Simultaneous study of pressure pulsation and structural fluctuations of a cavitated vortex core in the draft tube of a Francis turbine

Abstract The presence of excessive swirl at the runner outlet in Francis turbines operating at part load leads to the development of flow instabilities such as the rotating vortex rope (RVR). The presence of RVR causes severe pressure pulsations, power swings, and fatigue damage in the turbine unit. Air and water injection in the draft tube have been reported to reduce the detrimental effects of RVR formation in the Francis turbines. Air injection is one of the oldest and most widely used methods. In contrast, water jet injection is a relatively new methodology. The present work reports the numerical simulations performed to compare the respective effectiveness of these methods to mitigate the RVR and the related flow instabilities. The efficacy of the two methods has been compared based on the pressure pulsations and pressure recovery in the draft tube cone. The results show that the air and water injection influence the draft tube flow field in different ways. Both air and water injection led to a reduction in pressure pulsation magnitudes in the draft tube cone. However, the air injection led to a negative pressure recovery while the water injection improved the draft tube action.

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Space and time reconstruction of the precessing vortex core in Francis turbine draft tube by 2D-PIV

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/49/8/082011 ◽

2016 ◽

Vol 49 ◽

pp. 082011 ◽

Cited By ~ 1

Author(s):

A Favrel ◽

A Müller ◽

C Landry ◽

K Yamamoto ◽

F Avellan

Keyword(s):

Vortex Core ◽

Draft Tube ◽

Francis Turbine ◽

Space And Time ◽

Precessing Vortex Core

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A novel comprehensive evaluation method of the draft tube pressure pulsation of Francis turbine based on EEMD and information entropy

Mechanical Systems and Signal Processing ◽

10.1016/j.ymssp.2018.07.033 ◽

2019 ◽

Vol 116 ◽

pp. 772-786 ◽

Cited By ~ 8

Author(s):

Weiyu Wang ◽

Qijuan Chen ◽

Donglin Yan ◽

Dazhou Geng

Keyword(s):

Information Entropy ◽

Evaluation Method ◽

Pressure Pulsation ◽

Draft Tube ◽

Comprehensive Evaluation ◽

Francis Turbine ◽

Comprehensive Evaluation Method

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Experimental and Numerical Analysis of Pressure Pulsation in Francis Turbine

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2008-55238 ◽

2008 ◽

Cited By ~ 1

Author(s):

Yexiang Xiao ◽

Zhengwei Wang ◽

Zongguo Yan ◽

Yongyao Luo ◽

Ruofu Xiao ◽

...

Keyword(s):

Unsteady Flow ◽

Flow Pattern ◽

Pressure Fluctuation ◽

Pressure Pulsation ◽

Draft Tube ◽

Flow Distribution ◽

Internal Flow ◽

Operating Conditions ◽

Francis Turbine ◽

Spiral Case

The pressure fluctuation taking place at the whole passage of a prototype Francis hydraulic turbine is studied by carrying out both experimental and numerical simulation. Unsteady wall pressure measurements at six different typical operating conditions are performs to thoroughly investigate pressure fields in the spiral case and straight draft tube dynamically. 3-D unsteady turbulent simulations are performed and compared to the experimental data. The computed flow domain includes the spiral case, stay vanes, guide vanes, rotating runner and the draft tube. The characteristic of unsteady flow and the pressure pulsation as well as their relationships are discussed in this paper, which also analyzed the correlation between the unsteady flow pattern and the pressure fluctuation at different parts of the turbine. In order to optimize the internal flow distribution in Francis turbines at partial loads, this paper presents some preliminary methods to control the unsteady flow pattern.

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

Processes ◽

10.3390/pr9071182 ◽

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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Pressure Analysis in the Draft Tube of a Pump-Turbine under Steady and Transient Conditions

Energies ◽

10.3390/en14164732 ◽

2021 ◽

Vol 14 (16) ◽

pp. 4732

Author(s):

Jing Yang ◽

Yue Lv ◽

Dianhai Liu ◽

Zhengwei Wang

Keyword(s):

Steady State ◽

Pressure Pulsation ◽

Transient Flow ◽

Draft Tube ◽

Simulation Method ◽

Wall Pressure ◽

Pump Turbine ◽

Steady State Condition ◽

Transient Conditions ◽

Pumped Storage

Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.

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Numerical investigation of the cavitation dynamic parameters in a Francis turbine draft tube with columnar vortex rope

Journal of Hydrodynamics ◽

10.1007/s42241-019-0035-z ◽

2019 ◽

Vol 31 (5) ◽

pp. 931-939 ◽

Cited By ~ 3

Author(s):

Jing Yang ◽

Ling-jiu Zhou ◽

Zheng-wei Wang

Keyword(s):

Numerical Investigation ◽

Draft Tube ◽

Francis Turbine ◽

Dynamic Parameters ◽

Vortex Rope ◽

Columnar Vortex

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

Energies ◽

10.3390/en14227626 ◽

2021 ◽

Vol 14 (22) ◽

pp. 7626

Author(s):

Tao Guo ◽

Lihui Xu ◽

Wenquan Wang

Keyword(s):

Flow Field ◽

Vortex Structure ◽

Draft Tube ◽

Francis Turbine ◽

Vortex Identification ◽

Vortex Rope ◽

Blade Passage ◽

Small Opening ◽

Turbulent Characteristics ◽

Passage Vortex

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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