Effects of gaps between the side-walls and ribs on the rib-induced flow structure and heat transfer distribution inside a high aspect ratio cooling channel

The flow visualization and heat transfer experiments were performed in a rectangular test section with an aspect ratio of 5:1, representing a cooling channel inside a trailing edge of a gas turbine rotor blade. The experiments were performed for three 60° ribs arrangements. 1) 60° full ribs. 2) 60° ribs with the gaps between the Rear wall aid ribs and 3) 60° ribs with gaps between the Front wall and ribs. The obtained results showed strong effects of the rib-induced secondary flow on the heat transfer distribution. It was revealed that the heat transfer enhancement on the Rear ribbed walls is attributed to the rib-induced secondary flow, which carries the fresh cold air from the passage core region towards the Rear wall and enhances the Nu appreciably. It was also confirmed that while the existence of the gaps between the Front wall and ribs provides more even Nu distribution on the ribbed walls due to the strengthening of the flow structure, in the case of the gaps between the Rear wall and ribs, it causes a significant mean Nusselt number deterioration on the both ribbed and both smooth walls.