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 r epresentative of a Karman vortex street. Such noise generation problems due to fluid-blade interaction occur in helicopter rotor and turbomachinery bl ades. Interactions with both rigid and elastic airfoil/blade are considered . Under a vortical excitation, aerodynamic resonance of the airfoil/blade a t certain excitation frequencies is found to occur and loading noise is gen erated due to the fluctuations of the aerodynamic loading on the airfoil/bl ade. For an elastic blade, due the occurrence of structural resonance incit ed by the flow-induced vibration of the airfoil/blade, a stronger loading n oise is generated. The associated thickness effect due to the airfoil/blade vibration is extremely weak. The magnitude of the noise was found to depen d on the frequency of the oncoming vortical flow and the geometry and rigid ity of the blade. (C) 2001 Academic Press.