Turning Region Heat Transfer in Five, Stationary and Rotating, Multipass Channels With Various Aspect Ratios

This work summarizes studies that experimentally investigated the effect of rotation on heat transfer in the 180 deg tip and hub turns of cooling channels with various aspect ratios (ARs). The studied AR ranges from 1:4 to 4:1, which is the typical range within turbine blades. In addition to the smooth surface case (baseline case), the cases with 45 deg angled ribs and turning vanes are also included in this work. For several designs, the effect of channel orientation with respect to the angle of rotation is also investigated. This work covers a wide range of Reynolds and buoyancy numbers. The rib turbulators are found to have higher heat transfer enhancement and larger disturbance on the flow impingement on the tip and hub walls in channels with a wider aspect ratio. The rotational effect is reduced by the presence of ribs and turning vanes, and it is also reduced in the blade-shaped channels with the angled rotation feature. The tip wall heat transfer is increased by rotation due to the pumping effect from the centrifugal force; however, the hub wall heat transfer is reduced. The effect of rotation is most prominent in the first pass of the channels and is gradually mitigated in the following pass after the turns. This work provides stationary and rotational heat transfer coefficients in the tip and hub turning regions in blades, and heat transfer correlations for a variety of cooling channel designs are generated, which is of benefit to the gas turbine community.