Heat Transfer Coefficients Over a Flat Surface With Air and CO2 Injection Through Compound Angle Holes Using a Transient Liquid Crystal Image Method

Abstract

This paper presents the detailed heat transfer coefficients over a flat surface with one row of injection holes inclined streamwise at 35 deg for three blowing ratios (M = 0.5–2.0). Three compound angles of 0, 45, and 90 deg with air (D.R. = 0.98) and CO2 (D.R. = 1.46) as coolants were tested at an elevated free-stream turbulence condition (Tu ≈ 8.5 percent). The experimental technique involves a liquid crystal coating on the test surface. Two related transient tests obtained detailed heat transfer coefficients and film effectiveness distributions. Heat transfer coefficients increase with increasing blowing ratio for a constant density ratio, but decrease with increasing density ratio for a constant blowing ratio. Heat transfer coefficients increase for both coolants over the test surface as the compound angle increases from 0 to 90 deg. The detailed heat transfer coefficients obtained using the transient liquid crystal technique, particularly in the near-hole region, will provide a better understanding of the film cooling process in gas turbine components.