Supersonic impinging jet noise reduction using co-axial swirler

Supersonic impinging jet noise reduction is an important problem, especially in STOL aircraft, VTOL aircraft and rockets. These types of impinging jets generate a larger amount of noise and highly unsteady flows, which lead to noisy environment, posing a hazard to humans and materials in the proximity. The present study is carried out on supersonic impinging cold jets for nozzle pressure ratio (NPR) values of 2 and 5 with nozzle to plate distance (x / D) of 5, at different swirl numbers. The swirl flows are generated using co-axial curved blades and the results were compared with non-swirl or free jets. The vane angles considered here are 20°, 40°, 60° and the swirl numbers ranged from 0 to 1.31. At NPR 2, the weak swirl number of 0.27 reduced the OASPL level by around 7 dB compared to non-swirl jets. The non-swirl jet emitted impinging tones at NPR 5 and the swirl jet eliminated the impinging tones. At a high swirl number of 1.31, at NPR 5, OASPL is lowered by around 12 dB compared to non-swirl jets. The flow visualization study shows that the swirl disintegrates the repeated shocks and reduces the length of the shock cell system.