Simulation Study on Aeroacoustic Performance of Segmented Ducted Fan for Small UAVs

Small unmanned aerial vehicles (UAVs) are widely used in civil and military fields, and their noise problem has always been the industry’s focus. Compared with the traditional propeller fan, the ducted fan has the advantages of higher aerodynamic efficiency, lower aerodynamic noise, and higher safety. It has become the key power component of small UAVs. However, the aerodynamic acoustic performance, noise reduction effect, and noise reduction mechanism of the segmented ducted fan for small UAVs are still unclear, which restricts the noise reduction design process of the ducted fan. To solve these problems, RANS (Reynolds-Averaged Navier-Stokes) method, SST k-ω (Shear Stress Transport k-ω) turbulence model and broadband noise source model were used to establish a computational fluid dynamics model, and the effects of fan speed (20,000-40,000 r/min) and duct spacing (0-20 mm) on its aeroacoustic characteristics were systematically studied. The results show that the segmented ducted fan’s acoustic power level maximum (APLmax) is significantly higher than that of the traditional integral structure, especially at high speed. At 40,000 r/min, the increase of duct spacing to 20 mm led to the sudden increase of APLmax to 194.5 dB, 61.3 dB higher than that of the integral type. Its essence was derived from the three-stage chain amplification mechanism of “strong tip leakage vortex induced by geometric clearance → broadband noise caused by vortex impacting the duct wall → resonant coupling of leakage vortex harmonic frequency and duct cavity standing wave.” Based on this, a collaborative noise reduction path is proposed: compress the spacing to ≤ 10 mm to suppress the intensity of leakage vortex, design the periodicity of failure vortex combined with the serrated blade tip/inner wall rubber strip, and block the acoustic cavity resonance with non-uniform wall stiffness or 8-10 kHz Helmholtz resonator, providing a solution for the low-noise design of UAV propulsion system.