Numerical investigation on the temporal and spatial statistical characteristics of turbulent mass transfer above a two-dimensional wavy wall

The shape of a wall affects turbulent flow and scalar transport. In this paper, the turbulent mass transfer above a two-dimensional wavy wall was investigated by large-eddy simulation to analyze the temporal and spatial statistical characteristics, the effect of the convection-diffusion mechanism on the physical process of scalar transport, and the role of the dispersive quantity (form-induced quantity). The results show that the presence of the wavy wall leads to flow separation and changes in flow structures and scalar transport. The momentum is controlled by the enhanced turbulence level between crests, whereas there is a scalar transfer sink on both the leeward and windward sides. The former is due to the scalar diffusion-dominant mechanism triggered by reduced velocity of reversed flow in the separation zone, whereas the latter is attributed to strong convection due to an enhanced turbulent shear layer that stimulates the convection-dominant mechanism. The high-order dispersive quantity has a peak on the windward side and is phase-locked on the leeward side downstream of the separation point. Analysis of the quadrant distributions of the high-order dispersive quantities reveals that dispersive sweep and ejection events respectively occur at the separation point and in the intersection region of reattachment and reversed flow. We suggest that these two positions are the origins of quasi-streamwise vortices, which relates to the strong convection above the turbulent shear layer. The momentum and scalar transport are controlled by this type of vortex structure persistently disturbing the time-averaged flow field when the high-order dispersive quantity reaches its peak.