Gas turbine film cooling creates complicated and highly unsteady flow structures. This study seeks to examine the unsteady characteristics created by different film hole inlet geometries using a fast-response pressure sensitive paint (PSP) technique able to capture time-accurate measurements at 2000 frames per second, resolving frequencies up to 1000 Hz. Time accurate and time-averaged measurements are used to evaluate the performance of a plenum-style inlet and a crossflow-style inlet in varying turbulence environments over a flat plate. The results of this study are intended to begin the process of breaking down widely accepted time-averaged film effectiveness contours into the cumulative effects of smaller oscillating cooling jets. Jet behaviors observed in this study include a sweeping oscillation, unsteady attachment and separation from the plate, and time accurate and time average flow bias.
The behavior and performance of higher blowing ratio, separated film cooling jets depend heavily on the momentum flux ratio. Crossflow fed cooling holes show bias to the upstream side of the cooling hole with respect to the internal crossflow direction. Plenum fed cooling holes outperform crossflow fed cooling holes, and the difference increases with increasing momentum flux ratio. Cooling hole inlet geometry and momentum flux ratio affect the core of the jet, and freestream turbulence affects the periphery of the jet. Fluctuating frequencies of plenum fed and crossflow fed cooling holes were seen to be influenced by the turbulent velocity fluctuation frequency. The resulting mode shapes showed dominant side-to-side fluctuations for higher turbulence environments and a separation and reattachment motion for lower turbulence environments.