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JET-NOISE CONTROL BY FLUIDIC INJECTION FROM A ROTATING PLUG: LINEAR AND NON-LINEAR SOUND SOURCE MECHANISMS

M. Koenig
Acoustics Department SNECMA, SAFRAN Group Moissy-Cramayel, FRANCE

Andre V. G. Cavalieri
Institut Pprime CNRS - Universite de Poitiers - ENSMA 43, Route de I'Aerodrome 86036 POITIERS CEDEX, France; Laboratorio de Engenharia Aeronautica Instituto Tecnologico de Aeronautica Sao Jose dos Campos, SP, BRAZIL

Peter Jordan
Department of Fluid, Thermal and Combustion Sciences Pprime Institute, CNRS-Universite de Poitiers, ISAE-ENSMA 43 rue de I'Aerodrome, F-86036 Poitiers CEDEX, France

Yves Gervais
Département Fluides, Thermique et Combustion Institut Pprime CEAT, Poitiers, FRANCE

Résumé

We present a study of subsonic jets, controlled by means of a novel actuator that introduces perturbations via steady fluidic actuation from a rotating centerbody (Koenig et al. (2011a)). Preliminary results obtained with this kind of actuator were presented during AIAA conference in Portland in 2011 (Koenig et al. (2011b)). Louder and quieter jets are produced, and these are analysed using time-resolved, stereoscopic particle image velocimetry and a hot-wire anemometer. We place the analysis in the framework of wavepackets and linear stability theory, whence we show that the quieter flows can be understood to result from a mean-flow deformation that attenuates wavepacket growth rates. The mean-flow deformation is shown, by a triple decomposition, to be due to the generation of Reynolds stresses associated with incoherent turbulence (rather than coherent structures) which arises when the actuation energises the flow with a frequency−azimuthal wavenumber (ω − m) combination to which the mean flow is stable. When the actuation energises the flow with an ω − m combination to which the mean flow is unstable, the response is dominated by coherent structures, whose rapid growth takes them beyond the linear limit where they undergo quadratic wave interactions and, consequently, a louder flow.