Interscale transfer of turbulent energy in grid-generated turbulence with low Reynolds numbers

Direct numerical simulations are performed for grid-generated turbulence with low Reynolds numbers to study the interscale transfer of turbulent energy. The Reynolds numbers based on the uniform velocity and grid mesh size, M, are set to ReM=5000, 9000, and 15000. The results show that, for ReM=9000 and ReM=15000, the turbulent dissipation constant increases in the upstream region but it becomes nearly constant in the region of x/M>15. In contrast, for ReM=5000, it continues to increase and do not level off even in the downstream region. Scale-by-scale analysis using the Karman–Howarth–Monin–Hill equation indicates that, the non-linear transfer term balances with the dissipation term for all the cases. Instead, it is found that, in the downstream region of the ReM=5000 case, where the turbulent Reynolds number becomes Reλ<25, the contribution of the advection term varies depending on the streamwise positions. Further analysis for the one-point statistics indicates that, in such conditions, the coherences among the advection term, dissipation term, and diffusion term become small at small scales, while they are generally large in the other cases including the upstream region for ReM=5000. These indicate that energy cascade mechanism in the downstream region for ReM=5000 is different from the cases of 30更多