Volume 119, Issue 4, April 2006
Index of content:
- AEROACOUSTICS, ATMOSPHERIC SOUND 
119(2006); http://dx.doi.org/10.1121/1.2180530View Description Hide Description
Experimental measurements were conducted around a right-angle wall to investigate the effect of this obstacle on sound propagation outdoors. Using small explosions as the source of the acoustic waves allowed reflected and diffracted arrivals to be discerned and investigated in detail. The measurements confirm that diffraction acts as a low-pass filter on acoustic waveforms in agreement with simple diffraction theory, reducing the peak pressure and broadening the waveform shape received by a sensor in the shadow zone. In addition, sensors mounted directly on the wall registered pressure doubling for nongrazing angles of incidence in line-of-sight conditions. A fast two-dimensional finite difference time domain(FDTD) model was developed and provided additional insight into the propagation around the wall. Calculated waveforms show good agreement with the measured waveforms.
119(2006); http://dx.doi.org/10.1121/1.2171838View Description Hide Description
The sound generated by a single vortex and by two identical vortices in the presence of a half-cylinder made of porous material mounted on a rigid horizontal plane is studied theoretically using the acoustic analogy and the matched asymptotic expansion method. Both longitudinal and transverse dipoles are observed upon the introduction of the porous cylinder, but the former is considerably stronger than the latter in all the cases studied. Results suggest that the amplitudes of the dipoles and the overall acoustical energy radiated can be higher than that in the rigid cylinder case under some suitable combinations of flow parameters, especially when the flow resistance inside the porous material seen by the vortices is very small.