NOISE GENERATION OF BLADE–VORTEX RESONANCE

A numerical study of the aerodynamic noise generated when an airfoil/blade in a uniform flow is excited by an oncoming vortical flow is reported. The vortical flow is modelled by a series of flow convected discrete vortices representative of a Karman vortex street. Such noise generation problems due to fluid–blade interaction occur in helicopter rotor and turbomachinery blades. Interactions with both rigid and elastic airfoil/blade are considered. Under a vortical excitation, aerodynamic resonance of the airfoil/blade at certain excitation frequencies is found to occur and loading noise is generated due to the fluctuations of the aerodynamic loading on the airfoil/blade. For an elastic blade, due the occurrence of structural resonance incited by the flow-induced vibration of the airfoil/blade, a stronger loading noise is generated. The associated thickness effect due to the airfoil/blade vibration is extremely weak. The magnitude of the noise was found to depend on the frequency of the oncoming vortical flow and the geometry and rigidity of the blade.