Acoustic and flow characteristics of cold high-speed coaxial jets

Far-field noise of model coaxial supersonic cold jets exhausting from a coplanar convergent two-nozzle coaxial configuration was investigated. The pressure ratio (velocity) of the outer annular jet was maintained higher than the inner round jet. For each outer jet pressure ratio, the inner jet operating pressure ratio for the 'minimum' radiated noise was established. Experimental results on the noise reductions and the modifications of the shock structure and velocity distribution of coaxial flows at the 'minimum' noise conditions are presented and are compared with those of a single convergent underexpanded round as well as an annular jet at a wide range of operating pressure ratios.