Analysis of fluid dynamic characteristics of large francis turbine-under low flow conditions

Abstract The operational instability of hydraulic turbine units poses a prevalent and significant challenge. Pressure pulsations occupy a prominent position among the primary factors contributing to turbine vibrations. Consequently, exploring the correlation between the internal flow field and pressure pulsations within hydraulic turbines constitutes a pivotal research focus in the contemporary vibration studies of such units. In this study, a three-dimensional geometric model of the Wudongde Francis turbine was developed. Using ICEM CFD for meshing, the internal flow conditions of the turbine’s entire flow passage were simulated in CFX software, focusing on analyzing flow characteristics and internal flow field attributes under 510 MW and 764 MW operating conditions. The results indicate the emergence of a pronounced blade vortex phenomenon under the 510 MW operating scenario, whereas at 764 MW, which approximates the rated operating condition, the runner blade vortex phenomenon diminishes markedly. Furthermore, the central vortex rope observed under the 510 MW condition induces severe pressure pulsations. Conversely, under the 764 MW condition, the central vortex rope aligns nearly vertically downward from the tailwater inlet’s center, exerting minimal influence on the adjacent flow patterns and substantially reducing pressure pulsations.