Physical Mechanism of Interblade Vortex Development at Deep Part Load Operation of a Francis Turbine

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Keita Yamamoto ◽  
Andres Müller ◽  
Arthur Favrel ◽  
François Avellan
Keyword(s):  
Energy Loss ◽  
Physical Mechanism ◽  
Vortex Structures ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Deep Part ◽  
Seamless Integration ◽  
Part Load ◽  
Recirculating Flow ◽  
Runner Blade

For seamless integration of growing electricity production from intermittent renewable energy sources, Francis turbines are under increasing demand to extend their operating range. This requires Francis turbines to operate under off-design conditions, where various types of cavitation are induced. At deep part load condition, an interblade cavitation vortex observed in a runner blade channel is a typical cavitation phenomenon causing pressure fluctuations and erosion, which prevent a reliable operation of Francis turbines at deep part load. The underlying mechanisms of its development are, however, yet to be understood. In an objective of revealing its developing mechanisms, the present study is aimed at investigating flow structures inside runner blade channels by comparison of three different operating conditions at deep part load using numerical simulation results. After demonstrating interblade vortex structures are successfully simulated by performed computations, it is shown that flow inside the runner at deep part load operation is characterized by a remarkable development of recirculating flow on the hub near the runner outlet. This recirculating flow is concluded to be closely associated with interblade vortex development. The skin-friction analyses applied to the hub identify the flow separation caused by a nonuniform distribution of flow, which describes the underlying physical mechanism of interblade vortex development. Investigations are further extended to include a quantitative evaluation of the specific energy loss induced by interblade vortex development. The integration of energy flux defined by rothalpy evidences the energy loss due to the presence of strong interblade vortex structures.

Analysis of Inner Flow Inside Francis Turbine Runner Based on Dissipation Function

2008 ◽  
Author(s):  
Xiaojing Wu ◽  
Yulin Wu ◽  
Shuhong Liu
Keyword(s):  
Energy Loss ◽  
Flow Simulation ◽  
Dissipation Function ◽  
Operating Conditions ◽  
Surface Strain ◽  
Francis Turbine ◽  
Dominant Factor ◽  
Flow Energy ◽  
Runner Blade ◽  
Turbine Runner

Energy loss inside a Francis turbine runner is analyzed with dissipation function in this paper. The dissipation rate of a Newtonian flow with constant shear viscous has three constituents from dilation, vorticity, and surface strain, which is derived from kinetic energy equation presented in this paper. A commercial N-S equation solver has been employed for 3D turbulent flow simulation with a model Francis turbine, and three different operating conditions are chosen for comparison, which are part load, rated load, and excessive load. The results from simulation have been compared with model experiments to validate their preciseness and reliability. The distribution of dissipation constituents on runner blade surface have been extracted from the above simulation results. The distinction of these constituents can be used to identify flow structures inside runner. The flow energy loss is determined by dissipation function, thus it can affect the hydraulic efficiency of turbine runner. From the above results, it can be seen that what causes the energy loss, which is the dominant factor, and where it has the highest value. Thus this analysis based on dissipation function can be used for flow diagnosis inside the blade channel, and tell us which part of the blade should be improved to reduce the energy loss.

scholarly journals CFD Investigation of a High Head Francis Turbine at Speed No-Load Using Advanced URANS Models

2018 ◽  
Vol 8 (12) ◽  
pp. 2505 ◽  
Author(s):  
Jean Decaix ◽  
Vlad Hasmatuchi ◽  
Maximilian Titzschkau ◽  
Cécile Münch-Alligné
Keyword(s):  
Power Plants ◽  
Turbulence Modeling ◽  
Suction Side ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Hydroelectric Power ◽  
Electrical Grid ◽  
Runner Blade ◽  
Pumped Storage

Due to the integration of new renewable energies, the electrical grid undergoes instabilities. Hydroelectric power plants are key players for grid control thanks to pumped storage power plants. However, this objective requires extending the operating range of the machines and increasing the number of start-up, stand-by, and shut-down procedures, which reduces the lifespan of the machines. CFD based on standard URANS turbulence modeling is currently able to predict accurately the performances of the hydraulic turbines for operating points close to the Best Efficiency Point (BEP). However, far from the BEP, the standard URANS approach is less efficient to capture the dynamics of 3D flows. The current study focuses on a hydraulic turbine, which has been investigated at the BEP and at the Speed-No-Load (SNL) operating conditions. Several “advanced” URANS models such as the Scale-Adaptive Simulation (SAS) SST k - ω and the BSL- EARSM have been considered and compared with the SST k - ω model. The main conclusion of this study is that, at the SNL operating condition, the prediction of the topology and the dynamics of the flow on the suction side of the runner blade channels close to the trailing edge are influenced by the turbulence model.

