A Study on the Process of Low-Frequency Noise Generation in a Multi-Blade Centrifugal Fan

Abstract

This study numerically investigates the flow characteristics of a multi-blade centrifugal fan in order to identify the process of low-frequency aerodynamic noise generation. Computational analysis has been carried out using the large eddy simulation (LES) model. In the preliminary study, it was confirmed that the present computational fluid dynamics simulation using LES shows good agreement with the experimental results of the performance curve, sound pressure spectra, and the flow field obtained by using a time-resolved particle image velocimetry (PIV) system. Consequently, it was found that the appearance of an unexpected significant flow, which recirculated from the scroll casing, passed through the impeller, and returned to the scroll casing again to exit the scroll casing in a specific region, was similar to the flow suggested in the experimental results, which were obtained utilizing PIV measurement. The fluid flow related to the fluctuation, which was remarkably not included in the impeller main flow, existed beside the outer main flow. A certain amount of fluctuated flow bifurcated near the scroll end, one regurgitating into the impeller, and another colliding with the tongue. The former became a driving source of noise and the latter a direct noise-generating factor. Consequently, it was demonstrated that a significant fluctuation owing to flow collision with the tongue propagated through the impeller and formed a loop.