Methodology for the Residual Axial Thrust Evaluation in Multistage Centrifugal Pumps

One of the most challenging aspects in horizontal pumps design is the evaluation of the residual axial thrust acting on the rotating shaft. The thrust is affected by pump characteristics and working conditions. Solving this problem is easier for a single stage pump than for multistage pumps, even in partially self-balancing opposite impeller configuration. The challenge is then to individuate a procedure that will provide the residual thrust value with a moderate computational effort, dealing with the industrial requests of accuracy and reduced time consumption. A procedure is proposed, which consists in the numerical simulation of each pump component. For each component, the obtained mass-flow/thrust correlations are coupled by using a momentum balance equation used to calculate the axial thrust as a function of the working conditions. The main topic in multistage pump modeling is the leakage flows characterization by means of accurate numerical analysis. Therefore, the cavity flows behavior is investigated and the flow structures individuated. The numerical investigation of the pump’s components provides also a thorough knowledge of fluid dynamic fields. The proposed procedure is able to predict both the direction and the variation of the thrust in a selected range of flow rates, while the value of the thrust is affected by a non-negligible error generated by “real machine” effects.