An experimental investigation on the clocking effect between inlet guide vanes and vaned diffuser in a centrifugal compressor stage

Different circumferential angle positions between stator or rotor vane rows in turbomachinery can lead to different flow structures or stage performances. The clocking effect phenomenon has been detected in axial compressor and turbine by investigators, but rarely reported on centrifugal compressor. The present work is an experimental investigation on the stator clocking effect between inlet guide vanes (IGV) and vaned diffuser in a low-speed centrifugal compressor. The experimental rig consists of a circumferentially rotatable IGV, an unshrouded centrifugal impeller, a vaned diffuser, a volute and etc. The impeller diameter is 796mm, and the rotate speed is about 3100 rpm. At each inlet prewhirl angle of-20°, 0° and +20°, the stage performance curves are measured at three clocking angle positions of 0°, 8° and 16°. The result shows that at the circumferential angles of 0° and 8°, the efficiency curve has a double peak value feature, but at the angle of 16° being the conventional single peak value curve. Further, at the circumferential angles of 0° and 8°, the stage efficiency is bigger 3.6% than that case of the angle being 16°, where the IGV prewhirl angles are 0° and 20°. When the IGV prewhirl angle is changed into -20°, the stage efficiency increases about 2.0% near the first peak value position at the circumferential angles of 0°and 8° than at 16°, however, at the second peak value position, the stage efficiency at the circumferential angle of 0° is bigger about 1.4% than at 8° and 16°. Moreover, the circumferential angle positions between IGV and vaned diffuser have corresponding influence on the pressure ratio.