Euler/experiment correlations of sonic boom pressure signatures

The ability of inviscid computational fluid dynamics (CFD) codes to compute sonic boom pressure signatures is examined using three different codes that solve the Euler equations of fluid flow on structured hexahedral and unstructured tetrahedral grids. The results of these Euler codes were evaluated by comparing the computed pressure signatures with near-field experimental data. The computational pressure signatures were determined at distances of one body length or less below the configuration in the plane of symmetry and extrapolated to experimental distances using the waveform parameter method. The extrapolated CFD pressure signatures gave acceptable correlations with experimental data, provided that fine grids were used between the surface and the spatial location of the pressure signature. I. Introduction T HE feasibility of a low-boom supersonic transport is again being investigated. A commercial transport is more efficient when supersonic flight is maintained for the entire cruise portion of the mission. However, sonic boom noise may limit the extent of overland supersonic flight over populated areas. A major research effort has begun to design supersonic transport configurations which exhibit acceptable sonic boom characteristics. As part of the design process, computational methods have been developed for analyzing sonic boom characteristics. Over the past two decades, CFD codes have become capable of computing the flowfield about realistic high-speed civil transport configurations. The simultaneous increase in computational resources is the primary reason that use of these codes has become practical. The use of CFD codes for sonic boom prediction and configuration design offers the potential for making wind-tunnel testing more productive. However, the accuracy of CFD codes for sonic boom prediction needs to be evaluated before application to low-boom design. The use of Euler flow solvers coupled with extrapolation methods for the computation of sonic boom pressure signatures is a new application of CFD. For instance, Siclari and Darden1 applied a supersonic Euler code to two low-boom concepts, designed for Mach 2 and Mach 3. The near-field CFD results were extrapolated for comparison with extrapolated wind-tunnel data, corresponding to aircraft at cruise altitude, on and off ground track. The extrapolation method was similar to the one used in the present report. Also, Page and Plotkin2 calculated the flow about a cone-wing model at Mach 2.01, and extrapolated the near-field pressures on a cylinder around the model for comparison with near-field wind-tunnel data. The approach described below validates the concept of using a planar extrapolation method with an Euler flow solver by comparing extrapolated near-field pressure signatures with experimental data for a range of configurations and flow conditions. The original paper3 contains additional information, particularly about the grid systems which were used.