Book contents
7 - Pre- and Post-Processing
Published online by Cambridge University Press: 05 June 2016
Summary
Introduction
In this chapter, pre- and post-processing is discussed along with related aspects and the CFD process chain. Examples of the latter are given in Figure 7.1. Much of the contents link, in different ways, to those in other chapters. Grid generation is a key aspect of pre-processing but this was discussed in Chapter 3. Prior to grid generation, geometry is required. Hence in this chapter, geometry handling is first discussed. Once the geometry has been defined, the mesh can be generated. Then boundary conditions must be defined. However, during the mesh generation process, a clear idea of boundary conditions is needed and hence some understanding of the flow physics. For example, boundaries must be set sufficiently far away so that any uncertainties/deficiencies arising from them do not contaminate the solution. They ideally should be located where most information is available and hence the uncertainties relating to this aspect are minimal. The mesh may need to be deliberately constructed to dissipate waves through coarsening. Hence, as with most other aspects of CFD, there are intrinsic links. Once the boundary conditions have been defined, then numerous other simulation parameters need to be correctly specified. Hence, this aspect is also considered.
Generally, the governing equations are solved in an iterative fashion and hence there is the need to judge iterative convergence. This is also discussed in this chapter. However, the process of judging convergence also relates strongly to the numerical schemes used and hence this area could also have been addressed in Chapter 4. Another aspect is simulating unsteady flows. These can have transients, periodicity, a more stochastic nature or combinations of these things. For such flows it is necessary to detect the end of initial transients and also judge when the flow has reached a statistical steady state. It also needs to be further judged how long an averaging period is needed to gain statistically stationary data. This aspect is also discussed here. The wide range of post-processing techniques available is considered. Both flow visualization and approaches for gaining more quantative data are discussed. In this chapter, the assessment of the solution quality is also considered. However, the starting point for this chapter is the aspect of initial planning and also reporting on the simulation process to give consistency.
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- Advanced Computational Fluid and Aerodynamics , pp. 459 - 532Publisher: Cambridge University PressPrint publication year: 2016
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