CFD simulation of pressure and discharge surge in Francis turbine at off-design conditions

Чирков, Д. В.; Avdyushenko, Alexander; Panov, L. V.; Bannikov, Denis; Cherny, S. G.; Skorospelov, V. A.; Pylev, I. M.

doi:10.1088/1755-1315/15/3/032038

Cited by 8 publications

(11 citation statements)

References 1 publication

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“…At a large flow rate, a small eddy is seen towards the exit of duct. The operation of hydraulic turbines in some off-design conditions is accompanied by a local pressure pulsation caused by rotor/stator interactions and a draft tube vortex precession propagating along the whole water conduit [37].…”

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confidence: 99%

Simulations of Steady Cavitating Flow in a Small Francis Turbine

Laouari

Ghenaiet

2016

International Journal of Rotating Machinery

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The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine.

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confidence: 99%

Simulations of Steady Cavitating Flow in a Small Francis Turbine

Laouari

Ghenaiet

2016

International Journal of Rotating Machinery

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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%

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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“…The ratio δ QV for the coarser grid and larger time step equals to 0.8 and could be increased to a value of 0.96 after the mesh refinement and a reduction of the time step. To further improve the mass conservation, Chirkov et al [7] suggested a coupled solution algorithm for pressure and momentum equation together with the volume fraction, allowing coarser meshes and larger time steps (cf. #v03).…”

Section: Flow Visualisationmentioning

confidence: 99%

“…However, the biggest drawback of this approach, beside some uncertainties in the definition of the lumped parameters, are missing insights in complex three-dimensional (3D) flow features. Doerfler et al [1] used ANSYS CFX to investigate the transient behaviour depending on different numerical variations and boundary conditions, whereas Chirkov et al [7] or Cherny et al [8] coupled a 1D approach representing the waterway with a three-dimensional in-house CFD code. The present work combines the advantages of a well validated, efficient and maintained commercial code to simulate distributor, turbine and draft tube in an unsteady 3D manner and attaches a 1D model to represent the penstock and spiral case.…”

Section: Introductionmentioning

confidence: 99%

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

Mössinger

Conrad

Jung

2014

IOP Conf. Ser.: Earth Environ. Sci.

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Abstract. At high load operation points, Francis turbines generally produce large cavitation volumes of central vortex character in the draft tube. In order to gain a deeper understanding of the flow behaviour at high load conditions a combined 1D-3D transient two-phase numerical investigation at prototype size was carried out and these results were compared with measured site data. A one-dimensional model to capture hydroacoustic effects along a pipeline will be presented. The corresponding PDEs were solved using an implicit finite difference scheme on a staggered grid. In contrast to previous studies this model is coupled to the commercial software ANSYS CFX through an interface which exchanges pressure and discharge data within every time step until convergence. Results of the one-dimensional approach as well as the coupled solution were validated with commercial one-dimensional software (SIMSEN) and a full threedimensional calculation for hydroacoustic test cases. Unlike former investigations the described 1D-3D approach is used to compare site data with a numerical analysis at prototype size focused on the amplitude and frequency of the pressure pulsation at overload condition. The combined model is able to capture the occurring phase change in the draft tube as well as the propagating pressure oscillation through the hydraulic system without solving for the whole penstock in a 3D manner, thus saving time and computational resources.

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CFD simulation of pressure and discharge surge in Francis turbine at off-design conditions

Cited by 8 publications

References 1 publication

Simulations of Steady Cavitating Flow in a Small Francis Turbine

Simulations of Steady Cavitating Flow in a Small Francis Turbine

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

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

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