Prediction of Certification Noise Levels Generated by Contra-Rotating Open Rotor Engines

The tendency for environmentally friendlier aeronautic engines, led to the re-examination of the contra rotating open rotor (CROR) as a more efficient and less polluting propulsion system, thanks to its noticeably high propulsive efficiency. The geometrical and operational characteristics of these contra rotating propellers are examined in order to optimize the noise emissions, given the challenging regulation context for such an unducted concept. For this research, computational techniques have been used to develop a numerical model for prediction of noise levels generated by CRORs propellers. An extended database of unsteady CFD simulations, generated with innovative methods, namely a non-linear harmonic flow solver and an acoustic propagation model based on the Ffowcs Williams–Hawkings approach, have been used to assess the noise spectra measured in the certification points. Sound pressure levels and frequencies have been afterwards converted into EPN levels along the aircraft flight path, according to the ICAO regulation. The whole procedure has been applied to 102 different cases to establish the influence of several independent parameters on noise emissions. A surface response model has finally been developed, providing an easy tool of fast utilization to be implemented in optimization platforms.