Noise reduction of circular and non-circular jets surrounded by annular swirl flow

An experimental study of the acoustic far field and flow field of co-axial circular and non-circular jets with the vane angles of 0° and 30° are presented in this paper. Flat vanes are fixed in the annular passage of the coaxial jets, which cause trailing edge vortices and/or swirl flow. The co-axial jets with vane angles of 0° and 30° almost eliminate the transonic tones and screech tones entirely, in contrast to non-swirl jet. The broadband shock associated noise is also mitigated by the co-axial jets, irrespective of the vane angles. The co-axial jets are efficient in overall noise suppression at both subsonic and supersonic conditions. The co-axial jets diminish the low frequency noise and enhance the high frequency noise. Reduction in core length is highest for the co-axial jets compared to the non-swirl jet. The flow visualization study also confirms that the co-axial jets weaken or destroy the shock cells and reduce the number of the shock cells compared to non-swirl jet.