A highly loaded fan with the insufficiency of the stall margin in the states of off-design speed was studied. After numerical simulation of three dimensional flow using commercially available CFD code NUMECA

the change of aerodynamic performance of a variable inlet guide vane (VIGV)

and the improvement method of low-speed performance of the fan were investigated

when the VIGVs front and back vane parts can be rotated in large range of angle. Results of numerical simulation indicated that the camber angel of the VIGV was one of the most important influential factors to the performance of the VIGV. The front vane part of the VIGV was rotated at some angle

the actual camber angle of the vane was reduced

helping to delay flow separation on the vanes suction surface

and broaden the VIGVs adjustable angle with a low-loss level. Besides

the VIGV was not sensitive to the position of a slot between the two vane parts

if both of the vane parts were rotated with proper angles. The VIGV improved the adiabatic efficiency of the highly loaded fan under the off-designed conditions

the adiabatic efficiencies were improved by 2.04%

5.48%

6.18% and 6.82% at 90% speed

80% speed

70% speed and 60% speed. Because the throat line of the fan was further away from the throttle line

the fans surge margin was expanded obviously at off-speed.