Mitigation of flow-induced pressure fluctuations in a Francis turbine operating at the design and partial load regimes—LES simulations

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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“…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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“…In this work, the LES turbulence model was utilized to simulate the fluid flow in a hydro turbine system which proven to be reliable such as in studies of Su et al [11] and Altimemy et al [30]. The LES method was resolved explicitly that eddy smaller than the grid size was simulated by implementing a Subgrid-Scale (SGS) model.…”

Section: Governing Equationsmentioning

confidence: 99%

“…where s L is the mixing length for SGS, k is the Von Kármán constant, d is the shortest distance to the nearest wall, s C is the WALE constant of 0.325, and V is the mesh cell volume. The eddy-viscosity is solved nearly zero in areas close to walls without any application of the damping function [11,30].…”

Section: Governing Equationsmentioning

confidence: 99%

Angle Design of Stator-Rotor Blades for VLH Axial Flow Turbine using Surrogate-based Optimization

et al. 2021

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This paper demonstrates design of a Very Low Head axial flow turbine using surrogate-based optimization. The design variables were blade angles between guide vanes and runner blades, whereas the objective function was turbine efficiency. A Latin Hypercube Sampling method was initially used to design the experiment with thirty sampling points, and a Large Eddy Simulation was modeled to analyze the flow for all sampling points. A correlation between design variables and the turbine efficiency was then evaluated using the surrogate models while the optimal design variables were identified. Also, several optimizers were used to tackle the proposed problem and their performances were investigated. The optimal design of blade angles 18   being 10 o , 20 o , 30 o , 40 o , 25 o , 45 o , 55 o and 65 o respectively, increased the turbine efficiency up to 89.87 %. The approach of using surrogate modeling was proved to be very effective and simple for optimizing a design of blade angles of stator-rotor and it can be applied for designing any other new blades.

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“…Since its introduction, this method has been studied by many other researchers, see e.g. the work by Altimemy et al [9], Juposhti et al [10], and Khullar et al [11]. The latter two bring evidence that water jet injection may lead to stronger pressure pulsations under some circumstances.…”

Section: Introductionmentioning

confidence: 99%

On the existence of adverse pressure gradient in decelerated swirling flow and its suppression by water jet injection

Urban

Rudolf

2022

IOP Conf. Ser.: Earth Environ. Sci.

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The paper revisits the theory originally published by Hall that explains the presence of adverse pressure gradient at the axis of a diffuser with swirling flow. It presents the fields of the axial pressure derivative obtained by CFD simulations of flow in a swirl generator, which support the theory. The last part brings cautionary results regarding the suppression of the backflow caused by this adverse pressure gradient by water jet injection. On a case with a strong swirl intensity leading to a strong vortex rope, it is shown that the injected jet may be deflected to the outer walls and rotate with the outer swirling flow, eventually leading to stronger pressure pulsations than in the original state. Further investigation shows that high enough diameter of the jet is needed to ensure its stability.

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Mitigation of flow-induced pressure fluctuations in a Francis turbine operating at the design and partial load regimes—LES simulations

Cited by 20 publications

References 25 publications

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

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

Angle Design of Stator-Rotor Blades for VLH Axial Flow Turbine using Surrogate-based Optimization

On the existence of adverse pressure gradient in decelerated swirling flow and its suppression by water jet injection

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