Aeroacoustic calculation for helicopter rotor in hover and in forward flight based on FW-H equation

The Ffowcs Williams/Hawkings (FW-H) equation, which is directly derived from Navier-Stokes equations, has been the theoretical background of predicting the noise generated by moving bodies. For predicting the rotor noise, in the conventional solution of FW-H equation, the blade is utilized as the integration surface, and the complication is caused when calculating the quadrupole noise. In the present work, a form of FW-H equation applied for a permeable surface was employed for predicting the quadrupole noise aerodynamically generated by rotor both in hover and forward flight. Section 1 discusses the CFD calculation performed by solving the 3-D unsteady Euler's equations. Section 2 describes in detail the solution of the permeable-surface FW-H equation in the time domain. The computed results for all cases were compared with experimental data and a reasonable agreement has been achieved. It is also shown that the developed code is efficient and is capable of capturing the nonlinear quadrupole noise for transonic rotor.