Large eddy simulation and noise prediction of turbulent heated and swirling jets
Abstract
Jet noise is one of the major noise sources of jet-powered aircraft. To improve the understanding of noise generation mechanisms in turbulent jets and hence reduce the noise, innovative methods are needed for noise prediction. Large eddy simulation and noise prediction of several turbulent jets are conducted on a computational domain including both the aerodynamic near-field and a portion of the acoustic far-field. 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 the Fourier spectral method is used to discretize azimuthal spatial derivatives in the governing 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. The predicted near-field flow statistics and far-field sound of a Mach 0.9 cold jet are in good agreement with experimental data, except that the high-frequency portion of the noise spectra is much lower than experimental data. For a Mach 0.9 jet, jet heating is predicted to decrease the high-frequency components and decrease the OASPL at high angles. For a Mach 0.5 jet, jet heating is predicted to increase the OASPL at all angles. These predictions are consistent with previous experimental observations. 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 spectra and increases the OASPL at high angles. This agrees with previous experimental and numerical studies. Further studies are needed to examine some discrepancies between the predictions and experimental data.
Degree
Ph.D.
Advisors
Frankel, Purdue University.
Subject Area
Mechanical engineering
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