Effect of Internal Crossflow Velocity on Film Cooling Effectiveness—Part I: Axial Shaped Holes

Abstract

The effect of feeding shaped film cooling holes with an internal crossflow is not well understood. Previous studies have shown that internal crossflow reduces film cooling effectiveness from axial shaped holes, but little is known about the mechanisms governing this effect. It was recently shown that the crossflow-to-mainstream velocity ratio is important, but only a few of these crossflow velocity ratios have been studied. This effect is of concern because gas turbine blades typically feature internal passages that feed film cooling holes in this manner. In this study, film cooling effectiveness was measured for a single row of axial shaped cooling holes fed by an internal crossflow with crossflow-to-mainstream velocity ratio varying from 0.2 to 0.6 and jet-to-mainstream velocity ratios varying from 0.3 to 1.7. Experiments were conducted in a low speed flat plate facility at coolant-to-mainstream density ratios of 1.2 and 1.8. It was found that film cooling effectiveness was highly sensitive to crossflow velocity at higher injection rates while it was much less sensitive at lower injection rates. Analysis of the jet shape and lateral spreading found that certain jet characteristic parameters scale well with the crossflow-to-coolant jet velocity ratio, demonstrating that the crossflow effect is governed by how coolant enters the film cooling holes.