TABLE OF CONTENTS In the majority of moderate and high speed flow problems some form of random variation of flow variables exists. The laminar treatment discussed in the previous chapters is generally not applicable when such variations occur. Turbulent flow is defined as a flow with random variation of various flow quantities such as velocity, pressure and density. Turbulence is a property of a flow, not that of a fluid. Numerical solutions of the transient Navier Stokes equations are sufficient to resolve the turbulent behaviour if an adequate fine mesh resolution and time increment are used. However, this requires extremely large computer resources and with present day computers a direct numerical simulation is possible only at relatively low Reynolds numbers.
Despite significant progress in understanding turbulent behaviour during the last century, the modelling of turbulence is still an unresolved problem and will remain so for the foreseeable future. In this chapter we provide an overview for the numerical solution of turbulent fluid dynamics equations based on Reynolds decomposition of solution variables employed along with some existing turbulence models and the Characteristic Based Split (CBS) scheme. We also make reference to various other works on turbulent flows and numerical modelling. Before going into details on current modelling procedures we summarise some of the important fundamental properties of turbulence. At this point it is worth noting that a turbulent flow is an irregular dissipative three dimensional process that occurs at relatively high Reynolds numbers. A turbulent flow is marked with random variation of quantities...
