Abstract
Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.
Highlights
This analysis was used to investigate the effects of air injection on the internal flow characteristics of a draft tube (DT) with anti-swirl fins for a Francis turbine under low flow-rate conditions
The unsteady internal flow and pressure fluctuation characteristics were observed in the presence of a vortex rope via the application of air injection from the cone of the runner
The unsteady-state Reynolds-averaged Navier–Stokes (RANS) equations for the incompressible flow of the model were calculated from the governing equations, which were discretized with a finite volume method
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The effects of air injection in the DT with the application of anti-swirl fins considering both active and passive suppression methods on internal flow and vortex suppression characteristics have not been systematically elucidated with low flow-rate conditions in the Francis turbine model. Unsteady-state Reynolds-averaged Navier–Stokes (RANS) equations using the SAS-SST turbulence model were employed with a three-phase (water, vapor, and air) flow analysis This analysis was used to investigate the effects of air injection on the internal flow characteristics of a DT with anti-swirl fins for a Francis turbine under low flow-rate conditions. The unsteady internal flow and pressure fluctuation characteristics were observed in the presence of a vortex rope via the application of air injection (at different flow rates) from the cone of the runner.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
