Numerical Investigation of Outlet Hub Geometry on the Performance of Large Axial Fan

The large axial fan’s outlet hub shape changes with its working environment. Usually for saving cost, the hub geometry of fan’s outlet section is roughly processed. There is no geometry specification for the outlet hub section, which makes its structure seriously mismatched with other parts. When a blade which has good performance is fitted into an actual production, it probably couldn’t get a desired result. This shows that the effect of outlet-hub geometry on the performance of large axial fan couldn’t be neglected. To study the effect, four cases of different outlet hub geometries of a large axial fan have been designed and investigated in current paper. Each case has been carefully calculated by using numerical simulation methods. By comparing their aerodynamic characteristics and analyzing flow structures in the tip and hub region of the fan blade, the results show that with the same blade tip clearance, the shape of hub geometry has little effect on the tip flow field. However, the fan efficiency is obviously affected by the hub shape. Straight hub could approve the total pressure of the fan, while shrink hub could reduce shaft power more efficiently. A kind of proper outlet hub geometry could greatly improve the flow performance in the hub region and increase the fan efficiency. So we could choose a proper shape of outlet hub for different working requirements.