DNS of a turbulent Couette flow at constant wall transpiration up to Re-tau=1000

Abstract

[EN] We present a new set of direct numerical simulation data of a turbulent plane Couette flow with constant wall-normal transpiration velocity V-0, i.e. permeable boundary conditions, such that there is blowing on the lower side and suction on the upper side. Hence, there is no net change in flux to preserve periodic boundary conditions in the streamwise direction. Simulations were performed at Re-tau = 250; 500; 1000 with varying transpiration rates in the range V-0(+) approximate to 0.03 to 0.085. Additionally, a classical Couette flow case at Re-tau = 1000 is presented for comparison. As a first key result we found a considerably extended logarithmic region of the mean velocity profile, with constant indicator function kappa = 0.77 as transpiration increases. Further, turbulent intensities are observed to decrease with increasing transpiration rate. Mean velocities and intensities collapse only in the cases where the transpiration rate is kept constant, while they are largely insensitive to friction Reynolds number variations. The long and wide characteristic stationary rolls of classical turbulent Couette flow are still present for all present DNS runs. The rolls are affected by wall transpiration, but they are not destroyed even for the largest transpiration velocity case. Spectral information indicates the prevalence of the rolls and the existence of wide structures near the blowing wall. The statistics of all simulations can be downloaded from the webpage of the Chair of Fluid Dynamics.