NUMERICAL INVESTIGATION OF NOISE OF A HIGH SUBSONIC TURBULENT JET

To meet the regulations of aviation noise, noise control of jet engine has grown to become a major issue in aeroacoustics, therefore prediction of jet noise and unfolding its generation mechanism would lay a solid foundation for the noise control. Turbulence evolution and noise of a Mach 0.9 high subsonic jet are investigated by high-order accurate parallel LES (large eddy simulation). Firstly, the fidelity of turbulence result computed by LES is rigorously verified, and the evolution of multi-scale vortex structures is carefully analyzed. Secondly, based on the acoustic source in near field of the jet, the penetrable FW-H (Ffowcs Williams and Hawkings) wave extrapolation method is used to solve the farfield acoustic and analyze the behavior of the dominant modes. Finally, via analyzing mechanism of acoustic source and separating the acoustic modes, the role of the large-scale coherent vortex evolution in the end of potential core play in dominant acoustic modes generation as a form of low wave number wavepackets is investigated. Numerical results show that LES combined with the penetrable FW-H method is able to accurately predict the flow and acoustic features of the high subsonic jet. Furthermore, numerical analysis reveals that the large-scale coherent structure generated by the vortex ring pairing is merging along the jet centerline, which producing the primary acoustic modes dominated at the low azimuth direction and forming a superdirective acoustic field. The azimuth angle of the peak intensity is near to 30°.