A Tomographic Directivity Approach to Frequency Domain Beamforming

Abstract

Aeroacoustic measurements in wind tunnels are a common tool in the determination of sound sources on scaled models. Most of the algorithms used are based on the assumption that the unknown aeroacoustic sources radiate sound waves omnidirectionally, thus monopole sources are utilized. For the prediction of the noise footprint of aircrafts however, it is essential to have information on the directivity of the airframe sources. An approach to estimating this directivity is to use different array positions for measurement relative to the model which leads to different observation angles. The evaluation of measurements at several observation angles holds several issues, for example the difficult source localization due to the three-dimensionality of the point spread function and partial shadowing of sources at large observation angles. This paper therefore presents an approach to estimate the source positions taking into account information from all four observation angles at once. The positions estimated in this fashion are subsequently used for an improved prediction of source power and eventually lead to an estimation of directivity of the observed aeroacoustic sources.