Numerical simulation of pressure pulsations in Francis turbines

Magnoli, M V; Schilling, R.

doi:10.1088/1755-1315/15/6/062029

Cited by 4 publications

(4 citation statements)

References 4 publications

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“…There appears a high difference at off design operation condition, whose maximal value reaches to 180.4%. In several studies (Magnoli and Schilling 2012;Xiao et al 2008Xiao et al , 2010Liu et al 2012), the differences of ΔH/H between experiments and simulations also reach around 200% at the off-design operation conditions. The reasons for the differences mainly come from the following.…”

Section: Validation For Pressure Fluctuationsmentioning

confidence: 94%

“…At part load they are mainly caused by the vortex rope in the draft tube cone. At extreme off-design operating condition, the pressure fluctuations are due to draft tube instabilities, runner channel vortices and flow separation (Magnoli 2012). These pressure fluctuations not only generate lot of noises and serious oscillations, but also introduce unfavorable characteristics.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Rotor-Stator Interaction in Turbine Mode of a Pump-Turbine Model

Gong

Wang

et al. 2016

JAFM

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The highest-level fluctuations in large pump-turbines are usually originated from rotor-stator interaction (RSI) in the vaneless region. Hence, the studies of RSI phenomenon and corresponding unsteady effects are significantly important to reduce the pressure fluctuations. In this paper, firstly, RSI in a pump-turbine, featuring 20 stay vanes, 20 guide vanes and 9 runner blades, is analyzed through diameter mode theory, which has been used widely. Then, 3-D unsteady numerical simulations are performed under six guide vane openings in turbine mode. The comparison including performance and pressure characteristics between numerical and experimental results shows a good agreement. Finally, best guide vane opening 21° is chosen to analyze the distribution of pressure fluctuations. The detailed investigation of numerical results shows that frequencies in the vaneless region at best guide vane opening are mainly blade passing frequency (BPF) and its harmonic frequencies caused from RSI. The variation of BPF and its harmonic frequencies is confirmed by diameter mode theory. For this type of the pump-turbine, the amplitude of 2BPF (18fn) shows the highest corresponding diameter mode k2=-2, which indicates two high pressure regions caused by the component of 18fn in the vaneless region. Furthermore, the two high-pressure regions rotate in the counterclockwise direction with rotational speed of the runner blades. This research could provide a basic understanding of RSI to have a further study for pressure fluctuations in pump-turbines.

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Section: Validation For Pressure Fluctuationsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Analysis of Rotor-Stator Interaction in Turbine Mode of a Pump-Turbine Model

Gong

Wang

et al. 2016

JAFM

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“…The Reynolds Averaged Navier-Stokes (RANS) turbulence model is not appropriate for the unsteady flow prediction, while a fully-resolved Large Eddy Simulation (LES) is almost unfeasible nowadays [24]. Recently, the Detached Eddy Simulation (DES) showed the superiority of the prediction of unsteady flow phenomenon in studies by Magnoli and Schilling [25]. DES can be described as a hybrid RANS-LES turbulence modeling approach and can be applied in a numerical simulation of rotor-stator interaction, inter-blade vortices and vortex rope successfully.…”

Section: Methodsmentioning

confidence: 99%

Numerical Simulation of Axial Vortex in a Centrifugal Pump as Turbine with S-Blade Impeller

Wang

Kuang

et al. 2020

Processes

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Pump as turbines (PATs) are widely applied for recovering the dissipated energy of high-pressure fluids in several hydraulic energy resources. When a centrifugal pump operates as turbine, the large axial vortex occurs usually within the impeller flow passages. In view of the structure and evolution of the vortex, and its effect on pressure fluctuation and energy conversion of the machine, a PAT with specific-speed 9.1 was analyzed based on detached eddy simulation (DES), and the results showed that vortices generated at the impeller inlet region, and the size and position of detected vortices, were fixed as the impeller rotated. However, the swirling strength of vortex cores changed periodically with double rotational frequency. The influence of vortices on pressure fluctuation of PAT was relatively obvious, deteriorating the operating stability of the machine evidently. In addition, the power loss near impeller inlet region was obviously heavy as the impact of large axial vortices, which was much more serious in low flow rate conditions. The results are helpful to realize the flow field of PAT and are instructive for blade optimization design.

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“…For the numerical simulations of the transient fluid flow through the pump-turbine, the scale adaptive model (SAS) from Menter and Egorov [7] was the chosen turbulence model. As investigated by Magnoli [1], Magnoli and Schilling [8], Hasmatuchi [9], Benigni et al [10] and Wunderer [11], hybrid turbulence models deliver accurate numerical solutions for the transient fluid flow through hydraulic machines with currently acceptable computational costs. The turbulent flow viscosity, which brings the contribution of the turbulence modelling to the momentum transport equations, can be found in Figure 6.…”

Section: Numerical Setupmentioning

confidence: 99%

Simulation of pressure pulsations for pumped-storage units with wide operating range and comparison to experiments

Magnoli

Necker²

2022

IOP Conf. Ser.: Earth Environ. Sci.

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The diversity of energy conversion sources in the current energy market increases the demand for stabilizing the electrical grid through ancillary services, frequency and power regulation from the facilities. Pumped-storage units with reversible pump-turbines or ternary sets constitute the currently most advanced solution for providing these services. This implies that pumped-storage units are required to operate in larger head and power ranges than before. In order to increase their flexibility in pump mode, variable speed units have been applied more frequently with additional challenges for the operating range in pump mode. The extension of the operating flexibility in pump mode makes use of a large portion of the model pump characteristic curve, especially in the case of variable speed units. Important challenges to the hydraulic development are among others the cavitation behaviour, hydraulic stability and pressure pulsation level. This study concentrates on the pressure pulsations in pump mode, which are of great relevance for the machine smooth operation. The pressure pulsations in a regulated radial reversible pump-turbine with low specific speed are numerically simulated with computational fluid dynamics (CFD) for several points along the complete operating range of the pump characteristic curve. The finite volume model includes the complete hydraulic machine from draft tube to spiral case and hybrid turbulence models were used, in this case scale adaptive simulation (SAS). The numerical simulation offers the possibility to assess different flow quantities at any point of the finite volume model, providing additional data to the experimental model test results. The integral quantities, e.g. head, flow and efficiency, were compared to the model test results to validate the numerical model. The simulated pressure pulsation amplitude and frequency were also compared to the measured pressure pulsations at the model at the available measuring locations in the spiral case, vaneless space and draft tube cone. After the validation, the computed flow fields were used to derive the pressure pulsation amplitude at other machine locations and components, e.g. at the runner.

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Numerical simulation of pressure pulsations in Francis turbines

Cited by 4 publications

References 4 publications

Analysis of Rotor-Stator Interaction in Turbine Mode of a Pump-Turbine Model

Analysis of Rotor-Stator Interaction in Turbine Mode of a Pump-Turbine Model

Numerical Simulation of Axial Vortex in a Centrifugal Pump as Turbine with S-Blade Impeller

Simulation of pressure pulsations for pumped-storage units with wide operating range and comparison to experiments

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