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首页> 外文期刊>The Aeronautical Journal >The effect of gravity on a shaped sonic boom
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The effect of gravity on a shaped sonic boom

机译：重力对异型声波悬臂的影响

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Previously it was demonstrated that gravity is directly responsible for the attenuation of sonic booms as they propagate towards the ground, while the gradient in acoustic impedance has no effect on the wave strength. This was a significant departure from the well accepted acoustic theory and naturally led to questions concerning comparison with experiment and the implications for low boom design. This paper presents a comparison of measured ground signatures of the Northrup-Grumman Shaped Sonic Boom Demonstrator (SSBD) with a method of characteristics extrapolation from a close proximity flight measurement of static pressure under the aircraft. Comparison is also made with Whitham's theory, extended to include gravity and the ambient temperature variation, as presented in the previous paper. The calculations are both in good agreement with the experimental ground signature. The usual equations that define the acoustic propagation (gravitational body force neglected) are transformed so that the computational algorithms of the extended Whitham theory are applicable. The transformation simplifies the acoustic model and reveals the conditions under which the errors in its prediction will be large. At the Mach number of 1.4, corresponding to the SSBD flight, the error is relatively small and the acoustic prediction is also in close agreement with the ground signature.
机译：以前已经证明，重力是声爆声向地面传播时直接造成的衰减的原因，而声阻抗的梯度对波强度没有影响。这与公认的声学理论大相径庭，自然引发了有关与实验进行比较以及对低吊杆设计的影响的问题。本文通过对飞机静压的近距离飞行测量，采用特征外推法，比较了诺斯鲁普-格鲁曼形声波演示器（SSBD）的实测地面信号。还与Whitham的理论进行了比较，该理论已扩展到包括重力和环境温度变化，如先前的论文所述。计算结果均与实验地面信号非常吻合。定义声波传播（忽略重力）的常用方程式经过转换，因此可以应用扩展的Whitham理论的计算算法。该变换简化了声学模型，并揭示了其预测误差较大的条件。在1.4马赫数（对应于SSBD飞行）下，误差相对较小，声学预测也与地面信号非常吻合。

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