Free surface flow over two-dimensional dunes under different flow regimes

Abstract

To explore the influence of different flow regimes on fluid dynamics over dunes after the construction of the Three Gorges Dam, a model is applied by utilizing a large eddy simulation, immersed boundary method and level set method to address the turbulence, dune morphology and free water surface, respectively. Seven simulations with incrementally increased Froude numbers are simulated based on previous experimental work. The vertical profiles of the non-dimensional double-averaged streamwise velocity agree well with the experimental data. The profiles display an inflection caused by the effects of the dunes within the form-induced sublayer, where the individual profiles are reduced by wake flow. As the Froude number increases, the flow regime transitions from subcritical flow to supercritical flow, and the mean streamwise velocity and the shear velocity increase. Additionally, the reattachment location of the recirculation zone downstream of the crest moves upwards, while the location of the highest water elevation moves downwards, approaching the crest of the dune. The fluctuation in the free water surface increases as the Froude number increases.