Improvements to Rahman-Agarwal-Siikonen One-Equation Turbulence Model Based on k-epsilon[|#15#|] Closure

Abstract

Recently a new one–equation turbulence model was proposed by Rahman, Agarwal and Siikonen; the model is known as the Rahman–Agarwal–Siikonen (RAS) model. It is an isotropic model which accounts for the low–Reynolds number (LRN) effects in the wall proximity. In the model, the turbulent kinetic energy k and the dissipation rate are evaluated using the R (= k/) transport equation together with the Bradshaw and other empirical relations. The proposed eddy–viscosity formulation preserves the realizability constraints the physically necessary conditions in developing a turbulence model. An anisotropic destruction coefficient is used to obtain a faster decaying behavior of turbulence destruction in the outer region of the boundary/shear layer, thereby precluding the free–stream dependency. In this paper, several improvements to the original RAS model are made which include the introduction of damping functions in the wall region. The improved model is validated against the well–documented turbulent flow cases, yielding predictions in excellent agreement with the direct numerical simulation (DNS) and the experimental data. A comparative assessment of the improved RAS model with the Spalart–Allmaras one–equation model and the shear stress transport k–ω model is made for non-equilibrium flows.