An extension of the geometrical-acoustic model near a caustic with application to off-track sonic boom focusing

Abstract

A focused sonic boom or “superboom” is caused by the convergence of acoustic energy generated by a passing supersonic aircraft; this occurs along a surface known as a caustic. The term “superboom” is fitting, as the resulting ground pressure signature is invariably louder than any other boom event associated with the given aircraft configuration. Unfortunately, when an aircraft accelerates to supersonic speeds, boom focusing is unavoidable. Although previous research has modeled the focus boom expected under the flight track, relatively little is known about noise experienced away from the flight track. The most popular model for sonic boom focusing, the lossy nonlinear Tricomi equation (LNTE), breaks down when an observer is not directly undertrack. This presentation will recount recent work aimed at augmenting the LNTE model such that it remains accurate over the lateral extent of the boom carpet during focusing. Emphasis will be placed on the extension of the geometrical-acoustic approximation used above the boundary layer of the caustic via analysis of new expressions resulting from the addition of the off-track component to the problem. [This material was based upon work supported by the National Aeronautics and Space Administration under Grant No. 80NSSC19K1684 issued through the NASA Fellowship Activity.]