Numerical Analysis of Aeroacoustic Characteristics for Coaxial Counter Rotating Propellers Considering the Self-Interference Effect

Based on the FW-H equation and the CFD method, the coaxial counter rotating propellers aeroacoustic characteristics in hover are calculated and analyzed. First, a set of analysis method for aperiodic coaxial propellers aeroacoustic characteristics is developed. The aerodynamic and aeroacoustic characteristics of the Harrington coaxial rotor 1 (HC1) in hover and the AH-1G rotor in forward flight are calculated, and the employed numerical analysis method is validated through comparisons with experimental data. Then, the aeroacoustic characteristics of the coaxial propellers with different propeller spacings and rotational speed ratios between lower and upper propellers are analyzed, and the noise radiation characteristics are discussed in detail. Additionally, the A-weighted sound level is utilized to evaluate the impact of noise on urban residents, and some new conclusions are drawn. Decreasing the propeller spacing results in an increase in noise level within the central cross-sectional area beneath the propeller. By adjusting the rotational speed ratio, the acoustic distribution within this cross-shape area can be averaged, thereby reducing the maximum overall sound pressure level in the initial noise hotspot area by approximately 3 dB.