The Near Field Acoustics of the Active Noise Control of a Model Propeller

[摘要] The Near field properties of a 6" radius model propeller, and the Active Noise Control(ANC) of the Blade Passing Tone (BPT) have been studied. The study has been careful toidentify and separate the effects of the hydrodynamic near field and the geometric near field. The near and far field radiation regions of a model propeller were consideredseparately. Firstly to determine if far field control affects the near field noise levels and secondly to determine how the far field noise levels are affected by near field control. It has been found that active noise control (ANC) of the propeller blade passing tone (BPT)can be achieved within the geometric near field, however the extent of the effective control is small. The near field optimized ANC can result in as much as 10.5 dB ofreduction of the BPT, however this noise reduction can only be achieved over a small spatial region. For this experimental arrangement there is no effective ANC directlybehind the propeller. Whenever ANC is optimized for near field noise it results in far field noise levels of up to 15.2 dB above the uncontrolled far field propeller levels. The far field optimized control shows no detrimental effects in the near field noise environment.

[发布机构] University:North Carolina State University