AN EFFICIENT KIRCHHOFF INTEGRATION METHOD FOR ROTOR NOISE PREDICTION STARTING INDIFFERENTLY FROM SUBSONICALLY OR SUPERSONICALLY ROTATING MESHES

An original implementation of the Kirchhoff method which uses subsonically as well as supersonically rotating CFD grids for integration on a fixed axisymmetrical Kirchhoff surface is presented. The formulation is written for a propagation medium either at rest or in uniform translation. The particular time integration technique, which considers each grid element as acoustically non-compact, is described in details. It does not require solving the retarded time equation since it starts from the emission time, and a regular grid is not necessary. Numerical tests show the capability of the method to work well even with relatively wide surface elements and large emission time steps. The code KIM based on this integration technique is validated by comparisons with analytical calculations in the case of a rotating point dipole. KIM is also applied to the UH1H model rotor in delocalized hover conditions starting from high quality input data and successfully correlated to experiment. The method proves robust and very much computationally time saving.