基于K-FWH声比拟方法的串列双圆柱气动噪声研究

为了研究串列双圆柱的气动噪声与大尺度涡脱落之间的关系，采用大涡模拟并结合K-FWH方程的方法进行研究。采用标准算例的实验结果对数值模拟方法进行了验证，证实了壁面自适应局部涡黏（WALE）大涡模拟模型结合基于K-FWH方程的声比拟方法能够较好地预测不同频率下的噪声谱密度。数值模拟结果表明:上下游圆柱的涡脱落频率相同，大尺度涡呈现反相位脱落。上游圆柱表面平均阻力系数大于下游圆柱，而下游圆柱表面的压力脉动更为剧烈。双圆柱绕流的气动噪声来源主要为偶极子噪声（包括柱体表面瞬时压强及其时间导数），其中瞬时压强的时间导数是主要的声压组成部分。在此基础上，对某一观测点的瞬时声压及其分解项之间的物理关联进行了研究。观测点的瞬时声压主要由下游圆柱产生的声压主导。由于上游涡脱落对下游圆柱的涡脱落的影响，导致下游升力系数频谱及观测点总噪声频谱呈现次级峰的现象。此外，通过希尔伯特变换发现观测点的声压脉动值不受上下游旋涡脱落的相位差影响。研究结果能为后续降低双圆柱气动噪声的研究做出贡献，给工程降噪问题提供参考。 

Investigation on aeroacoustic of tandem double cylinders by K-FWH acoustic analogy method

To study the intrinsic relation between the aerodynamic noise of tandem double cylinders and the large-scale vortex shedding behavior, we carry out large eddy simulations combined with the K-FWH equation. Firstly, the high-fidelity of the numerical treatment is verified by a comparison with the corresponding experimental results, and it has been proved that the combination of Wall Adaptive Local Eddy (WALE) viscosity model and K-FWH equation can accurately predict the distribution of noise spectrum density under different frequencies. The numerical results show that the vortex shedding frequencies of the upstream and downstream cylinders are the exactly same and the large-scale vortex shedding prove to be antiphase shedding. The mean surface drag coefficient of the upstream cylinder is larger than that of the downstream cylinder, but the pressure fluctuations on the downstream cylindrical surface are much more significant. The main contribution of the aerodynamic noise generated by flow around tandem cylinders is the dipole noise term (i.e. effects of the instantaneous pressure on the cylinder surface and the time derivative of the pressure), in which the time derivative of instantaneous pressure is the dominant component of sound pressure. The physical correlation between the instantaneous sound pressure and the lift and drag forces at a selected observation point is also explored. It is shown that the instantaneous sound pressure is mainly dominated by the sound pressure generated by the downstream cylinder. Owing to the influence of the upstream vortex shedding on the downstream cylinder vortex shedding, the downstream lift coefficient spectrum and the total noise spectrum exhibit discernable secondary peaks. Furthermore, by the Hilbert transform, it is found that the acoustic pressure strength at the observation point is not affected by the phase difference of the upstream and downstream vortex shedding. This research contributes to the understanding of the reduction of the aerodynamic noise of tandem double cylinders and sheds light on the engineering noise reduction.