Abstract
Pump-turbines are often used to provide a stable power supply with a constant frequency in response to intermittent renewable energy resources. However, existing pumped-storage power stations often operate under off-design conditions because of the increasing amounts of inconsistent renewable resources that have been added to the grid. Under off-design low flow rate conditions, inter-blade vortex and vortex rope phenomena usually develop in the runner and draft tube passages, respectively, in turbine mode. These vortices cause complicated flow patterns and pressure fluctuations that destabilize the operation of the pump-turbine system. Therefore, this study investigates the influence of correlation between the inter-blade vortex and vortex rope phenomena under low flow rate conditions. Three-dimensional steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were calculated with a two-phase flow analysis using a shear stress transport as the turbulence model. The inter-blade vortices in the runner passages were captured well at the low flow rate conditions, and the vortex rope was found to develop within a specific range of low flow rates. These vortex regions showed a blockage effect and complicated flow characteristics with backflow in the passages. Moreover, higher unsteady pressure characteristics occurred at locations where the vortices were especially pronounced.
Highlights
Pumped-storage hydroelectric power stations generally operate by transferring water from the lower to the upper reservoir using idle power in pump mode during light load times, and after saving energy, discharging water in turbine mode during peak load times
The flow structures, correlations, and unsteady pressure characteristics of numerical analyses compared the best efficiency point (BEP) condition with various low flow rate the inter-blade vortex and vortex rope were investigated according to flow rate, and the swirl number conditions according to the guide vane angle (GVA)
The internal flow and vortex rope characteristics inside the draft tube under the low flow rate conditions depend on the flow and velocity characteristics at the outlet of the runner, which is closely related to the swirl intensity
Summary
Pumped-storage hydroelectric power stations generally operate by transferring water from the lower to the upper reservoir using idle power in pump mode during light load times (low electrical power demand), and after saving energy, discharging water in turbine mode during peak load times (high electrical power demand). Cause and relationship of the vortex characteristics is essential to ensure stable operations under offIn this study, three-dimensional (3D) steady- and unsteady-state RANS analyses were conducted design low flow rate conditions. The numerical analyses conducted using a SST turbulence model with two-phase flow analysis to investigate the compared the best efficiency point (BEP) condition with various low flow rate conditions according to characteristics of correlations between the vortices in the passage of the runner and draft tube. The flow structures, correlations, and unsteady pressure characteristics of numerical analyses compared the best efficiency point (BEP) condition with various low flow rate the inter-blade vortex and vortex rope were investigated according to flow rate, and the swirl number conditions according to the guide vane angle (GVA). P Equations (2)–(4) [16]
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