Fluctuating Thermal Field in the Near-Hole Region for Film Cooling Flows

The film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. Understanding this interaction is important in order to explain the physical mechanisms involved in the rapid decrease of effectiveness, which occurs close to the hole exit. Not surprisingly, it is this region that is not modeled satisfactorily with current film cooling models. This study uses a high-frequency-response temperature sensor, which provides new information about the film cooling flow in terms of actual turbulence levels and probability density functions of the thermal field. Mean and rms temperature results are presented for 35 deg round holes at a momentum flux ratio of I = 0.16, at a density ratio of DR = 1.05. Probability density functions of the temperature indicate penetration of the mainstream into the coolant core, and ejection of coolant into the mainstream. Extreme excursions in the fluctuating temperature measurements suggest existence of strong intermittent flow structures responsible for dilution and dispersion of the coolant jets.