Magne Stéphan, Moreau Stéphane, Berry Alain
Mechanical Engineering Department, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada.
J Acoust Soc Am. 2015 Jan;137(1):228-37. doi: 10.1121/1.4904489.
In order to highlight the mechanisms responsible for subharmonic tonal noise, a complete aeroacoustic study of a ring fan in presence of a uniform inlet flow is conducted. Unsteady RANS simulations with a compressible flow solver are used to compute the flow field and identify the acoustic sources on the rotor. The tip clearance recirculation shows upstream vortices that impinge the rotor blades and create the main source of unsteadiness on the fan. Since these vortices rotate at a lower speed than the rotor, the frequency of the impact is lower than the blade passing frequency. The acoustic signature is computed by propagating the noise sources located on the rotor surfaces using two methods: A Ffowcs-Williams and Hawkings analogy in the time-domain and an analytical model in the frequency-domain based on the compact rotating dipole formulation. A comparison with experimental results confirms that the aeroacoustic phenomena responsible for the subharmonic tonal noise are well captured and properly propagated by the acoustic codes.
为了突出产生亚谐波音调噪声的机制，对存在均匀入口流的环形风扇进行了完整的气动声学研究。使用可压缩流求解器进行非定常雷诺平均纳维-斯托克斯（RANS）模拟，以计算流场并识别转子上的声源。叶顶间隙再循环显示出上游涡流，这些涡流冲击转子叶片并产生风扇上不稳定的主要来源。由于这些涡流的旋转速度低于转子，冲击频率低于叶片通过频率。通过两种方法传播位于转子表面的噪声源来计算声学特征：时域中的Ffowcs-Williams和Hawkings类比以及基于紧凑旋转偶极子公式的频域解析模型。与实验结果的比较证实，声学代码能够很好地捕捉并正确传播导致亚谐波音调噪声的气动声学现象。
