Turbofan Aeroacoustics with a Serrated Stator: Design, Predictions, and Comparisons with Measurements

This work is devoted to the design and evaluation of a low-noise outlet guide vane (OGV) aiming to reduce the rotor–stator interaction noise using leading-edge serrations and tested on the ECL5 ultrahigh-bypass-ratio model in the PHARE-2 rig at Ecole Centrale Lyon. First, a radially varying 2D design is proposed and evaluated by means of a fast analytical prediction tool and using a strip approach. Then, an iterative process combining 3D Reynolds-averaged Navier–Stokes (RANS) calculations with an in-house modeler is carried out to achieve a suitable 3D geometry while minimizing the aerodynamic penalties. Following this design process, high-fidelity simulations based on a lattice Boltzmann solver are performed to assess the sound power level reduction achieved by the serrated OGV (by comparison to the untreated baseline case primarily tested). Due to the low-compressibility assumptions of the present lattice Boltzmann method, simulations are limited to the reachable higher regime (45% of nominal rotational speed). Hence, available analytical and numerical predictions are compared to the experimental data in terms of both aerodynamic and acoustic performances. A rather good agreement is obtained with sound power level reductions up to 3 dB from broadband intake radiation and 6 dB in the bypass duct at the considered operating points. In addition, around 4 dB power reduction has been achieved at the most energetic blade passing frequency.