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.

CFD Predictions of Heat Transfer Coefficient Augmentation on a Simulated Film Cooled Turbine Blade Leading Edge

“…Several flow condition parameters such as the turbulence intensity and the shape of the holes have been tested. Mick and Mayle (1988) injection were found to be as much as two times those without. Far downstream, the heat transfer coefficients remained about 10 percent above that without injection.…”

Turbine Blade Film Cooling Using PSP Technique

“…Shower-head holes inclined at different angles were tested and a correlation for the optimum blowing ratio was arrived at. Film cooling effectiveness measurements on a simulated leading edge were also presented by Mick and Mayle (1988) and Mehendale and Han (1992), showing phenomenon of jet penetration into the mainstream (lift-off ) at high blowing ratios.…”

A Three-Dimensional Coupled Internal/External Simulation of a Film-Cooled Turbine Vane

“…Low momentum cooling jets perform better on the suction side, while high momentum jets do better on the pressure side. Mick and Mayle (1988) showed through experiment that leading edge film cooling, also known as showerhead film cooling, reduces heat flux over the entire flat test body for moderate blowing ratios, despite large increases in heat transfer coefficient in the leading edge region. Garg and Gaugler (1995) computationally demonstrated the profound effect of film hole exit velocity and temperature profile variations on blade surface heat transfer.…”