Research On Bionic Noise Reduction Of UAV Propeller Based On Owl Feather Characteristics

With the development of small UAVs in military,scientific and commercial fields,noise level has become one of the important parameters to evaluate its comprehensive performance.As the main noise of UAVs,propeller noise has attracted extensive attention in recent years.The control of propeller discrete and broadband noise without aerodynamics lose is not only a new challenge and opportunity in the development of UAVs,but also a hotspots and difficulties of current research.Aiming at the bionic leading-edge(LE),trailing-edge(TE)and LE-TE coupled serrations which are simulated from the characteristics of owl’s feathers,an experimental and numerical research on aerodynamic performance and noise characteristic of serrated UAV propellers has been carried out.The main work and results of this paper are as follows:(1)The three-dimensional Navier Stokes equations(N-S equations)based on the improved delayed separated eddy simulation(IDDES)model and the trimmedpolygonal mesh technology are combined to calculate the incompressible flow of a 2blade 17-inch propeller of UAVs in turbulent environment and free sound field.The hybrid computational aeroacoustics(HCAA)method combining IDDES model and Ffowcs Williams-Hawkings(FW-H)equations is used to calculate the mechanical and acoustic characteristics of propeller.Compared to experimental values,the results show that the values of IDDES model are more accurate than those of shear stress transfer(SST)k-ω model.The characteristics of frequency spectrum of propeller noise calculated by the HCCA method are similar to that of the experimental results.(2)The owl inspired bionic LE propellers(LEP)with different morphologies and parameters are designed.The results of LEP parametric and morphological effects show that the noise reduction effect on bionic propeller is the most sensitive to the distribution length of LE serrations,followed by the width and length.The sharp and symmetrical serration structure is more conducive to noise suppression.Computational fluid dynamics(CFD)simulation reveals that the noise reduction mechanism of LEP is to change the flow distribution at the LE of propeller.The serration induced vortex can reduce the unsteady load of blade and the intense of turbulence-LE interaction,which can effectively suppress the discrete noise in the frequency range below 2kHz.The vortex can also reduce broadband noise by weakening the random pulsation of turbulent on the propeller blades.Compared with the baseline propeller,the best LEP design(LEsawtooth)measured 3.5%promotion on aerodynamic performance,2.7dB and 2.3dB noise reduction on overall sound pressure level.The LEP produces 3.8-4.7dB actual noise reduction effect on the hovering UAV at different heights.(3)The owl inspired bionic TE propellers(TEP)with different morphologies and parameters are designed.The results of TEP parametric and morphological effects show that the distribution length of TE serration have a significant impact on the aerodynamic and acoustic performances of bionic propeller,the spacing of TE serration is the key to generate noise reduction effects.CFD simulation reveals that that the noise reduction mechanism of TEP lies in the joint action of the serration induced micro jet-flow and vortex.The turbulence-TE interaction is suppressed by the delayed separation of TE airflow fluctuations.The reduced scale of separation bubble and shedding vortex leads to the lower random pulsation amplitude which caused a significant reduction of broadband noise in the frequency range of 2-12kHz.Compared with the baseline propeller,the best TEP design(TE-3/4DL)measured 6.2%promotion on aerodynamic performance,2.6dB and 2.8dB noise reduction on overall sound pressure level.The TEP produces 3.4-4.5dB actual noise reduction effect on the hovering UAV at different heights.(4)Based on the studies of LEP and TEP,a LE-TE coupled bionic propeller(BCP)is designed to simulate the cooperative noise reduction mechanism of different feather structures of owl’s wing.The coupled serration structure on BCP has the noise reduction characteristics of two single serration structures:LE and TE serrations.The BCP design can not only suppress the tonal noise below 2kHz frequencies,but also significantly reduce the broadband noise in the frequency range of 2-12kHz.The overall acoustic performance of BCP is better than that of LEP and TEP.The noise reduction mechanism of BCP lies in the synergy of the LE and TE serrations on the passive flow control.Compared with the baseline propeller,the BCP design measured 8%promotion on aerodynamic performance,3.1dB and 2.9dB noise reduction on overall sound pressure level.The BCP produces 4.1-4.9dB actual noise reduction effect on the hovering UAV at different heights.