Volume 126, Issue 5, November 2009
Index of content:
- AEROACOUSTICS, ATMOSPHERIC SOUND 
126(2009); http://dx.doi.org/10.1121/1.3238236View Description Hide Description
This paper describes methodology and results from a model-based analysis of data on sound transmission from controlled sound sources at sea to a 10-km distant shore. The data consist of registrations of sound transmission loss together with concurrently collected atmospheric data at the source and receiver locations. The purpose of the analysis is to assess the accuracy of methods for transmission loss prediction in which detailed data on the local geography and atmospheric conditions are used for computation of the sound field. The results indicate that such sound propagation predictions are accurate and reproduce observed variations in the sound level as function of time in a realistic way. The results further illustrate that the atmospheric model must include a description of turbulence effects to ensure predicted noise levels to remain realistically high during periods of sound shadow.
126(2009); http://dx.doi.org/10.1121/1.3224764View Description Hide Description
An acoustic intensity-based method (AIBM) is extended and verified for predicting sound radiation in a subsonic uniform flow. The method assumes that the acoustic propagation is governed by the modified Helmholtz equation on and outside of a control surface, which encloses all the noise sources and nonlinear effects. With acoustic pressure derivative and its co-located acoustic pressure as input from an open control surface, the unique solution of the modified Helmholtz equation is obtained by solving the least squares problem. The AIBM is coupled with near-field Computational Fluid Dynamics (CFD)/Computational Aeroacoustics (CAA) methods to predict sound radiation of model aeroacoustic problems. The effectiveness of this hybrid approach has been demonstrated by examples of both tonal and broadband noise. Since the AIBM method is stable and accurate based on the input acoustic data from an open surface in a radiated field, it is therefore advantageous for the far-field prediction of aerodynamics noise propagation when an acoustic input from a closed control surface, like the Ffowcs Williams–Hawkings surface, is not available [Philos. Trans. R. Soc. London, Ser. A264, 321–342 (Year: 1969)].