EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF THE INFLUENCE OF CAVITATION ON THE HEAD DROP CURVES OF CENTRIFUGAL PUMPS

Cavitation is a major problem in pump operation because this phenomenon may lead to hydraulic performance loss, increased noise levels, and various types of instabilities. Therefore, fast and robust calculation methods that the industry can confidently use to predict cavitation are being actively studied. In the present work, the cavitation performance of pumps designed at two specific speeds is studied numerically and experimentally. Net positive suction head (NPSH) measurements for the pumps are performed over their operating ranges. Moreover, Q-NPSH3 and head drop curves are obtained for the pumps at metric specific speeds of 22.4 (rotating at 2950 rpm) and 12.5 (rotating at 1475 rpm), respectively. Cavitation is visualized by a stroboscopic light source and recorded at various NPSH levels for three different flow rates. The relationship between cavity length and head drop is revealed. The Singhal [18] model, a homogeneous mixture cavitation model, is typically used in numerical calculations. A turbulent viscosity correction for the multiphase calculations of cavitating flow around hydrofoils is proposed in the literature. In the present work, this correction is applied to modify the Singhal [18] cavitation model, and the head drop curve of the pump with ns = 22.4 is computed using this modified model. Consequently, the compatibility between the numerical and experimental results is found to improve. Accordingly, the cavitation calculations for the pump with ns = 12.5 are performed using the modified model. The computed cavitation structures at various points on the head drop curves are compared with experimental images. Geometrically similar forms are achieved.