Aero-mechanical optimization of a contra-rotating open rotor and assessment of its aerodynamic and acoustic characteristics

Within the frame of the ongoing 7th Framework European Project DREAM, this article presents a synthesis of Cenaero, DLR, and Onera's joint effort to demonstrate the aerodynamic and acoustic optimization potential of a contra-rotating open rotor. Within WP 3.2 led by Snecma, the objective was to maximize the propellers efficiency at top-of-climb conditions and to minimize the noise emission at take-off focusing on interaction noise while fulfilling the thrust and torque split specifications at both operating points. These objectives were successfully met by the development and exploitation of efficient multi-objective three-dimensional Reynolds-averaged Navier–Stokes (RANS)-based surrogate-assisted optimization strategies. In order to assess the aerodynamic and acoustic characteristics of both baseline and optimized geometries, coupled unsteady RANS (URANS) simulation and farfield prediction based on an integral Ffowcs Williams–Hawkings approach were then carried out. The results demonstrate that although the acoustic criterion driving the optimization process did not lead to an improvement of the noise characteristics over the whole directivity range, it may be regarded as a cost-effective way to incorporate noise-related aspects into the design intent.