Flowfield of a Shaped Film Cooling Hole Over a Range of Compound Angles

Abstract

Film cooling holes are a well-established cooling technique used in gas turbines to keep component metal temperatures in an acceptable range. A streamwise-oriented film cooling hole creates a symmetric counter-rotating vortex pair (CRVP) due to the jet interaction with the crossflow. As the orientation of the film cooling hole is incrementally misaligned with the streamwise direction (known as a compound angle), one of the vortices in the CRVP gains strength at the expense of the other until there is a single streamwise vortex that dominates the flowfield. This vortex diffuses the coolant jet and impinges hot gas onto the surface, which can augment heat transfer coefficients in a region uncovered by coolant. Although this has been well studied for cylindrical holes, there is less understanding about the nature of this phenomenon for shaped holes, which are intended to diffuse coolant laterally to minimize flowfield interaction. In the present study, particle image velocimetry (PIV) was used to measure the flowfield of compound angled shaped film cooling holes at several downstream planes normal to the streamwise direction. Five compound angled 7-7-7 holes were tested, from a streamwise oriented hole (0° compound angle) to a 60° compound angle hole, in increments of 15°. All cases were tested at a density ratio of 1.0 and blowing ratios ranging from 1.0 to 4.0. Experimental data shows that the circulation increases as compound angle increases because the flowfield transitions from a CRVP to a single streamwise vortex. For large compound angles, the streamwise vortex lifts the core of the jet off of the surface, isolating the coolant from the endwall. Measurements also indicate hole-to-hole interaction downstream for cases with high blowing ratio and large compound angle. Flowfield results are compared with adiabatic effectiveness results from a companion study in order to explain hole-to-hole interaction trends.