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Mach Cutoff Analysis and Results from NASA's Farfield Investigation of No-boom Thresholds

机译：马赫边界分析和美国国家航空航天局无臂阈值远场调查的结果

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In support of the ongoing effort by the National Aeronautics and Space Administration (NASA) to bring supersonic commercial travel to the public, the NASA Armstrong Flight Research Center and the NASA Langley Research Center, in partnership with other industry organizations and academia, conducted a flight research experiment to analyze acoustic propagation in the Mach cutoff shadow zone. The effort was conducted in the fall of 2012 and named the Farfield Investigation of No-boom Thresholds (FaINT). The test helped to build a dataset that will go toward further understanding of the unique acoustic propagation characteristics below Mach cutoff altitude. FaINT was able to correlate sonic boom noise levels measured below cutoff altitude with precise airplane flight conditions, potentially increasing the accuracy over previous studies. A NASA F-18B airplane made supersonic passes such that its Mach cutoff caustic would be at varying distances above a linear 60-microphone, 7375-ft (2247.9 m) long array. A TG-14 motor glider equipped with a microphone on its wing-tip also attempted to capture the same sonic boom waves above ground, but below the Mach cutoff altitude. This paper identified an appropriate metric for sonic boom waveforms in the Mach cutoff shadow zone called Perceived Sound Exposure Level; derived an empirical relationship between Mach cutoff flight conditions and noise levels in the shadow zone; validated a safe cutoff altitude theory presented by previous studies; analyzed the sensitivity of flight below Mach cutoff to unsteady atmospheric conditions and realistic aircraft perturbations; and demonstrated the ability to record sonic boom measurements over 5000 ft (1524.0 m) above ground level, but below Mach cutoff altitude.
机译：为了支持美国国家航空航天局（NASA）正在进行的将超音速商业旅行带给公众的努力，NASA阿姆斯特朗飞行研究中心和NASA Langley研究中心与其他行业组织和学术界合作进行了一次飞行马赫截止阴影区的声传播分析的实验研究。这项工作于2012年秋季进行，并命名为“无爆炸臂阈值远场调查”（FaINT）。该测试有助于建立一个数据集，该数据集将有助于进一步了解Mach截止高度以下的独特声传播特性。 FaINT能够将在截断高度以下测得的声波吊臂噪声水平与精确的飞机飞行条件相关联，从而有可能在以前的研究中提高准确性。一架NASA F-18B飞机进行了超音速通行，因此其马赫数截止苛性碱在线性60麦克风，长7375英尺（2247.9 m）的阵列上方的距离不同。 TG-14电动滑翔机的翼尖装有麦克风，该滑翔机还试图在地面以上但在马赫截断高度以下的情况下捕获相同的声波。本文为马赫截断阴影区中的声波波形确定了一个合适的度量，称为感知声音暴露水平。得出了马赫数截止飞行条件与阴影区噪声水平之间的经验关系;验证了先前研究提出的安全截止高度理论;分析了马赫数截止点以下的飞行对不稳定的大气条件和现实的飞机扰动的敏感性;并展示了记录高于地面5000英尺（1524.0 m）但低于马赫截止高度的声波臂测量值的能力。

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