Numerical simulations on the unsteady inlet guide vane(IGV)-impeller interaction were performed under different prewhirl angles.The main factors to IGV-impeller interaction were also discussed to analyze the influence of unsteady flow effect upon flow field of impeller.The results show that the impeller flows periodically under large negative prewhirl angle.In such case

the wake of IGV outlet

especially the large size vortice formed behind IGV

was the key factor to strong unsteady flow in the downstream impeller inlet.The unsteady influence of IGV wake involved only a part of impeller passage(about 30 percent of the blade chord)

and the potential repercussion of the impeller ranged from IGV trail edge to 20 percent of the chord.Both the passing frequency and rotating frequency of the blade have influence on the unsteady flow in IGV.