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 tur bulent heat transfer in radially rotating circular smooth-walled and s quare rib-roughened ducts with focuses on the variable rotational effe cts along the leading and trailing surfaces of these two test ducts du e to differences in the shape of the cross section and the surface con ditions 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 trai ling surface. On the leading surfaces of both test sections, heat tran sfer was significantly less than that of the pure forced convection le vel. In qualitative terms, even with the agitated flow field caused by ribs inside the square ribbed duct, considerable rotational effects w ithin the ribbed duct occurred in a similar manner to that found insid e the circular smooth-walled duct. However, with equivalent rotating c onditions, the heat transfer impediment on the leading surface was mor e severe for the ribbed duct than for the smooth-walled duct and the h eat transfer enhancement on the trailing surface of the ribbed duct wa s significantly alleviated. A low degree of peripheral heat transfer v ariation was found in the ribbed test duct. Since the difference betwe en smooth-walled or rib-roughened ducts is considerable, the selection of either circular smooth-walled or square rib-roughened coolant chan nel for gas turbine rotor blades must be performed after considering t he variable rotational effects in order to achieve the optimum design of an internal cooling system.