Faculty of Physics, Moscow State University, 119991 Moscow, Russia.
J Acoust Soc Am. 2011 Dec;130(6):3595-607. doi: 10.1121/1.3652869.
A laboratory experiment was conducted to study the propagation of short duration (25 μs) and high amplitude (1000 Pa) acoustic N-waves in turbulent flow. Turbulent flows with a root-mean-square value of the fluctuating velocity up to 4 m/s were generated using a bidimensional nozzle (140 × 1600 mm(2)). Energy spectra of velocity fluctuations were measured and found in good agreement with the modified von Kármán spectrum for fully developed turbulence. Spherical N-waves were generated by an electric spark source. Distorted waves were measured by four 3 mm diameter microphones placed beyond the turbulent jet. The presence of turbulence resulted in random focusing of the pulse; more than a threefold increase of peak pressures was occasionally observed. Statistics of the acoustic field parameters were evaluated as functions of the propagation distance and the level of turbulence fluctuations. It is shown that random inhomogeneities decrease the mean peak positive pressure up to 30% at 2 m from the source, double the mean rise time, and cause the arrival time about 0.3% earlier than that for corresponding conditions in still air. Probability distributions of the pressure amplitude possess autosimilarity properties with respect to the level of turbulence fluctuations.
进行了一项实验室实验，以研究在湍流中传播短持续时间（25 μs）和高幅度（1000 Pa）的声 N 波。使用二维喷嘴（140×1600 mm²）产生具有最大均方根值的湍流，其波动速度高达 4 m/s。测量了速度波动的能量谱，并发现其与完全发展湍流的修正 von Kármán 谱非常吻合。球形 N 波由电火花源产生。通过放置在湍流射流之外的四个 3 毫米直径的麦克风测量失真波。湍流的存在导致脉冲随机聚焦；偶尔会观察到峰值压力增加三倍以上。评估了声场参数的统计数据作为传播距离和湍流波动水平的函数。结果表明，随机非均匀性在距声源 2 米处将平均峰值正压降低了 30%，将平均上升时间增加了一倍，并导致到达时间比静止空气中对应条件早约 0.3%。压力幅度的概率分布具有与湍流波动水平相关的自相似性特性。
