Vertical rotation effect on turbulence characteristics in an open channel flow

This paper solves the three-dimensional Navier--Stokes equation by a fractional-step method with the Reynolds number Re_\tau =194 and the rotation number N_\tau =0--0.12. When N_\tau is less than 0.06, the turbulence statistics relevant to the spanwise velocity fluctuation are enhanced, but other statistics are suppressed. When N_\tau is larger than 0.06, all the turbulence statistics decrease significantly. Reynolds stress budgets elucidate that turbulence kinetic energy in the vertical direction is transferred into the streamwise and spanwise directions. The flow structures exhibit that the bursting processes near the bottom wall are ejected toward the free surface. Evident change of near-surface streak structures of the velocity fluctuations are revealed.