Controlling Flow in Draft Tube of Francis Turbine by Vortex Preventing Element

Abstract

As importance of renewable energy sources increase with respect to energy demands, turbine efficiencies become more important. Francis turbines are one of the most common turbine types in use at hydroelectric power plants.In some cases such as load rejection and high load operations, pressure fluctuations and vortex formation cause Francis turbine efficiency and endurance to decrease. To prevent these effects, a new component named Vortex Preventing Element (VPE) is designed. The main idea of this new design is damping the swirling slow with Vortex Preventing Element and improving the performance of suction side of runner blades. This new element is mounted between turbine runner and draft tube. CFD analyses are carried out with and without VPE. Preliminary results show that VPE with having only one spiral element provides more uniform flow through the draft tube. According to the preliminary results, the new design also provides an efficiency increment about 4%.

Vortex breakdown in discharge cone of the Francis Turbine

“…A new concept is revealed [17] for damping the swirling effect of runner outflow. It is considered that damping effect will prevent the low-pressure regions occurring at draft tube inlet.…”