TOWARDS THE DEVELOPMENT OF 2ND-ORDER CLOSURE MODELS FOR NONEQUILIBRIUM TURBULENT FLOWS

A new approach for the development of second-order closure models suit able for nonequilibrium turbulent shear flows is presented. The centra l idea is based on the implementation of a relaxation time approximati on to the nonequilibrium extension of an explicit algebraic stress mod el. Here, the algebraic stress model is systematically derived from th e full Speziale et al. 1991 (SSG) second-order closure in the equilibr ium limit of homogeneous turbulence. It is then extended to nonequilib rium turbulent flows by means of a Pade approximation, whereby approxi mate consistency with the rapid distortion theory (RDT) solution for h omogeneous shear flow is established. The resulting model is tested in homogeneous shear flow turbulence under a wide range of shear rates. Substantially improved results are obtained in comparison to conventio nal second-order closure models that are based on the direct modeling of terms in the Reynolds stress transport equation.