Two-dimensional orthogonal wavelet multi-resolution analysis on multi-scale flow structures behind triangle cylinder.

This study focuses on the multi-scale turbulent structures of triangle cylinder wake flow measured by high-speed particle image velocimetry (PIV). The measured turbulent structures were spatially extracted into large-, intermediate-, relatively small-, and small-scale components using two-dimensional orthogonal wavelet analysis. Then the features of multi-scale turbulent structures were analyzed in terms of two-point auto correlation, power spectra, turbulent kinetic energy and Reynolds shear stress. It is found that the large-scale structure attributed to coherent motions in the wake flow makes largest contribution to the total fluctuating energy and maximum Reynolds shear stress, accounting for 84% and 92% respectively. The intermediate scale structures, which are unidentifiable by PIV measurement, are found to shed into the separated shear layer due to Kelvin-Helmholtz instability, and the central frequency of intermediate scale vortex is approximately twice of Kármán vortex shedding frequency. Besides, two symmetric regions of intensive velocity fluctuations having relatively small-scale are observed near the cylinder surface and the boundary of separation region, and they are not dominant. [ABSTRACT FROM AUTHOR]