Abstract
Typical measured sonic boom rise times are two to five times longer than rise times calculated using molecular relaxation theory [J. Kang, Ph. D. thesis, Pennsylvania State Univ. (May 1991); A. D. Pierce and V. W. Sparrow, NASA First Annual High-Speed Research Workshop, Williamsburg, Virginia, May 1991]. Pierce etal. have proposed that the difference is due to atmospheric turbulence. A model experiment has been set up to study the influence of turbulence on waveform and rise time of spark-produced N waves. The N waves propagate through turbulence generated by a plane jet. The model turbulence is scaled down from atmospheric turbulence by approximately the same factor as the model N wave is scaled down from the sonic boom. Our experiments show that passage through the turbulence produces a wide variety of changes in the N waveform. Spiked and rounded N waves are observed, and average rise time is increased by a factor of about 2. A tentative observation based on data obtained so far is that turbulence never decreases rise time. [Work supported by NASA.]
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