Experimental Investigation Of Multi-scale Coherent Structures' Effect On Scale-similar Sub-grid Model Of Large Eddy Simulation

The influence on LES sub-grid scale model, by multi-scale coherent eddy structures in the near wall region of turbulent boundary layer, is studied, on the basis of scale similar hypothesis on LES sub-grid model.The experimental investigation for LES scale similar sub-grid model is carried out in a wind tunnel with IFA300 constant-temperature anemometer. The time sequence of longitudinal velocity component at different vertical locations in turbulent boundary layer, at low, middle and high Reynolds numbers, was finely measured respectively, with temporal resolution higher than the frequency corresponding to Kolmogorov dissipation scale. Mean flow field of turbulent boundary layer is verified by dimensionless logarithm law mean velocity profile.Fluctuating velocity signals, at different temporal scales, are acquired, after primal signals are decomposed by wavelet transfer and inverse transfer successively on the basis of multi-scale resolution theory. Multi-scale Reynolds normal stress, the left term of scale similar hypothesis formulation, and the right terms, are obtained through low-pass filtering multi-scale fluctuating velocity signals. The correlation factors between the two sides of formulation are found to be different from scale to scale. Then, the valid scale rang of scale-similar sub-grid model is studied further, as well as its evolution at vertical locations in turbulent boundary layer.Multi-scale coherent eddy structures are eliminated from turbulent velocity signals by conditional sampling method, and the velocity signals, including and excluding coherent eddy structures, are acquired. The changes on correlation factors, before and after multi-scale coherent eddy structures have been eliminated, is obtained. The influence of coherent eddy structures, especially for the near wall region of turbulent boundary layer, on LES scale- similar sub-grid model, is studied.