Effects of Inlet Flow Conditions on the Performance of Equiangular Annular Diffusers

Abstract

The effects of inlet swirl and “wall layer” thickness on the performance of equiangular annular diffusers were investigated. Three diffusers with area ratios of 1.25, 1.50 and 3.0 were used. The total expansion angle of the inner and outer cones was 40°. The study was conducted in two parts. In the first part, the inlet flow had thick “wall layers”, while in the second part the “wall layers” were thinner. The blockage factors for the thick and thin “wall layers” were 0.10 and 0.06 respectively. In both cases, the performance of each diffuser was investigated for various amounts of inlet swirl (from 0° to about 25°). It was found that equiangular annual diffuser performance increased as swirl increased. Performance also improved as diffuser length increased. For short diffusers, performance was better with a thin “wall layer”. For long diffusers, the opposite occurred. As the diffuser length increased, diffuser efficiency first decreased and then increased. This initial decrease was more pronounced with a thin “wall layer”.