A semi-adapted space marching method for fast sonic boom prediction

Abstract

This study describes an explicit space marching method that utilises semi-adapted structured grids, enabling fast simulation of near- to mid-field sonic boom propagation. Grid topology is restricted for space marching, and shock-fitted grids have not been applicable to the analysis of complex flow behaviours. In this work, we develop an automatic semi-adapted grid generation method considering the constraints related to space marching. The three-dimensional Euler equations are solved by employing an explicit space marching method that leverages semi-adapted grids over a radial distance 10 times the length of an aircraft. For enhancing the simulation efficiency, the computational domain is moved radially according to the locations of shock waves. The computational accuracy is investigated via the analysis of the C608 low-boom demonstrator used in the third American Institute of Aeronautics and Astronautics (AIAA) sonic boom prediction workshop. The results show that the shock-wave resolution is significantly enhanced using semi-adapted grids. The obtained waveforms agree well with those presented in the workshop. The azimuthal dependence of sonic boom signatures is compared by conducting three-dimensional simulation that utilises the space marching method and multipole analysis that utilises the small perturbation theory. Each of the grid generation and the simulation on a standard laptop takes only a minute, which is at least 30 times faster than the previous simulation methods without grid adaptation. These results demonstrate that the developed simulation method enables fast and accurate sonic boom prediction that is effective for parametric studies used in low-boom aircraft designs.