EDDY-VISCOSITY VS 2ND-ORDER CLOSURES FOR FLOWS IN NONCIRCULAR DUCTS

This article deals with prediction of turbulent flows in ducts of nonc ircular cross sections and, in particular, assessment of the performan ce in such flows of two very different models of turbulence. One model is of the two-equation, eddy-viscosity type, which is used in conjunc tion with a non-linear stress-strain relationship. The other is a comp lete Reynolds-stress transport closure that involves the solution of a differential transport equation for each of the sk components of the Reynolds-stress tenser. The flows considered are characterized by the presence of secondary motions that are largely driven by the turbulenc e anisotropy and whose prediction remains a severe challenge to turbul ence closures. Data from several experiments involving such flows are used here to assess the overall performance of the two models. It is f ound that; the two models yield very similar results that are also of adequate engineering accuracy - an outcome that argues in favor of the use of the nonlinear two-equation model in practical computations.