A comparative study of heat transfer between rotating circular smooth-walled and square rib-roughened ducts with cooling application for gas turbine rotor blades

In this paper we describe a detailed experimental investigation of turbulent heat transfer in radially rotating circular smooth-walled and square rib-roughened ducts with focuses on the variable rotational effects along the leading and trailing surfaces of these two test ducts due to differences in the shape of the cross section and the surface conditions of duct walls. The experimental data reconfirmed the presence of strong rotation-induced secondary flows for both the test sections with an attendant relative increase in local heat transfer on the trailing surface. On the leading surfaces of both test sections, heat transfer was significantly less than that of the pure forced convection level. In qualitative terms, even with the agitated flow field caused by ribs inside the square ribbed duct, considerable rotational effects within the ribbed duct occurred in a similar manner to that found inside the circular smooth-walled duct. However, with equivalent rotating conditions, the heat transfer impediment on the leading surface was more severe for the ribbed duct than for the smooth-walled duct and the heat transfer enhancement on the trailing surface of the ribbed duct was significantly alleviated. A low degree of peripheral heat transfer variation was found in the ribbed test duct. SInce the difference between smooth-walled or rib-roughened ducts is considerable, the selection of either circular smooth-walled or square rib-roughened coolant channel for gas turbine rotor blades must be performed after considering the variable rotational effects in order to achieve the optimum design of an internal cooling system.