Pipe jet noise reduction using co-axial swirl pipe

Abstract

The present experimental work highlights the acoustic far field and flow field characteristics of confined co-axial swirling pipe jets. Co-axial confinements with six vanes at angles of 0°, 20° and 40° are considered here. Two pipe lengths of L/D=0.5 and 2 are studied. The Mach numbers studied range from 0.85 to 1.83. An increase in the pipe length causes suppression of the transonic tones in non-swirl pipe jets. Swirl reduces the low frequency noise components and increases the high-frequency components compared to non-swirl jet. The broadband shock associated noise is mitigated by the swirl pipe jets. However, the screech tone is completely eliminated by the swirl pipe jets. Further, swirl pipe jets radiate low levels of noise at all the emission angles compared to non-swirl pipe jets, for both the pipe length cases at supersonic Mach numbers. Increase in the pipe length enhances the shock associated noise and OASPL for the non-swirl pipe jet. Centreline pitot survey and schlieren visualisation show a reduction in core length, reduction in the number of shock cells, weakening/destruction of the shock cells by the swirl pipe jets compared to the non-swirl pipe jets.

Effects of Porous Parameters on the Aerodynamic Noise of the Blowing Device of Guardrails

“…Anyoji and Tabaru (2017) investigated the characteristics of transonic resonance and tones using a circular C-D nozzle and evaluated the effects of the boundary layer trip using a tripping wire. Balakrishnan and Srinivasan (2017) In previous studies, the researchers focused on the characteristic analysis of the flow field and sound field and the research on the noise reduction mechanism for round or square nozzles. This type of nozzle has a simple structure, and the position of the object to be blown off is fixed, or the ejected gas is directly discharged into the atmosphere.…”