Application Of Flat Tip Sawtooth Structure On Rotating Blades And Research On Noise Reduction Mechanis

With the constant increase of market demand and the continual enhancement of application scenarios in the civil drone sector,the noise problem of civil drones is becoming more relevant.Inspired by the bionics of the “serrated” structure of the trailing edge of an owl’s feather,this paper investigates the application of a new flat-tipped serrated structure for noise reduction in rotating blades:(1)Based on the serrated trailing edge noise reduction theory,the baseline and flat-tipped serrated rotating blade models were designed.On an acoustic measurement experimental platform established in a semi-anechoic chamber,the baseline and flat-tipped serrated rotating blades were tested experimentally.In this manner,the effectiveness of the flat-tipped serrated structure for noise reduction was examined.The results show that the flat-tipped serrated rotating blade achieves effective noise attenuation in the overall range(16～10000 Hz)at different rotational speeds,which confirms the effectiveness of the flat-tipped serrated structure in noise reduction.In addition,the flat-tip serrated structure’s optimum noise reduction frequency band is in the difficult-to-treat low frequency range(frequency< 500 Hz).(2)In order to improve the noise reduction performance of the flat-tipped serrated rotating blade,the parameters of the flat-tipped serrated structure are optimized by Taguchi’s method.With the help of signal-to-noise ratio analysis,the range analysis and the contribution analysis,the flat-tipped serrated rotating blade with better noise reduction performance was obtained.The blade was re-prepared based on the improved results,and the noise reduction performance of the optimized flat tip sawtooth revolving blade was investigated using the same acoustic studies.The experimental results show that the noise reduction performance of the flat-tipped serrated rotating blade obtained through structural parameter optimization is significantly improved compared with the original flat-tipped serrated rotating blade,which indicates that this optimization method has reference value in other similar bionic structural parameter optimization.(3)The three-dimensional models of the baseline and optimized flat-tipped serrated rotating blades are established.ANSYS FLUENT numerical simulation software is used to obtain the flow and sound field information of the two rotating blades,so as to investigate the noise mechanism causes and aerodynamic performance changes of the flat-tipped serrated rotating blade.The results show that the equivalent sound pressure levels calculated by the numerical simulation and the experimental measurement basically match,which verifies the reliability of the numerical simulation.The flat tip serrated structure can improve the noise reduction performance of the rotating blade,but it also weakens the aerodynamic performance.The flat tip serrated structure can form the counter-rotating vortex structure at the trailing edge of the rotating blade to suppress the formation of large vortices,thus achieving the purpose of reducing the noise of the rotating blade.The flat-tip serrated structure transfers rotating blade noise energy from low to high frequency,which serves to lessen the difficulties of future rotating blade noise control.The noise source of the rotating blade reflects the dipole source.The equivalent sound pressure level of the flat-tipped serrated rotating blade at all noise monitoring points is substantially lower than that of the baseline rotating blade.