Comparative analysis of acoustic and flow characteristics in co-axial flat and curved vane swirl jets

The investigation of jet noise behaviour and mitigation using co-axial vane swirl jet configurations addresses crucial aeroacoustic challenges in balancing noise reduction with improved mixing. The comparative performance of flat versus curved vane swirl geometries remains underexplored across different nozzle pressure ratios (NPRs), necessitating a systematic investigation. This experimental study employed far-field acoustic measurements, schlieren flow visualization, and centerline pitot pressure analysis for flat and curved vane swirl jets at vane angles of 20°, 40°, 50°, and 60° (swirl numbers 0-1.31) across NPRs of 2, 4, and 6. At low NPR of 2, SCV20 achieved 4–5 dB noise reduction, while at higher NPRs of 4 and 6, SFV50 demonstrated higher performance with 11–15 dB reductions and up to 16 dB at upstream angles. Swirl jets eliminated screech tones and significantly reduced BSAN, shortening shock cell lengths from x/D = 9 to x/D = 4, with flat vanes consistently surpassing curved vanes in reducing shock structures and enhancing centerline decay, though incurring 15%–25% momentum deficits. These findings provide optimization guidelines for swirl jet designs in propulsion, combustion, and mixing systems. Future research should explore hot jets, thrust impacts, and hybrid swirl methods.