ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

3aPAb8. Wideband sound propagation in a refractive shadow zone: Tests of turbulence models.

Xiao Di

Kenneth E. Gilbert

Appl. Res. Lab. and the Graduate Prog. in Acoust., Penn State Univ., P.O. Box 30, State College, PA 16804

David I. Havelock

Michael R. Stinson

Gilles A. Daigle

Inst. for Microstructural Sci., Natl. Res. Council, Ottawa, ON K1A 0R6, Canada

A wideband sound propagation experiment using discrete tones from 40 to 940 Hz has been conducted and analyzed to determine sound-pressure levels in a refractive shadow zone. It was found that at 40 and 90 Hz, the effect of turbulence was negligible. At 210 Hz and above, turbulence effects were significant. From 380 to 940 Hz, the shadow zone levels showed a relatively weak dependence on frequency. To test two turbulence models (Gaussian and Kolmogorov), the experimentally observed levels in the shadow zone were compared with parabolic equation calculations. The parameters of the turbulence models were determined from meteorological measurements. The Gaussian model, which agreed with acoustic data only over a fairly narrow range of frequencies, gave a strong frequency dependence for the levels in the shadow zone. The Kolmogorov model, on the other hand, gave good agreement with experiment over the entire band of frequencies, showing a relatively weak dependence on frequency from 380 to 940 Hz. It was concluded that the Kolmogorov turbulence model, which is consistent with inertial subrange turbulence, is a valid model for outdoor sound propagation predictions over a wide frequency range. The Gaussian model, which over predicts the frequency dependence, is valid only in a narrow range of frequencies. [Work partially supported by the Army Research Laboratory.]