Aeroacoustic source characterisation using inverse methods

Measurements of the sound field radiated by aeroacoustic sources, usually acquired at a distance using some form of sensor array, can be used to reconstruct the sources that generated that sound field by using inverse methods. However, many aeroacoustic sources of practical interest are usually distributed in extent and the inverse methods can then only be applied to a discretised representation of the source. For the inversion process to yield a unique solution, the number of observations must be equal to or exceed the number of unknown source elements - the system needs to be square or over-determined, and if the source is large compared to the acoustic wavelength of interest, a prohibitively-large number of sensors is required. In addition, these measurements may be taken in a reverberant environment in the presence of significant air flow. This paper describes the practical application of a technique, known as the "Bounded Correlation Length (BCL) Inverse Method", first described by the authors at ICSV13. This method allows the number of required sensors to be significantly reduced by exploiting the fact that many aeroacoustic source distributions have finite correlation lengths. The BCL Inverse Method is applied to a real aeroacoustic source problem, in a reverberant space, and it is shown that a distributed source divided into 84 source elements can be successfully characterised by using only 20 microphones.