The moving wall effects on turbulent Couette-Poiseuille flows

Abstract

It is known that turbulent Couette-Poiseuille flow (hereafter, CP-flow), which is generally generated by applying a moving velocity condition on the top wall to the main flow direction, is characterized by sufficiently large turbulent activity near the centerline by presence of counter-rotating large-scale structures [1]. In the present study, direct numerical simulations of CP-flows are performed in order to understand the effects of the moving wall condition on turbulent characteristics. In contrast to previous studies, the constant moving wall velocity condition is imposed in the opposite direction to the main flow as shown in Fig 1, and the velocity on the top wall is varied systematically. As the moving wall velocity increases, the friction Reynolds number on both walls increases, and the logarithmic layer is clearly established on the moving wall, whereas it is shortened on the stationary wall. Furthermore, inspection of the turbulent intensities shows that the turbulent activity increases/decreases near the moving/stationary wall with an increase of the moving wall velocity. Comparison with dataset from turbulent pure Poiseuille flows at similar Reynolds numbers suggests that the unique features in the CP-flows dominantly come from the variation of the wall-normal extent for the positively/negatively signed shear layers on both walls. The increase of the negatively signed shear layer on the moving wall leads to active development of large-scale motions in the outer layer, whereas it is not on the stationary wall.