This paper describes a two-dimensional formulation of the Ffowcs Williams a
nd Hawkings equation in the frequency domain. By assuming subsonic rectilin
ear motion of all acoustic sources, an efficient and easily implemented for
m of the equation is developed. This method is capable of predicting the fa
rfield noise from non-linear nearfield flow quantities. The ability to use
non-linear input data is a clear advantage over Kirchhoff methods, that are
only valid in regions where the linear wave equation accurately describes
the flow. Several example problems are used to demonstrate that the new met
hod performs well for problems with a mean flow, tonal and broadband noise
signatures, and non-linear near fields. In most practical acoustic problems
, three-dimensionality is important and should not be neglected. For these
real-world applications, two-dimensional solutions can be used to guide and
augment full three-dimensional calculations, but not replace them.