旋翼流动对桨-涡干扰噪声的影响机理试验OA

The Blade-Vortex Interaction(BVI)noise of helicopter rotor is a severe impulsive noise source.In order to investigate the influence mechanism of the unsteady flow of the rotor on the BVI noise characteristics,the noise char-acteristics,pressure distribution,and unsteady flow characteristics of the different rotor conditions are measured based on the microphone spherical array measurement technology,the blade surface pressure measurement technol-ogy,and the Particle Image Velocimetry(PIV)technology in an acoustic tunnel environment.The influences of the advance ratio,oblique descent angle,and lift coefficient on the BVI noise are obtained.The influence mechanism of the rotor surface pressure and the vortex motion trajectory on the BVI noise are revealed.The analysis results show that the main radiation direction of BVI noise covers most of the first to third quadrants.In the time domain,it shows a high peak pulse noise pressure,and the main sound energy frequency is concentrated on the multiples of the rota-tional frequency in the medium-and high-frequency bands.The BVI noise mainly occurs at the blade leading edge,generally within 0.3 times of the chord length,with intensity inversely proportional to the distance.Upper and lower surface interaction loads exhibit opposing impulsive directions.For 5-bladed rotors,parallel BVI phases approximate 60°.Spanwise cumulative noise effects arise from extensive BVI during parallel BVI.The change of the rotor advance ratio and oblique descent angle will cause the change of the flow near the rotor,which will change the motion trajectory of the blade tip vortex,and then change the relative angle,distance,and interference phase between the blade and the vortex,thus affecting the BVI noise.Vertical force coefficient modifications impact vortex strength rather than tra-jectory,which directly influence BVI noise intensity.