RADIAL FORCES IN A CENTRIFUGAL COMPRESSOR EQUIPPED WITH VANED DIFFUSERS

A non-uniform pressure distribution in a volute of a centrifugal compressor causes a radial force on the impeller and the rotating shaft. The diffuser preceding the volute determines how the flow field entering to the volute, and affects the radial forces that are caused by the volute towards the impeller. The radial forces were measured for three different vaned diffuser geometries and one vaneless diffuser with a pinch. The force measurements were made for each assembly with the same compressor using active magnetic bearings. The impeller forces were found to be the smallest near the design flow and higher at choke and at stall for all configurations. The radial forces on the impeller were higher with the vaneless diffuser than with the vaned diffuser. The force distributions with the vaned diffusers were uniform and clearly different from those of the vaneless diffuser. In addition, the radial forces were estimated using static pressure distributions measured at the impeller outlet. The radial force determined from the pressure measurements verified the measured forces obtained in the magnetic bearing measurements.