Theory and modelling of jet noise

• Main Author: Afsar, M. L.
• Published: University of Cambridge 2009
• Subjects: 629.13
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595370

We present a unified analysis of the jet noise problem for non-heated subsonic jet flows using an acoustic analogy approach. The solution is formulated using the Navier Stokes equations; and we manipulate the equations to show how the pressure fluctuations in the far field can be expressed in terms of the turbulence properties within the jet flow. Our analysis confirms that the jet noise spectrum can be understood by two terms within an integral formula for the sound pressure. One of these terms dominates the overall sound pressure when the observation angle is perpendicular to the jet flow. The second term, on the other hand, is most significant at low frequencies, and especially dominant at small observation angles, closer to the jet axis. This second term corresponds to the peak sound pressure of the jet flow and was found in previous mathematical studies as well. By defining the jet flow properties using a Reynolds averaged Navier Stokes (RANS) computational solution we show accurate jet noise predictions are possible that only require a modicum of empirical tuning. Finally, we develop a ‘hybrid approach’ and show how the data from a large eddy simulation (LES) can be used to design a mathematical model that avoids any need for empirical tuning. The jet noise predictions using the LES-based model are very close to experiment, at various observation positions.