3D PIV and LDV Measurements at the Outlet of a Francis Turbine Draft Tube

2002 ◽  
Author(s):  
Monica Sanda Iliescu ◽  
Gabriel Dan Ciocan ◽  
Franc¸ois Avellan
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Small Variation ◽  
Hydraulic Turbine ◽  
Field Analysis ◽  
Francis Turbine ◽  
Outlet Section ◽  
Recovery Coefficient ◽  
Transversal Section ◽  
Operating Points

For certain geometries of elbow draft tubes of a hydraulic turbine, a drop in the pressure recovery coefficient is observed for a small variation of the flow rate. In order to determine the possible causes of this characteristics shape, the flow field analysis for 4 nearby operating points have been investigated. For velocity and turbulence fields investigation in the outlet section of the studied draft tube, LDV measurements were performed in a transversal section and the 3D-PIV system was qualified for global velocity measurements in longitudinal sections, with an accuracy of less than 3%. By correlating the LDV and PIV results, the quantification of the flow rate through each channel, related to the operating points, and the description of the secondary flow in the outlet zone are possible.

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 Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

2018 ◽  
Vol 180 ◽  
pp. 02090 ◽  
Author(s):  
Pavel Rudolf ◽  
Jiří Litera ◽  
Germán Alejandro Ibarra Bolanos ◽  
David Štefan
Keyword(s):  
Swirling Flow ◽  
Flow Instability ◽  
Draft Tube ◽  
Water Injection ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Necessary Condition ◽  
Vortex Rope ◽  
Wide Range

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga’s idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.

Long-Period Pressure Pulsation Estimated in Numerical Simulations for Excessive Flow Rate Condition of Francis Turbine

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Kenji Shingai ◽  
Nobuaki Okamoto ◽  
Yuta Tamura ◽  
Kiyohito Tani
Keyword(s):  
Numerical Simulations ◽  
Flow Rate ◽  
Draft Tube ◽  
Homogeneous Model ◽  
Francis Turbine ◽  
Computational Time ◽  
Condensation Process ◽  
Rate Condition ◽  
Long Period ◽  
Rotor Stator Interaction

A series of numerical simulations for a Francis turbine were carried out to estimate the unsteady motion of the cavity in the draft tube of the turbine under a much larger flow rate condition than the swirl-free flow rate. The evaporation and condensation process was described by using a simplified Rayleigh–Plesset equation. A two-phase homogeneous model was adopted to calculate the mixture of gas and liquid phases. Instantaneous pressure monitored at a point on the draft tube formed long-period pulsations. Detailed analysis of the simulation results clarified the occurrence of a uniquely shaped cavity and the corresponding flow pattern in every period of the pressure pulsations. The existence of a uniquely shaped cavity was verified with an experimental approach. A simulation without rotor-stator interaction also obtained long-period pulsations after an extremely long computational time. This result shows that the rotor-stator interaction does not contribute to the excitation of long-period pulsations.

Analysis and Prevention of Vortex Rope Formation in the Draft Tube Cone of a Hydraulic Turbine

2012 ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Control Technique ◽  
Low Velocity ◽  
Recovery Coefficient ◽  
Outer Flow ◽  
Vortex Rope ◽  
Stagnant Region ◽  
Inner Region ◽  
Pressure Recovery Coefficient

Numerical simulations and analysis of the vortex rope formation in a draft tube cone of a Francis turbine operating at part-load conditions are carried out. Steady simulations are performed using a 2-D axisymmetric computational grid and unsteady simulations are carried out using a 3-D computational grid for a simplified axisymmetric draft tube. Two part-load operating conditions with same head and different flow rates are considered. The flow rates of these two operating points correspond to 91% of the flow rate at best efficiency point (case I) and 70% of the flow rate at best efficiency point (case II). Steady, axisymmetric simulations show the formation of a central stagnant region in the draft tube which becomes larger as flow rate decreases. This region results in flow blockage and reduction of the pressure recovery coefficient. It is shown that the pressure recovery coefficient is reduced by 46% by decreasing the flow rate from 91% of the best efficiency point (case I) to 70% of the best efficiency point (case II) while loss coefficient becomes 5 times larger. Present unsteady, three-dimensional simulations correctly predict the overall shape of the vortex rope and the calculated vortex rope frequency differs only 5% from experimental data. It is shown that the vortex rope is formed due to the roll-up of the shear layer at the interface between the low-velocity inner region (results from the crown cone wake) and highly swirling outer flow. Finally a flow control technique which uses a water jet injected from the runner crown tip along the axis is investigated. The jet accelerates the flow near the centerline (stagnant region) and decreases the relative velocity and thereby the shear between low-velocity inner region and high-velocity outer flow and hence prevents the vortex rope formation. The jet discharge is optimized for minimum overall losses. The optimized jet decreases total losses by 13% for case I and the vortex rope is eliminated. The fraction of water used for the optimized jet is less than 0.5% of the turbine discharge. As shown in the present study, this control technique can suppress severe pressure fluctuations resulting from the vortex rope formation.

Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part II: Control of the Vortex Rope

2014 ◽  
Vol 81 (6) ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Companion Paper ◽  
Francis Turbine ◽  
Control Technique ◽  
Outer Flow ◽  
Vortex Rope ◽  
Stagnant Region ◽  
Partial Load

Numerical simulations and investigation of a method for controlling the vortex rope formation in draft tubes are carried out in this paper, which is the second part of a two-paper series. As shown in the companion paper, formation of the vortex rope is associated with a large stagnant region at the center of the draft tube. Therefore, it is concluded that a successful control technique should focus on the elimination of this region. In practice, this can be performed by axially injecting a small fraction (a few percent of the total flow rate) of water into the draft tube. Water jet is supplied from the high-pressure flow upstream of the turbine spiral case by a bypass line; thus, no extra pump is needed in this method. It is shown that this method is very effective in elimination of the stagnant region in a simplified draft tube operating at two part-load conditions, i.e., at 91% and 70% of the best efficiency point (BEP) flow rate. This results in improvement of the draft tube performance and reduction of hydraulic losses. The loss coefficient is reduced by as much as 50% for the case with 91% of BEP flow rate and 14% for the case with 70% of BEP flow rate. Unsteady, three-dimensional simulations show that the jet increases the axial momentum of flow at the center of the draft tube and decreases the wake of the crown cone and thereby decreases the shear at the interface of the stagnant region and high velocity outer flow, which ultimately results in elimination of the vortex rope. Furthermore, reduction (by about 1/3 in the case with 70% of BEP flow rate) of strong pressure fluctuations leads to reliable operation of the turbine.

scholarly journals Numerical Study on Performance Characteristics of Draft Tube of Mixed Flow Hydraulic Turbine

2012 ◽  
Vol 10 ◽  
pp. 48-52
Author(s):  
Ruchi Khare ◽  
Vishnu Prasad
Keyword(s):  
Coming Out ◽  
Draft Tube ◽  
Numerical Study ◽  
Flow Simulation ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Mixed Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Overall Performance

Draft tube is an important component of the hydraulic reaction turbine and affects the overall performance of turbine to a large extent. The flow inside the draft tube is complex because of the whirling flow coming out of runner and its diffusion along the draft tube. The kinetic energy coming out of runner is recovered in draft tube and part of recovery meets the losses. In the present work, the computational fluid dynamics (CFD) has been used for flow simulation in complete mixed flow Francis turbine for performance analysis for energy recovery, losses and flow pattern in an elbow draft tube used in Francis turbine at different operating conditions. The overall performance of the turbine at some typical operating regimes is validated with the experimental results and found to be in close comparison.DOI: http://dx.doi.org/10.3126/hn.v10i0.7103 Hydro Nepal Vol.10 January 2012 48-52

Detection of Unsteady Flow in a Kaplan Hydraulic Turbine Using Machine Mechanical Model and Rotor Measured Vibrations

2012 ◽  
Author(s):  
Paolo Pennacchi ◽  
Andrea Vania ◽  
Steven Chatterton ◽  
Ezio Tanzi
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Mechanical Model ◽  
Turbine Unit ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Design Stage ◽  
System Response ◽  
Model Based

Hydraulic stability is one of the key problems during the design stage of hydraulic turbines. Despite of modern computational tools that help to define dangerous operating conditions and optimize runner design, hydraulic instabilities may fortuitously arise during the turbine life, as a consequence of variable and different operating conditions at which a hydraulic turbine can be subject. In general, the presence of unsteady flow reveals itself in two different ways: at small flow rate, the swirling flow in the draft tube conical inlet occupies a large portion of the inlet and causes a strong helical vortex rope; at large flow rate conditions the unsteady flow starts midway and causes a breakdownlike vortex bubble, followed by weak helical waves. In any case, hydraulic instability causes mechanical effects on the runner, on the whole turbine and on the draft tube, which may eventually produce severe damages on the turbine unit and whose most evident symptoms are vibrations. This notwithstanding, condition monitoring systems seldom are installed on this purpose in hydraulic power plants and no examples are reported in literature about the use of model-based methods to detect hydraulic instability onset. In this paper, by taking the advantage of a testing campaign performed during the commissioning of a 23 MW Kaplan hydraulic turbine unit, a rotordynamic model-based method is proposed. The turbine was equipped by proximity and vibration velocity probes, that allowed measuring lateral and axial vibrations of the shaft-line, under many different operating conditions, including also some off-design ones. The turbine mechanical model, realized by means of finite beam elements and considering lateral and axial degrees of freedom, is used to predict turbine unit response to the unsteady flow. Mechanical system response is then compared to the measured one and the possibility to detect instability onset, especially in real-time, is discussed.

