A new strategy of designing micro vortex generators to mitigate tonal noise generation from voluteless centrifugal fan

Paper in proceeding, 2022

Low-speed voluteless centrifugal fans are typically used in ventilation systems. The negative side of the fans is noise, particularly tonal noise of which the dominant tone is at the blade passing frequency (BPF). One of the important noise contributors is the gap between the rotating shroud and the stationary inlet duct. Previous studies have shown that the flow passing through the gap causes turbulence that interacts with the blade leading edge (BLE), rendering surface pressure fluctuations that are the tonal noise sources at BPF. In this study, a method of assembling micro vortex generators (MVGs) to control the turbulence for voluteless centrifugal fans is proposed for the first time. The assembling is made in two different ways: 14 add-ons on the shroud surface at the gap, and 7 ones on the BLE surface near the shroud. The effects of the MVGs are investigated using the hybrid computational aeroacoustics method, which couples the improved delayed detached eddy simulation method with the Ffowcs Williams and Hawkings acoustic analogy. Our simulations show that the MVGs are effective to control the turbulence and mitigate the tonal noise. The assembled array of 7 MVGs achieves more reduction of the tonal noise than the 14-MVGs array.