Direct numerical simulation of turbulent flows in a wall-normal rotating channel

Abstract

Direct numerical simulation (DNS) is carried out to study turbulence characteristics in a wall-normal rotating channel with the rotation number N τ from 0 to 0.12 and the Reynolds number 194 based on the friction velocity of the non-rotating case and the half-height of the channel. Based on the present calculated results, two typical rotation regimes are identified. When in weak rotation regime with 0 < N τ < 0.05, turbulence statistics correlated with the spanwise velocity fluctuation are enhanced since the shear rate of the spanwise mean flow induced by the Coriolis force increases, but other statistics are suppressed. When in strong rotation regime with N τ > 0.05, all the turbulence statistics decrease as the effect of the Coriolis force plays a dominant role. The budgets of transport equations for the Reynolds stresses are calculated to reveal the effect of the Coriolis force on the dynamic process of turbulent kinetic energy production, dissipation and redistribution. With the increase of N τ in weak rotation regime, the main mechanism for the generation of the streamwise turbulent energy is gradually altered from the shear production effect related to the streamwise mean flow to the energy redistribution due to the pressure strain correlation. Correspondingly, the generation of the spanwise turbulent energy also changes from the energy redistribution effect to the shear production of the spanwise mean flow. In strong rotation regime, the mean flow shear rate is found to be a key factor to the turbulence production and dissipation. The redistribution between the streamwise and spanwise components of turbulent kinetic energy due to the effect of the Coriolis force becomes weak. A remarkable change of the direction of the near-wall vortical structures, nearly in alignment with the absolute mean flow direction, is observed. An attempt to evaluate the mean spacing between the streaky structures and the angle between the wall structures and streamwise direction has been examined based on the two-point correlations of the velocity fluctuations to reveal the change of the near-wall structures.