scholarly journals Multi-objective Optimization of Draft Tube in Francis Turbine Using DOE, RBF and NSGA-II

2017 ◽  
Author(s):  
Chol Nam Mun ◽  
De Chun Ba ◽  
Xiang Ji Yue ◽  
Myong Il Kim
Keyword(s):  
Draft Tube ◽  
Fluid Dynamic ◽  
Hydraulic Turbine ◽  
Optimization Method ◽  
Approximate Model ◽  
Francis Turbine ◽  
Design Parameters ◽  
Geometrical Parameters ◽  
Design Matrix ◽  
Nsga Ii

In order to improve the performance of the draft tube in hydraulic turbine, a multi–objective optimization method for the draft tube is developed by combining the design of experiment (DOE), the radial basis function (RBF) and the non–dominated sorting genetic algorithm (NSGA–II) in this paper. The geometrical design variables of the median section in the draft tube and the cross section in its exit diffuser are considered as design parameters in this optimization, which objective function is to maximize the pressure recovery factor (Cp) and minimize the energy loss coefficient (ζ). The limited numbers of design matrix required for the shape optimization of the draft tube is generated by optimal Latin hypercube (OLH) method of the DOE technique, of which performances are evaluated through computational fluid dynamic (CFD) numerical simulation. For reducing of the computational consumption, the approximate model is used based on the RBF. The Pareto optimal solutions are finally performed using the NSGA–II for obtaining the best geometrical parameters of the draft tube. The optimization result of the draft tube shows a marked performance improvement over the original, which verifies the theoretical validity and feasibility of the proposed method in this paper.

3D Unsteady Turbulent Simulation of the Runaway Transient of the Francis Turbine

2007 ◽  
Author(s):  
Jinwei Li ◽  
Yulin Wu ◽  
Shuhong Liu ◽  
Yuliang Zhu
Keyword(s):  
Transient Process ◽  
Stokes Equations ◽  
Draft Tube ◽  
Guide Vane ◽  
Hydraulic Turbine ◽  
Moment Equation ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Volume Discharge ◽  
Navier Stokes Equations

Based on Reynolds-averaged continuity and Navier-Stokes equations, and moment equation of the rotational system in the accelerated rotational relative coordinate, the governing equations of the runner region are obtained. The runaway transient simulation of the Francis turbine based on HL220 is made with RNG k-ε turbulence model under 9 guide vane openings. The variation diagrams of volume discharge, moment, rotational speed, and efficiency with respect to time are gained. Through further analysis of simulation results the transient process curve as well as the flow pattern under 9 guide vane openings are obtained, and detailed analysis is focused on flow in the draft tube to obtain variation of pressure distribution on symmetry surface of the draft tube with respect to time and pressure fluctuation of all test points in the turbine. Comparison between simulation and experiment results shows that they both are in good agreement, and it demonstrates that variation of all the parameters of the hydraulic turbine can be forecast accurately during the transient process.

scholarly journals Experimental and Numerical Simulations Predictions Comparison of Power and Efficiency in Hydraulic Turbine

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Laura Castro ◽  
Gustavo Urquiza ◽  
Adam Adamkowski ◽  
Marcelo Reggio
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Draft Tube ◽  
Flow Simulation ◽  
Numerical Data ◽  
Hydroelectric Power Plant ◽  
Hydraulic Turbine ◽  
Hydroelectric Power ◽  
Spiral Case

On-site power and mass flow rate measurements were conducted in a hydroelectric power plant (Mexico). Mass flow rate was obtained using Gibson's water hammer-based method. A numerical counterpart was carried out by using the commercial CFD software, and flow simulations were performed to principal components of a hydraulic turbine: runner and draft tube. Inlet boundary conditions for the runner were obtained from a previous simulation conducted in the spiral case. The computed results at the runner's outlet were used to conduct the subsequent draft tube simulation. The numerical results from the runner's flow simulation provided data to compute the torque and the turbine's power. Power-versus-efficiency curves were built, and very good agreement was found between experimental and numerical data.

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