Numerical Simulation Of Density Current Descending A Slope Into Homogeneous Environment And Stratified Environment

The reservoir density current is common in nature,and there are many influencing factors,including the incoming flow conditions,reservoir topography,dam boundary,varying water level etc.In order to know more about the local movement of density current under the influence of single variable,the density current in generalized reservoir model under ideal boundary conditions is studied.The results may theoretically serve to the density current research in a real reservoir model.The numerical method is adopted to simulate density current in this paper,and the RNG k-? turbulent model is solved through SIMPLER algorithm,using the codes programmed by the author.The typical case of two-layer intrusive density current is employed to verify the model.The results of current pattern and head velocity are compared with experimental data,which shows good feasibility and accuracy.The reservoir topography is generalized to a slope.The dam boundary is not concerned,and the water level is considered as steady.The slope angle and incoming flow conditions are controlled as variables,and the density difference is formed by solute.Under such conditions the density current is simulated.Both the homogeneous environment and stratified environment are considered.The development of head velocity and head pattern is analyzed,and the different impacts due to different slope angle,inlet discharge,inlet density,density stratification,etc.are studied as well.The main conclusions are as follow:(1)In homogenous environment,the growth rate of head pattern is constant,and the growth rate of the thickness is lower than that of the length.The core region is near the bottom of the head.The flow velocity,density and kinetic energy are dominant in the core region.The head velocity increases with the growth of slope angle and then decreases,and the maximum head velocity appears at about 20° slope angle.The head velocity is proportional to the buoyance flux only with moderate discharge.The inlet discharge influences the density distribution of the head,which influences the head movement.The head density grows with the increase of inlet discharge,and the upper limit is the inlet density.(2)In leaping stratified environment,when the head density is between the upper and lower density of the environment,the density current propagates along the slope until exceeding the density leaping interface and then turns back because of the upward buoyance.There is an obvious V-shape flow at the turning point,after which the flow oscillates up and down around the density leaping interface with smaller amplitude.The head moves forward in a decreasing speed.The inlet discharge and inlet density influences the density current similarly,both by controlling the density distribution in the head.The greater density,the lower turning point,and the greater amplitude of oscillating movement,and the greater deceleration of the head.Specially,when the inlet density exceeds the bottom environment density to the amount that is close to the maximum density difference within the environment,the flow structure of density current will be destroyed near the leaping interface.The slope angle mainly impacts the oscillating process,steeper angle produces greater amplitude of oscillation.(3)In uniform stratified environment,when the head density is within the range of environment density,the density current decelerates along the slope,and turns to center flow at its neutral buoyance position.The V-shape turning flow and oscillating flow is clear at the core region,but not clear when considering the whole structure of the flow.The growth of the head slows down while the tail part near the turning point grows fast.The vortical flow around the head becomes weaker and the vortex center is gradually leaving the head.