Zero-mean-absolute-vorticity state and vortical structures in rotating channel flow

The plane-Poiseuille-type flow is numerically investigated in a rotating coordinate system with small system rotation rates for low Reynolds numbers. We obtained two-dimensional and three-dimensional solutions which exhibit characteristic coherent vortical structures by time-evolution calculations of the Fourier and Chebyshev expansions. It is interesting that mean-absolute-vorticity becomes nearly zero in the region where the vortical structures concentrate. We found for relatively small Reynolds number and rotation number ranges that two-dimensional solutions and traveling-wave solutions having the same spatial symmetry are stably maintained. We also found a two-dimensional periodic solution which switches two and four vortices states. The asymptotic states of the time-developing solutions are obtained as steady or traveling-wave solutions by the Newton-Raphson iteration method.