Predicting Aerodynamic Noise - Which Model to Use and When?

Aeroacoustics aims at describing the generation of sound by fluid flow, a task which requires, in general, a somewhat arbitrary decision on what part of the flow is responsible for the sound generation process, which refers to propagation. Starting with Lighthill's analogy in the early 1950's, a number of models have been developed since. This paper reviews the modeling basics, with emphasis on the physics of the fluid dynamics/acoustic processes, discussing different acoustic analogies as well as its limitations. The discussion proceeds by comparing different models and solutions, notably, Ligthill's orginal formulation, Lilley's equation and its recent extension by Goldstein. Howe's analogy is also briefly commented. The context in which each model should be used is discussed, as is the question of the sensitivity of results to details of the modeling.