The upstream and downstream flowfields of a straight blade inlet guide vane(IGV)for a centrifugal fan were measured with a five-hole probe. The result shows that the radial distribution of the flowfield is unsymmetrical

while the circumferential distribution of flow is nearly symmetrical

and that IGV has nearly no influence on distribution of upstream flow. The resistance coefficient and the prerotation coefficient increase with the increment of the pitch angles of IGV. Moreover

the increment of resistance coefficient is much greater than that of prerotation coefficient when the pitch angles exceeds 40 - 50 degrees. Therefore the prerotation coefficient and the resistance coefficient could be used as major parameters to evaluate the performance of IGV. The optimal gap between IGV and the impeller is about 4 - 8 times the length of the blade chord considering the symmetry and prerotation of the flow field. Based on the characteristics of the radial

circumferential and axial distribution of the flow field

some proposals are provided to enhance the performance of IGV

such as the increment of the blade chord at the center of IGV

improvement for the airfoil shape

and optimization of the cascade solidity.