Effect of Entrance Geometry on Heat Transfer in a Narrow (AR=1:4) Rectangular Two Pass Channel With Smooth and Ribbed Walls

Abstract

This paper studies the effect of entrance geometries on the heat transfer in a narrow aspect ratio (AR=1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade. Detailed heat transfer coefficient distributions are measured for three different entrance geometries: S-shape entrance, 90 degree bend entrance and a twisted entrance with changing AR. Both smooth and ribbed channels are used in a two pass channel configuration. A baseline straight-entry channel is used as a reference for comparison. The tests are done for Reynolds number ranging from 15000 to 55000. The ribs are placed at an angle of 45° to the mainstream flow. The results show that the effects of entrance geometry persist throughout the first pass (up to a distance of 9 times the hydraulic diameter) for the smooth channel. All the entrance geometries provided enhancement in heat transfer compared to the straight fully developed entrance, with the 90 degree bend entrance providing the highest enhancement. The effect of entrance is less pronounced for the ribbed test section case with the effects confined more in the early developing regions. The 90 degree bend entrance and the twisted-entry cases enhance heat transfer for the ribbed test section, while the S-shape entrance reduces the heat transfer for the ribbed test section relative to the straight entry channel.