Numerical analysis of turbulent flow developing in a 90° bend with weakly swirling flows

A numerical analysis has been performed for turbulent flow developing in 90 degrees bend with weakly swirling flows, The ratio of bend mean radius of curvature to diameter is 2.0 and straight duct of 25 and 35 diameters are attached to the inlet and outlet of the bend, respectively. In numerical analysis, an algebraic Reynolds stress model is adopted in order to predict precisely the swirling flow induced by anisotropic turbulence and boundary-fitted coordinate system was introduced as the method of coordinate transformation. Mean velocity in axial direction, secondary flow generated by interaction between pressure gradient and centrifugal forces, pressure distributions in bend and turbulent energy distribution are compared with the experimental data. The present method could predict well the streamwise mean-velocity, i.e. maximum mean-velocity located inner wall at bend inlet and low velocity region produced near inner wall at bend outlet. As for the comparison of secondary flow, acceleration of secondary flow near upper wall, deceleration of it near lower wall at bend inlet and a pair of asymmetrical vortices observed in bend tube could be reproduced by an algebraic Reynolds stress model. Moreover, numerical results show that characteristic phenomena of turbulent energy are reproduced by the present method although agreement between both results is certainly not perfect in all detail.