Reduction of Jet Impingement Noise by Addition of Swirl

Experimental investigations are carried out with an objective of reducing impingement jet noise using coaxial swirl jets. Two nozzle-to-plate distances have been considered and the Mach number values ranged from 0.95 to 1.83. The vane angles of the coaxial swirlers ranged from 0 deg to 60 deg, corresponding to swirl numbers that ranged from weak to high. Flow visualization has also been conducted to understand the shock-cell structure for each case. The results indicate that swirl jets are highly efficient in the control of impingement noise. Transonic, screech, and impinging tones are completely eliminated by the swirl jets. A weak swirl seems efficient for lower Mach numbers while higher amounts of swirl are efficient at higher Mach numbers.