Numerical Evaluation of the Effects of the Rotating Cavities on the Axial Thrust Evaluation in Centrifugal Pumps

From an experimental point of view, the effects of the leakage flows in centrifugal pumps have been widely investigated. The leakage mass-flow and the losses have been correlated to the geometrical parameters that characterize the cavities and to the working conditions. Nevertheless, specific studies on particular geometries are sometimes necessary. To accomplish this necessity a numerical approach based on the CFD simulation of the leakage flows is presented. The leakage flow rate, the thrust acting on the walls and the losses are evaluated and correlated with the working conditions through a 2D/3D CFD study. Several simulations have been performed to account for the possible shift in the shaft positioning, the rotational velocity, the wear of the ring and the three dimensional effects. The front and back shroud of a centrifugal impeller and the central balancing drum of a multistage pump in opposite configuration have been considered. In order to validate the used CFD methodology, the results are compared with the data given by the experimental correlations used by the industry. The results obtained for the leakage flows are used to evaluate the variations in the residual axial thrust in multistage pumps using an in-house developed tool. The obtained thrust curves are compared with each other and show a good agreement with the real thrust supported by the bearing rings.