Experiments with rectangular supersonic jets with potential noise reduction technology

This paper describes the aeroacoustics experiments conducted with supersonic jets, exhausting from rectangular nozzles with an aspect ratio of 2, to examine the jet noise reduction by two different methods. The first method involves the use of fluid inserts, which are produced by distributed air blowing into the diverging section of a convergent-divergent exhaust nozzle. The second method involves the integration of fluid shields in dual flow rectangular jets. In the dual flow nozzle, a single shield below the exit is augmented with fluid shields extending on both sides of the rectangular jet. The purpose of the extended bypass flow is to reduce the noise radiated to the sides of a jet aircraft. In addition to the nozzles with the two noise reduction configurations, acoustic measurements are performed with a single flow rectangular jet, referred to as the baseline. In all cases, the jets are operated as overexpanded, shock-containing jets. In some cases, the jets are operated with the core flow mixtures of helium and air to simulate high temperature jets. The far-field noise measurements are performed on an arc with the microphones approximately 70 equivalent nozzle diameters from the nozzle exit. For the purposes of assessing the noise reduction capability of the dual stream jet, comparisons are made with a baseline rectangular jet on an equal thrust per unit exit area basis. The nondimensional acoustic spectra and overall sound pressure level directivities are shown and compared.