The computation of turbulent flow through stationary and rotating U-bends with rib-roughened surfaces

摘要

This study focuses on the numerical computation of turbulent flow through stationary and rotating U-ducts of square cross-section, with rib-roughened inner and outer walls along the straight sections. Square-sectioned ribs, normal to the flowdirection are employed in a staggered arrangement. The rib height-to-diameter ratio is 0.1 and the rib pitch-to-rib height ratio is 10. The bend curvature ratio (R{sub}c/D) is 0.65 and the flow Reynolds number is 100000. The duct rotates about an axisparallel to that of curvature, at a rotation number (Ro≡±0.2). The preliminary computations presented suggest that grid requirements can be significantly reduced, through a combination of body fitted grids and high-order convective discretisationschemes in all transport equations. The presence of regions of flow separation, necessitates the use of low Re second-moment closures. Flows through negatively rotating U-bends are found to be especially challenging to turbulence models.