Two Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

Abstract

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different Rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with 8 ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10 per cent. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state Liquid Crystal Thermography was employed to quantify a detailed two dimensional distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the 6th and 8th rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15000, 20000, 30000 and 40000. The maximum Rotation number values were ranging between 0.12 (Re = 40000) and 0.30 (Re = 15000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the Rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case the secondary flows are responsible for high heat transfer gradients on the investigated area.