Mitigation of high load flow instabilities using axial water jet injection in Francis turbines

Abstract The high load (HL) operations in Francis turbines lead to the inception of unsteady phenomena causing pressure pulsations, vibrations, and cavitation. The flow instabilities at HL differ from that of part load operation (PL). At high load, an axisymmetric vortical structure, rotating opposite to the runner develops in the draft tube. The authors had previously successfully employed axial water jet injection in the draft tube to mitigate flow instabilities at different part loads. The present numerical work is performed to investigate the effect of water jet injection on flow instabilities at a high-load operating condition. The simulations are performed on a model Francis turbine unit installed at IIT Roorkee. The study presents changes in the velocity and pressure distribution along with turbine characteristics, such as efficiency, and pressure recovery with the water jet injection.