Controlling Sonic Boom Loudness Through Outer Mold Line Modification: A Sensitivity Study
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2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This paper presents a sensitivity and uncertainty analysis of the under-track loudness for a low-boom concept aircraft that has been modified to include small-scale surface deformations placed along the centerline of the aircrafts underside. The small-scale surface deformations, or bumps, were defined using a one-dimensional Gaussian function and inverse distance weighting interpolation. The near-field solution of the low-boom concept aircraft was predicted by the in-house CFD solver UNS3D. Sonic boom propagation and loudness calculations were done by the NASA codes sBOOM and LCASB. The predicted near-field solution and loudness of the baseline aircraft geometry were found to be in excellent agreement with previously published CFD predictions of the same geometry. A surrogate model, based on radial basis functions, of the PLdB loudness metric was created with respect to the height and length of the bumps to perform the sensitivity and uncertainty analysis based on the discreet CFD data. It was found that the aircraft was relatively insensitive to bumps with a height less than 2 cm, and most sensitive to bumps with heights equal to or greater than 3 cm. The location and amplitude of the region of largest sensitivity was found to vary with respect to the length of the bump. Uncertainties in the bump lengths and height were introduced into the problem formulation and propagated using Monte Carlo sampling. The impact of the uncertainty in only bump height, only bump length, and in both bump length and height on the uncertainty of the loudness was examined. It was found that, by itself, the uncertainty in the height of the bump resulted in higher uncertainties in the loudness than when only considering the uncertainty in the length of the bump. Accounting for the uncertainties in both the length and height of the bump resulted in significantly higher variation of under-track loudness, but with the main source of loudness uncertainty still being related to the uncertainty in the height of the bump.
