Jet Noise Simulations for Complex Nozzle Geometries

Abstract

The jet flow from a complex engine nozzle system with multiple jet streams is computed using large eddy simulations. The effects of the fan flow, the impact of installation effects created by the addition of a pylon, and the influence of the core-fluidic injection on the resulting flow field and the acoustic radiation are studied. The potential core length reduces slightly with the introduction of the fan flow and further reduces with the introduction of the fluidic injection nozzle geometry. Computations of fluidic-injection nozzle configurations are validated with experimental data. The agreement in the farfield spectra along the sideline and in the peak propagation directions is good for both the baseline nozzle and the fluidic-injection nozzle configurations. The centerline velocity and the turbulent kinetic energy distribution along the nozzle symmetry plane are in good agreement with the experiments. The parametric study varying the pressure ratio shows that as the injection pressure ratio is increased the jet core moves towards the pylon. For a fluidic injection pressure ratio of 4.0, a reduction of 2.0dB - 2.5dB is observed with respect to the baseline nozzle with a pylon. Fluidic injection is found to produce two sets of counter rotating vortices, one along the nozzle lip line and the second penetrating the nozzle core flow. The potential reason for the noise reduction is investigated from the changes in the turbulence intensity and the convective velocity in the shear layer. It is shown that the turbulence intensity is reduced and the convective velocity at the end of the potential core remains nearly constant for all injection pressure ratios studied.