Prediction of noise generated by complex flows at low Mach number

We present a computational aero-acoustics method to evaluate noise generated by low Mach number flow over complex configurations. This method is a hybrid approach which uses Lighthill's acoustic analogy in conjunction with source-data from an incompressible calculation. Scattering of sound waves are computed using a Boundary Element Method. This approach can be applied to flow configurations with practical complexities where turbulence interacts with arbitrary shaped solid objects. We present a validation study for sound generated by flow over a circular cylinder at $Re=100$ and $Re=10000$. The hybrid method is validated against directly computed noise using a high order compressible flow solver as well as solution of the Ffowcs Williams-Hawkings equation in conjunction with compressible noise sources. We concluded that the noise predicted by a $2^{nd}$ order hybrid approach is as accurate as directly computed noise by a $6^{th}$ order compressible flow solver in the low frequency range where the low order numerics can accurately resolve the flow structures.