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Jet noise modelling

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In this presentation it is shown how very accurate jet noise predictions can be made using an acoustic analogy. The analogy is based on a form of the linearized Navier Stokes equations derived by Goldstein (2002), 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 how 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 represents the peak sound pressure observed at small angles. In this case, the 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 properties. The 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 are now found by directly post processing a Large Eddy Simulation (LES) of the jet flow and in this particular case a high Reynolds number jet, where Re = 106 and M = 0.75, is analyzed. It is shown how 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 the jet axis where the peak noise occurs.

This talk is part of the Engineering Department Acoustics/Combustion Student seminars series.

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