Dynamic evolutions between the draft tube pressure pulsations and vortex ropes of a Francis turbine during runaway

2017 ◽  
Vol 10 (4) ◽  
pp. 404-411 ◽  
Author(s):  
Xiaoxi Zhang ◽  
Qiuhua Chen ◽  
Jie Liao
Keyword(s):  
Draft Tube ◽  
Francis Turbine ◽  
Pressure Pulsations

Comparison of Axial Water and Air Injections in the Draft Tube of a Francis Turbine for RVR Mitigation

2021 ◽  
Author(s):  
Subodh Khullar ◽  
Krishna M. Singh ◽  
Michel J. Cervantes ◽  
Bhupendra K. Gandhi
Keyword(s):  
Pressure Pulsation ◽  
Draft Tube ◽  
Water Injection ◽  
Air Injection ◽  
Flow Instabilities ◽  
Pressure Recovery ◽  
Francis Turbine ◽  
Tube Flow ◽  
Pressure Pulsations ◽  
Jet Injection

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.

The numerical simulation of draft tube cavitation in Francis turbine at off-design conditions

2016 ◽  
Vol 33 (1) ◽  
pp. 139-155 ◽  
Author(s):  
Jing Yang ◽  
Lingjiu Zhou ◽  
Zhengwei Wang
Keyword(s):  
Draft Tube ◽  
Francis Turbine ◽  
Pressure Pulsations ◽  
Cavitation Flow ◽  
Vortex Rope ◽  
Content Type ◽  
Columnar Vortex ◽  
Spiral Vortex ◽  
Mesh Density ◽  
Load Conditions

Purpose – The vortex ropes in draft tube of Francis turbine always cause fluctuation and vibration, which consequently threaten the safety and stability of hydro turbines. The purpose of this paper is to use a cavitation flow computational method to simulate spiral vortex ropes under part load conditions and columnar vortex ropes under high-load conditions in draft tube. The unsteady cavitating flow characteristics in draft tube and its interaction with runner cavitation were analyzed. Design/methodology/approach – The calculation method was verified by cavitation simulation around a 3D hydrofoil. The results show that the Large Eddy Simulation (LES) turbulence model with the Zwart-Gerber-Blemari cavitation model have comparative advantage in cavitation simulations whether from capture of cavity shape or prediction of pressure changes. So it was chosen to simulate the two-phase cavitation flow in Francis turbine. The boundary conditions for inlet and outlet were set to inlet total pressure and outlet static pressure. The finite volume method with the central difference was adopted to discretize the equations. Findings – The calculated Thoma number agreed well with the experimental data. The vortex rope diameter and length increased with the cavitation development for both of the two types of vortex ropes conditions. The maximum peak-to-peak values of pressure pulsations located in the draft tube elbow part under all of the Thoma numbers conditions. Under spiral vortex rope conditions, the pressure pulsation in the same section of draft tube cone show obviously phase shift. The vortex rope affects the development of runner cavitation, which induces the symmetric and axisymmetric cavitation region in the suction side of blades for spiral and columnar vortex rope condition, respectively. Research limitations/implications – The mesh independence had been checked only in non-cavitation flow; in addition, the mesh density did not well satisfy the requirements of LES due to the limitations of computing power. The higher mesh density on a simplified model with one blade flow path and the entire draft tube may be helpful for obtaining more precise results. Originality/value – The spiral and columnar vortex ropes in a Francis turbine were compared and analyzed. The annular hydraulic jump appeared in the columnar vortex rope conditions has little effects on the pressure pulsations. The uneven flow field caused by spiral vortex led to the asymmetric cavitation development.

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.

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

Energies ◽  
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.

Influence of the velocity field at the inlet of a Francis turbine draft tube on performance over an operating range

2012 ◽  
Vol 15 (3) ◽  
pp. 032008 ◽  
Author(s):  
R Susan-Resiga ◽  
S Muntean ◽  
T Ciocan ◽  
E Joubarne ◽  
P Leroy ◽  
...  
Keyword(s):  
Velocity Field ◽  
Draft Tube ◽  
Francis Turbine ◽  
Operating Range

scholarly journals Numerical study of a case of the free discharge of water through the turbine with a braked runner

2021 ◽  
Vol 2119 (1) ◽  
pp. 012152
Author(s):  
D V Platonov ◽  
A V Minakov ◽  
A V Sentyabov
Keyword(s):  
Finite Volume Method ◽  
Finite Volume ◽  
Numerical Study ◽  
Francis Turbine ◽  
Flow Structures ◽  
Pressure Pulsations ◽  
Integral Characteristics ◽  
Free Discharge ◽  
Simulation Results ◽  
Volume Method

Abstract The paper presents a numerical study of the free discharge of water through the turbine with a braked runner. The simulation was carried out for a unit of a full-scale Francis turbine. The finite volume method was employed for unstructured meshes using the DES method. The simulation results show the flow structures, integral characteristics, and pressure pulsations in the flow path. The analysis of the applicability of this approach to real conditions is carried out.

Model and Prototype Draft Tube Pressure Pulsations

1996 ◽  
pp. 994-1003 ◽  
Author(s):  
Vladimir Kercan ◽  
Marin Bajd ◽  
Vesko Djelić ◽  
Andrej Lipej ◽  
Dragica Jošt
Keyword(s):  
Draft Tube ◽  
Pressure Pulsations
Sign in / Sign up

Export Citation Format

Share Document