Effect of Runner Blade Thickness on Flow Characteristics of a Francis Turbine Model at Low Flowrates

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Seung-Jun Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi ◽  
Jin-Hyuk Kim
Keyword(s):  
Stokes Equations ◽  
Guide Vane ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Hydroelectric Power ◽  
Runner Blade ◽  
Blade Thickness ◽  
Interblade Vortices

Abstract Francis turbines are often used for generating hydroelectric power, but their performance characteristics significantly depend on the operating conditions. In particular, interblade vortices in the passages between runner blades can occur at low flowrates, which can degrade performance, and increase vibrations and instability during operation. In a previous study, we showed that the hydraulic performance and flow characteristics depend on the flow passage area of runner blades under low-flowrate conditions. Under such operating conditions, the runner blade thickness can affect the interblade vortex characteristics, and in turn, affect the performance of the turbine. In this study, we investigated the effect of runner blade thicknesses in the presence of interblade vortices under low flowrates; steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were solved using a shear stress transport as a turbulence model. The interblade vortices were described well at the near leading and trailing edges near the hub. These vortex regions showed flow separation and stagnation flow, and the interblade vortex characteristics were dependent on the high-magnitude unsteady pressures at the low-frequency region. For the same guide vane opening, at lower flowrates, higher blockage ratios reduced interblade vortex formation and unsteady pressure.

Generation of Twin Vortex Rope in the Draft-Tube Elbow of a Francis Turbine During Deep Part-Load Operation

2021 ◽  
Author(s):  
Mohammad Hossein Khozaei ◽  
Arthur Favrel ◽  
Toshitake Masuko ◽  
Naoki Yamaguchi ◽  
Kazuyoshi Miyagawa
Keyword(s):  
Linear Correlation ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Model Tests ◽  
Francis Turbine ◽  
Deep Part ◽  
Swirl Number ◽  
Vortex Rope ◽  
Part Load

Abstract This paper focuses on the generation of twin vortex rope in the draft-tube elbow of a Francis turbine at deep part-load operation through analyzing the results of model tests along with numerical simulations. Model tests, including pressure fluctuations measurements, are conducted over 10 speed factors. By considering the frequency of the pressure fluctuations with respect to the swirl intensity at the runner outlet, the part-load operating range is divided into three regimes, with two clear transitions between each occurring at swirl numbers 0.4 and 1.7. For operating conditions with a swirl number S>0.4, a linear correlation between the frequency of the precessing vortex core and the swirl number is established. During deep part-load regime (S>1.7), low-frequency pressure fluctuations appear. Their frequency feature another linear correlation with the swirl number. Unsteady CFD simulation of the full domain is performed to elucidate the generation mechanisms of the low-frequency fluctuations. By tracking the center of the vortical structures along the draft-tube, generation of three vortices in the elbow responsible for the pressure fluctuations at the lowest frequency is highlighted: the main PVC hits the draft-tube wall in the elbow resulting in its break down into three vortices rotating with half the rotational speed of the PVC. Two of the vortices rotate with opposite angular position, constituting a structure of twin vortices. The periodic rotation of these three vortices in the elbow induces the low-frequency pressure fluctuations.

CFD-Based Energy Improvement of a Parametric Blade Model for a Francis Turbine Runner

2008 ◽  
Author(s):  
Jose´ Manuel Franco-Nava ◽  
Erik Rosado-Tamariz ◽  
Jose´ Manuel Ferna´ndez-Da´vila ◽  
Reynaldo Rangel-Espinosa
Keyword(s):  
Reference Model ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Optimization Process ◽  
Francis Turbine ◽  
Power Stations ◽  
Runner Blade ◽  
Turbine Runner ◽  
Blade Model

The computational fluid dynamic (CFD) based energy improvement of the parametric blade model for a Francis turbine runner is presented. The evaluation of the energy improved uses the results of CFD based optimization of a hydraulic Francis turbine runner. The parametric runner model used by the CFD based optimization process was obtained by applying a parametric blade modeller for turbomachinery based on a geometric reference model. This parametric runner model and the optimization process were computed by using a three dimensional Navier-Stoke commercial turbomachinery oriented CFD code. The flow within hydraulic turbines has a thin boundary layer and noticeable pressure gradients. Hence, the CFD computations were carried out using the Sparlat-Allmaras turbulence model. The aim of the optimization process was improve the performance of the machine. This process was computed by a CFD code integrated environment which combines genetic algorithms and a trained artificial neural network. After optimization cycle convergence, an increment not only in efficiency but also in power was obtained. The energy that is transferred to the runner blade and transformed in torque and power was obtained by using CFD results. From pressure distribution along the normalized arc length of the runner blade for three operating conditions (100%, 85% and, 75% of load) the energy distribution was computed not only for the reference runner but also for the optimized parametric model of the turbine runner. Finally, the averaged energy saved for the same operating conditions was evaluated. Results have shown that application of CFD based optimization can modify and improve runners design so as to increase the efficiency and power of installed hydraulic power stations.

scholarly journals A Turbulence Model Assessment for Deep Part Load Conditions of a Francis Turbine

2021 ◽  
Vol 774 (1) ◽  
pp. 012072
Author(s):  
J Wack ◽  
J Beck ◽  
P Conrad ◽  
F von Locquenghien ◽  
R Jester-Zürker ◽  
...  
Keyword(s):  
Turbulence Model ◽  
Francis Turbine ◽  
Model Assessment ◽  
Deep Part ◽  
Part Load ◽  
Load Conditions
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