Large Eddy Simulation Study Of The Turbidity Current With Slope Transition

Large Eddy Simulation(LES)is one of the important simulation methods for the gravity flows.It can get more flow information than RANS simulation and less computation cost compared with Direct Numerical Simulation(DNS).So far,we have not found LES applied to turbidity current with slope transition.In this paper,different sub-grid scale models Dynamic Smogrinsky(DS)and WALE applied LES and RANS k-? model were used to simulate experiment turbidity current and compared.The density counters,profile velocity and concentration at slope up and down,depth-averaged velocity and concentration,current thickness,specific energy,densimetric Froude Number and Richardson number,as well as deposition thickness and bedform simulated were compared with experiment data and analyzed.The following conclusions are drawn.(1)The 2D LES simulation vortex extends excessively in the vertical direction,resulting in flow velocity slower than that of experiment,and the profile velocity and concentration,depth-averaged concentration and velocity,current thickness are quite deviated from experimental data,not even as good as those from k-? modeling;(2)3D LES turbidity current qualitatively reflected the large-scale vortex observed by experiment,and the flow characteristics from 3D LES DS are better than those from LES WALE..(3)the specific energy analyses from 3D LES DS show that in the slop section 0 ~ 5.5 m the current is subcritical,and then turns into supercritical at the slope transition,and then after 6.5m,it transforms back into subcritical flow again.(4)The LES DS simulated densimetric Froude number is greater than 1 at both the slope and flat sections.The character of the flow cannot be judged with traditional critical unity of Fr,supplemented with the specific analyses is necessary.(5)LES DS produces proper sedimentation thickness of turbidity current,but fails to generated the sediment waves observed by experiment.This means that the existing LES DS model has certain deficiencies in the simulation of deposition,especially regarding the bottom boundary conditions.These conclusions may be used for further exploring the flowcharacteristics of turbidity currents,the mechanism of their deposition and related hydrocarbon reservoirs.