Thermal performance of rotating two-pass ribbed square channel with wavy sidewalls

Abstract

Detailed Nusselt number (Nu) distributions over Leading Endwall (Le-E) and Trailing Endwall (Tr-E), Fanning friction coefficients (f) and thermal performance factors (TPF) of a radially rotating two-pass square channel enhanced by in-line 45° endwall ribs and wavy sidewalls were measured at the test conditions of 5000⩽Re⩽20,000, 0⩽Ro⩽0.3 and 0⩽Bu⩽0.053. No previous study has examined the thermal performances of a rotating ribbed two-pass channel with wavy sidewalls. A selection of heat transfer data illustrates the individual and interdependent effects of Re, Ro and Bu on local and region-averaged Le-E and Tr-E Nu. A set of Le-E and Tr-E heat transfer correlations that determines the rib-wise and regionally averaged Nu over the inlet and outlet ribbed endwalls, as well as over the smooth bend endwall is generated. Along with the f data detected from the ribbed endwalls and wavy sidewalls at isothermal conditions, the TPF values at various rotating conditions are evaluated. The heat transfer, pressure drop and TPF performances for the two-pass channel with present combined passive Heat Transfer Enhancement (HTE) device at rotating conditions are subsequently compared with those generated by the typical HTE devices deployed in the internal coolant channels of a gas turbine rotor blade. Acting by the combined Re, Ro and Bu effects, present region-averaged Nusselt numbers over the rotating Le-E (Tr-E) of the inlet-leg, sharp bend and outlet-leg are respectively raised to 3.20–5.80 (4.10–8.59), 4.26–10.48 (5.03–15.47) and 1.48–12.47 (4.64–8.24) times of the Dittus–Boelter reference levels. With the f coefficients increased to 9.61–25.7 times of the Blasius equation levels by present HTE measure and the 180° sharp bend, present TPF values obtained at the rotating test conditions fall in the range of 2.87–0.71, suggesting the favorable heat transfer effectiveness with cooling applications to gas turbine rotator blades.