Numerical and Mesh Resolution Requirements for Accurate Sonic Boom Prediction

Abstract

A careful study is conducted to assess the numerical mesh resolution requirements for the accurate computation of sonic boom ground signatures produced by complete aircraft configurations. The details of the ground signature can depend heavily on the accurate prediction of the pressure distribution in the near field of the aircraft. It is, therefore, important to accurately describe the geometric details of complete configurations (including the wing, fuselage, nacelles, diverters, etc.) and to precisely capture the propagation of shock and expansion waves at large distances from the aircraft. Unstructured, adaptive mesh technologies are ideally suited for this purpose as they use mesh points only in the appropriate locations within the flowfield. In this work, we consider a supersonic business jet configuration that was tested at the NASA Langley Research Center. Near-field data were measured at several locations underneath the flight track. The propagation of these near-field signatures from different altitudes can be shown to result in near N-wave ground booms. To examine the effect of both nacelles and empennage, results for three test cases are presented. These test cases represent the complete configuration, the configuration without the nacelles, and the configuration without the nacelles and empennage. Inviscid solution-adaptive unstructured meshes with up to 7.2 million nodes and 42.1 million tetrahedra are used to calculate the pressure distributions at several locations below each configuration where comparisons with experimental data are performed. All near-field pressure distributions are propagated to the ground (from an altitude of 50,000 ft) to predict the ground boom and the perceived noise level of the ground signature. Both the near-field overpressures and ground boom signatures are compared between experimental data and computational fluid dynamics simulation, and the results show good agreement in all cases. The minimum number of mesh nodes and elements and the levels of refinement needed for the accurate computations of near-field pressure distribution and ground boom signature are discussed for each of the three cases.