Numerical study of the optimal position of the leading edge of the impeller blade of the feed pump’s stage

BACKGROUND: An impeller is the most important element of the pump unit, determining its main parameters. When designing an impeller’s blade system, one of its most critical components is the leading edge of the blade. Its geometric parameters have a significant impact on flow formation, stability of operational characteristics and cavitation qualities. One of these important parameters is the optimal position of the leading edge of the blade, which is often chosen using the existing alternatives, since the study of this issue requires a significant number of physical experiments, the implementation of which is quite expensive. Considering the trend of rapid development of digitalization processes and increasing computing power, the abovementioned difficulties can be minimized with the use of mathematical modeling methods. The objects of this study are multi-stage feed pumps used at nuclear power plants with stage delivery rates n_s=70, 100 and 125.

AIM: Conducting the study of the optimal position of the leading edge of the impeller blade and determination of the influence of this parameter on the main integral parameters of the flow path using numerical methods.

METHODS: The search for the optimal position of the leading edge of the impeller blade was carried out using mathematical modeling of the three-dimensional flow of a viscous fluid in the computational domain of the studied object. The calculation models of flow parts are full-sized, consist of impellers, diffusers, inlets, outlets, and front and rear gap seals. Using the computational fluid dynamics (CFD) software package, calculations were carried out for various positions of the leading edge of the impeller blade.

RESULTS: Numerical research of the position of the leading edge showed that its optimal position for n_s=70, 100 and 125 corresponds to the values ${\overline{Z}}_{ср}$=0.095; 0.15 and 0.17 respectively. A stable falling shape of the head-capacity curve is ensured for n_s=70 and n_s=100 at ${\overline{Z}}_{ср}$=0.08 … 0.12, and for n_s=125 at ${\overline{Z}}_{ср}$=0.08 … 0.20. The best cavitation properties are found for the blade system with ${\overline{Z}}_{ср}$=0.08 at n_s=70, at n_s=100 with ${\overline{Z}}_{ср}$=0.12, and at n_s=125 with ${\overline{Z}}_{ср}$=0.16.

CONCLUSION: Numerical research and analysis of existing designs of multistage pumps showed that for the studied stage delivery rates from the point of view of energy and cavitation parameters, the optimal relative axial position of the middle point of the leading edge, measured from the intra-channel part of the hub, is in the range of ${\overline{Z}}_{ср}$=0, 9 ... 0.11 for n_s=70 in the range of ${\overline{Z}}_{ср}$=0.14 ... 0.16 for n_s=100, and in the range of ${\overline{Z}}_{ср}$=0.16 ... 0.18 for n_s=125.