Turbulence Models

This chapter provides an overview of turbulence modeling based on Reynolds-averaged Navier–Stokes (RANS) equations. It introduces turbulence and Reynolds averaging, then derives the RANS equations and explains the closure problem. The chapter emphasizes the limitations of linear models in complex flows and introduces Reynolds Stress Models (RSM) and Explicit Algebraic Reynolds Stress Models (EARSM) as more advanced alternatives capable of capturing anisotropic stress behavior. Turbulent scalar transport is covered through algebraic and differential scalar-flux models. Near-wall treatments, including wall functions and enhanced low-Reynolds models, are explained. A case study involving square duct flow illustrates the performance of various RANS models.