Numerical and Mesh Resolution Requirements for accurate Sonic Boom Prediction

A careful study is conducted to assess the numerical mesh resolution requirements for the accurate computation ofsonic boom ground signatures produced by complete aircraft configurations. The details of the ground signature candepend 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 distancesfrom the aircraft. Unstructured, adaptive mesh technologies are ideally suited for this purpose as they use meshpoints only in the appropriate locations within the flowfield. In this work, we consider a supersonic business jetconfiguration that was tested at the NASA Langley Research Center. Near-field data were measured at severallocations underneath the flight track. The propagation of these near-field signatures from different altitudes can beshown to result in near N-wave ground booms. To examine the effect of both nacelles and empennage, results forthree test cases are presented. These test cases represent the complete configuration, the configuration without thenacelles, and the configuration without the nacelles and empennage. Inviscid solution-adaptive unstructured mesheswith up to 7.2 million nodes and 42.1 million tetrahedra are used to calculate the pressure distributions at severallocations below each configuration where comparisons with experimental data are performed. All near-fieldpressure distributions are propagated to the ground (from an altitude of 50,000 ft) to predict the ground boom andthe perceived noise level of the ground signature. Both the near-field overpressures and ground boom signatures arecompared between experimental data and computational fluid dynamics simulation, and the results show goodagreement in all cases. The minimum number of mesh nodes and elements and the levels of refinement needed for theaccurate computations of near-field pressure distribution and ground boom signature are discussed for each of thethree cases.