Large Eddy Simulation Of Gravity Currents On Slope And Slope Transition

Large Eddy Simulation is an important method of modeling gravity currents,which can fully reflect the characteristics of large scale parts.In this study,laboratory experiments of continuous release gravity current with slope transition have been simulated by 2D,3D LES and compared with that of Reynolds-averaged method.Simulated velocity,concentration,depth-averaged velocity,depth-averaged concentration,specific energy,Froude number and Richardson number of gravity currents are compared with the experimental data.Some specific conclusions are as the following:(1)Compared with the 2D LES,3D LES obtains more accurate simulation of gravity currents.2D LES has no horizontal extension,simulated eddies extents too much in the depth direction.(2)Time and distance step have great influence on the LES;However,the change of the time step in the range of 0.1 s to0.01 s has no obvious effect on the k-? simulation.(3)The time scale and distance step of small eddy are decided based on the Kolmogorov hypotheses respectively as0.02 s,0.001 m.The vertical profile velocity,depth-averaged velocity and concentration of three-dimensional large eddy simulation are better than that from k-?simulation when the time step is chosen a litter larger than the characteristic time of small eddies.(4)The specific energy diagram of 3D LES suggests that the simulated currents is supercritical only on a short region around slope transition while on other region of the slope,it is subcritical.(5)The densimetric Froude number from experiment or our LES is greater than unity along all flume.It cannot reflect the characteristic change of gravity currents around slope transition if we do not give up the belief that critical densimetric number is unity.This is consistent with a previous theoretic analyses of gravity currents.Slope transition is an important place for oil and gas deposition from turbidity currents.Understanding the flow characteristics gravity currents in these region is of vital importance in predicting sedimentary morphology of turbidity currents and understanding its deposition mechanism,and further for the exploration of hydrocarbon reservoir related.