Sound Propagation from a Supersonic Jet Flowing through a Rigid-walled Duct with a J-Deflector

An experimental study is performed on the acoustical characteristics of a scale-model, perfectly expanded, cold supersonic jet of gaseous nitrogen (Mach 2.5, nozzle exit diameter of 1 inch) flowing through a rigid-walled duct having an upstream J-deflector. The nozzle is mounted vertically, with the nozzle exit plane at a height of 73 jet diameters above ground level. Relative to the nozzle exit plane, the location of the duct inlet is varied at 10, 5, and -1 jet diameters. Far-field sound pressure levels were obtained at 2 levels (54 jet diameters and 10 jet diameters above ground) with the aid of 9 acoustic sensors equally spaced around a circular arc of radius equal to 80 jet diameters. Comparisons of the acoustic field were made with and without the duct.