Full-field simulation for sonic boom cutoff phenomena

Abstract

This study describes an application of full-field, direct simulation in the entire domain involving the near-field around an aircraft, the far-field toward the ground, and the caustic region as an approach to investigate sonic boom cutoff phenomena. A flow field around an axi-symmetric paraboloid has been analyzed by solving three-dimensional (3D) Euler equations with a gravity term for considering atmospheric stratification with altitude. A solution-adapted grid is constructed to align the grid lines with front and rear shock-wave surfaces. The flight is assumed to have a speed of Mach 1.1 at an altitude of 10 km. This study presents the world's first successful numerical simulation for a 3D structure of cutoff phenomena. The results show that the incoming wave generated from the paraboloid is divided into an outgoing wave in the upward direction and an evanescent wave in the downward direction at the cutoff altitude by the diffraction effect. In the cutoff region, the sonic boom reaches the peak intensity by focusing the rays. The evanescent wave under the cutoff region is reduced rapidly. Moreover, the shape of the cutoff surface is obtained for sonic and lateral cutoffs.