SCREECH TONE NOISE AND MODE SWITCHING IN SUPERSONIC SWIRLING JETS

An experimental study of mode switching phenomena of supersonic jets w ith swirl is reported. A convergent nozzle with four tangential inlets was used. The pressure ratio corresponds to a fully expanded Mach num ber up to 1.80. Schlieren visualization of shock structures and pressu re measurements indicated effects of swirl, such as flow recirculation . Screech tone frequencies and phase information were measured for bot h nonswirling and strongly swirling jets. Results suggest existence of quasiperiodic shock structure in strongly swirling jets in spite of s wirl generated recirculation. However, pressure fields are quite diffe rent between swirling and nonswirling jets. Both helical and toroidal screech tones were found to exist in strongly swirling jets. Strouhal numbers of the swirling jet screech tones are compared with published theory for nonswirling jets.