Abstract
Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga’s idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.
Highlights
Both financial subsidies and technological advancement enabled wide spread of renewable energy sources, especially wind and photovoltaic power plants
Grid control can be realized by such devices that have both sufficient power and short response time
Vortex breakdown is usually defined as sudden change of the flow structure at critical swirl level and is characterized by flow deceleration in vicinity of the axis, formation of stagnation point, onset of recirculation bubble and eventually vortices are rolled-up (KH instability) along the shear layer in-between the two opposing streams
Summary
Both financial subsidies and technological advancement enabled wide spread of renewable energy sources, especially wind and photovoltaic power plants. Vortex breakdown is usually defined as sudden change of the flow structure at critical swirl level and is characterized by flow deceleration in vicinity of the axis, formation of stagnation point, onset of recirculation bubble and eventually vortices are rolled-up (KH instability) along the shear layer in-between the two opposing streams. It means that the resulting vortex rope is wrapped around the low velocity zone, Fig.
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