This study aims to minimize the noise generated by automobile cooling fans. Fan blade structures with ridged surfaces based on bio-inspired principles are 3D printed and used to replace the conventional fan blades. The effect of the bio-inspired ridge structures on the noise reduction of the cooling fan is demonstrated by orthogonal experiments in a semi-anechoic chamber. Experimental results show that with an increase in the rotational speed, the effect of the surface textures on the acoustic performance of the cooling fan becomes more significant. For example, at a fan speed of 1750 r/min, all the bio-inspired blade designs reduce noise compared with the original fan and, in particular, the sound pressure level is reduced by 3.83 dB(A) for the design with a ridge width of 4 mm and a ridge pitch of 15 mm. Through variance analysis of the measured noise, the ridge pitch distance has the most significant impact on noise reduction under low speed conditions whilst, under high speed conditions, the ridge width has the most significant influence. In addition to the experimental studies, computational fluid dynamics (CFD) simulations of the cooling fan are carried out to explain the mechanism of noise reduction for the ridged fan blades. When the fan runs, the horseshoe vortexes generated by the ridge structures disturb the flow of the boundary layer, reduce the influence of the fluid flow on the boundary layer, and delay the transition of the fan blade laminar flow to turbulence. It is also seen that there is a reduction of the intensity of the fan blade trailing edge vortices and the scale of the secondary vortices, thereby achieving the overall aim of noise reduction. This research has significance in the noise reduction design of automobile cooling fans.

中文翻译：

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基于仿生设计的汽车冷却风扇降噪

本研究旨在尽量减少汽车冷却风扇产生的噪音。基于仿生原理的具有脊状表面的风扇叶片结构是 3D 打印的，用于替代传统的风扇叶片。通过半消声室中的正交实验证明了仿生脊结构对冷却风扇降噪的影响。实验结果表明，随着转速的增加，表面纹理对冷却风扇声学性能的影响变得更加显着。例如，风扇转速为1750转/分时，所有仿生叶片设计与原风扇相比均降低了噪音，特别是带脊设计的声压级降低了3.83 dB(A)宽度为 4 毫米，脊间距为 15 毫米。通过对实测噪声的方差分析，在低速条件下，脊间距对降噪的影响最显着，而在高速条件下，脊宽度的影响最显着。除了实验研究外，还对冷却风扇进行了计算流体动力学 (CFD) 模拟，以解释脊状风扇叶片的降噪机制。风机运行时，山脊结构产生的马蹄形涡旋扰动边界层的流动，减少流体流动对边界层的影响，延缓扇叶层流向湍流的转变。还可以看出，风扇叶片后缘涡的强度和次级涡的规模都有所降低，从而达到降噪的总体目标。该研究对汽车散热风扇的降噪设计具有重要意义。