Eddy-resolving simulation of flows over macro-roughness

Authors: F. Zabaleta, F.A. Bombardelli

Recent techniques for turbulence modelling such as hybrid RANS-LES closures currently allow for unsteady computations of turbulent flows with high Reynolds numbers at increasingly affordable costs for river applications. In this study, we present additional results of a Detached-Eddy Simulation (DES) of the nonaerated skimming flow over a stepped spillway for a Reynolds number of approximately 105 (started several years ago) as well as results from new simulations using DES coupled with a VOF method to capture the free surface. Instantaneous velocity and vorticity fields are analyzed with special detail. Instantaneous fields of vorticity confirm intermittent ejections of patches of vorticity from the cavities, which eventually reach the free surface. Large-scale structures manifested by iso-surfaces of Q-criteron show a well-organized, randomly distributed thin tubes of vorticity. The vorticity generated in the steps seems to compensate the decay of turbulence among the steps. Analysis of the patches of vorticity on the central plane of the spillway show a strong agreement with distributions of turbulent kinetic energy (TKE).

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