Calculation of High-speed Noise from Helicopter Rotor Using Different Descriptions of Quadrupole Source

The problem of quadrupole noise prediction is addressed and treated through the acoustic analogy approach, comparing different solution forms for the FW-H equation including the nonlinear source term. In particular, results obtained using the volume integration of the quadrupole source are presented. A comparison is established with results from a set of acoustic Euler calculations; a comparative analysis of the computing time is conducted, and methods to reduce the computational effort requested by the volume integration are proposed. Then, a particular description of quadrupole source term is introduced, giving rise to some surface integrals. Their role is investigated in order to asses how they affects the quadrupole noise calculation.