Stabilizing pump-turbine operations using water injection passive control

Computational fluid dynamics simulations are carried out to characterize the spatial and temporal characteristics of the velocity and pressure field of turbulent flows through a pump-turbine unit operating with the turbine mode. The high-fidelity large eddy simulations turbulence model is utilized to examine the flow-induced vibrations in the draft tube of the unit. The water injection from the runner cone is considered as the control strategy to mitigate the flow-induced fluctuations. The simulations are conducted for the turbine flow rate of 0.2 m³/s without and with the water injection at a rate of 0.008 m³/s. The pressure along the surface of the draft tube is probed at various locations to access the effectiveness of the water injection to mitigate fluctuations. Water injection at 4% rate is demonstrated to be effective in attenuating the pressure fluctuation inside the draft tube. The amplitude of fluctuations is reduced by nearly 50% by the water injection. The generated power is hardly influenced by water injection. Thus, the control strategy considered here could be employed effectively without a penalty on the power generation.