Blade-Vortex Interaction Noise Predictions Using Measured Blade Surface Pressures

Predictions of acoustic time histories using measured airloads for a helicopter operating in descent at impulsive conditions are compared with measured acoustic data. The use of the dipole source term of the Ffowcs-Williams and Hawkings equation is shown to be a promising tool to predict blade-vortex interaction noise. Noise predictions are sensitive to both input data resolution and the calculation step size. The effect of spanwise and chordwise input locations are examined, but conclusions cannot be made until further studies are conducted. An interpolation scheme is needed to realistically distribute the chordwise and spanwise loading, although current predictions using only leading edge blade pressures show fair correlation with measured acoustic data.