Computation of helicopter BVI noise by coupling free-wake, Euler and Kirchhoff method

Abstract

The present paper discusses an approach to predict blade vortex interaction (BVI) noise of helicopter rotors by direct solution of the aerodynamic and acoustic equations. The approach uses the particular advantages of different computational methods. The rotor wake system is predicted by a free-wake method without numerical dissipation errors. Euler and Kirchhoff method allow to predict noise generation and radiation in unsteady, compressible flows. The coupling of free-wake and potential method is realised at the outer boundary of the Euler grid which enables to compute the three-dimensional BVI phenomenon including inertia and compressibility effects. In order to validate the overall scheme a test case with strong BVI from the HELISHAPE project has been investigated. Agreement between measured and computed aerodynamic results is fairly good. However, the acoustic results are very sensitive to small discrepancies between experiment and computational model. For a direct comparison of measured and computed acoustic results aeroelasticity had to be considered. Nevertheless, application of the presented aerodynamic/acoustic method showed that realistic, complex BVI phenomena can be predicted as well as the resulting noise. Additionally, the results give a good insight into the three-dimensional, unsteady mechanisms leading to BVI noise.