Research On Flow And Characteristics Of Ejector By Large Eddy Simulation

Turbulence is one of the hottest and the most difficult topics in hydrodynamics.Researchers has focused on the circular turbulent jet.There is coherent structure which is produced because of the shear layer.And it is only can be seen the time-average characteristics but the evolution of coherent structure by RANS models.However,large scale vortex can be calculated directly by filter filter function in large eddy simulation(LES)model,for small vortex,it is calculated by subgrid model.So the large eddy simulation method is becoming more and more widely used as the improvement of computer technology,which becomes the main means to calculate the turbulence information in the project.In this paper,it is analysised turbulence characteristics and aerodynamic characteristics of round turbulent jet by LES,and the results of LES are compared with experiment,which is verified that LES method is reliable on round turbulent jet's simulation.Compared with results calculated by RANS models,we found that the Reynolds stress can be observed accurately by LES models,which is agree well with experiment.Thus LES models is more practical than RANS models on the prediction of the second-order stress.We analysised flow structure of parallel jet by LES.Compared the results of parallel jet based on different speed ratio,it is found that maximum mean velocity decay rate is slower and the potential core lengths is increase with the increase of relative velocity ratio.Through the simulation,it can be seen that the flow characteristics between free jet and parallel jet are significantly different.With the increase of second flow,the jet entrainment has been enhancement and the expansion of jet is suppressed,so the half-width decrease gradually.The energy transfer of the steam ejector is depending on mixing process and impacting process between working fluid and suction fluid.Its essential of ejector flow is strong shear and turbulent jet at high Reynolds number.The flow in the steam ejector is complex,and there are some complex flow phenomena,such as turbulent flow,entrainment hybrid and so on.Thus there are few investigations on turbulent flow inside the ejector.So the last chapter analysis the flow mechanism of ejector by LES method based on the first two chapters for the understanding of turbulent jet.It analysis the instantaneous flow information through turbulent intensity and coherent structure based on LES results.And it is found that the evolution of vortex is the same as the free jet that mainly include three stages.From these results,it is deepening the understanding on mixing process and the flow mechanism of ejector.