ASA 124th Meeting New Orleans 1992 October

4pPA4. A discrete implementation of a Hankel transform technique for predicting multipole sound propagation over plane, absorbing surfaces.

Z. Hu

Noise Cancellation Technol., Inc., 1015 W. Nursery Rd., Linthicum, MD 21090

J. S. Bolton

Purdue Univ., West Lafayette, IN 47907

Many theories are available for predicting sound propagation outdoors; they are usually expressed in terms of sound radiation from a source (e.g., a monopole) that generates a cylindrically symmetric sound field that propagates over a homogeneous, finite impedance plane. However, not all practical noise sources are monopolar in character nor do they necessarily generate azimuthally symmetric sound fields. In this paper, a discrete implementation of a two-dimensional finite Hankel transform technique is described that makes it possible to predict sound propagation from higher-order sources that generate noncylindrically symmetric sound fields: e.g., arbitrarily oriented dipole and quadrupoles. As a result, the proposed technique may prove useful for predicting sound propagation from aerodynamic noise sources place near plane outdoor surfaces. The prediction procedure is based on representing the field of a source as a two-dimensional wave-number spectrum. The wave-number spectrum of the source field is then combined with the reflection coefficient of the impedance plane to yield the wave-number spectrum of the reflected field. The latter component is then added to the direct wave-number spectrum and the result is inverse transformed to give the sound pressure as a function of radius and azimuth angle. Predictions made using the new technique will be compared with experimental results.