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• W2550573265 abstract "ii ABSTRACT Hydro Turbines are being operated on very high levels of efficiency, characterised by peak efficiencies beyond 95%. Thus, the margin for further increasing the efficiencies in the best point of operation and in the vicinity of it is very small. However, considering operating points away from the optimum, in extreme part or over load operation, the efficiency drop may be very high. This phenomenon is combined with a strong increase of the pressure pulsations, decreasing the life endurance limit of turbines. To reduce the time-dependent pressure loading of Francis turbine runners several possibilities of active flow control have been studied. The most promising solution to reduce the time-dependent pressure loading of turbine runners is the excitation of the flow by pitching the guide vanes with variable frequencies and amplitudes. To investigate this fluid flow problem in detail an LES code has been developed and applied to solve it. The paper shows simulation results for a 2D tandem cascade as well as for a Francis Turbine runner of specific speed nq = 85 min. The simulations were carried out with different parameter combinations regarding the frequency and the amplitude of the pitching guide vanes. The results show that the losses can be reduced considerably, concerning the tandem cascade and the hydraulic efficiency can be increased, concerning the radial runner. Furthermore the amplitude of the pressure pulsations can be diminished as well as their characteristic frequencies can be shifted towards lower or higher values. Thus, a resonance effect in the turbine may be avoided by modifying the pitching frequency.Hydro Turbines are being operated on very high levels of efficiency, characterised by peak efficiencies beyond 95%. Thus, the margin for further increasing the efficiencies in the best point of operation and in the vicinity of it is very small. However, considering operating points away from the optimum, in extreme part or over load operation, the efficiency drop may be very high. This phenomenon is combined with a strong increase of the pressure pulsations, decreasing the life endurance limit of turbines. To reduce the time-dependent pressure loading of Francis turbine runners several possibilities of active flow control have been studied. The most promising solution to reduce the time-dependent pressure loading of turbine runners is the excitation of the flow by pitching the guide vanes with variable frequencies and amplitudes. To investigate this fluid flow problem in detail an LES code has been developed and applied to solve it. The paper shows simulation results for a 2D tandem cascade as well as for a Francis Turbine runner of specific speed nq = 85 min. The simulations were carried out with different parameter combinations regarding the frequency and the amplitude of the pitching guide vanes. The results show that the losses can be reduced considerably, concerning the tandem cascade and the hydraulic efficiency can be increased, concerning the radial runner. Furthermore the amplitude of the pressure pulsations can be diminished as well as their characteristic frequencies can be shifted towards lower or higher values. Thus, a resonance effect in the turbine may be avoided by modifying the pitching frequency." @default.
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• W2550573265 date "2009-01-01" @default.
• W2550573265 modified "2023-09-27" @default.
• W2550573265 title "Numerical Simulation of the Active Flow Control in Turbomachinery" @default.
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