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

To investigate buoyancy influence on flow and heat transfer characteristics of U-duct in high rotation number range from 0 to 2.013, k-ω SST two-equation turbulence model was adopted. The same rotation number, different temperature ratios (0.12, 0.17 and 0.22) and the same temperature ratio(0.22), different rotation numbers U-duct were studied. The results show that in radial outward passage buoyancy induces the flow seperation in the vicinity of leading surface. Heat transfer intensity of leading surface firstly increased and then decreased with the increasing of rotation numbers. In radial inward passage, due to buoyancy effect the velocity profile presents in double peaks pattern. With the increasing of rotation number, the Nu/Nu_s difference between leading surface and trailing surface is reduced. When the rotation number increases approximately to 1.0, the Nu/Nu_s value of trailing surface is beyond that of leading surface. In stationary U-duct, heat transfer is enhanced at lower temperature ratio, while it is just reversed in rotating U-duct. The calculation results prove that buoyancy number is appropriate to evaluate the combined effect of rotation number and temperature ratio on heat transfer.