Impact of tip leakage flow on endwall heat transfer in a square duct featuring an isolated pin

Abstract In this study, transient liquid crystal thermography is employed to determine detailed endwall heat transfer associated with tip leakage flows in a square duct featuring a single pin fin aligned with the duct centerline. Four different pin fin shapes, cylinder, cube, triangle, and diamond, have been studied where the cylinder pin fin diameter (dp) was 25% of the duct hydraulic diameter (dh). For consistency in flow blockage, all non-cylindrical pin geometries were generated by preserving the same cross-sectional area as the reference cylindrical pin. Liquid crystal experiments were conducted at Reynolds numbers (based on duct hydraulic diameter) varying between ≈989,300 to 18,900, for each pin shape. Detailed endwall heat transfer coefficient data is presented in normalized form (Nu/Nu0) over the region x/dh = −2 to 4, with x/dh = 0 denoting the pin fin center. In addition, static pressure measurements were conducted at the channel centerline for each flow condition. Experimentally obtained local heat transfer data reveals primary and secondary heat transfer behavior as a result of tip leakage flows, where the primary heat transfer location aligned closely with projection of pin fin's center on to the endwall. The dip in heat transfer in the immediate downstream vicinity of the pin, followed by heat transfer recovery, was found to be strongly dependent on the pin fin shape.