Turbulent flow over a wavy surface: Neutral case

In many geophysical flows the passage of a turbulent fluid over a wavy surf ace significantly affects quantities of interest, such as momentum flux, mi xing and transport of scalars. Large-eddy simulation is used here to invest igate neutrally stratified flow over a wavy bed. A wavy surface tends to or ganize the turbulent flow by imposing its wavelength and phase on the near- wall field. Both instantaneous turbulent structures and turbulence statisti cs provide evidence of this organization. For example, a vortex identificat ion method applied to the instantaneous flow field reveals streamwise vorti ces that are locked into a phase relationship with the wavy boundary. These vortices may be linked to a Gortler instability mechanism caused by the wa vy wall. Statistical analyses are also presented to gain insights into the effect of the wavy surface. In particular, we compare the effects of three different hill heights. Finally, a brief analysis of the components of drag is given.