ABSTRACT
Most of the flows encountered in nature or in industrial applications are turbulent in nature. Turbulence plays a major part in the design of industrial equipment. Thus, modelling of turbulent flow is one of the important and challenging areas in CFD. Chapter 9 deals with introduction to turbulence, need for turbulence modelling. Popularly used turbulence models like k-ε, k-ω, Shear Stress Transport SST k-ω are discussed. Reynolds Stress Transport models and Large Eddy Simulation (LES) are briefly described. The k-ε model is the most widely used two-equation model for engineering application problems. However, the model cannot be applied to viscous sublayer where low Reynolds number corrections are recommended. The k-ω model is accurate for flow with variable pressure gradient. However, this model is sensitive to the free stream boundary conditions for free-shear flows. Two-equation model based on the concept of isotropic eddy viscosity fails in flow situations where anisotropy in the normal Reynolds stress components is significant due to sudden change in mean strain rate. Future trend is moving from the Reynolds Averaged Navier-Stokes Equation (RANSE) modelling to LES. Direct Numerical Simulation remains out of reach for all engineering use.
