URANS study of flow and heat transfer in a rotating rib-roughened internal cooling channel

The flow field and heat transfer in a rotating ribbed duct is investigated by means of U-RANS. The duct has an almost square cross-section. Square-sectioned, equally spaced ribs, oriented perpendicular to the flow direction, are mounted on one of the walls. The bulk Reynolds number is 15,000 and the Prandtl number 0.7. This configuration is analysed in a rotating configuration aiming increasing turbulence on the ribbed surface (i.e. destabilizing configuration). Comparisons with non-rotating configuration are carried out to investigate influence of Coriolis Force. Such configuration mimics the flow in internal cooling channels in the high pressure (HP) rotor and vane blade. The bottom walls are uniformly heated, except the rib walls. The turbulent flow field is modelled by the elliptic-relaxation-type k- ε-ζ-f model. This model was modified by the authors, to take in account the turbulence anisotropy derived by the Coriolis force through the sensitizing of turbulent viscosity to angular velocity vector. Results demonstrate heat transfer enhancement due to the rib induced secondary flows. The ribs cause an increase of turbulence, thus increasing heat transfer. In addition to it, rotation promotes turbulence close to the heated wall. Consequently, the heat transfer is found to be higher in the rotating case than in a non-rotating case. Secondary motions play an important role in removing hot fluid from the ribbed surface, enhancing mixing of hot and cold fluid. The Taylor-Görtler vortices produced by the Coriolis force bring hot gas far from the heated wall to the centre of the channel, increasing Nusselt number.