Experimental measurement of multi-scale coherent structures in turbulent flows using multi-scale locally averaged strain method

Experimental investigation is performed to study multi-scale coherent structures in turbulent boundary layer. Based on the physical background of local multi-scale eddy structures in real turbulent flows with definite Reynolds number, the concept of locally averaged structure function is put forward to describe two adjacent eddy structures' interaction and relative strain distortion due to the effect of fluid viscosity. 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 resolution higher than dissipative scale in a wind tunnel. The turbulent velocity fluctuations are decomposed into multi-scale eddy structures by locally averaged structure functions. Multi-scale coherent structures are identified by multi-scale flatness factor based on locally averaged velocity structure functions. Phase-averaged waveforms for multi-scale coherent eddy structures in wall turbulence are extracted by conditional sampling detection scheme. The dynamics course of multi-scale coherent eddy structures and their effects on statistics of turbulent flows are extensively studied.