STEADY STATE OPERATION

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CONTENTS

Organizing committee

1. Torbjørn Kristian Nielsen (NTNU), Chair
2. Michel Cervantes (LTU & NTNU), Co-chair
3. Ole Gunnar Dahlhaug (NTNU)
4. Chirag Trivedi (NTNU)
5. Kaveh Amiri (LTU)
6. Joel Sundström (LTU)

Test case: Francis-99 turbine

Experiments were conducted at the Waterpower laboratory during 2012 - 2013 on a model Francis turbine considering open loop hydraulic system. The model Francis turbine available in the Waterpower laboratory, also known as Francis-99 turbine, is a scaled (1:5.1) model of the turbines operating at Tokke power plant in Norway. The Francis turbine is a splitter blade type runner consisting of 15 blades and 15 splitters (short blades). The leading edge profiles of the blades and splitters are similar. The blades are twisted upto180 degree along the chord length from inlet to the outlet of the runner. The blade thickness at the trailing edge is around 3 mm. Runner inlet and outlet diameters are 0.630 m and 0.349 m, respectively. Operating head was approximately 12m and the discharge was 0.2 m³ s^-1 the best efficiency point (BEP). 

Location of sensors and instrumentation

Two logging systems were used to acquire data from the turbine. One logging system was used to acquire data related to the hill diagram and another was used to acquire pressure values from the additional pressure sensors. Total six pressure sensors were mounted in the turbine, one sensor (VL01) was located at the vaneless space, three sensors (P42, S51 and P71) were located in the runner, and two sensors (DT11 and DT21) were located in the draft tube cone. The pressure values were acquired at the sampling rate of 2083 Hz. A wireless telemetry system was used to acquire data from the runner sensors. IEC 60193 was followed for the calibration, measurements, and computations of the data. Uncertainties in the discharge, inlet pressure, and differential pressure measurements were ±0.1%, ±0.05%, and ±0.018%, respectively. The uncertainties in the generator input torque measurement, friction torque measurement, and runner angular speed measurement were ±0.034%, ±0.052, and ±0.05%, respectively. Total uncertainty in hydraulic efficiency was ±0.16%.

Figure 1. Francis-99 instrumentation and locations of the sensors.

Steady state measurements

Before the pressure and velocity measurements, detailed analysis of the turbine performance was carried out. Total 10 different angle of guide vane were selected and 15 different speed values for each angle of the guide vane were selected. Thus, efficiency measurements were conducted at total 150 points. The iso-efficiency hill chart was prepared as shown in Figure 2. The maximum efficiency of 93.4% was obtained at n_ED=0.18 and Q_ED=0.2, marked as the best efficiency point (BEP). Guide vane angles 3.9 degree and 14 degree correspond to minimum and the maximum loads of the turbine, respectively. For this workshop, three operating point are considered: (1) Part load (PL), n_ED=0.215 and Q_ED=0.07, (2) BEP, n_ED=0.18 and Q_ED=0.2, (3) High load (HL), n_ED=0.195 and Q_ED=0.19. Table 1 shows the obtained parameters at these operating points. These parameters can be used for the boundary conditions for numerical simulations and its validation. Cross sectional areas at the turbine inlet and outlet pressure measurement sections are 0.0872 m² and 0.2360 m², respectively. The Gravitational constant at the laboratory location is 9.821 m s^-2. The reference diameter of the model Francis runner is 0.349 m. The kinematic viscosity is 9.57e-7 m² s^-1. The Reynolds numbers at BEP are 1.8e6. Detailed information on the measurements is presented in the research article .

Figure 2. Iso-efficiency hill diagram of Francis-99 turbine.

Table 1 Experimental data at steady state operation of the Francis-99.

Pressure

Unsteady pressure measurements were carried out at six different locations. The pressure values were acquired at a sampling rate of 2083 Hz, and the data may contain frequencies related to electrical power, 50 Hz and its harmonic. The pressure sensors and data acquisition system were powered by grid supply. However, this can be filtered out by using cut-off filters. The uncertainties observed during the calibration of VL01, P42, S51, P71, DT11, and DT21 sensors are ±0.15%, ±0.62%, ±0.22%, ±0.45%, ±0.15, and ±0.15% of the measured value, respectively. Download high frequency pressure data from the following links. Exact locations of the pressure sensors in the turbine is shown in Table 2.

Table 2. Exact locations of the pressure sensors in the turbine.

