Séminaire de Mécanique d'Orsay
Jeudi 17 février à 14h au LIMSI
Coherent structures in jet noise: the sound producing flow skeleton?
Peter Jordan
PPRIME
 

The talk will overview our recent attempts to identify and model the salient features of the turbulent jet understood as a source of sound. The work described is essentially an exercise in system reduction via physical analysis: our departure point is information from full Navier-Stokes solutions, obtained both experimentally and numerically; our objective is the construction of simplified kinematical and dynamical models for the guidance and eventual design of closed-loop control strategies. Experimental and numerical databases are generated and mined using a suite of analysis tools, including stochastic estimation, wavelet transforms and flow visualisation, and by way of which we endeavour to discern that subspace of the high Reynolds number jet which drives the sound field. A special emphasis is placed on space- and time-local analyses and the importance of intermittent phenomena is bourne out both in the analysis and the modelling. We show, in particular, how the unsteady 'jittering' of coherent structures, modelled as wavepackets, may underpin generation of the most energetic sound pressure fluctuations observed in the farfield. Key results include: an explanation of the noise-suppression physics associated with an adjoint-based optimal control study; a wavelet-based characterisation of jet noise; and a hierarchy of analytical, jittering wavepacket models which help understand the role played by intermittent phenomena in the generation of jet noise.