Numerical Study On Buoyancy-opposed Wall Jet Flow By Large Eddy Simulation And Low Reynolds K-? Models

Buoyancy-opposed flow is a widespread flow phenomenon in nature and engineering applications.In this kind of flow,the fluid is affected by the effect of the buoyancy caused by the temperature difference,such as the movement of flame in confined spaces,flow of cooling fluid in nuclear reactor core,discharge of industrial wastewater and convection of atmosphere and oceans.Therefore,the research of buoyancy-opposed flow is of great significance to both nature and engineering applications.The buoyancy-opposed flow studied in this paper is reformed by injecting a plane jet of warm water down one wall of a vertical passage of rectangular cross section into a slowly moving upward stream of cooler water.Standard k-? turbulence model and four of its corresponding low Reynolds number k-? turbulence models and three different large eddy simulations are used to simulate buoyancy-opposed wall jet flow.The flow characteristics is numerically studied,and the differences of the simulation results are compared.First of all,in this paper,the standard k-? turbulence model,LS model,YS model,AKN model and C HC model are used to numerically simulate the buoyancy-opposed wall jet flow with Richardson number Ri = 0.02.The differences between the calculated results and the experimental results are compared from the prediction of velocity,temperature,turbulent kinetic energy and its dissipation rate,and analyzed from the wall-limiting behavior of turbulence.The results show that there is larger deviation in the predictions made by LS model and CHC model,while YS model and AKN model have more advantages in the simulation of this kind of flow.In addition,AKN1 model obtained by applying the model coefficients of the standard k-? model to AKN model shows a significant improvement over the original AKN model in terms of buoyancy-opposed wall jet flow,and is also slightly better than the standard k-? model and YS model.Secondly,the Smagorinsky model,the dynamic Smagorinsky mode l and the kinetic-energy transport model are applied to the large eddy simulation of three different working conditions.The flow structure of buoyancy-opposed wall jet flow is studied,and the calculation results of different models are compared and analyzed.It is found that the kinetic-energy transport model can achieve better prediction results in all working conditions,while the accuracy of the Smagorinsky model and the dynamic Smagorinsky model increases with the increase of Richardson number.And the simulation results of the Smagorinsky model are better than the dynamic Smagorinsky model in the presence of buoyancy.This shows that dynamic Smagorinsky model with dynamic model coefficient Cs is not more advantageous than the constant coefficient Smagorinsky model in all cases.