A KAPPA-EPSILON-GAMMA EQUATION TURBULENCE MODEL

By considering the entrainment effect on the intermittency in the free boundary of shear layers, a set of turbulence model equations for the turbulent kinetic energy k, the dissipation rate-epsilon, and the intermittency factor-gamma is proposed. This enables us to incorporate explicitly the intermittency effect in the conventional k-epsilon-turbulence model equations. The eddy viscosity v(t) is estimated by a function of k, epsilon and gamma. In contrast to the closure schemes of previous intermittency modelling which employ conditional zone averaged moments, the present model equations are based on the conventional Reynolds averaged moments. This method is more economical in the sense that it halves the number of partial differential equations to be solved. The proposed k-epsilon-gamma-model has been applied to compute a plane jet, a round jet, a plane far wake and a plane mixing layer. The computational results of the model show considerable improvement over previous models for all these shear flows. In particular, the spreading rate, the centreline mean velocity and the profiles of Reynolds stresses and turbulent kinetic energy are calculated with significantly improved accuracy.