Numerical and experimental investigation of the effect of balancing holes on pump performance in single stage centrifugal pumps

In the thesis study, the effect of drilling balancing holes, which is used to reduce axial loads in centrifugal pumps, on pump efficiency and axial loads has been investigated numerically and experimentally. A commercially produced single-stage centrifugal pump was chosen for the study. The design optimization of the balancing holes was carried out with the help of Computational Fluid Dynamics (CFD), by using only optimization methods and programs in line with the parameters and levels on the impeller, without making any changes in the body designs of the selected pump. Taguchi Experimental Design Method (TDTY) and Direct Optimization were used for optimization study and Ansys Fluent program was used for CFD analysis. In order to achieve the optimum result, four parameters were determined on the balancing holes: hole center angle, hole diameter, hole center diameter and number of holes. In the first stage of the optimization studies, TDTY was used in the L16 orthogonal array. The obtained results were evaluated with single and multi-purpose signal/noise (S/N) ratio and analysis of variance (ANOVA). Compared to the pump without balancing hole, the bearing life of the pump with balancing hole designed with TDTY increased from 2160 operating hours to 510000 operating hours, while the Minimum Efficiency Index (MEI) decreased from 0.462 to 0.276. In the second stage of the optimization studies, Direct Optimization was used. According to the definitions and limitations made, a total of 111 numerical analyzes were carried out until the optimization approached the targeted results. The optimization study was completed in approximately 280 hours and 3 candidate geometries with the best results were obtained. As a result of numerical analyzes and comparisons, the bearing life of the pump with optimized balancing hole compared to the pump without balancing hole increased from 2160 to 320000 operating hours and the MEI value was calculated as 0.435. In the last part of the study, a pump with optimized balancing hole was manufactured and performance tests were carried out. As a result of the performance tests, the head and pump efficiency values of the pump with optimized balancing hole decreased by 0.23% and 0.28%, respectively, while the power values increased by 0.05% compared to the pump without balancing hole. Therefore, the MEI values decreased from 0.435 to 0.415. However, bearing temperatures are measured at 65 °C for the pump without balancing hole and 40 °C for the pump with optimized balancing hole.