Emission surfaces and noise prediction from rotating sources

An accurate and efficient prediction method for noise emanating from rotating sources such as helicopter rotors and aircraft propellers, is presented. Combining bifurcation analysis of the retarded time equation with different emission surface topologies, a new Emission Porous Surface (EPS) algorithm has been developed. The algorithm can be used in the framework of hybrid methods that combine Computational Fluid Dynamics, for noise generation, and integral formulations for noise propagation. A panel-by-panel reconstruction of the supersonic emission surface is also proposed, which allows to manage an unstructured mesh. The noise prediction method is applied to the analysis of the UH1H rotor in strong shock delocalization conditions, a well known and extensively studied case of High Speed Impulsive (HSI) noise. The present results are compared with experimental and numerical data available in literature.