Simulation of Helicopter Community Noise in Complex Urban Geometry

The problem of helicopter noise generation, fuselage scattering, and propagation in an urban environment is solved using a wave-splitting technique based on a coupled Ffowcs Williams and Hawkings and finite element method computation. This original technique allows the forward and backward propagation of the noise generated by a rotating device through a computational domain in the presence of reflecting obstacles, both in the source region and in the far field. The acoustic pressure on the boundaries of two overlapping chimera grids are computed in the time domain using the Ffowcs Williams and Hawkings analogy and are used to prescribe jump conditions across the chimera interface. The coupled Ffowcs Williams and Hawkings and finite element method technique is verified only for wave propagation in a quiescent medium, but the proposed formulation can take into account the convective effects associated with a flow medium. To reduce the computational time required to compute the noise signals on the chimera interface, a fast rotor noise model is used that consists of replacing the blade with a wedge of equivalent sectional area and equivalent unsteady aerodynamic action on the fluid. The fast rotor noise model is verified and validated in helicopter blade vortex interaction conditions and constitutes the second original contribution of this work.