Segmental pin and endwall heat transfer for a staggered pin fin array in a stationary and rotating channel

Abstract

An experimental study is conducted to separate the heat transfer contributions of the pin surfaces and endwalls in a staggered circular pin fin array subjected to straight flow ejection in a low aspect ratio rectangular channel, representative of gas turbine trailing edge cooling passages. The array has a height-to-diameter ratio of 2, a streamwise pitch of 2.5D (where D is the pin diameter), and a spanwise pitch of 2D. Two geometrically identical test sections, one with copper pins and the other with perspex pins, are used to isolate the pin and wall heat transfer contributions under identical operating conditions. Experiments are performed over a Reynolds number range of 3000 - 25000 under stationary conditions, while rotating experiments cover Reynolds numbers of 3000 - 5000 and rotation numbers up to 0.26. Under stationary conditions, both wall and pin Nusselt numbers increase with Reynolds number. The pin Nusselt number is approximately 50% higher than the wall Nusselt number in the second row. However, the overall wall and pin heat transfer contributions are comparable because of the larger endwall area. Separate correlations are developed for the average wall and pin Nusselt numbers under stationary conditions. At Re = 3000 and Ro = 0.26, the average pin Nusselt number increases by approximately 70% relative to the stationary value, while the average wall Nusselt numbers remain close to their stationary values. These results indicate that the two surfaces should be treated separately in thermal analysis of rotating pin fin channels.