| Noise generated by a turbofan engine has both tonal and broadband noise components. It is shown in this thesis that a computationally efficient method for tonal noise can be applied for broadband noise as well. In the thesis, both types of noise are studied using linearized three-dimensional Euler equations model. First, a numerical method for tonal noise calculation is formulated using a high accuracy implicit scheme for the spatial derivatives and the assumption that the flow variables depend on time in a periodic fashion. The system of equations is then solved in frequency domain using time-marching technique. The high accuracy approximation allows to reduce the number of grid points while, due to factoring out of the time variable, grid-dependent time step can be used. In order to verify the method, comparison with existing codes is made for a number of geometries. Several acceleration techniques are tested, including parallel computing, grid clustering, and multigrid.; Second, for an annular cascade with zero blade loading the results show that the mean flow swirl changes the physics of scattering in three major ways: (i) it modifies the number of acoustic modes in the duct, (ii) it changes their duct radial profile, and (iii) it causes significant amplitude and radial phase variations of the incident disturbances. The method is also applied toward loaded cascades and the results indicate significant effect of thickness at high frequency for cases of non-zero stagger and camber.; Finally, a three-dimensional model is presented for fan broadband interaction noise based on spectral representation of the impinging upstream turbulence and a multiple scale analysis for the evolution of turbulence in a nonuniform swirling flow. Comparison of the radiated noise spectra for three-dimensional and two-dimensional cascades is presented. |
