Experiments on local heat transfer in a rotating square-ended U-bend

The paper reports measurements of local heat-transfer coefficients and the associated velocity field measured in turbulent flow through a square-ended U-bend which may be rotated in orthogonal mode. The flow thus has close generic similarities with that arising in the internal cooling passages of modern gas turbine blades. While for no rotation, the separation ahead of the flat end wall of the U-bend provokes an unstable non-repeating flow pattern, the secondary flow created by the duct's rotation gives rise to a strong stable vortex originating near the upstream trailing side of the duct and terminating on the downstream leading side. Within and immediately downstream of the U-bend the corresponding heat transfer data exhibit a significant effect of the rotation of the heat-transfer levels which can be linked with changes in the associated velocity and turbulence field.