Time-Accurate Evaluation of Film Cooling Jet Characteristics for Plenum and Crossflow Coolant Supplies
Abstract Gas turbine film cooling creates complicated and highly unsteady flow structures. This study examines the unsteady characteristics created by different cooling 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. Cooling hole inlet geometry and momentum flux ratio affect the core of the jet, and freestream turbulence affects the periphery of the jet. 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 grows with increasing momentum flux ratio. The frequency of oscillation for both plenum and crossflow fed cooling holes are influenced by the freestream turbulent velocity fluctuations. The resulting mode shapes showed dominant side-to-side sweeping for higher turbulence environments and a separation and reattachment motion for lower turbulence environments. At higher momentum flux ratio, the jets were seen to increasingly favor separation and reattachment motion. The results of this study are intended to better inform existing predictive tools. With better understanding of the time- accurate behaviors responsible for creating the commonly accepted time-average coolant distributions, simple predictive tools may be better equipped to accurately model film cooling flows.