Effects of Meteorological Variability on Sonic Boom Propagation from Hypersonic Aircraft

Abstract

A numerical study of primary sonic boom propagation from a hypersonic Mach 6 cruise aircraft is performed, including the effects of nonlinearity, atmospheric absorption and dispersion, and atmospheric stratification. A second-order split-step algorithm alternating between the time domain for nonlinearity and the frequency domain forabsorptionallowsforafasterconvergenceofresultsthanconventional first-orderalgorithms.Dailyvariabilityof meteorological parameters is used to investigate the variability of sonic boom shock overpressure, rise time, and carpet width over the span of a year. Two locations are chosen based on their difference in climates, especially humidity, and two flight directions are considered. It is found that sonic boom rise time is especially susceptible to variability in humidity, whereas shock overpressure and carpet width are most sensitive to winds. A statistical analysis and comparison between hypersonic and supersonic aircraft configurations reveal that all sonic boom characteristics are highly dependent on the aircraft and flight conditions, so that generalizations of statistics cannot be made. simulated for lower Mach numbers than what is being considered in the present study. This paper investigates the sonic boom ground impact for an aircraft flying at Mach 6 cruise at a 28 km altitude. Sonic boom impactisestimatedintermsofthepeakoverpressureattheverticalof the flight track, the front shock rise time, and the lateral extent of the geometricalcarpet.The firsttwoparametersprovideanestimationof theloudestboomlikelytoinducemaximumannoyance,andthethird parameter estimates the lateral impact of the boom during the cruise phase. As a sonic boom propagates over long distances, it isstrongly affected by the atmosphere and thus is dependent on meteorology and geographical location. The impact is quantified statistically, based on numerical simulations using an extensive meteorological database. A numerical study of primary sonic boom propagation from the Mach 6 aircraft is performed, including the effects of nonlinearity, absorption and dispersion, and stratification. Tests of accurate numerical parameters for varying strengths of nonlinearity and absorptionareperformedtodeterminethemostefficientalternatives. An extended absorption model is adopted that accounts for changes in the atmosphere up to the high flight altitude required by Mach 6 operation. The effects of meteorological variability on sonic boom propagation are investigated by considering the climate at two different geographical locations over the course of a year at a 6 h resolution. Vertical gradients of meteorological parameters at a coastal areawithhighgroundhumidityarejuxtaposedwith thosefor a desert region. Key sonic boom parameters are compared with predictions for other aircraft configurations at Mach 1.6 and with a previous study for a Mach 2 aircraft (9). Section II presents the meteorological data. In the following Sec. III, an extended absorption model is presented to take into account the high flight altitudes (about 30 km) for the Mach 6 case. Modifications to include high-altitude sound absorption in the sonic boom code are briefly presented. A brief explanation of the theory behind the sonic boom algorithm is outlined in Sec. IV, and Sec. V presents the specific parameters used in the simulations. Sonic boom predictions at the ground level are synthesized and compared with other cases and previous studies in Sec. VI.