Velocity

LDA and 2D PIV were used for the velocity measurement in the draft tube cone. LDA is composed of a Spectra-Physics Model 177G, equipped with a Burst Spectrum Analyzer (BSA) from Dantec Dynamics. The LDV probe was mounted on a traverse table with the probe perpendicular to the glass wall of the index-matching box. The perpendicularity was checked with optical methods with an accuracy of 0.2 degree. The front lens had a focal length of 310 mm. The seeding particles of Expancel 46 WU 20 with an average diameter of six µm were used. The L1 and L2 sections are at the distance of 0.064 and 0.382 m from the runner outlet, respectively. For the 2D PIV system, pulse light sheets with a thickness of about 3 mm were generated by a Litron Laser NANO L100-50PIV. The illuminated field was recorded by a four megapixel camera (VC-4MC-M180). TSI seeding particles, with a density of 1.016 g/cc, refractive index of 1.52 and mean diameter of 55 µm was used during the measurements. The PIV measurement data were sampled at the rate of 40 Hz. About 750 paired images with a time difference of 200 µs were recorded at each measurement section. For velocity measurements were conducted during second round of measurements therefore there may be small variation in global parameters presented Table 1 and Table 3. We tried our best to reproduce the similar operating conditions to make accurate comparison of both pressure and velocity data at PL, BEP and HL. Velocity measurements (axial and tangential) were performed with LDA along two horizontal lines in the draft tube. The two lines L1 and L2 are located 64 mm and 382 mm below the draft tube inlet, respectively. More information about the measurements is presented in the research article .

Table 3. Overall parameters of the turbine at velocity measurements in the draft tube.

The velocity data is available in the following file for the three operating points investigated, PL, BEP and HL. Positive axial velocity is defined in the stream-wise direction and the tangential velocity is positive in the runner rotational direction. However, vibration were induced in the test rig at the BEP and HL, Which interfered with the measurements at these conditions. The coordinates for the LDA measuring lines are presented in Table 4.

Table 4. Coordinates for the LDA measurement lines in the draft tube.

Numerical model

The complete three-dimensional geometry of the turbine is created and provided for this workshop. The geometry and mesh are prepared using ICEM CFD v14. Therefore, ICEM CFD mesh at these three operating points is also provided. One can directly use this mesh and perform numerical studies by setting up own flow physics. The provided experimental data were used for the necessary boundary conditions and comparison of the numerical results. The geometries include wetted surfaces only. The geometry files also includes block (*.blk) file and the block file can be used to create mesh in ICEM CFD. The explanation about creating mesh from the block is given in ANSYS help manual. First, you may need to create pre-mesh then convert to unstructed by right clicking on pre-mesh, and export the mesh for the simulation. The locations of pressure sensors and velocity measurements are provided in three-dimensional geometry that can be used to create monitoring points during the simulation for validation with the provided experimental pressure data.

Figure 3. Computational domain of the model Francis turbine. Inlet face is identical to the pressure measurement location. The turbine includes three domain, spiral casing with distributor, runner, and draft tube. The domain can be connected using appropriate interface. Runner is a rotating domain. The rotation direction, clockwise/anti-clockwise, must be checked with reference to the guide vane position. Three dimensional geometry of the runner is prepared in two parts: (1) complete runner and (2) small area below the runner cone. There was difficulty in creating ICEM CFD blocks below the runner cone therefore it is divided in two parts. However, one can select part-1, you choose to create own mesh.

Figure 4. Spiral casing with stay vane and guide vane.

Figure 5. Cross section of the Francis-99 runner.

Figure 6. Three-dimensional view of the draft tube.

Author centre

Important dates

Experimental data and results will be available before 01 January 2014.

Last date for the abstract submission is 15 March 2014.

Accepted abstract will be notified before 01 April 2014.

Last date for the submission of full length paper is 15 September 2014.

Notification of the finally accepted full length papers is before 01 October 2014.

Last date for the submission of final formatted full length paper is 31 October 2014.

Abstract and paper submission is closed.

Abstract and manuscript submission

Formatting the abstract: Submission file format should be pdf. Maximum numbers of words in abstract are 500. Maximum length of the paper title is 25 words, no special character, only "dash" can be used if needed.

Formatting the full length final paper: Please follow the guideline available for Journal of Physics: Conference Series.

Registration

The registration to the workshop is made by sending to Debbie Koreman (debbie.w.koreman@ntnu.no , tel. +47-73593561) the form below and paying the required fees. The registration fees include 25% VAT and are as follow:

- Participants with Paper: 1500 NOK.

- Participants without paper: 3100 NOK.

- Student (MSc, PhD): 1500 NOK.

- NTNU and LTU staff: 1500 NOK.

- Late Registration (after 01 December 2014): 4500 NOK.

- Accompanying person (dinner): 1000 NOK.

