Institutional and Legal Aspects
May 18 of 2011
NUMERICAL STUDY ON THE EFFECT OF IMPELLER TRIMMING ON THE PERFORMANCE AND LOW CHARACTERISTICS OF A CENTRIFUGAL PUMP WITH VOLUTE-CASING
Raúl Barrio / Eduardo Blanco / Jorge Parrondo / Carlos Santolaria
Paper published on PCH Notícias & SHP NEWS #45.
The trimming of the impellers of centrifugal pumps is a usual practice in industry in order to adapt the pump performance features to the requirements of a specific hydraulic system, but it also affects the general properties of the flow through the machine. On one hand, it affects the matching of the flow exiting the impeller and the flow along the volute and, on the other hand, the increment of the impellertongue gap is expected to result in a decrease of the fluid dynamic loads on the machine. A numerical study is presented on the flow through a conventional vaneless volute centrifugal pump, equipped with four impellers so that the impeller-tongue gap ranged from 8.8% to 23.2%. Five different flow rates, ranging for 20% to 160% of the nominal flow rate, were simulated for each of the impellers by means of commercial software that solved the 3D-URANS equations. Sensitivity tests for one of the impellers proved that the predictions were independent of the numerical parameters and, additionally, the predictions were compared to experimental data which allowed for the validation of the numerical model. This paper reports on the variation of the general performance characteristics of the pump operating with the different impellers tested, resumed in the proposition of pseudo-similarity correlations. Also, an analysis is presented on the effect of impeller trimming on the local flow changes at the tongue region that are related to the passage of the impeller blades. Finally, the dynamic loads on the machine are estimated as a function of flow rate and impeller-tongue gap. Key words: centrifugal pump, impeller trimming, numerical simulation, unsteady flow, blade-passing frequency, fluid-dynamic load.