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

This paper presents a numerical study of the turbulent flows through a number of 2D and 3D 180 deg $U$-ducts, with and without guide vanes, using the Reynolds-averaged Navier–Stokes method. Computations have been first carried out for a 2D $U$-duct flow $(W/H=1.0)$ with four turbulence models (V2F, $k-ε$⁠, shear stress transport (SST), and Reynolds stress). The models’ capability for predicting 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 3D $U$-ducts with square cross section and sharp 180 deg 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 are found to improve the flow distribution and reduce the pressure loss significantly.