1 ver 1.05 FLOW STRUCTURE of SUPERSONIC JETS from

This paper examines the flow structures emanating from convergent-divergent nozzles with conical sections like those used in practical high-speed propulsion applications. LES simulations and experimental measurements in the form of PIV and shadowgraph imaging and far-field acoustic measurement are employed. The development of the supersonic jets from these nozzles are examined in underexpanded, perfectly expanded and overexpanded conditions. It is found that in addition to the shock diamond features expected of smoothly contoured nozzles at off-design conditions, these nozzles produce a second set of shock diamonds anchored at the nozzle throat and overlaid on the shock diamonds shed from the nozzle lip. These together form a double-diamond appearance. These nozzles do not exhibit any shock-free condition at or near the expected design condition. As a consequence, there is no absence of shock noise at or near the design condition. Near the design condition there is a diminution in the intensity of the screech tone, but no diminution in the broad-band shock-associated noise. These nozzles produce shock cells 9%-25 % shorter than cells from a comparable smoothly contoured nozzle. Nomenclature a speed of sound Ae Nozzle exit area A * Nozzle throat are