Numerical analysis for active noise control of rotor based on dynamic variable-diameter method

Helicopters operating in high-speed forward flight conditions frequently generate High-Speed Impulsive (HSI) noise, posing significant challenges for effective noise control and limiting their operational flexibility. To address this critical issue, this study proposes a novel active noise reduction approach that dynamically adjusts rotor diameter, aiming to alleviate the generation and intensity of HSI noise. Utilizing the Chinese Laboratory of Rotorcraft Navier-Stokes (CLORNS) solver combined with the Ffowcs Williams-Hawkings (FW-H) acoustic analogy, aerodynamic and acoustic characteristics of the AH-1G helicopter rotor undergoing diameter adjustments were comprehensively simulated. This study methodically investigated key factors influencing the acoustic field, including the scale of rotor diameter retraction and the speed of retraction. The results clearly demonstrate the effectiveness of the proposed approach, achieving significant noise reductions ranging from 4 dB to 7 dB at crucial operational points while ensuring aerodynamic stability. Parametric analyses further reveal that the scale of rotor diameter retraction is a decisive factor in noise mitigation, and slower retraction speeds are beneficial, contributing to smoother flow transitions and diminished sound pressure fluctuations. Moreover, to overcome potential noise amplification induced by rotor control actions, this research introduces a compensation method incorporating a dynamic parameter adjustment mechanism. The developed control strategy is particularly effective in eliminating the noise growth observed in regions characterized by abrupt noise increases. Overall, this study provides an innovative and practical solution for helicopter noise management, substantially enhancing operational flexibility and acoustic comfort in high-speed flight conditions.