Numerical analysis of Sonic Boom Noise Based on Aerological Observation Data Under the Mach Cutoff Condition

In this paper, two-dimensional linear sound wave analysis method in the stratified atmosphere with temperature gradient and velocity disturbance is numerically applied to the analysis and prediction of sonic boom noise propagating below the caustic generated under the Mach cutoff condition. The compact-explicit finite difference-time domain method is applied to the two-dimensional linear sound wave propagation. Since Mach cutoff noise is greatly affected by the sound speed gradient in the atmosphere, the real altitude distribution of sound speed and density from the aerological observation data is used in the calculation. Some numerical experiments are carried out. As a result, it is shown that a disturbance wave with a larger amplitude than the evanescent wave may be transmitted to the ground due to the velocity disturbance on the propagation path. It can be inferred that the essence of Mach cutoff noise is that a strong sonic boom above the caustic is scattered and diffracted by atmospheric turbulence comparable to the boom wavelength. It is also shown that the Mach cutoff noise varies greatly depending on the season.