CONVECTIVE DISCRETIZATION SCHEMES FOR THE TURBULENCE TRANSPORT-EQUATIONS IN FLOW PREDICTIONS THROUGH SHARP U-BENDS

This paper presents finite volume computations of turbulent flow throu gh a square cross-sectioned U-bend of curvature strong enough (Rc/D = 0.65) to cause separation. A zonal turbulence modelling approach is ad opted, in which the high-Re k-epsilon model is used over most of the f low domain with the low-Re, 1-equation model of k-transport employed w ithin the near-wall regions. Computations with grids of different size s and also with different discretization schemes, demonstrate that for this flow the solution of the k and epsilon equations is more sensiti ve to the scheme employed in their convective discretization than the solution of the mean flow equations. To avoid the use of extremely fin e 3-Dimensional grids, bounded high order schemes need to be used in t he discretization of the turbulence transport equations. The predictio ns, while encouraging, displayed some deficiencies in the downstream r egion due to deficiencies in the turbulence model. Evidently, further refinements in the turbulence model are necessary. Initial computation s of flow and heat transfer through a rotating U-bend, indicate that a t rational numbers (R(o) = OmegaD/W(b)) relevant to blade cooling pass ages, the Coriolis force can substantially modify the hydrodynamic and thermal behaviour.