OPTIMIZATION OF ACOUSTIC AND AERODYNAMIC PERFORMANCE FOR A LOW NOISE CONTRA-ROTATING OPEN ROTOR AT TAKEOFF CONDITION

In this paper, the acoustic and aerodynamic performance of a contra-rotating open rotor (CROR) is optimized and verified through wind tunnel experiment. The aerofoil thickness, chord length and the twist angle for rotor blades are adjusted to improve the load distribution along spanwise direction, which can bring the reduction of tonal noise from both the front and rear rotor. Subsequently the swept and turning angle distribution from the 70% radial position to the tip end of the blade is recast to mitigate the interaction effect between the front and rear rotor. The aerodynamic and aeroacoustic parameters are calculated by numerical simulation with high fidelity, and compared with the experimental data from large-scale wind tunnel tests. The results show that under 0.25 Ma inflow speed the main radiation range of the OASPL of the baseline CROR is located between 103 ° and 108 °, and the prediction accuracy is within 1.5dB in the main radiation direction. The optimized CROR obtained a 10.65% positive margin of the total thrust compared to the baseline CROR, while maintaining the same propulsion efficiency. The noise reductions of 1st and 2nd order Blade Passage Frequency (BPF) components are 6.4dB and 5dB in the main radiation direction respectively, the maximum OASPL is reduced by 2.3dB. Moreover, the noise could be further attenuated if a portion of the obtained thrust improvement was scarified. After lowering the total thrust margin of optimized CROR to 1.9%, the maximum OASPL reduction was achieved with 3.5dB, meanwhile the aerodynamic efficiency improved by 1.7%.