Structure of turbulent channel flow under spanwise system rotation

Direct numerical simulations of a turbulent channel flow under spanwise system rotation are performed. When the system rotation is imposed on the turbulent Poiseuille flow, the Reynolds number decreases in one side of a channel, while it increases in the other side. Hence, the effects of the Reynolds number as well as spanwise system rotation cannot be negligible in the turbulent Poiseuille flow. To exclude the Reynolds-number effects, we performed the numerical simulations of the open channel flow where the free-slip-boundary condition is imposed on a wall, and the Reynolds number can be set constant. When the spanwise system rotation is imposed to enhance mean spanwise vorticity associated with the mean shear, turbulence at the large scale is attenuated and the mean velocity gradient increases over the entire channel. In contrast, when the system rotation is imposed in the opposite sense to the mean spanwise vorticity, the mean velocity is leveled and turbulence at the higher wavenumbers is markedly decreased. We also investigate the effects of spanwise system rotation on the longitudinal vortical structure typically observed in the near-wall turbulence.