Tones Encountered with a Coannular Nozzle and a Method for their Suppression

Abstract

With multi-stream coannular nozzles, sometimes tones are generated that make the nozzle fail noise regulation criteria. A two-stream nozzle was studied experimentally in an attempt to identify the sources of such tones and explore remedies. With the given nozzle configuration, sharp tones occurred in a range of low jet Mach numbers (M (sub j)). The tones could be traced to a coupling of vortex shedding from the struts, that hold the nozzles and the center-body together, and various acoustic resonance modes of the ducts. A leading edge treatment of the struts is shown to suppress the vortex shedding and eliminate the tones.