Impingement cooling in triangular ducts using an array of side-entry wall jets

Abstract

An experimental study has been performed to measure local heat transfer coefficients and static wall pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right triangular ducts of the same altitude and different apex angles of β=30° (Duct A), 45° (Duct B) and 60° (Duct C) are tested for various jet Reynolds numbers (3000 ≦ Re j ≦ 12 600) and jet spacing ( s/ d=3.0 and 6.0). Results show that an increase in Re j increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Re j, Duct C has the highest wall-averaged heat transfer rate because of the highest jet center velocity as well as the smallest jet inclined angle. The distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.