Outdoor measurements of shock-wave propagation from exploding balloons

Previous anechoic measurements of exploding latex balloons filled with stoichiometric mixes of acetylene and oxygen revealed how these sources could be used to study weak-shock decay over relatively short ranges [M. B. Muhlestein et al., J. Acoust. Soc. Am. 131, 2422–2430 (2012)]. This paper describes an experiment conducted using a larger balloon over much longer propagation ranges at the Bonneville Salt Flats, which represents a hard, flat, relatively homogeneous ground surface. Measurements of a 0.56 m balloon were made along a propagation radial from 0.31 m from the balloon surface to 1600 m. Data were collected at a sampling rate of 204.8 kHz using piezoresistive pressure gauges and Type-1 condenser microphones. Described are waveform and spectral characteristics, as well as comparisons of the peak pressure decay with the weak-shock model employed previously. Waveform inspection and the comparison indicate that weak shocks are present out to at least 305 m and the amplitude decay rate can be predicted reasonably well using the model. Deviations from the model may be evidence of Mach-like reflections [K. M. Leete et al., Four Corners Ann. Meet. Am. Phys. Soc. 59, I7.00007 (2014)]. This work extends the previous laboratory experiments and serves as a foundation for further studies using this relatively low-cost source.