Numerical Simulation of Multiple Reflections and Diffractions of Sonic Boom Around Buildings

Abstract

Sonic boom prediction around buildings has previously been conducted under the assumption of linear wave propagation. In this work, a more detailed analysis considering the nonlinear effect is achieved by means of computational fluid dynamics (CFD). The two-dimensional Euler equations are solved by employing a level set method for tracking a moving supersonic body, a ghost fluid method for applying the immersed boundary condition at the surface of the body, and an adaptive mesh refinement method. Simulations are made under the frame of reference of a flight object moving at Mach 1.6. Incident waves are composed of a single oblique shock wave, as well as N, flat-top, and ramp waves. The computational results clarify the complex flow behaviors around a building, involving the incident, reflected, and diffracted waves. At the bottom-front edge of a building, the waveform behind the shock waves is spiked, and the pressure rise is amplified due to double reflections. The diffracted waves are repeatedly reflected at the top corners of a building, resulting in amplification of the perceived level over a wide range. The results of this work demonstrate that CFD can provide more detailed information compared to previous approaches and can be deployed for practical applications.