Immersed-boundary simulations of turbulent flow past a sinusoidally undulated river bottom

Turbulent flow past a sinusoidally undulated river bottom is a classical problem that arises in the stability analysis of a dune-forming erodible sand bed. Past studies by the present author and others of this problem in a long-wave perturbation expansion have provided seemingly contradictory results. Direct numerical simulations performed through an immersed-boundary technique now uncover an unexpectedly rich scenario, of which the previous findings were just a facet.