Numerical simulations of sonic boom propagation over urban areas

Acceptability of supersonic transportation by population requires an accurate prediction of ground noise levels generated by sonic boom. This study aims at predicting sonic boom propagation over urban areas. For this purpose, numerical simulations are performed; the full 2D Euler equations are solved using high-order finite-difference time-domain techniques. First, the case of an isolated building is considered. From a geometrical analysis, two characteristic zones are highlighted: an illumated region in front of the building and a shadow zone at its rear. The sonic boom waveforms at the ground are composed of several arrivals, related to reflection at the building facades and diffraction at the building corners. The evolution of the noise levels is then shown to follow closely the geometrical analysis, with an amplification in the illuminated region and a large reduction in the shadow zone. Second, the case of two identical buildings is investigated. The acoustic field inside the street canyon is examined. In particular, the boom waveforms exhibit low-frequency oscillations, in addition to the geometrical arrivals. They are related to resonant modes of the canyon. Finally, an urban geometry representative of European city centres is considered. The variability of the boom waveforms and the noise levels is shown.