ASA 124th Meeting New Orleans 1992 October

2pPA10. Further report on the propagation of spark-produced N waves through turbulence.

Bart Lipkens

David T. Blackstock

Appl. Res. Labs., Univ. of Texas at Austin, Austin, TX 78712-8029

Mech. Eng. Dept., Univ. of Texas at Austin, Austin, TX 78712-1063

A laboratory model experiment to study the effect of turbulence on waveform and rise time of sonic booms has previously been reported [B. Lipkens and D. T. Blackstock, J. Acoust. Soc. Am. 90, 2307(A) (1991)]. Electric sparks produce the N waves, which then propagate through turbulence generated by a plane jet. Downscaling of the model turbulence from atmospheric turbulence was designed to match downscaling of the model N wave (in terms of duration and rise time) from the sonic boom. Reported here are hot wire anemometry measurements of the jet, which confirm that the turbulence characteristics are indeed those of a classical plane jet. The measured values of the integral length scale, Taylor microscale, and Kolmogorov microscale show that the desired downscaling from atmospheric turbulence was achieved. Also reported are measurements that show how rise time and wave shape distortion vary with propagation distance through the jet, turbulence intensity, and peak amplitude of the N wave. [Work supported by NASA.]