Analyses on Aeroacoustic Characteristics of Coaxial Rotor in Forward Flight

Based on CFD method and FW-Hpds equations, a numerical method for predicting aeroacoustic characteristics of coaxial rotor is established. In order to accurately simulate the flowfield of coaxial rotor, several techniques including moving-embedded grids, implicit LU-SGS scheme, ROE-MUSCL scheme and Spalart-Allmaras turbulence model are adopted to solve the RANS equations. The aeroacoustic characteristics of coaxial rotor in forward flight are calculated and analyzed by using FW-Hpds equations. The calculated acoustic characteristics of the AH-1/OLS model in forward flight for validation are in good agreements with the experimental data. The acoustic characteristics of coaxial-rotor in forward flight including the sound pressure time history and directivity patterns are investigated in detail. Some meaningful conclusions are obtained from the calculated results. The counter-rotation of upper and lower rotors has significant effects on the sound pressure time history and leads to different phases of peak value at different observation points. The noise radiation intensity of coaxial rotor in forward flight exhibits an approximately symmetrical distribution on both sides of the forward flight direction, which is one of the important differences between the coaxial rotor and the single rotor.