Index of content:
Volume 126, Issue 1, July 2009
- AEROACOUSTICS, ATMOSPHERIC SOUND 
126(2009); http://dx.doi.org/10.1121/1.3129125View Description Hide Description
This paper examines the impact of meteorological conditions on the propagation of vehicular noise from urban freeways. A parabolic equation model coupled to an analytical Green’s function solution close to the source field is used to compute the refracted sound field up to half a mile from the freeway to predict the noise exposure of residential areas nearby. The model was used in conjunction with meteorological and sound-levelmeasurements taken at two freeway sites over the course of four days in Phoenix, AZ. From the data collected, three test cases of varying levels of atmospheric stratification and wind shear are presented and discussed. The model demonstrates that atmospheric effects are able to raise sound levels by at significant distances away from the highway, causing violations of acceptable limits imposed by the Federal Highway Administration in residential areas that are normally in compliance.
Asynchronous control of vortex-induced acoustic cavity resonance using imbedded piezo-electric actuators126(2009); http://dx.doi.org/10.1121/1.3143784View Description Hide Description
This paper presents an experimental investigation of the control of a vortex-induced acoustic cavityresonance from flow over a bluff body using embedded piezo-ceramic actuators in order to alter the resonant flow-acoustic interactions. The action of the actuators was asynchronous. Experiments were mainly conducted at the flowvelocity of acoustic resonance, where the vortex shedding frequency from the upstream bluff body approached the frequency of the first acoustic mode of two downstream cavities. The fluctuating acoustic pressure was measured using a microphone. The perturbed flow field around the bluff body was monitored using two single hot wire anemometers and one -wire. It was found that the induced transverse vibrations were effective to reduce the acoustic resonance. The cavitysound pressure level at resonance was reduced by in presence of actuation. The physics behind the control mechanism is discussed.