Effects of Compound Angle Injection on Flat-Plate Film Cooling Through a Row of Conical Holes

Abstract

This paper presents the measured heat transfer and film cooling results over a flat plate as the secondary flow is ejected into the mainstream through a row of conical holes. A transient liquid crystal thermography was employed to derive the film cooling performance and heat transfer distribution over the test flat plate. Each conical injection hole, with a pitch-to-diameter ratio of 3 on the exit plane, had an expanded angle of 8 degrees. The effects of changing the spanwise injection angles and blowing ratios on both film cooling and heat transfer distributions were investigated. Test pieces in this study used different spanwise injection angles of β = 0°, 45°, and 90° but maintained the same inclination angle of γ = 35°. For each test piece, four different blowing ratios of 0.5, 1.0, 1.25 and 1.5 were tested at Re = 44,000, Tu = 2.3%, δ1/d = 0.22, p/d = 3, and R = 1.06. A baseline check was also conducted for the flat-plate film cooling through the use of straight circular holes. In addition, a comparison was made between the film cooling results using conical holes with those using straight circular holes. Measured results showed that the laterally averaged heat transfer coefficient increases with the blowing ratio for both straight circular and conical hole configurations. For the simple injection, a conical configuration was found to have better film cooling protection only at higher blowing ratio (M = 1.25 and 1.5). Compound angle injection does not have specific advantage for the film cooling protection in the case of conical configuration.