Effect of Blowing Ratio on Film Cooling Effectiveness of Cylindrical and Shaped Holes

摘要

Film cooling is vital to allow for high temperatures and pressures at inlet of gas turbines to cope with the continuous demand of power and efficiency. To optimize distribution of film-cooling effectiveness, improvements have been made to the shape of the cooling hole. Effects such as orientation angles, length-to-diameter ratio, hole spacing-to-diameter ratio, blowing ratio, density ratio and temperature ratio have been studied, influencing heat transfer coefficients and film cooling effectiveness. The present literature studies the effect of blowing ratio on local and spatially-averaged cooling effectiveness for two geometries, namely classical cylindrical holes and shaped (laidback fan-shaped) holes at lateral and forward diffusion angles of 10° each. Blowing ratio was varied over the values 0.5, 1 and 2 and it was concluded that it negatively affects the effectiveness of cylindrical hole effectiveness, but enhances that of shaped holes. This is due to lift-off phenomenon that occurs at zero diffusion angles, and hence reduces the effectiveness with increase of blowing ratio.