We propose a hybrid Finite Volume (FV) - Spectral Element Method (SEM) for
modelling aeroacoustic phenomena based on the Lighthill's acoustic analogy.
First the fluid solution is computed employing a FV method. Then, the sound
source term is projected onto the acoustic grid and the inhomogeneous
Lighthill's wave equation is solved employing the SEM. The novel projection
method computes offline the intersections between the acoustic and the fluid
grids in order to preserve the accuracy. The proposed intersection algorithm is
shown to be robust, scalable and able to efficiently compute the geometric
intersection of arbitrary polyhedral elements. We then analyse the properties
of the projection error, showing that if the fluid grid is fine enough we are
able to exploit the accuracy of the acoustic solver and we numerically assess
the obtained theoretical estimates. Finally, we address two relevant
aeroacoustic benchmarks, namely the corotating vortex pair and the noise
induced by a laminar flow around a squared cylinder, to demonstrate in practice
the effectiveness of the projection method when dealing with high order
solvers. The flow computations are performed with OpenFOAM [46], an open-source
finite volume library, while the inhomogeneous Lighthill's wave equation is
solved with SPEED [31], an opensource spectral element library