Investigation of a Francis turbine during speed variation: Inception of cavitation

Trivedi, Chirag; Iliev, Igor; Dahlhaug, Ole Gunnar; Markov, Zoran; Engström, Fredrik; Lysaker, Henning

doi:10.1016/j.renene.2020.11.108

Cited by 32 publications

(8 citation statements)

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“…[42]. In view of the cavitation in Francis turbines [27], generally, there are leading edge cavitation, travelling bubble cavitation, draft tube vortex cavitation, channel vortex cavitation, Karman vortex cavitation [43], etc. Partial flow conditions aggravate the complexity of the flow field in the blade passage and the intensity of the vortexes in the Francis turbine, which may exacerbate the cavitation in the flow field when the latter is unstable.…”

Section: Analysis Of Cavitation Around the Runnermentioning

confidence: 99%

“…Su Wentao et al [24] carried out numerical simulations and tests on a Francis turbine, which verified the feasibility and accuracy of the LES method based on a cavitation model in predicting the performance of Francis turbines under partial flow conditions, while Trivedi Chirag et al [25,26] used the LES method to simulate the load change of a Francis turbine and compared the results with experimental data. Trivedi Chirag [27] took the extreme operating conditions of the turbine into consideration, and he found that the cavitation phenomenon in hydraulic turbine gradually disappeared with the increase of rotation speed; however, when running at high rotating speed, the intensity of cavitation reached its maximum. Sun Longgan et al [28] found that the position of channel vortexes in Francis turbines shows a clearer correlation to rotating speed than that to guide vane opening.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Channel Vortex and Cavitation Performance of the Francis Turbine under Partial Flow Conditions

2021

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To realize a multienergy complementary system involving hydropower and other energy sources, hydraulic turbines frequently run under partial flow conditions in which a unique flow phenomenon, the channel vortex, occurs in the runner, causing fatigue failure and even cavitation to the turbine blade. Cavitation severely shortens the service life of the unit and terribly limits the output of the turbine under partial flow conditions. In this paper, a numerical model of a Francis turbine was created with tetrahedral grids; the large eddy simulation (LES) method based on the WALE subgrid scale model and the Schnerr–Sauer cavitation model was adopted to carry out numerical simulation of the Francis turbine; and a vortex identification method based on the Q criterion was used to capture and analyze the channel vortex. The calculation results showed that a negative impact angle at the inlet of the runner occurred when the turbine ran under partial flow conditions, leading to three different types of channel vortexes in the blade channel. Also, different channel vortexes caused cavitation on different positions on the runner, and the volume change of cavitation showed periodic properties.

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Section: Analysis Of Cavitation Around the Runnermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Analysis of Channel Vortex and Cavitation Performance of the Francis Turbine under Partial Flow Conditions

2021

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“…With the rapid development of modern numerical software, computational fluid dynamics (CFD) has become a useful tool to simulate the evolution law of the internal flow field in pump units 5 , 12 , 13 . At the same time, three-dimensional (3D) numerical method has been widely applied on the simulation of various transient processes, such as start-up, shut down, runaway process, power off and so on 3 , 4 , 14 .…”

Section: Introductionmentioning

confidence: 99%

Study on a horizontal axial flow pump during runaway process with bidirectional operating conditions

Kan

Zhang

et al. 2021

Sci Rep

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The ultra-low head pump stations often have bidirectional demand of water delivery, so there is a risk of runaway accident occurring in both conditions. To analyze the difference of the runaway process under forward runaway condition (FRC) and backward runaway condition (BRC), the whole flow system of a horizontal axial flow pump is considered. The Shear-Stress Transport (SST) k–ω model is adopted and the volume of fluid (VOF) model is applied to simulate the water surface in the reservoirs. Meanwhile, the torque balance equation is introduced to obtain the real time rotational speed, then the bidirectional runaway process of the pump with the same head is simulated. In addition, the vortex transport equation and swirl number are proposed to reveal the flow characteristics during the runaway process. The results show that the runaway process can be divided into five stages: the drop, braking, rising, convergence and runaway stages, according to the changing law of torque curve. In the rising stage, the pressure difference on the blade surface continues to increase, which contributes to the abnormal torque increase. In this stage, the flow hits the pressure surface (PS) at a faster speed enlarging the pressure on PS, and the flow separation takes place on the suction surface (SS) weakening the pressure on SS. During the convergence and runaway stage, the pulsation amplitude of torque and axial force under FRC is obviously larger than those under BRC. This is because the rotation frequency of the vortex rope is the same as main pressure fluctuation frequency in impeller under FRC, which enhances the pulsation amplitude. Whereas the vortices are broken due to the inhibitive effect from guide vanes under BRC.

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“…The turbines need to operate with more start-stop cycles and high ramping rates. Variable-speed operation of Francis turbines is seen as an alternative solution to achieve high ramping rates and more efficient energy production in off-design operating conditions [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Constraints of Parametrically Defined Guide Vanes for a High-Head Francis Turbine

et al. 2021

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This paper is focused on the guide vane cascade as one of the most crucial stationary sub-systems of the hydraulic turbine, which needs to provide efficient inflow hydraulic conditions to the runner. The guide vanes direct the flow from the spiral casing and the stay vanes towards the runner, regulating the desired discharge. A parametric design tool with normalized geometrical constraints was created in MATLAB, suitable for generating guide vane cascade geometries for Francis turbines. The goal is to determine the limits of these constraints, which will lead to future faster prediction of initial guide vane configurations in the turbine optimal operating region. Several geometries are developed using preliminary design data of the turbine and are investigated using CFD simulations close to the best efficiency point (BEP) of the turbine. This research is part of the Horizon-2020—HydroFlex project led by the Norwegian University of Science and Technology (NTNU), focusing on the development of a flexible hydropower generation.

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Investigation of a Francis turbine during speed variation: Inception of cavitation

Cited by 32 publications

References 50 publications

Analysis of Channel Vortex and Cavitation Performance of the Francis Turbine under Partial Flow Conditions

Analysis of Channel Vortex and Cavitation Performance of the Francis Turbine under Partial Flow Conditions

Study on a horizontal axial flow pump during runaway process with bidirectional operating conditions

Constraints of Parametrically Defined Guide Vanes for a High-Head Francis Turbine

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