ASA 125th Meeting Ottawa 1993 May

3aEA4. Acoustical holography with arbitrarily shaped sources in a cylindrical duct.

Charles J. Konzelman

Dept. of Mech. Eng., Univ. of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6, Canada

Radiated sound-pressure measurements of a device designed to operate in the presence of a fluid flow are frequently conducted in wind or water tunnels in order to control flow conditions. However, due to environmental reverberation, these sound-pressure measurements may bear little resemblance to those obtained when the device operates in a free-field environment. In particular, it may be impossible to infer the far-field radiation pattern from such measurements. This study examines the possibility of using acoustical holography to determine the far-field radiation pattern in such cases. Numerical simulations are used to synthesize the pressure field radiated by an arbitrarily shaped source that has a prescribed normal velocity distribution and which operates in a rigid-walled cylindrical duct. Acoustical holography is then used to reconstruct the velocity distribution. Assuming that the source velocity does not change when the device is operated in a free-field environment, the reconstructed source velocity is used to determine the far-field radiation pattern. This far-field radiation pattern is compared with that obtained using the exact source velocity in order to assess the performance of the technique.