Heat/mass transfer in a two-pass rotating rectangular duct with and without 70°-angled ribs

The present study investigates convective heat/mass transfer and flow characteristics inside a cooling passage of rotating gas-turbine blades. The rotating duct with and without rib turbulators are used. The ribs of 70°attack angle are attached on leading and trailing surfaces in a staggered arrangement. A naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. Additional numerical calculations are conducted to analyze the flow patterns in the cooling. The local heat/mass transfer and the flow pattern in the passage are changed significantly according to rib configurations, duct turning geometry and duct rotation speed. The results show that the duct rotation generates the heat transfer discrepancy between the leading and trailing walls due to the secondary flows induced by the Coriolis force. The heat/mass transfer on the ribbed duct shows 80% higher than the smooth duct because the ribs attached on the walls disturb the mainflow resulting in recirculation and secondary flows near the rib with the secondary flow generated by rotation. The overall heat transfer pattern on the leading and trailing walls for the first and second passes depend on the rotating speed and the turning geometry, but the local heat transfer trend is affected mainly by the rib arrangeements.