Large eddy simulation and noise prediction of turbulent swirling jets

Large eddy simulations of noise radiation from a Mach 0.9 non-swirling jet and two Mach 0.9 swirling jets with swirl ratios 0.2 and 0.4, respectively, are conducted on a com- putational domain including both the aerodynamic near-field and a portion of the acoustic far-field. For comparison purposes, Kirchhoff's method is also used to predict the far-field sound. The dynamic Smagorinsky model is used for subgrid-scale stresses. A sixth-order compact finite-difference scheme is used to discretize axial and radial spatial derivatives and a Fourier spectral method is used to discretize azimuthal spatial derivatives in the gov- erning equations. A standard explicit fourth-order Runge-Kutta scheme is used for time advancement. An eighth-order tri-diagonal filter is used to damp high-frequency spurious waves. Nonreflecting characteristic boundary conditions are used with inflow and outflow buffer zones to damp acoustic reflections at the boundaries. The predicted near-field flow statistics and far-field sound of the Mach 0.9 non-swirling jet are in good agreement with experimental data, except that the high-frequency portion of the noise spectra is much lower than experimental data. The predicted near-field flow statistics for the SR = 0.2 swirling jet are also in good agreement with available experimental data. For the two swirling jets with swirl ratios 0.2 and 0.4, the predicted results show that swirl increases the high-frequency components of the noise and increases the OASPL at high angles. This agrees with previous experimental and numerical studies. The increase of low-frequency components of the noise does not agree with some previous studies and needs to be further investigated.