Aeroacoustics of Twin Supersonic Jets: A Review

Interaction of twin supersonic jets can dramatically alter the dynamic pressures in the near-field and cause fatigue of aircraft structures. This review paper focuses on the twin jet coupling situation that is rich in fluid flow physics, requires sophisticated analysis tools and is of relevance to aircraft with closely spaced engines and other industrial situations involving multiple jet flows. The review consists of four sections: (i) a historical survey of twin jet exhaust coupling, (ii) rectangular twin jets with both spanwise uniform and non-uniform geometry, (iii) a description of multi-modes and mode jumps using higher order spectral analysis, and (iv) the suppression of twin jet coupling. The parameters that affect twin jet coupling include nozzle geometry, internozzle spacing and nozzle operating conditions. Certain modes of resonant coupling increase the dynamic pressures drastically in the inter-nozzle region, whereas other coupling modes can suppress unsteady pressure levels. Since coupled resonances can cause fatigue failure of components, mitigation approaches need to be considered. Successful techniques include nozzle inserts, beveled nozzles, water injection, and miniature pins and cavities.