are of key interest both in fundamental research and in engineering development. Contemporary vortex identification criteria are based on the evaluation of the three-dimensional velocity gradient tensor of the flow. Numerical simulations can provide the necessary time-resolved volumetric flow data. From experimental investigations using present optical measurement techniques, however, only planar data—sectional two- or three-componential velocity fields—is available. Then, two-dimensional representations of the three-dimensional identification criteria have to be applied. The different, commonly used criteria are shown to be fully equivalent when applied to sectional velocity data. However, future measurement systems will allow to obtain time-resolved volumetric velocity data. Then, three-dimensional vortex identification criteria can be employed to extract vortical structures, and thus, to assess their topology in full spatial coherence. This requires the proper implementation of identification schemes into PIV evaluation and flow analysis software.