Measurements in film cooling flows: Hole L/D and turbulence intensity effects

Hot-wire anemometry measurements of simulated film cooling are presented to document the influence of the free-stream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and on turbulence intensity. Measurements are taken in the zone where the coolant and free-stream flows mix. Flow from one row of film cooling holes with a streamwise injections of 35 deg and no lateral injection and with a coolant-to-free-stream flow velocity ration of 1.0 is investigated under free-stream turbulence levels of 0.5 and 12 percent. The coolant-to-free-stream density ratio is unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. The measurements document that under low free-stream turbulence conditions pronounced differences exist in the flowfield between L/D = 7.0 and 2.3. the differences between L/D cases are less prominent at high free-stream turbulence intensities. Generally, short-L/D injection results in "jetting" of the coolant farther into the free-stream flow and enhanced mixing. Other changes in the flow field attributable to a rise in free-stream turbulence intensity to engine-representative conditions are documented.