离心风机基频气动偶极子噪声的数值研究

Numerical Study on Blade-Passing Frequency Noise of Aerodynamic Dipole in a Centrifugal Fan

运用计算流体动力学技术及声比拟理论研究了离心风机3个不同流量下蜗壳及叶片表面偶极子声源产生的基频噪声.风机内部三维瞬态流场由计算流体动力学模拟得到.根据气动声学的FW-H方程对蜗壳内表面提取偶极子声源,对于叶片噪声利用Lowson公式进行建模.为了使计算模型更符合实际,建立了以蜗壳为界的内外声学直接边界元模型,使用多区域声学边界元模型,考虑蜗壳对声传播的散射作用,内部噪声通过蜗壳的进出口传播到风机外部.结果表明:在非定常流场中,蜗壳表面的压力波动以基频为主,而叶片上的压力波动并没有明显的基频分量;蜗舌是基频噪声的最主要声源;随着流量变大,蜗壳辐射的噪声急剧增加;由叶片产生的偶极子基频噪声比蜗壳小,特别是在大流量工况下.

The computational fluid dynamics （CFD） technique combined with the acoustic analogy theory is employed to study the blade passing frequency （BPF） noise caused by the volute casing surface dipole and the blade rotating dipole in a centrifugal fan. A 3D unsteady turbulent internal flow is obtained by CFD at three different flow rates. The volute surface dipole is extracted based on the FW-H equation and the blade noise is modeled by the Lowsoffs formula. The multi-domain direct boundary element method is applied to study the noise propagation including the interior acoustic problem and the exterior acoustic problem, and these two models established are coupled together at the casing inlet and outlet openings. It is considered that the interior noise will spread outside through the casing openings by the sound scattering effect of the casing. The results show that the pressure fluctuation on the casing surface had the clear BPF component while there was no obvious BPF fluctuation on the blade. The volute tongue was the main contributor to the BPF fan noise. In addition, the casing noise strength was increased dramatically with the flow rate and the BPF blade noise was smaller than the casing noise, especially at large flow rates.