Effect of partial blockage on flow and heat transfer of film cooling with cylindrical and fan-shaped holes

Abstract

Large eddy simulation is used to study the effect of partial blockage on the film cooling characteristics of cylindrical and fan-shaped holes at the blowing ratio of M=0.5. The results show that severe blockage (H/D=0.75) resulted in a decrease of about 97% and 27% in the laterally-averaged film cooling effectiveness of cylindrical and fan-shaped holes. Slight blockage (H/D<0.5) improved the cooling performance of the fan-shaped hole by about 13%. The blockage tolerance of the fan-shaped hole is stronger than that of the cylindrical hole. The blockage alters the flow characteristics in the tube and downstream. A "hairpin vortex forest" is formed downstream of the blocked fan-shaped hole with more hairpin vortexes than the unblocked one. These large-scale coherent structures dominate the mixing and dispersion. The deterioration of the cooling performance of the blocked cylindrical hole is mainly caused by the strengthening of the head and horizontal legs of the hairpin vortex. Several rows of smaller scale hairpin vortexes downstream of the blocked fan-shaped hole and the streak structure near the wall improved the film cooling effectiveness.