Aerodynamic noise optimization of a voluteless centrifugal fan with biomimetic blades inspired by eagle-owl wingtip morphology

Inspired by the low-noise characteristics of the eagle-owl nocturnal flight, two novel designs for blades of the voluteless centrifugal fan are proposed to improve the aerodynamic performance and reduce the noise. A serrated structure inspired by the eagle-owl wingtips at the trailing edge is adopted to design and optimize the blade. Based on the computational fluid dynamics methods and the Ffowcs Williams–Hawkings equation, the impact of the serrated leading and trailing edges on the aerodynamic performance and acoustic characteristics of a fan is investigated. The optimal geometric parameters of the bionic sawtooth are determined. Subsequently, a comprehensive comparison of the flow characteristics and noise spectra among the fan with the original blade (OBLE), the serrated leading-edge blade (SLBE), and the serrated trailing-edge blade (STBE) is conducted, revealing the control mechanism of the SLBE and STBE on the flow properties and noise optimization principles. Results demonstrate that the SLBE fan not only mitigates pressure fluctuations and optimizes vortices but also increases the maximum flow rate by 1.76%. Although the STBE fan also optimizes pressure and vortices, its efficiency slightly decreases due to reduced blade lift. However, the STBE fan achieves outstanding noise suppression, reducing the sound pressure level (SPL) by 6.42 dB compared to the OBLE fan. While the SLBE fan yields a limited SPL reduction of only 1.97 dB. Additionally, the noise energy shift at 1364 Hz demonstrates frequency modulation caused by the serrations. The blade trailing edge is identified as the primary noise source, and the STBE fan significantly attenuates broadband and tonal noise by optimizing the airflow disturbance suppression at the impeller outlet. These findings validate the feasibility of using biomimetic serrated designs to optimize the performance of voluteless centrifugal fans.