The aerodynamic noise generated from a cooling fan and its support frame is one of the major noise sources of many engineering machines, such as automobile engines and communication base-stations. A generic model composed of a vertically-installed flat strut behind an asymmetrical airfoil is used to investigate numerically the noise characteristics and generation mechanism of a cooling fan by using the SST-SAS turbulence model combining with FW-H formula. The airfoil–strut configuration is varied either by changing the perforation rate of the strut or by adjusting the streamwise gap between the airfoil trailing edge and the strut. The motivation is to investigate the effects of the two parameters on the aerodynamic and noise behaviors of the airfoil–strut​ model and evaluate the influences of noise control methods. The analysis of noise generation mechanism and far-field directivity indicates that in the vertical direction both the unsteady lift forces acting on the airfoil and strut contribute equally to the far-field noise, whereas in the upstream/downstream direction the noise is produced mainly by the unsteady drag on the strut. In addition, the whole model shows the directivity characteristic of an omnidirectional noise source. With the increase of the strut perforation rate, both the unsteady lift and drag on the airfoil and strut are reduced due to the attenuation of the Karman vortex street in the flow field, resulting in a far-field noise reduction. There exists a frequency lock-in (i.e. a resonance) between the airfoil and the strut in which the unsteady characteristic of the airfoil is induced by the downstream strut. However, this lock-in loses its strength with the increase of the streamwise separation between the airfoil and strut, accompanying with a change of far-field noise.

冷却风扇及其支撑框架产生的空气动力学噪声是许多工程机械（例如汽车发动机和通信基站）的主要噪声源之一。利用SST-SAS湍流模型结合FW-H公式，利用不对称翼型后方垂直安装的扁平支撑组成的通用模型，对冷却风扇的噪声特性和产生机理进行了数值研究。通过改变支撑杆的穿孔率或通过调节翼型后缘与支撑杆之间的沿流方向的间隙，可以改变翼型-支撑杆的配置。目的是研究这两个参数对翼型-支撑模型的空气动力学和噪声行为的影响，并评估噪声控制方法的影响。对噪声产生机理和远场方向性的分析表明，在垂直方向上，作用在翼型和支柱上的不稳定升力均对远场噪声产生同等贡献，而在上游/下游方向，噪声主要是由支杆上的不稳定阻力。此外，整个模型还显示了全向噪声源的方向性特征。随着支柱射孔率的增加，由于流场中的Karman涡街的衰减，翼型和支柱上的不稳定升力和阻力都减小了，从而降低了远场噪声。翼型件和支柱之间存在频率锁定（即共振），其中，翼型的不稳定特性是由下游支柱引起的。然而，