Research On Numerical Simulation Of Curved Roof In High Reynolds Number Based On Explicit Runge Method

Obtaining wind load on structures by computational fluid dynamics(CFD)is a low-cost,flexible method,but it is necessary to improve the computational accuracy to gain credible fluctuating pressure information on structure especially in high Reynolds number.The accuracy order of common CFD software is restricted to two.In order to improve the simulation accuracy,Runge method is applied to calculation of incompressible flow based on open source platform OpenFOAM,which provides help for the research work about numerical simulation in high Reynolds number on curved roof.Existing Runge method in compressible flow is revised to fit for simulation in incompressible flow,and parameters are determined,improving the accuracy order of time integration scheme;The influence of key parameters in large eddy simulation(including subgrid models,discretization scheme and wall function)is compared and analyzed,aiming at simulation of fluctuating pressure.The appropriate key parameters are provided.The laws of flow distribution and pressure distribution on structure with respect to different Reynolds numbers are analyzed by the simulation of cylindrical roof and spherical roof,and the simulation results accords with wind tunnel experiments,which prove the effectiveness of this method and provides technical help for research work in Reynolds number effect.The main content of this work can be summarized as follows:(1)The new parameters of Runge method are obtained based on the theory of differential algebraic equation,improving the accuracy order of time integration scheme to three by combining the pressure projection method.The singular Poisson equation is discussed,and the treatments are provided.Multigrid method is used to solve the Poisson equation,and computation efficiency is improved by parallel computing.The simulation method and accuracy of time integration scheme are proved by three traditional examples(Taylor vortex,cavity flow and double shear layer).(2)Using large eddy simulation method,cylinder model with Re=6.9×10~4 is set to reference case,and the effects of different subgrid models,different discretization schemes and different wall models are analyzed.The dissipation from subgrid model is determined by parameter of subgrid model,Smagorinsky model with Cs=0.104 is recommended;Fluctuating pressure with Gamma scheme is lower than that with central scheme,and velocity is polished by Gamma scheme.Central scheme is recommended in large eddy simulation.The influence of wall function is restricted in near wall region,and u wall function is recommended.(3)Cylindrical roof and spherical roof in different Reynolds numbers are simulated,analyzing the Reynolds number effect on mean pressure coefficient,fluctuating pressure coefficient,separation angle,pressure gradient,velocity gradient.Simulation results in mean pressure coefficients and fluctuating pressure coefficients match with experiment results,providing technical support for the research in Reynolds number.