Modeling of Broadband Moving Sources for Time-Domain Simulations of Outdoor Sound Propagation

Abstract

Although time-domain solutions of the linearized Euler equations are well adapted to study the acoustic propagation in an outdoor environment, the modeling of sources in motion in time-domain solvers has not been investigated in the literature yet. This is done here by considering distributed volume sources. First, the influence of the spatial distribution of the source on the acoustic field is analyzed. Results obtained for a nonmoving source are summarized, and the example of a Gaussian spatial distribution is presented. The case of a harmonic volume source moving at a constant speed is then investigated in the geometrical far field. The directivity of a noncompact source is shown to be dramatically different from that of a point source. Numerical simulations are performed in a three-dimensional geometry in free-field configurations, and waveforms of the acoustic pressure exhibit Doppler shift and convective amplification. Finally, simulations of a broadband moving source above an impedance ground surface are presented. For a rigid ground, strong destructive and constructive interferences are observed. The numerical solution is in a very good agreement with an analytical solution. For finite-impedance surfaces, interferences are smoothed, and the acoustic pressure strongly depends on the impedance model. A low-frequency contribution is observed close to the ground in accordance with the ground characteristics.