계단 형상의 단차가 적용된 팬 형상 막냉각 홀 하류에서의 막냉각 효율에 관한 실험적 연구

Abstract

In this study, the adiabatic film cooling effectiveness downstream of a row of the fan-shaped film cooling holes with various staircase geometries at hole exit was measured and analyzed using a pressure sensitive paint method. Experiments were conducted with baseline fan-shaped film cooling hole and the three different configurations with staircase geometry, in which ‘two-step’ geometry was applied to the hole exit and its lateral length is changed from 2.3D to 6D. A low-speed open-type wind tunnel was used for the experiments. The density ratio of the coolant fluid to main stream was 1.0 and the blowing ratio ranged between 0.5 and 2.0. The result showed that the staircase geometry promotes lateral spreading of the coolant at the hole exit, which results in better film coverage near the hole. At low blowing ratio, the film cooling effectiveness distributions are quite similar for all the tested cases except near the hole exit because the momentum of the coolant is low and baseline configuration also has good coverage downstream of the hole. However as the blowing ratio becomes higher, the effect of the staircase geometry becomes stronger and higher film cooling effectiveness values are obtained due to increased film coverage with reduced momentum of the coolant on the whole measured area.