Liutex Structures in Turbulent Channel Flows with Wall Oscillations

The Liutex method is used to analyze the vortex structures in turbulent channel flows. The magnitude of Liutex and its components is compared to find the dominant rotation axis. The azimuth angles of Liutex and their probability density function are computed to describe the types of vortex structures in the buffer layer. The modifications of Liutex in the channel flow with wall oscillation control are also analyzed. The vortex strength is much reduced and the vortices are more likely aligned in wall-normal and streamwise directions. The lift-up effects and mean shear are thus weakened, leading to the drag reduction.