title: Measurement of an aeroacoustic dipole using a linear microphone array.
abstract: It is shown that the standard beamformer technique is inadequate for both the source location and the measurement of a simple dipole and that this is due to the assumption of monopole propagation in the calculation of the phase weights used to steer the focus of the array. A numerical simulation is used to illustrate the problem and to develop a correction to the signal processing algorithm to account for the dipole propagation characteristic. This is then applied to array measurements for an aeroacoustic dipole produced by a cylinder in a cross flow. The resulting source map and the beamformed spectrum are shown to give a true representation of the source energy and frequency content. A secondary effect of this correction is that the array becomes insensitive to other source types so that in addition to acting as a spatial filter, the array can perform as a source filter. This work also demonstrates how an array measurement can be misinterpreted if applied without consideration of the source mechanism.
authors.affiliation: Department of Mechanical Engineering, Trinity College, Dublin, Ireland.
authors.forename: Peter
authors.initials: P
authors.lastname: Jordan
authors.forename: John A
authors.initials: JA
authors.lastname: Fitzpatrick
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Valière