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SUMMARY:Jet noise modelling - Mohammed Afsar (Engineering\, Cambridge)
DTSTART:20090216T130000Z
DTEND:20090216T140000Z
UID:TALK16276@talks.cam.ac.uk
CONTACT:Dr Ed Brambley
DESCRIPTION:In this presentation it is shown how very accurate jet noise p
 redictions can be made using an acoustic analogy. The analogy is based on 
 a form of the linearized Navier Stokes equations derived by Goldstein (200
 2)\, and it is used to analyze the sound pressure of a non-heated jet flow
 . A unified approach to jet noise modeling is developed and it is shown ho
 w the jet noise spectrum can be thought of as being composed of two terms\
 , one that accounts for the high frequency noise\, and another term that r
 epresents the peak sound pressure. In this case\, the sound predictions sh
 own are based on a Reynolds averaged Navier Stokes (RANS) calculation of t
 he Stromberg jet\, which has a Reynolds number (Re) of 3600 and Mach numbe
 r (M) of 0.9. Although the jet noise predictions are reasonable\, they req
 uire some empirical tuning of the turbulence properties.\n\nThe jet noise 
 model is extended and it is shown that very accurate noise predictions can
  be made without having any empirical tuning. The turbulence properties ar
 e now found by directly post processing a Large Eddy Simulation (LES) of t
 he jet flow and in this particular case a high Reynolds number jet\, where
  Re = 10^6 and M = 0.75\, is analyzed. It is shown how the LES-based turbu
 lence properties are in good agreement with the data from experiment\, for
  the fourth-order longitudinal correlation function. The final optimized j
 et noise model gives very accurate predictions across the spectrum for var
 ious observation locations\, at 900\, and closer to the jet axis where the
  peak noise occurs.  
LOCATION:MR15\, CMS
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