Influence Of Shroud On Performance Of Axial Flow Fan

In order to improve the aerodynamic performance and reduce the noise of air conditioner outdoor unit, it is important to study flow characteristics of blade-tip region and aeroacoustics characteristics of half ducted axial flow fan, which has already become a research hotspot in outdoor units. In this paper half ducted axial flow fan system with shroud are investigated. Influence of Shroud's width, axial location and shroud's inlet structure on inflow and aeroacoustics performance of axial flow fan is researched, which aims to provide theoretical basis for improving aerodynamic performance and reduce the noise of half ducted axial flow fan.Influence of shroud's width on performance of axial flow fan is studied. The variation of radial and axial trail of tip vortex core with shroud's width is concluded. The research points that for a fan with a narrow shroud, the fan flux increases linearly with increase of shroud's width. For a fan with a wide shroud, the flux doesn't increase obviously with increase of shroud's width. Shroud's width has some influence on tip recirculation zone and vorticity of shroud's internal surface. With shroud's width increases to a certain extent, tip vortex will generate at somewhere which is more far away from the suction side of the impeller in the circumferential direction. For a fan with a narrow shroud, the trail of the tip vortex core moves toward to axis with the shroud's width increases. For a fan with a wide shroud, the radial trail of tip vortex core doesn't change obviously with the shroud's width increases because of the development of tip vortex is limited. The axial trail of tip vortex core moves upstream and the static pressure of tip vortex core decreases with the shroud's width increases, but too wide shroud will change the form of tip vortex.Influence of shroud's axial location on performance of axial flow fan is analyzed. The variation of radial and axial trail of tip vortex core with shroud's axial location is concluded. The research points that the fan flux is maximal when shroud's outlet plane keeps within the outlet plane of the blade. Shroud's axial location has some influence on tip recirculation zone and vorticity of shroud's internal surface. When shroud covers the leading-edge of blade-tip, With the shroud moving from downstream to upstream, tip vortex will generate at somewhere which is more far away from the suction side of the impeller in the circumferential direction. With the shroud moving from downstream to upstream, the radial trail of the tip vortex core moves toward to axis and the axial trail of tip vortex core moves toward upstream one after another. The tip vortex moves far away from axis suddenly when the tip vortex is not covered by shroud. With the shroud moving from downstream to upstream, the static pressure of tip vortex core presents downtrend basically.LES/FW-H was applied in researching aero-acoustic performance of half-ducted axial flow fan with curve serrated inlet. The results show that using unequal width shroud with curve serrated inlet can decrease the tip vortex region and reduce the strength of tip vortex. Inlet of the shroud has some influence on tip vortex core trail. Shroud with curve serrated inlet make the trail of tip vortex more far away from axis. With the increasing number of curve serration, the trails of tip vortex are more far away from axis. The overall noise of half-ducted axial flow fan is closely related to the acoustic radiation characteristics of shroud. Using shroud with curve serrated inlet can reduce fan noise. It can reduce more than 3 dB at the downstream of axis direction. With the increasing number of curve serration, the noise reduction level is more obvious.The present work is financially supported by the Fundamental Research Funds for the Central Universities under the grant No. 2013QN080.