Affordable and Accurate Numerical Predictions of Helicopter Rotor Noise inForward Flight

In the present work, a numerical methodology is developed for affordable and accurate analysis of helicopter rotor noise in forward flight. The flow field is obtained using unsteady compressible flow analyses using commercially available computational fluid dynamics (CFD)solver FLUENT. Azimuthal variations of the flap and pitch motions of the blades are prescribed a priori as high order polynomial equations through a user-defined function. The rotor noise is predicted using Fluent Acoustic module based on the Ffowcs-Williams and Hawking's equations. Methodology is verified using HART II experimental setup and data which includes flapping, pitching, lead-lag motion and elastic torsion for each rotor blade. Individually defined blade motion is found critical for an accurate acoustic prediction based on the obtained CFD calculation. The present predictions compare very well and performs better than other previous CFD analysis both for minimum noise and baseline case at maximumsound pressure level(SPL)of HART II data, even with meshes of 7-8 million cells rather than tens of millions usually needed.