Experimental and Numerical Study of Three-Dimensional Unsteady Incompressible Flow Past Two Identical Circular Cylinders in Tandem Arrangements

The possible states in the flow past two identical cylinders in tandem arrangements are investigated. The effect of the gap （L/D = 1.5, 1.75 and 2） between the two cylinders at Reynolds number （Re = 52,639） is taken into consideration. The presence of three-dimensional flow structures was observed to include notable changes to the response of the flow as result of variation of cylinder separation. A number of planes （z/h = 0.02, 0.25, 0.5 and 0.98） were taken at 20 step times of interval 0.005 s. to cover the details of flow along the cylinders. CFD FLUENT program was used to detect the flow structure. It is observed that the gap between the two cylinders affects the flow regime, i.e., there is no distinct vortex shedding downstream of the first cylinder.

Implicit numerical scheme based on SMAC method for unsteady incompressible Navier-Stokes equations

An implicit numerical scheme is developed based on the simplified marker and cell （SMAC） method to solve Reynolds-averaged equations in general curvilinear coordinates for three-dimensional （3-D） unsteady incompressible turbulent flow. The governing equations include the Reynolds-averaged momentum equations, in which contravariant velocities are unknown variables, pressure-correction Poisson equation and k- s turbulent equations. The governing equations are discretized in a 3-D MAC staggered grid system. To improve the numerical stability of the implicit SMAC scheme, the higherorder high-resolution Chakravarthy-Osher total variation diminishing （TVD） scheme is used to discretize the convective terms in momentum equations and k- e equations. The discretized algebraic momentum equations and k- s equations are solved by the time-diversion multiple access （CTDMA） method. The algebraic Poisson equations are solved by the Tschebyscheff SLOR （successive linear over relaxation） method with alternating computational directions. At the end of the paper, the unsteady flow at high Reynolds numbers through a simplified cascade made up of NACA65-410 blade are simulated with the program written according to the implicit numerical scheme. The reliability and accuracy of the implicit numerical scheme are verified through the satisfactory agreement between the numerical results of the surface pressure coefficient and experimental data. The numerical results indicate that Reynolds number and angle of attack are two primary factors affecting the characteristics of unsteady flow.

A semi-implicit three-step method based on SUPG finite element formulation for flow in lid driven cavities with different geometries

A numerical algorithm using a bilinear or linear finite element and semi-implicit three-step method is presented for the analysis of incompressible viscous fluid problems. The streamline upwind/Petrov-Galerkin (SUPG) stabilization scheme is used for the formulation of the Navier-Stokes equations. For the spatial discretization, the convection term is treated explicitly, while the viscous term is treated implicitly, and for the temporal discretization, a three-step method is employed. The present method is applied to simulate the lid driven cavity problems with different geometries at low and high Reynolds numbers. The results compared with other numerical experiments are found to be feasible and satisfactory.

A Scalable Numerical Method for Simulating Flows Around High-Speed Train Under Crosswind Conditions

This paper presents a parallel Newton-Krylov-Schwarz method for the numerical simulation of unsteady flows at high Reynolds number around a high-speed train under crosswind.With a realistic train geometry,a realistic Reynolds number,and a realistic wind speed,this is a very challenging computational problem.Because of the limited parallel scalability,commercial CFD software is not suitable for supercomputers with a large number of processors.We develop a Newton-KrylovSchwarz based fully implicit method,and the corresponding parallel software,for the 3D unsteady incompressible Navier-Stokes equations discretized with a stabilized finite element method on very fine unstructured meshes.We test the algorithm and software for flows passing a train modeled after China’s high-speed train CRH380B,and we also compare our results with results obtained from commercial CFD software.Our algorithm shows very good parallel scalability on a supercomputer with over one thousand processors.