Numerical simulations of the cavitation phenomena in a Francis turbine at deep part load conditions

Wack, J; Riedelbauch, Stefan

doi:10.1088/1742-6596/656/1/012074

Cited by 29 publications

(14 citation statements)

References 2 publications

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“…Nevertheless, in terms of vapor volume size only minor differences are present between both turbulence models. This is in contrast to observations made for a deep part load operating point where the SAS model predicted a significantly bigger cavitation volume of the inter-blade vortices in the runner compared to the SST model [11]. This can be explained by the fact that the occurring vortex rope at part load conditions has a much bigger diameter compared to the inter-blade vortices.…”

Section: Cavitating Vortex Ropecontrasting

confidence: 98%

Numerical simulation of a cavitating draft tube vortex rope in a Francis turbine at part load conditions for different σ-levels

Wack

Riedelbauch

2017

J. Phys.: Conf. Ser.

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Section: Cavitating Vortex Ropecontrasting

confidence: 98%

Numerical simulation of a cavitating draft tube vortex rope in a Francis turbine at part load conditions for different σ-levels

Wack

Riedelbauch

2017

J. Phys.: Conf. Ser.

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“…Away from the design point, the flow field entering the runner is misaligned with the geometry of the blades. Wack [3] suggests that this poor incidence angle generates the inter-blade vortices. Zhou et al [4] also studied the occurrence and the location of the vortices depending on the operating point.…”

Section: Introductionmentioning

confidence: 99%

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Doussot¹,

Balarac²,

Brammer³

et al. 2020

IJFMS

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Hydraulic machines are designed to operate in flow conditions close to the best efficiency point. However, to respond to the increasing demand for flexibility mainly due to the integration of renewable energy in the electric grid, the operating range of Francis turbines has to be extended towards smaller discharge levels without restriction. When Francis turbines are operated typically between 30% and 60% of the rated output power, the flow field is characterized by the appearance of inter-blade vortices in the runner. In these off-design operating conditions and due to these phenomena, dynamic stresses level can increase, and potentially lead to fatigue damage of the mechanical structure of the machine. The objective of this paper is to present investigations on the dynamic behaviour of the inter-blade vortices and their impact on the runner by using numerical simulations. Computations were performed with different turbulence modelling approaches to assess their relevance and reliability: Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). Computations aimed to better understand the emergence condition of the inter-blade vortices. The analysis showed that vortices can be generated due to poor inlet adaptation at part load, however other vortices can also be due to a local backflow in the runner. The competition between these both phenomena leads to various topologies of the inter-blade vortices. The numerical results were compared to experimental visualizations performed on scaled model as well as to previous numerical studies results. The impact of these inter-blade vortices on the runner were also investigated by considering the pressure fluctuations induced on the blades. The dynamic loading on the blade has to be known in order to evaluate the lifetime of the runner by mechanical analysis. Different operating conditions have been simulated to understand how the pressure fluctuations depend on the operating conditions. The localization of the pressure fluctuations and their consequences on the frequency signature of the torque fluctuations have been analyzed. This article is presenting a part of the work presented at the 29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, 2018 [1], and presents another vortex topology and a comparison of LES results of several operating conditions.

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“…The swirl flow at the runner outlet plays an important role in the formation of vortex rope, causing asymmetric cavitation which gives rise to modifications of the swirl flow at the runner blades and thereby affects the characteristics of the vortex rope. Wack and Riedelbauch [17] studied the occurrence of cavitating interblade vortices at deep part load conditions in a Francis turbine using two-phase flow simulations and highlighted the necessity of fine grids in the runner to resolve the vortex core of the interblade vortices. Mousmoulis et al [18] studied the effects of draft tube vortex cavitation on Francis turbine, numerically and based on the measurements of dynamic pressure and vibration.…”

Section: Introductionmentioning

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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Numerical simulations of the cavitation phenomena in a Francis turbine at deep part load conditions

Cited by 29 publications

References 2 publications

Numerical simulation of a cavitating draft tube vortex rope in a Francis turbine at part load conditions for different σ-levels

Numerical simulation of a cavitating draft tube vortex rope in a Francis turbine at part load conditions for different σ-levels

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Simulations of Steady Cavitating Flow in a Small Francis Turbine

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