Investigation of the flow mechanisms in an axial fan with casing treatment at different Reynolds numbers

This study investigates the effects of Reynolds number (Re) and axial slot casing treatment (ASCT) on the performance and internal flow mechanisms of a single-stage fan using a validated numerical method. The effect of Re and ASCT on the performance of the fan are studied. A dimensionless loss analysis method based on the first law of thermodynamics is adopted to quantitatively assess the flow loss inside the fan. The results show that there are significant differences in the flow field and efficiency at different Re due to differences in the boundary layer thickness and the spanwise separation degree. The difference between the boundary layer and secondary flow losses is the main reason for the efficiency discrepancy at different Re. The thicker boundary layer at low Re and the more severe secondary flow make the loss caused by the velocity gradient more significant. The broadening of the stall margin is attributed to the bleed and injection of the secondary flow caused by the recirculation of the ASCT. The ASCT has a significant effect on the inner loss of the rotor but no obvious effect on the stator. The source distribution of the loss is almost unaffected by the ASCT.