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

Doussot, François; Balarac, Guillaume; Brammer, James; Laurant, Yann; Métais, Olivier

doi:10.5293/ijfms.2020.13.1.012

Cited by 8 publications

(7 citation statements)

References 6 publications

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“…The closer it is to the upper crown position, the closer the vortex structure is to the runner inlet. The same phenomenon was found in related experiments [20] and CFD simulations [21][22][23].…”

Section: Test Results Of Different Sectionssupporting

confidence: 86%

Particle Image Velocimetry Test for the Inter-Blade Vortex in a Francis Turbine

Jin²,

et al. 2021

Processes

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Hydropower units are usually operated in non-design conditions because of power grid requirements. In a partial-load condition, an inter-blade vortex phenomenon occurs between the runner blades of a Francis turbine, causing pressure pulsation and unit vibration, which hinder the safe and stable operation of power stations. However, the mechanism through which the inter-blade vortex generation occurs is not entirely clear. In this study, a specific model of the Francis turbine was used to investigate and visually observe the generation of the blade vortex in Francis turbines in both the initial inter-blade and vortex development zones. Particle image velocimetry was used for this purpose. In addition, we determined the variation law of the inter-blade vortex in the Francis turbine. We found that the size and strength of the inter-blade vortex depend on the unit speed of the turbine. The higher the unit speed is, the stronger the inter-blade vortex becomes. We concluded that the inter-blade vortex of such turbines originates from the pressure surface or secondary flow and stall of the blade at the inlet side of the runner at high unit speeds, and also from the backflow zone of the suction surface of the blade at low unit speeds.

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Section: Test Results Of Different Sectionssupporting

confidence: 86%

Particle Image Velocimetry Test for the Inter-Blade Vortex in a Francis Turbine

Jin²,

et al. 2021

Processes

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“…Cheng [40][41][42] demonstrated that applying large eddy simulation to the Francis turbine has notable advantages over other methods.…”

Section: Les Numerical Modelmentioning

confidence: 99%

Influence of Upstream Disturbances on the Vortex Structure of Francis Turbine Based on the Criteria of Identification of Various Vortexes

Tao

Wang

2021

Energies

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The inter-blade passage vortex, the vortex rope of the draft tube, and the vortex in the guide apparatus are the characteristics of flow instability of the Francis turbine, which may lead to fatigue failure in serious cases. In the current study, in order to accurately capture the transient turbulent characteristics of flow under different conditions and fully understand the flow field and vortex structure, we conduct a simulation that adopts sliding grid technology and the large-eddy simulation (LES) method based on the wall-adapting local eddy viscosity (WALE) model. Using the pressure iso-surface method, the Q criterion, and the latest third-generation Liutex vortex identification method, this study analyzes and compares the inter-blade passage vortex, the vortex rope of the draft tube, and the outflow and vortex in the guide apparatus, focusing on the capture ability of flow field information by various vortex identification methods and the unique vortex structure under the condition of a small opening. The results indicate that the dependence of Liutex on the threshold is small, and the scale range of the flow direction vortex captured by Liutex is wider, but the ability of the spanwise vortex is relatively weak. The smaller the opening, the more disorderly the vortexes generated in each component and the more unstable the flow field. In the draft tube, the original shape of the vortex rope is destroyed due to the interaction between vortexes. Under the condition of a small opening, an inter-blade passage vortex is generated, affecting the efficient and stable operation of the turbine.

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“…To maintain grid stability and perform both primary and secondary load balancing functions, hydraulic turbines are an essential part of energy conversion technologies [3]. Hydraulic turbines can be modified to match the total energy output to the energy demand at any given moment [4]. Hydraulic turbines must operate in a very wide operating range with a decent level of safety and without experiencing excessive vibrations to achieve this goal [1].…”

Section: Introduction 11 Hydro Turbine and Off-design Conditionsmentioning

confidence: 99%

Numerical investigation of model Francis turbine for performance enhancement with geometrical modification

Kayastha,

Ghimire,

Bijukchhe

et al. 2023

J. Phys.: Conf. Ser.

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Most of the hydropower plants in Nepal are run-of-river type and over 60% of them are operating with Francis turbines. There are huge fluctuations in flow during the dry and wet seasons, which force the power plant owner to operate the turbines at off-design conditions which can induce cavitation and fatigue loads on the turbines. This study focuses on numerical analysis of a model turbine designed for the Jhimruk hydropower plant in Nepal. A geometrical modification is made to the model turbine runner blades by attaching two pairs of vortex generators (VGs) to each blade surface on the pressure side at 0.5% span, at the leading edge. The flow on the blade breaks off and separates from the surface during the off-design conditions so VGs are introduced to mitigate swirls generated at the inlet of the turbine. VGs can help to reattach the flow and improve off-design performance of the turbine. The performance of model turbine is analyzed at different guide vane openings to simulate different operating conditions by keeping the operating head constant and varying the rotational speed of the turbine from 500 to 1500 rpm. Performance curves and hill diagrams of the turbine are generated for each case with and without VGs. The results show that VGs at off-design conditions show a maximum increment in efficiency by 12% and 1 to 5% on average. The power output is also boosted by 1 to 6 kW at off-design conditions. This objective has been achieved when compared to efficiency and power at low-discharge and high-speed regions. In conclusion, VGs are simple but effective tools to enhance the performance of hydraulic turbines as well.

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

Cited by 8 publications

References 6 publications

Particle Image Velocimetry Test for the Inter-Blade Vortex in a Francis Turbine

Particle Image Velocimetry Test for the Inter-Blade Vortex in a Francis Turbine

Influence of Upstream Disturbances on the Vortex Structure of Francis Turbine Based on the Criteria of Identification of Various Vortexes

Numerical investigation of model Francis turbine for performance enhancement with geometrical modification

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