Mean Flow and Acoustics of Dual - Stream Jets

This study examines the connection between the mean ow shape and the acoustic emission of dual-stream jets. The experimental investigation encompassed jets issuing from coaxial, eccentric, and arcuate nozzles, as well as nozzles with de ectors in the secondary stream. The in ection points of the transverse velocity pro le were used to de ne the generalized secondary core (GSC) of the jet. In coaxial and arcuate jets, the length of the GSC roughly equals that of the secondary potential core. In eccentric jets and in jets with de ection of the bypass stream, the GSC is much longer than the secondary potential core. As a result, a long secondary shear layer is formed that reduces the primary convective Mach number throughout the dominant noise source region. The acoustic results indicate that, when the GSC is shorter than the primary potential core, noise reduction is modest, whereas when the GSC is longer than the primary potential core, noise reduction is substantial. The mean ow data were distilled into simple models for the primary and secondary convective Mach number distributions. The jet with de ected secondary ow achieved the lowest average convective Mach number and produced the largest noise reduction.