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SUMMARY:Jet noise modelling - Mohammed Afsar (University of Cambridge)
DTSTART:20081128T120000Z
DTEND:20081128T130000Z
UID:TALK13456@talks.cam.ac.uk
CONTACT:Carlo Quaglia
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 large angle noise\, and another term that repr
 esents the peak sound pressure observed at small angles. In this case\, th
 e sound predictions shown are based on a Reynolds averaged Navier Stokes (
 RANS) calculation of the Stromberg jet\, which has a Reynolds number (Re) 
 of 3600 and Mach number (M) of 0.9. Although the jet noise predictions are
  reasonable\, they require some empirical tuning of the turbulence propert
 ies. \n	The jet noise model is extended and it is shown that very accurate
  noise predictions can be made without having any empirical tuning. The tu
 rbulence properties are now found by directly post processing a Large Eddy
  Simulation (LES) of the jet flow and in this particular case a high Reyno
 lds number jet\, where Re = 106 and M = 0.75\, is analyzed. It is shown ho
 w the LES-based turbulence properties are in good agreement with the data 
 from experiment\, for the fourth-order longitudinal correlation function. 
 The final optimized jet noise model gives very accurate predictions across
  the spectrum for various observation locations\, at 900\, and closer to t
 he jet axis where the peak noise occurs.
LOCATION:Language Unit Meeting Room
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