This paper describes a methodology for the direct calculation of noise from realistic nozzle geometries. The focus of the paper is on the numerical approach to this problem to provide noise predictions to engineering accuracy in an efficient manner. In addition, issues related to grid generation are discussed. The methodology uses structured multiblock grids. The block surrounding the jet centerline has a Cartesian form and the surrounding grid blocks have a cylindrical polar form - at least for nearly axisymmetric jet nozzle geometries. Appropriate block interface conditions are used. In the case of military style jet nozzles the nozzles are not smooth in the azimuthal direction but have facets representative of the movable flaps in such variable area nozzles. These features must be included in the grid. To enable efficient calculations, in addition to parallel computation, a dual time-stepping approach is used. The sub-iterations in the fictitious time are accelerated using a two-level multigrid approach. A Detached Eddy Simulation (DES) approach based on the Spalart-Allmaras (S-A) one-equation turbulence model is used. Comparisons are made between flow predictions using the DES with the S-A model everywhere and with the turbulence model turned off in the jet external flow. Noise predictions are made with the permeable surface Ffowcs Williams - Hawkings (FW-H) solution. Noise predictions are presented for both a smooth convergent-divergent nozzle as well as a nozzle representative of a military aircraft engine. Comparisons are made with available experimental data.
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