Abstract: In order to reduce the aerodynamic performance degradation caused by the downsizing of the multi-blade centrifugal fan volute, a combined cutting strategy with equal depth proportions is proposed on the basic of the single-sided cutting method. Taking the spiral volute of a multi-blade centrifugal fan used in range hoods as the research object,the schemes obtained by the combined cutting method, the single-sided cutting method, the shrinking method and the prototype fan are numerically investigated, and detailed comparative analysis of their internal flow and aerodynamic performance is then carried out under full working conditions. It is illustrated that different downsizing strategy had varying impacts on the fan pressure and efficiency in different flow-rate. The combined cutting strategy weakened the negative effect caused by the excessive cut depth during single-sided cutting, reached a best comprehensive aerodynamic performance among all volute downsizing schemes. Compared with the shrinking scheme with a continuous curvature volute profile, the discontinuous volute obtained by the combined cutting achieved a smaller decline in the impeller efficiency and the static pressure recovery capacity relative to the prototype fan, lead to an distinct performance advantage.

Key words: multi-blade centrifugal fan, volute, downsizing design, numerical simulation, aerodynamic performance