Distributions of Local Heat Transfer Coefficient on Surfaces with Solid and Perforated Ribs

Abstract

In this experimental investigation, the variations of the local heat transfer coefficient in rib-roughened turbine blade internal cooling passages are examined. Using liquid crystal thermometry, the detailed local heat transfer distributions are determined for turbulent flows through a long, straight, square test channel model with ribs of various configurations, including perforated ribs, on two opposite walls. Angled and V-shaped solid ribs enhance more heat transfer than transverse solid ribs. Angled solid ribs cause very large spanwise variations of the local heat transfer distribution. With the highest overall heat transfer and relatively small spanwise heat transfer variation, V-shaped ribs are recommended for internal cooling of gas turbine blades. Perforated ribs enhance less heat transfer than solid ribs, because the jet streams leaving the holes interrupt and weaken flow reattachment on the wall downstream of a rib. Increasing the size or the number of holes, or the total hole area, lowers the overall heat transfer. The lower pressure drop caused by perforated ribs reduces the required pumping power, but does not improve the thermal performance.