LOCALLY AVERAGED VELOCITY STRUCTURE FUNCTIONS AND MULTI-SCALE COHERENT STRUCTURES IN TURBULENT FLOWS

摘要

The concept of coarse-grained velocity structure functions, which describes the relative motions of straining and compressing for multi-scale eddy structures in turbulent flows, is put forward. The time sequence of longitudinal velocity component at different vertical locations in turbulent boundary layer has been finely measured by IFA300 constant-temperature anemometer with fine resolution higher than Kolmogorov scale in a wind tunnel. The experiment approves that the coarse-grained velocity structure function is in identical with wavelet transformation. It is represented that the coherent structures and intermittency are identified by multi-scale flatness factor based on locally averaged velocity structure functions. Phase-averaged evolution course for multi-scale coherent eddy structures in wall turbulence are extracted by this conditional sampling educe scheme. The dynamics course of multi-scale coherent eddy structures and their effects on statistics of turbulent flows are studied.