Sonic boom near-field predictions and its impact on the accuracy of ground signature predictions

Abstract

The widely adopted sonic boom prediction process contains two steps: the near-field signature prediction from a 3D supersonic flow solver, and the ground signature prediction from a quasi-one-dimensional far-field propagation model following the acoustic ray path. The far-field propagation prediction has to start at a near-field distance sufficiently far away from the airplane flight path to ensure accuracy from the quasi-one-dimensional model. A recent study indicates that the widely adopted practice of using 2-3 body length from the flight path is not sufficient for all airplane configurations. Using a larger near-field distance, however, creates a serious challenge to the CFD based near-field prediction method which will suffer with either degradation in solution accuracy or sharp increase in computational cost, or both. A newly developed space marching approach for high fidelity and high efficiency near-field prediction is revisited here. It is capable of providing high accuracy solution at large near-field distance with a small fraction of computational cost required by conventional CFD solvers. It is applied here to study the sensitivity of the ground signatures to the near-field signature distance for a notional low sonic boom airplane configuration to find the optimal near-field signature distance.