scholarly journals On the upper part load vortex rope in Francis turbine: Experimental investigation

2010 ◽  
Vol 12 ◽  
pp. 012053 ◽  
Author(s):  
C Nicolet ◽  
A Zobeiri ◽  
P Maruzewski ◽  
F Avellan
Keyword(s):  
Experimental Investigation ◽  
Francis Turbine ◽  
Vortex Rope ◽  
Part Load

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.

Prediction of the Pressure Pulsation in a Draft Tube for a Part Load Condition Using the LES Approach

2015 ◽  
Author(s):  
Olivier Pacot ◽  
Chisachi Kato ◽  
Yang Guo ◽  
Yoshinobu Yamade
Keyword(s):  
Load Condition ◽  
Francis Turbine ◽  
Sharp Change ◽  
Back Side ◽  
Vortex Rope ◽  
Part Load ◽  
Eddy Simulation ◽  
Computational Mesh ◽  
Large Eddy ◽  
Lift And Drag

The present paper focuses on the vortex rope that arises when operating a model Francis turbine at a part load condition: 65% of the Best Efficiency Point (BEP). The investigation is performed numerically using the Large Eddy Simulation (LES) approach with the Dynamic Smagorinsky Model (DSM). Such approach and turbulence model are implemented in the overset finite element open source code, FrontFlow/blue (FFB). Furthermore, a cavitation model is implemented allowing computations for non-cavitating and cavitating conditions. Thanks to the use of the K supercomputer, located at Kobe in Japan, and to the use of large computational mesh (123 million elements), it is shown that the frequency of the precession of the vortex rope as well as the head can be accurately computed. However, the predicted amplitude of the fluctuation did not fully agree with the experiment. Differences in a particular region near the back side of the elbow are about 35%. A comparison between the variation of the size of the vortex rope and the swirl number has been investigated and showed a clear relation. The location of the vortex rope and the minimum of the pressure were also investigated and showed that they do not fully share the same location. Furthermore, in a preliminary study to the computation of the cavitating vortex rope, computations of the flow around a Clark-11.7% hydrofoil under cavitation condition and for angles of attack of 2° and 8° are carried out. The results showed the common issue for this computation, i.e. the sharp change of the lift and drag coefficients could not be accurately predicted. Currently underway are the computation of the cavitating vortex rope. The effect of the cavitation on the vortex rope will be studied and reported at a later stage.

scholarly journals Analysis of the part load helical vortex rope of a Francis turbine using on-board sensors

2015 ◽  
Vol 656 ◽  
pp. 012061 ◽  
Author(s):  
F Duparchy ◽  
A Favrel ◽  
P-Y Lowys ◽  
C Landry ◽  
A Müller ◽  
...  
Keyword(s):  
Francis Turbine ◽  
Vortex Rope ◽  
Part Load ◽  
Helical Vortex

Numerical Simulation of Pressure Vibrations in a Francis Turbine Draft Tube With Air Admission

2014 ◽  
Author(s):  
Renfang Huang ◽  
An Yu ◽  
Xianwu Luo ◽  
Bin Ji ◽  
Hongyuan Xu
Keyword(s):  
Draft Tube ◽  
Load Condition ◽  
Flow Simulation ◽  
Rotation Frequency ◽  
Francis Turbine ◽  
Stable Operation ◽  
Hydraulic Efficiency ◽  
Operation Condition ◽  
Vortex Rope ◽  
Part Load

The pressure vibrations in a draft tube are harmful for the stable operation for a Francis turbine at part load conditions. In this paper, air admission is proposed to depress those pressure vibrations. The unsteady flow in a Francis turbine, whose hydraulic performance has been tested experimentally, is simulated at a part load operation condition. The flow simulation is conducted using RANS methods coupling with SST k-ω turbulence model. The results indicate the pressure vibrations in the turbine are reasonably predicted by the present numerical method. Based on the calculations, the dominant pressure vibration component for a hydro turbine operated at part-load condition is caused by the vortex rope in draft tube, and its frequency is near 0.2 times of the runner rotation frequency. The frequencies of pressure vibration do not change by air admission, and the pressure vibration amplitude decreases with the air admission. Further, the depression effect for pressure vibration would be improved if air admission is from the crown holes instead of the spindle hole. The results also indicate that the turbine hydraulic efficiency changes periodically with the pressure vibration induced by vortex rope in turbine draft tube, would be degraded with air admission from the spindle hole, and improved with air admission from the crown holes. With the increase of air admission, the turbine hydraulic efficiency would improve. The present research will be helpful for the safe operation of Francis turbines.

scholarly journals Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1182
Author(s):  
Seung-Jun Kim ◽  
Yong Cho ◽  
Jin-Hyuk Kim
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Air Injection ◽  
Low Flow ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

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