Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : March 12, 2018 - March 13, 2018
To understand the generation mechanism of small-scale vortices in a high-Reynolds-number turbulent boundary layer, we identify coherent structures by applying a Gaussian filter to the velocity. By evaluating the contribution of the coarse-grained strain to the stretching of coarse-grained vortices, we show that small-scale vortices are generated predominantly by twice larger vortices rather than by the mean flow stretching, which is consistent with the picture of the energy cascade. In contrast, small-scale vortices are directly stretched by the mean flow at low Reynolds numbers. The disappearance of hairpin vortices as the Reynolds number increases is therefore explained by the difference of these two mechanisms.
