Development of immersed boundary computational aeroacoustic prediction capabilities for open-rotor noise

A sharp immersed boundary computational aeroacoustic simulation approach for open-rotor direct noise predictions is presented. A specific feature of the finite-difference based immersed boundary method is that the stencil coefficients in the vicinity of the immersed boundary are determined in such a way that the stability of the numerical scheme is improved. The characteristics of this immersed boundary method are discussed for acoustic scattering and the treatment of moving boundaries, such as accounting for freshly cleared and dead cells, efficient geometry queries and efficient computation of irregular boundary stencils and point clouds in the vicinity of the immersed boundary. It is shown that the numerical error when considering moving boundary problems consistently scales with the order of accuracy of the boundary discretization. Finally, the method is applied to simulate the flow around a contra-rotating open rotor at take-off and cruise conditions where experimental data is available for comparison. Excellent agreement for the noise predictions of the contra-rotating open rotor system are obtained between the numerical simulations and the experimental noise measurement.