A review of recent advances in the use of Kirchhoff's method in COmputational AeroAcoustics (CAA) is given. Kirchhoff's integral formulation allows the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calaulation of the far-field sound, instead of the volume integrals required by the traditonal acoustic analogy method (i.e. Lighthill, Ffowcs Williams-Hawkings equation). A numerical CFD method is used for the evaluation of the flow=field solution in the near field and thuse on the control surface. However, diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivative needed can be easily evaluated rom the near-field numerical aerodynamic data. The equivalence of Kirchhoff's method and Acoustic analogy methods was recently proven rigorously. Kirchhoff's integral for,i;atoopm was a;sp extended to include nonlinear source regions as well as refraction effects outside the Kirchhoff control surface. The method has been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A sim,ple set of portable Kirchhoff/Acoustic Analogy subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field code.
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