Effects of the spanwise heterogeneity of a three-dimensional wavy wall on momentum and scalar transport

We numerically investigate turbulent flow and scalar transport over a three-dimensional wavy wall using a large eddy simulation. The results show that the spanwise heterogeneity of the three-dimensional wall affects the characteristics of turbulent flow as well as momentum and scalar transport. The 3D wavy wall induces alternating distributed secondary flows along the spanwise direction, which weakens the intensity of the streamwise turbulent shear layer and Reynolds stress. The double-averaged streamwise velocity profile displays an obviously upward shift relative to the two-dimensional case. The magnitude of the dispersive stress is modulated in the spanwise direction, suggesting the formation of low- and high-momentum pathways. The peak convection intensity is independent of the wall topography, albeit with shifts along the spanwise direction due to the strong shear layer between the inflow and reversed flow. The profiles of the vertical turbulent scalar flux show positive-negative variance in the viscous sublayer in both the streamwise and spanwise directions. This is also induced by the secondary flow. Vortices around a hill have a spanwise-bend feature, which strongly affects the turbulent scalar flux. The spanwise heterogeneity modulates the mean flow fields through the formation of a secondary flow ahead of the hill and a reversed vortex pair after the crest develops downstream. Both the secondary flow and reversed vortex pair have an orderly and alternating distribution near the wall.