Analysis of Turbulent Flow in 180° Turning Ducts With and Without Guide Vanes

Abstract

This paper presents a numerical study of the turbulent flows through a number of 2-D and 3-D 180° U-ducts, with and without guide vanes, using the Reynolds-averaged Navier-Stokes method. Computations have been first carried out for a 2-D U-duct flow (W/H = 1.0) with four turbulence models (V2F, k-ε, SST and Reynolds stress). The models’ capability for streamline curvature effects on turbulence and separation has been assessed, using flow and turbulence data. The effects of adding a guide vane inside the bend have been analyzed, to reduce/avoid flow separation. Three vanes with different radial locations have been studied, and the mechanism for pressure loss reduction has been examined. Analyses have been performed for turbulent flows in 3-D U-ducts with square cross-section and sharp 180° turning (W/D = 0.2), similar to the U-bends in typical turbine blade cooling passages. The predictions are compared with the data of outer wall pressure. The effects of the guide vane and outer-wall shape on the flow separation, secondary-flow vortices and pressure loss have been evaluated. The combined vane and uniform cross-section area provide a large benefit for the flow distribution and pressure loss reduction.