Hydroelectric power generations using hydro energies of nature-friendly renewable energy resources are characterized by flexible power generating characteristics and a wider operating range. The hydroelectric power generations have traditionally operated to provide electrical energy during the peak ...
Hydroelectric power generations using hydro energies of nature-friendly renewable energy resources are characterized by flexible power generating characteristics and a wider operating range. The hydroelectric power generations have traditionally operated to provide electrical energy during the peak load times. Meanwhile, the demand for hydroelectric power generations have been increasing in response to the crisis of climate change and the increasing proportion of electrical power demand and fluctuating renewable energy resources.
To respond to renewable energy resources with intermittent power generation, such as solar and wind power, hydro power plants and pumped-storage power stations are now often operated to be system stability by providing a constant frequency with a stable power supply. Due to these changes in operating conditions, hydro power plants and pumped-storage power stations are being operated at off-design conditions. Under low flow rate conditions in off-design conditions, undesirable flow phenomena such as the interblade vortices in the passages of runner and the vortex rope in the draft tube, which can degrade hydraulic performance, cause the vibration and instability of the turbine’s operations. Thus, the expansions of the stable operating range are required, particularly in low flow rate conditions.
Meanwhile, the runner blade thickness that change the flow passage areas and internal flow characteristics in the runner region can be expected to affect the interblade vortex phenomena. Furthermore, the anti-swirl fins have been often used with the air or water injections in the draft tube to suppress the vortex rope with precession in the draft tube.
Therefore, in this research, in order to investigate the unsteady flow characteristics in the runner and the draft tube regions at off-design conditions of Francis type hydraulic turbines, including the effects of runner blade thickness and anti-swirl fins in the daft tube, the three-dimensional (3D) unsteady state RANS analyses were performed using a k-ω-based SST or a shear stress transport-scale adaptive simulation (SST-SAS) as the turbulence models. The unsteady internal flow in the presence of vortices in the passages of runner and draft tube were compared at low flow rate conditions. The effects of the runner blade thickness and the anti-swirl fins were discussed with respect to the vortex phenomena. Furthermore, the influences of correlation between the interblade vortex and vortex rope were analyzed at low flow rate conditions. Additionally, the pressure measurement points were applied for investigating the unsteady pressure characteristics induced by the unsteady flow characteristics with vortices.
The blockage effect with higher runner blade thickness significantly affected to reduce the interblade vortices and unsteady pressure. Furthermore, the use of anti-swirl fins was confirmed to affect the degradation of hydraulic performance; however, the effects of reducing the unsteady pressure in the low frequency regions were confirmed in the draft tube. In addition, within the specific flow rate range, where the interblade vortices were developed in the middle passages of the runner, the flow in the passages of runner affected the flow phenomena at the outlet of runner and led to the generation of the vortex rope with precession.
Hydroelectric power generations using hydro energies of nature-friendly renewable energy resources are characterized by flexible power generating characteristics and a wider operating range. The hydroelectric power generations have traditionally operated to provide electrical energy during the peak load times. Meanwhile, the demand for hydroelectric power generations have been increasing in response to the crisis of climate change and the increasing proportion of electrical power demand and fluctuating renewable energy resources.
To respond to renewable energy resources with intermittent power generation, such as solar and wind power, hydro power plants and pumped-storage power stations are now often operated to be system stability by providing a constant frequency with a stable power supply. Due to these changes in operating conditions, hydro power plants and pumped-storage power stations are being operated at off-design conditions. Under low flow rate conditions in off-design conditions, undesirable flow phenomena such as the interblade vortices in the passages of runner and the vortex rope in the draft tube, which can degrade hydraulic performance, cause the vibration and instability of the turbine’s operations. Thus, the expansions of the stable operating range are required, particularly in low flow rate conditions.
Meanwhile, the runner blade thickness that change the flow passage areas and internal flow characteristics in the runner region can be expected to affect the interblade vortex phenomena. Furthermore, the anti-swirl fins have been often used with the air or water injections in the draft tube to suppress the vortex rope with precession in the draft tube.
Therefore, in this research, in order to investigate the unsteady flow characteristics in the runner and the draft tube regions at off-design conditions of Francis type hydraulic turbines, including the effects of runner blade thickness and anti-swirl fins in the daft tube, the three-dimensional (3D) unsteady state RANS analyses were performed using a k-ω-based SST or a shear stress transport-scale adaptive simulation (SST-SAS) as the turbulence models. The unsteady internal flow in the presence of vortices in the passages of runner and draft tube were compared at low flow rate conditions. The effects of the runner blade thickness and the anti-swirl fins were discussed with respect to the vortex phenomena. Furthermore, the influences of correlation between the interblade vortex and vortex rope were analyzed at low flow rate conditions. Additionally, the pressure measurement points were applied for investigating the unsteady pressure characteristics induced by the unsteady flow characteristics with vortices.
The blockage effect with higher runner blade thickness significantly affected to reduce the interblade vortices and unsteady pressure. Furthermore, the use of anti-swirl fins was confirmed to affect the degradation of hydraulic performance; however, the effects of reducing the unsteady pressure in the low frequency regions were confirmed in the draft tube. In addition, within the specific flow rate range, where the interblade vortices were developed in the middle passages of the runner, the flow in the passages of runner affected the flow phenomena at the outlet of runner and led to the generation of the vortex rope with precession.
주제어
#Hydraulic turbine Francis turbine Pump-turbine Off-design conditions Interblade vortex Vortex rope Numerical analysis Unsteady RANS
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