Cooling fan aerodynamic noise reduction with short inlet duct and its applicability

• Published in: International journal of refrigeration 2023-04, Vol.148, p.117-130
• Main Authors: Sun, Zonghan, Tian, Jie, Zhang, Tong, Du, Zhaohui, Ouyang, Hua
• Format: Article
• Language: English
• Subjects: Acoustic mode; Conduit d'entrée court; Cooling fan; Flux d'entrée non uniforme; Mode acoustique; Noise reduction; Non-uniform inlet flow; Réduction du bruit; Short inlet duct; Ventilateur de refroidissement
• ISSN: 0140-7007; 1879-2081
• DOI: 10.1016/j.ijrefrig.2023.01.013

•User friendly short inlet duct design for cooling fan noise reduction.•Far-field noise tests show the stable suppression of short duct on forward propagation tonal noise.•Full passage unsteady CFD reveals the flow control effect of the short inlet duct.•Mode test and acoustic analogy are combined to clarify the principle of short duct noise reduction.•The applicability of short duct to cooling fans with different sizes and configuration is expanded. This paper presents experimental and numerical analyses of the noise-reduction method of applying short inlet ducts to axial-flow cooling fans. Far-field noise tests of three different-sized cooling fans with tip Mach numbers of 0.143, 0.156, and 0.174 demonstrated that tonal noise was the primary source of aerodynamic noise. Through the installation of short inlet ducts on these fans, the upstream propagation of tonal noise was reduced. The average total sound pressure levels were decreased by up to 3.5, 4.8, and 7.1 dBA, respectively. At the blade passing frequency, the dominant upstream-propagating azimuthal acoustic modes were suppressed. Full-passage unsteady computational fluid dynamics calculations revealed that the duct transforms multiple suction vortices into a single annular vortex structure and weakens the interaction with the rotor blades. In addition, the acoustic analogy was used to compute the reduction of far-field noise and the variations in the major acoustic modes. This revealed a noise-reduction trend similar to that seen in the experiments. Essentially, the duct restrains the non-uniform inlet flow to influence the various inlet–rotor–stator interaction modes. The application of this approach to various fan configurations confirmed that a duct with a parameter of L/D (duct length/duct inner diameter) equal to 0.08 can be recommended as a compact and efficient way to reduce noise.