Transient two-phase CFD simulation of overload pressure pulsation in a prototype sized Francis turbine considering the waterway dynamics

Mössinger, Peter; Conrad, P; Jung, Alexander

doi:10.1088/1755-1315/22/3/032033

Cited by 11 publications

(5 citation statements)

References 4 publications

(6 reference statements)

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“…To compute an unstable vortex rope, it is therefore necessary to take care of the time integration set up by increasing at least the number of internal loops. To improve the accuracy of the simulation, the U-RANS simulation needs, in addition, to be coupled with a 1D hydroacoustic model allowing for adjusting the boundary conditions at the inlet and outlet boundaries of the computational domain [6,7].…”

Section: Discussionmentioning

confidence: 99%

“…On one hand, various studies have been performed to better understand the selfoscillating behaviour of the cavitating vortex rope based on mathematical approaches [2] or 1D analyses [3], experimental investigations [4], 3D CFD [5] and coupling between 1D-3D numerical simulations [6,7]. On the other hand, several investigations look at identifying some key parameters (mainly the mass flow gain factor) useful for the calibration and the development of 1D hydro-acoustic models [8,9] using either experimental measurements [10,11] or CFD simulations [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine

et al. 2021

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The flow in a Francis turbine at full load is characterised by the development of an axial vortex rope in the draft tube. The vortex rope often promotes cavitation if the turbine is operated at a sufficiently low Thoma number. Furthermore, the vortex rope can evolve from a stable to an unstable behaviour. For CFD, such a flow is a challenge since it requires solving an unsteady cavitating flow including rotor/stator interfaces. Usually, the numerical investigations focus on the cavitation model or the turbulence model. In the present works, attention is paid to the strategy used for the time integration. The vortex rope considered is an unstable cavitating one that develops downstream the runner. The vortex rope shows a periodic behaviour characterized by the development of the vortex rope followed by a strong collapse leading to the shedding of bubbles from the runner area. Three unsteady RANS simulations are performed using the ANSYS CFX 17.2 software. The turbulence and cavitation models are, respectively, the SST and Zwart models. Regarding the time integration, a second order backward scheme is used excepted for the transport equation for the liquid volume fraction, for which a first order backward scheme is used. The simulations differ by the time step and the number of internal loops per time step. One simulation is carried out with a time step equal to one degree of revolution per time step and five internal loops. A second simulation used the same time step but 15 internal loops. The third simulations used three internal loops and an adaptive time step computed based on a maximum CFL lower than 2. The results show an influence of the time integration strategy on the cavitation volume time history both in the runner and in the draft tube with a risk of divergence of the solution if a standard set up is used.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine

et al. 2021

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“…The model constants R nuc = 1µm, r nuc = 5 × 10 4 , F condensation = 0.01 and F vapor = 50 are chosen based on experience gathered by previous investigations and validations of the model [33,34]. According to Figure 4a, inlet mass flow condition is applied, while at the outlet a constant pressure boundary condition is chosen.…”

Section: Cfd-setupmentioning

confidence: 99%

Investigation on the Impact of Air Admission in a Prototype Francis Turbine at Low-Load Operation

2019

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Due to significant changes in the energy system, hydraulic turbines are required to operate over a wide power range. In particular, older turbines which are not designed for these environments will suffer under off-design conditions. In order to evaluate whether or not such a turbine could fulfill the new requirements of the energy market, a study about the behavior of a prototype plant in low-load operation is presented. Therefore, prototype site measurements are performed to determine the most damaging operating point by means of acceleration sensors and pressure transducers. Moreover, unsteady computational fluid dynamics (CFD) simulations considering two-phase flow and two hybrid turbulence models are used to analyze the flow conditions inside the turbine. The resulting pressure pulsations are mapped onto the runner blade to obtain stress and further calculate damage factors. Accordingly, the stresses are compared to those obtained by the strain gauge measurement. Moreover, the influence of active flow control by means of air injection on plant behavior and runner lifetime is discussed as well.

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“…The results were input to a statistical identification procedure. In order to gain a deeper understanding of the flow behavior at high load conditions in [18]a combined 1D-3D transient two-phase numerical investigation at prototype size was carried out and these results were compared with measured site data.…”

Section: Introductionmentioning

confidence: 99%

Assessment of the Embedment of Francis Turbine for Pumped Hydraulic Energy Storage

Todorov,

Kralov,

Kamberov

et al. 2024

Preprint

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In the paper analyzes of Francis turbine failures for a powerful Pumped Hydraulic Energy Storage (PHES) are conducted. The structure is part of the PHES Chaira, Bulgaria (HA4 - Hydro-Aggregate 4). The aim is assessment of the structure-to-concrete embedment for possible cause of damages and destructions of the HA4 Francis spiral casing units. The embedment methods applied in the practice for decades are discussed and compared to that used for HA4. An innovative virtual prototype is built based on the finite element method to clarify the influence of workloads under generator mode. The stages of the simulation include:- complete structural analysis of the spiral case and the concrete under loads in generator mode;- complete structural analysis of the spiral case under loads in generator mode but without the concrete.Both procedures of simulations (with and without the concrete) are of major importance. Since a failure of the surface between the turbine, the spiral case and the concrete is observed the effect of the increasing contact gap (no contact) is analyzed. The stresses, strains and displacements of the turbine units are simulated followed by important analysis for reliability. The conclusions reveal the possible reasons for cracks and destruction in the main elements of the structure.

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Transient two-phase CFD simulation of overload pressure pulsation in a prototype sized Francis turbine considering the waterway dynamics

Cited by 11 publications

References 4 publications

Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine

Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine

Investigation on the Impact of Air Admission in a Prototype Francis Turbine at Low-Load Operation

Assessment of the Embedment of Francis Turbine for Pumped Hydraulic Energy Storage

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