Turbulence Characteristics of the Flows in a Wavy Channel
Hang Seok Choi, Tae Seon Park and Kenjiro Suzuki
Large Eddy Simulation has been applied to the flows in a wavy channel varying the wave amplitude. To identify the turbulence characteristics of the flows, statistical quantities of the turbulence and vortical flow structures aligned in the streamwise direction were scrutinized. With increasing the slope of wall undulation or the wall wave amplitude, a recirculation zone appears and above it a separated shear layer develops. In the up-slope region of the wavy wall, streamwise vortices are generated near the wall. The characteristics of separated shear layer and near-wall streamwise vortices and related statistical quantities affecting the turbulence structure of the flow were discussed. Especially, to see the characteristics of nearwall streamwise vortices in wavy wall channel flows, distributions of l2 and l’2, relations of inclined angles for vorticity and principal axis of mean strain rate, probability of alignment angle between vorticity and vortex stretching vector and production term of 1/2 wiwi by mean strain rate wiwjSij were investigated. Near the up-slope region, inclined angles for vorticity and principal axis of mean strain rate agreed well and probability of alignment between vorticity and vortex stretching vector in the same direction was higher. So, near the up-slope region, the near-wall streamwise vortices are strengthened by the vortex stretching mechanism. Furthermore, with increasing wave amplitude the production of turbulent vorticity caused by stretching of vorticity fluctuation by mean strain rate was increased. Discussions were developed on how the structure of the near-wall streamwise vortices varies with the change of the wall wave amplitude and how these near-wall streamwise vortices affect the turbulent transport phenomena in wavy wall channel flows.