Stagnation Film Cooling and Heat Transfer, Including Its Effect Within the Hole Pattern

Abstract

Detailed film effectiveness and surface heat transfer measurements were obtained for secondary air injection through rows of holes into the stagnation region of an incident mainstream flow. Tests were performed using a blunt body with a circular leading edge and a flat afterbody. Rows of holes were located at ±15 deg and +44 deg from stagnation. The holes in each row were spaced four hole diameters apart and were angled 30 deg to the surface in the spanwise direction. Measurements were taken for three cooling-to-incident flow mass flux ratios both in the leading edge region within the hole pattern and downstream to a distance of about 85 hole diameters. The results indicate that large spanwise variations in both film effectiveness and heat transfer coefficient exist, and that the highest values of each do not in general correspond. Near the holes, film effectiveness values as high as 0.7–0.8 were found, while heat transfer coefficients with injection were as much as three times those without. Far downstream the film effectiveness decayed to values near 0.1, while the heat transfer coefficient remained about 10 percent above that without injection. Nevertheless, it is shown that for typical turbine temperatures, leading edge injection reduces the surface heat load everywhere for all but the highest mass flux ratio. The exception produces an increase in heat load within the injection region.