Model experiment to study sonic boom propagation through turbulence. Part I: General results

Abstract

A model experiment to study the effect of atmospheric turbulence on sonic booms is reported. The model sonic booms are N waves produced by electric sparks, and the model turbulence is created by a plane jet. Of particular interest are the changes in waveform, peak pressure, and rise time of the model N waves after they have passed through the model turbulence. A review is first given of previous experiments on the effect of turbulence on both sonic booms and model N waves. This experiment was designed so that the scale factor ͑approximately 10 Ϫ4 ͒ relating the characteristic length scales of the model turbulence to those of atmospheric turbulence is the same as that relating the model N waves to sonic booms. Most of the results reported are for plane waves. Sets of 100 or 200 pressure waveforms were recorded, for both quiet and turbulent air, and analyzed. Sample waveforms, scatter plots of peak pressure and rise time, histograms, and cumulative probability distributions are given. Results are as follows: ͑1͒ The model experiment successfully simulates sonic boom propagation through the atmosphere. The waveform distortion of actual sonic booms is reproduced, both in scale and in character, in the laboratory study. ͑2͒ Passage through turbulence almost always causes rise time to increase; decreases are rare. ͑3͒ Average rise time is always increased by turbulence, threefold for the particular data reported here. ͑4͒ Average peak pressure is always decreased by turbulence, but the change is not as striking as that for average rise time.

Evidence of wave front folding of sonic booms by a laboratory-scale deterministic experiment of shock waves in a heterogeneous medium

“…Let us recall that the only objective here is to investigate in the laboratory the detailed physical effects associated with the interaction of a shock wave with a heterogeneity, and to profit from the opportunity offered by the deterministic aspect of the experiment. In particular, this deterministic aspect will now allow us to make a detailed comparison with a numerical model, including a waveform to waveform comparison at the same point in the same propagation conditions, something that is impossible to perform in a statistical propagation case, either during flight tests or even in a laboratory turbulence experiment ͑such as Lipkens and Blackstock, 1998 or Blanc-Benon et al 2002͒.…”

Sonic Boom Variability Due to Homogeneous Atmospheric Turbulence

“…The resulting 100 different sonic boom signatures were assessed with regard to the nondeterministic effects of atmospheric turbulence on sonic boom [15]. In addition, the turbulent field was assumed to be frozen (i.e., the turbulent velocity is constant during sonic boom propagation).…”

Turbulent jet interaction with a long rise-time pressure signature

“…In the laboratory-scale experiments which simulate the N-shaped waveform, a front and tail shock waves have the same waveform deformed by turbulent effects [10,30]. It seems that the front and tail shock waves receive the same shock focusing/diffracting effects.…”

“…Additionally, the strong atmospheric turbulence leads to a high probability of these deformed waveforms; the deformation depends on the turbulence intensity. According to a laboratory-scale experiment, in the case of a shockturbulence interaction, the mean overpressure decreases, the mean rise time increases, and the standard deviations increase [10]. The larger standard deviations suggest that the large overpressure and short rise time may occur.…”

“…Averiyanov et al [28,30] showed that an overpressure decrease and the arrival time are governed by the large scale of a velocity fluctuation, and the small scales of a velocity fluctuation mainly cause increasing the rise time. In the typical model experiments [10,29,30], in order to simulate the N-shaped sonic boom propagation in the real atmosphere, the characteristic length scales, such as a wavelength, a turbulent interaction distance, and the geometrical turbulence length scales, were adjusted. A generated N-shaped pressure waveform in the model experiments is categorized as a short rise time signature.…”