离心泵特性曲线-cfdprocess.pdf

8. THE CFD PROCESS SPRING 2005 8.1 Introduction 8.2 The computational mesh 8.3 Boundary conditions 8.4 Flow visualisation 8.1 Introduction 8.1.1 Stages of a CFD Analysis A complete CFD analysis consists of: • p re-p rocessing ; • solving ; • p ost-p rocessing . This course has focused on the “solving” process, but this is of little use without pre- processing and post-processing programs. Commercial CFD vendors supplement their flow solvers with grid-generation and flow-visualisation tools. These are specialist areas in their own right, with much money and effort expended on developing “user-friendly” interfaces to make CFD generally accessible and to facilitate its application to very complex flows Pre-Processing The pre-processing stage consists of: –determining the equations to be solved; – specifying the boundary conditions; – generating a computational mesh. It depends upon: – the desired outcome of the simulation (e.g. forces, loss coefficients, flow rate, concentration distribution, heat transfer, ...); – the capabilities of the solver. Solving In commercial CFD packages the solver is often operated as a “black box”. Nevertheless, intelligent user intervention is necessary – to set under-relaxation factors and input parameters, for example – whilst an understanding of discretisation methods and internal data structures is necessary in order to supply mesh data in an appropriate form and to analyse the output. Post-Processing The raw output of the solver is a set of numbers corresponding to the values of each field variable (u, v, w, p , …) at each point of the mesh. This huge quantity of numbers must be reduced to some meaningful subset and, usually, manipulated further to obtain the desired predictive quanti