Numerical simulation of cavitating flow in a centrifugal pump as turbine

In this study, the cavitating flow and cavitation performance are studied by employing the computational fluid dynamics method in the turbine mode of a centrifugal pump at part-load, best efficiency, and over-load points. The flow models are validated in the pump mode under noncavitation condition. The relationships between the performance variables and net positive suction head available are obtained, and the corresponding net positive suction heads required are extracted. The flow patterns, location, and shape of the cavity are illustrated; the pressure coefficient profiles on the blade surfaces are clarified and compared with those in the pump mode under both noncavitation and critical cavitation conditions. The cavitation performance and flow pattern as well as cavity shape in the turbine mode are distinguishably different from the pump mode. It is found out that the cavitation behavior in the turbine mode exhibits three notable features: a lower and less flow rate-dependent net positive suction head required, a flow rate-dependent suppressed rotational flow in the draft tube, as well as a rotational and extendable cavitating rope originated from the impeller cone. The results and methods can be important and useful for the design and selection of a centrifugal pump as turbine.