Heat transfer measurements and analysis have been performed on a uniquely designed multi-channel passage consisting of a slot shaped channel with a 3:1 aspect ratio with coolant-feed tubes located adjacent to the main slot shaped channel. Small round jets connect the outer feed passages to the main channels at a 15 degree angle relative to the main channel flow direction and at a position tangent to the floor/roof of the main channel. Flow entering the multi-channel passages is directed into the main channel through orifices that reduce the pressure in the main channel, thereby enabling positive pressure differences between the feed and the main channel and allowing high velocity flow through the jets. The flow enters the main channel via a 90-degree turn through the orifice. The resulting flow through the side jets and main channel causes high shear flow along the roof and floor of the channel where the jet flow enters the main channel, swirl motion as the high velocity side jet flow enters the main channel flow at an angle relative to the main flow direction, and high turbulence regions as the lower velocity main channel flow tumbles when coming in contact with the high velocity jets issuing from the side channels. The heat transfer characteristics were compared to the slot channel with a 90 degree inlet with no additional heat transfer enhancements. Four different jet configurations are presented along with three different orifice diameters. While a single channel passage with flow exiting freely is not a design typically found in a turbine airfoil, the benefits of this unique concept can be a basis for further studies with geometries more typical of a production airfoil. The results yield average normalized Nusselt numbers enhancement for the entire main channel as high as 10.7, when compared to a smooth slot channel without heat transfer enhancements. Pressure losses, mainly due to the orifices, were high but the overall performance shows significant improvements when compared to other heat transfer enhancement methods in turbine airfoil mid-span regions.
Influence of streamwise vortical structures on heat transfer in the far cylinder wake in a slot channel flow
