In this paper, a method to determine the jet noise source input for shielding calculations is described. The method involves three steps – localisation, propagation and simplification. Firstly, for the frequency of interest, a small, localised source region is determined, using Goldstein-Rosenbaums’ acoustic model, with a numerical RANS solution providing local flow properties. A number of distinct incoherent noise sources may be located in this region, using the turbulence length scales. In the second step, each source is propagated out through the jet flow using the wave expansion method (WEM) to solve the Helmholtz equation, with local Mach values acquired from the RANS solution. The third step is to define a Kirchhoff surface outside the jet flow, from which, the sound may be propagated further by simply using the Helmholtz-Kirchhoff integral equation, which, can account for any mean flow present. This method is relatively robust, as it is a shielding factor or ratio, rather than an absolute value, which is of interest in acoustic design evaluation. Preliminary results, presented in this paper, provide encouragement that this new three-step jet noise source modelling method can be used to provide a source input for use in airframe shielding calculations, that is equivalent – in terms of source frequency, distribution and directivity – to the noise produced by a jet flow.
8th International Symposium Transport Noise and Vibration, 4 - 6 juni 2006, St. Petersburg, Russia