For Francis turbines,frequent operations under extremely low load conditions result in significant noise and pressure fluctuation issues.These issues may cause vibration and fatigue damage to the unit,accompanied by d...For Francis turbines,frequent operations under extremely low load conditions result in significant noise and pressure fluctuation issues.These issues may cause vibration and fatigue damage to the unit,accompanied by difficulties in connecting to the grid and reductions in the power generation efficiency of renewable energy.However,there is limited research on the relationship between pressure fluctuations and the induced noise of Francis turbines during extreme operations.In the present study,an acoustic numerical simulation based on the Ffowcs Williams-Hawkings equation and large eddy simulation is used to analyze the acoustic performances of Francis turbines.In the current study,for evaluating the acoustic characteristics under such terrible conditions,the results of variable flow rate and guide vane opening conditions are compared.Results indicated that Francis turbine noise is mostly due to pressure fluctuations brought on by rotor-stator interference and corkscrew-shaped vortices.The blade passing frequency(BPF)of 130.00 Hz and the low frequency of 0.33 f_(n)(where f_(n)denotes the rotating frequency)are the key factors affecting pressure and noise fluctuations.The influence of low frequency is reduced as the flow rate rises,whereas the influence of BPF gradually increases.Besides,the hydrodynamic noise of Francis turbines is primarily low-frequency,with discrete and broad-band features.The rotating noise with distinct peak values and the turbulence noise produced by large-scale vortices(corkscrew-shaped vortices)make up the majority of low-frequency noise.Therefore,reducing pressure fluctuations is a key strategy for lowering flow-induced noise radiation.展开更多
Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential v...Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube.It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section.Thus,the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity.However,the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52179087).
文摘For Francis turbines,frequent operations under extremely low load conditions result in significant noise and pressure fluctuation issues.These issues may cause vibration and fatigue damage to the unit,accompanied by difficulties in connecting to the grid and reductions in the power generation efficiency of renewable energy.However,there is limited research on the relationship between pressure fluctuations and the induced noise of Francis turbines during extreme operations.In the present study,an acoustic numerical simulation based on the Ffowcs Williams-Hawkings equation and large eddy simulation is used to analyze the acoustic performances of Francis turbines.In the current study,for evaluating the acoustic characteristics under such terrible conditions,the results of variable flow rate and guide vane opening conditions are compared.Results indicated that Francis turbine noise is mostly due to pressure fluctuations brought on by rotor-stator interference and corkscrew-shaped vortices.The blade passing frequency(BPF)of 130.00 Hz and the low frequency of 0.33 f_(n)(where f_(n)denotes the rotating frequency)are the key factors affecting pressure and noise fluctuations.The influence of low frequency is reduced as the flow rate rises,whereas the influence of BPF gradually increases.Besides,the hydrodynamic noise of Francis turbines is primarily low-frequency,with discrete and broad-band features.The rotating noise with distinct peak values and the turbulence noise produced by large-scale vortices(corkscrew-shaped vortices)make up the majority of low-frequency noise.Therefore,reducing pressure fluctuations is a key strategy for lowering flow-induced noise radiation.
基金supported by the open fund of State Key Laboratory of Hydroscience and Engineer of Tsinghua University(No.sklhse-2013-E-02)the Special Major Project of Science and Technology of Zhejiang province(No.2013C 01139)
文摘Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube.It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section.Thus,the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity.However,the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.
