Intermittency modeling for computation of turbulent free shear flows

Abstract

By considering the entrainment effect on the intermittency in free boundary shear layers, a set of computational turbulence model equations for the turbulent kinetic energy $\kappa$, the dissipation rate e, and the intermittency factor $\gamma$ is brought forward. The proposed model enables us to explicitly incorporate the inetrmittency effects in the conventional $\kappa-\varepsilon$ turbulence model equations. In this case, the eddy viscosity $\nu_t$ is estimated by a function of $\kappa$, $\varepsilon$ and $\gamma$. COntrary to the closure shcemes of previous intermittency modelling which employ conditional zone averaged moments, the present model equations are based on the conventional Reynolds averaged moments. The proposed $\kappa-\varepsilon-\gamma$ model has been applied to compute a plane jet, a round jet, a plane far wake and a plane mixing layer, of which predictions by any current closure scheme poses anomaly problems. The computational results of the present model shows considerable improvment over the previous models for all these shear flows. Especially, the signkficantly improved accuraty. Consequently, the spreading rates and the centerline mean velocity decays are all correctly estimated in comparison with available data sources.