Transient Flow Dynamics Analysis of a Large Prototype Francis Turbine at Different Loads

It is important to study the dynamic characteristics of flow transients in prototype Francis turbines as they play a vital role in understanding and optimizing turbine performance, ensuring stability and reliability, and preventing flow-induced structural vibration problems in hydropower plants. In this study, a prototype of a large-scale low-head Francis turbine installed in a hydropower plant is used to study its flow transient dynamics. The site measurement was conducted and the pressure levels in the inlet and outlet of the unit at various operating conditions were obtained. Using the measured data to set up the boundary conditions of the unsteady CFD calculations, and analyze the flow dynamics in the turbine channels at different operating conditions. The results show that pressure from the spiral case inlet to the draft tube outlet is a gradual downward trend at all loads. At 25% load, the guide vane opening is relatively small, a high-speed water ring is formed in the vaneless space, and a turbulent flow appears in the draft tube. With the increase of the guide vane opening, the high-speed water ring in the vaneless space gradually disappears. At 100
^%
load, the flow line is very smooth in the whole flow passage and the flow rate reaches the maximum value at the runner inlet. The calculated pressure distributions of the turbine flow domain under different operating conditions can be applied to the finite element model of the runner to study its flow-induced structural dynamics characteristics. The obtained results and conclusions provide references for the optimal operation of low-head Francis turbine units in other different power plants.