Numerical investigation of flow and heat transfer characteristics in rotating square U-duct

k -ω SST (shear stress transport) two-equation turbulence model was used to analyze the flow and heat transfer characteristics in rotating square U-duct at different inlet Reynolds numbers (10 000~60 000) and rotation numbers (0~2.013). Results show that both in stationary and rotating state, Nusselt numbers are augmented with the increase of inlet Reynolds number. Comparing with stationary state, at the same Reynolds number, the intensity of heat transfer in radial outward passage is dramatically enhanced by rotating, while the radial inward passage is just enhanced a little. Rotation number influences the U-duct heat transfer through changing the values of Coriolis force and buoyancy force. Coriolis force enhances greatly the heat transfer of trailing surface in radial outward passage, while the leading surface weakens. Buoyancy force causes flow separation in the vicinity of the wall, so it alters the heat transfer characteristics. In different positions of the radial inward passage, the heat transfer intensity of the leading surface firstly decreases and then increases with the rise of rotation number. The critical rotation numbers got by calculation are in good agreement with the experimental results. The product of dimensionless distance parameter and critical rotation is a constant.