Aerodynamic noise reduction of small unmanned aerial vehicle rotors via steady suction and blowing control

To address the pronounced noise generated by the rotors of a small-scale unmanned aerial vehicle (UAV) during hover, this study investigates two active boundary-layer control schemes—BR-S (baseline rotor with suction) and BR-SB (baseline rotor with combined suction and blowing). Three-dimensional large-eddy simulations capture the near-field unsteady flow, while the Ffowcs-Williams–Hawkings acoustic analogy predicts the far-field noise. Across rotational speeds of 2000–7000 rpm and suction–blowing velocities of 0–12 m/s, overall sound-pressure level and spectral characteristics are systematically evaluated. Results show that BR-SB markedly outperforms BR-S, achieving up to 6.5 dB reduction at lateral microphones and mean reductions of 3.21 dB (aft) and 5.38 dB (lateral). By contrast, BR-S suppresses low-order blade-passing-frequency peaks but introduces localized mid-frequency sidebands. Flow-physics analysis reveals that leading-edge suction delays boundary-layer separation, whereas trailing-edge blowing persistently perturbs the shear layer and fragments nascent vortex structures, thereby attenuating both discrete harmonics and broadband turbulent noise. Overall, the combined suction–blowing strategy offers an effective and practically feasible pathway toward quieter operation of small UAV rotors.