Influence of Surface Roughness on Cavitation in a Centrifugal Pump

Cavitation in centrifugal pumps is still a problem that must be dealt with by engineers and operators of such devices. Noise and vibration, erosion and limitations of the operating range (NPSH(3%)) are the most obvious consequences caused by cavitation. An efficient and reliable operation of centrifugal pumps is only possible if operators and designers have experience and knowledge about the different cavitation regimes that might occur and that differ in erosive potential and aggressiveness. The present paper shows how different surface roughnesses on the blades of the impeller influence the form of appearance of cavitation. Different cavitation regimes influence the NPSH curves and the corresponding NPSH(3%) values only slightly even if appearance and size of the cavitation areas differ remarkably. The experiments also showed that cavitation and cavitation inception in centrifugal pumps is strongly affected by the occurrence of gap cavitation at the impeller side gap. Cavitation clouds produced at the gap are sucked into the pump and initiate cavitation at the leading edge of the blades. In this way large cavitation areas can develop even if the NPSH value is far away from the NPSH(3%) limit.