Influence of Boundary Conditions on Oscillatory Flow in a Grooved Channel

In this study, a numerical analysis was performed to simulate the flow in a grooved channel with a periodic boundary condition in the main flow direction, and three-dimensional oscillatory flow was obtained. The influence of different streamwise boundary conditions was examined by comparing with previous experimental results. Furthermore, the impact of spanwise boundary conditions—either wall or periodic—on the flow characteristics was investigated. Under the wall boundary condition, as the Reynolds number increases, the flow transitions from symmetric three-dimensional oscillatory flow to asymmetric three-dimensional oscillatory flow. Under the periodic boundary condition, the flow evolves from two-dimensional oscillatory flow to symmetric three-dimensional oscillatory flow, and eventually to asymmetric three-dimensional oscillatory flow. As the Reynolds number increases, the waveform of the time-evolving velocity component changes from a simple sinusoidal wave to one accompanied by long-period undulations, followed by irregular short-period oscillations, and finally, the amplitude spectrum no longer shows a distinct fundamental frequency. Vortex structures evolve from spanwise-elongated shapes to massive vortex clusters, which further subdivide into finer structures. The time-averaged wall shear stress at the center of the channel exhibits the largest discrepancy from experimental results around a Reynolds number of 548, which is attributed to long-period flow undulations. However, no significant difference in wall shear stress was observed between wall and periodic boundary conditions.