Three-dimensional Dynamic LES Combined with Free Surface Poisson Equation

Abstract

Three-dimensional flows around a non-submerged groyne are computed numerically using Large Eddy Simulation (LES) and are investigated experimentally. Based on Smagorinsky model, a second-order dynamic sub-grid-scale (SGS) model combined with a pressure Poisson equation for free surface flow, in which the SGS stress is a function of both the strain-rate tensor and the rotation tensor, is proposed to model secondary flows near a groyne. All these vortex flows around the groyne, which probably affect the whole flow field, are numerically simulated and analyzed. The strength of the largest circulating flow caused by the groyne behind it is weak, which naturally leads to sedimentation for silt-laden two-phase flows. The analysis of the predicted shear stress field near the channel bed bottom presents a particular interest for studying the sediment transport around the groyne. The criterion of starting motion for particle placed at the bottom is generally estimated from a critical shear stress constituting a threshold. The water depths at various cross-sections are predicted, and the surface level in the upper groyne was higher than that in lower groyne because of the groyne blockage, and the water depths in front of the groyne reached the highest value, the water level gradient was much steeper around the groyne than anywhere else. The finite volume method (FVM) was used to discretize the Navier-Stokes equations and the SIMPLEC algorithm was used to solve them. Meanwhile, these flows were investigated experimentally in a 2-meter wide flume with a groyne fixed along the flume side. All the computational results were in fairly good agreement with the experimental data.