Numerical Simulation Of Density Currents In Thermally Stratified Environments

The current research on the generation and evolution of density currents was mainly focused on those caused by single factor of sand concentration,but little has been done on the density currents caused by high sediment concentration and water temperature.Although the domestic and foreign scholars have carried out a large number of studies on the prediction and application of water temperature in reservoirs,due to the lack of correct understanding of the dynamic process of evolution of the density currents,the accuracy of the numerical simulation about density currents was generally not satisfactory.Two-dimensional numerical simulation was performed with Fluent,the generation and evolution of density currents were numerically simulated,and the simulated results were verified against the experimental data.Main conclusions were as followed:(1)The simulation model was calibrated with the measured data of a pilot stratified reservoir,the inflow sediment concentrations were 1.25 g / L,2.5 g / L,3.75 g / L,5 g / L,the inflow rates were 0.00125 m / s,0.0025 m / s,0.005 m / s,0.0075 m / s and 0.01 m / s,and the stratification indexes were 0.24,0.28,0.36,0.45 and 0.49 respectively.The simulated results of separation depth,the thickness and velocity of interflow agreed well with the measured results,and the relationship between the interflow parameters with the inflow sediment concentration,inflow velocity,and stratification level was analyzed.(2)The inflow sediment concentration,the inflow velocity and the stratification level have a significant effect on the motion of the density currents.With the increase of inflow sediment concentration,the separation depth and the thickness of interflow were increased.With the increase of inflow velocity,the separation depth and thickness of interflow were increased.With the increase of strength of stratification,the separation depth and thickness of interflow were decreased.With the increase of inflow sediment concentration,the velocity of interflow on the sloped bed was increased.The relation between the thickness of the interflow and the stratification index was characterized as a power function,and a negative linear relationship between the thickness of the interflow and the stratification index was determined.With the increase of the buoyancy coefficient,the upper boundary depth of the interflow was increased in the form of a logarithmic function.With the increase of inflow velocity,the velocity amplitude of density currents decreased on the sloped.With the increase of the buoyancy coefficient,the upper boundary depth of the interflow was increased in the form of a logarithmic function.With the increase of stratification index,the average velocity of interflow was increased.The relation between the thickness of the interflow and the stratification index was characterized as a power function and a linear relationship between the separation depth and the stratification was determined.