Venue

The workshop will be held at the Norwegian University of Science and Technology, Trondheim, Norway. The exact address is: Electric Power Engineering Building (room EL6), OS Bragstads plass 2E, N-7034 Trondheim. Conference location

Accommodation

A large number of hotels are available around the University (BEST WESTERN Chesterfield Rica Bakklandet, Clarion Grand Olav Clarion Hotel & Congress Trondheim, Comfort Hotel Park, Scandic Lerkendal, City Living, Trondheim Youth hostels ...).

Programme

Day 1 (15 December 2014)

1000‐1130: Registration

1130‐1230: Lunch

1230‐1240: Prof. T. Nielsen: Introduction

1240‐1320: Prof. M. Raisee: Uncertainty quantification in CFD with application to hydropower

1320‐1410: C. Trivedi and C. Bergan: Francis‐99 test case
1410‐1430: J Nicolle and S Cupillard: Prediction of dynamic blade loading of the Francis‐99 turbine

1430‐1450: Coffee break

1450‐1510: D Stefan and P Rudolf: Proper orthogonal decomposition of pressure fields in a draft tube cone of the Francis (Tokke) turbine model

1510‐1530: H. Wallimann and R. Neubauer: Numerical study of a high head Francis turbine
with measurements from the Francis‐99 project

1530‐1550: A V Minakov, A V Sentyabov, D V Platonov, A A Dekterev and A A Gavrilov: Numerical modelling of flow in the Francis‐99 turbine with Reynolds stress model and detached eddy simulation method

1550‐1610: P Mössinger, R Jester‐Zurker, A Jung: Investigation of different simulation approaches on a high‐head Francis turbine and comparison with model test data: Francis‐99

1610‐1630: D Jošt, A Škerlavaj, M Morgut, P Mežnar and E Nobile: Numerical simulation of flow in a high head Francis turbine with prediction of efficiency, rotor stator interaction and vortex structures in the draft tube

1630‐1900: (free time)

1900‐2100: Dinner

Day 2 (16 December 2014)

0830‐0850: Carl Bergan, Kaveh Amiri, Michel J Cervantes and Ole G Dahlhaug: Preliminary measurements of the radial velocity in the Francis‐99 draft tube cone

0850‐0910: D Čelič and H Ondráčka: The influence of disc friction losses and labyrinth losses on efficiency of high head Francis turbine

0910‐0930: M Lenarcic, M Eichhorn, SJ Schoder and C Bauer: Numerical investigation of a high head Francis turbine under steady operating conditions using foam‐extend

0930‐0950: O Amstutz, B Aakti, E Casartelli, L Mangani, L Hanimann: Predicting the performance of a high head Francis turbine using a fully implicit mixing plane

0950‐1010: B Aakti, O Amstutz, E Casartelli, G Romanelli, L Mangani: On the performance of a high head Francis turbine at design and o‐design conditions

1010‐1030: Coffee break

1030‐1050: L Stoessel, H Nilsson: Steady and unsteady numerical simulations of the flow in the Tokke Francis turbine model, at three operating conditions

1050‐1110: Z Yaping, L Weili, R Hui, L Xingqi: Performance study for Francis‐99 by using different turbulence models

1110‐1130: JD. Buron, S Houde, R. Lestriez and C Deschênes: Application of the non‐linear harmonic method to study the rotor‐stator interaction in Francis‐99 test case

1130‐1230: Lunch

1230‐1410: Visit Waterpower Laboratory

1410‐1430: Coffee break

1430‐1610: Discussion: geometry, mesh, and experimental data

1610‐1620: Prof. Ole‐Gunnar Dahlhaug: Francis‐99 II

1620‐1630: Prof. T. Nielsen: Conclusion

Workshop summary

The first Francis-99 workshop was organized on 15 - 16 December 2014. Total 14 research papers were presented in the workshop. More than 50% participants were from the different hydropower industries. Over 50 researchers from different countries America, Austria, Canada, China, Czech republic, Germany, Italy, Korea, Russia, Sweden, Slovenia, Switzerland, and Spain were participated in the workshop. Extensive numerical studies on the model Francis turbine was performed by the researchers. The steady-state measurements were conducted on a model Francis turbine. Three operating points, part load, best efficiency point, and high load, were investigated. The complete geometry, meshing, and experimental data concerning the hydraulic efficiency, pressure, and velocity were provided to the academic and industrial research groups. Various researchers have conducted extensive numerical studies on the high-head Francis turbine, and the obtained results were presented during the workshop. The first workshop attempted to determine the state of the art in the simulation of high-head Francis turbines under steady operations, namely, at part load, best efficiency point and high load. The motivation resided in the continuous development of more powerful computers, thereby facilitating the use of more advance turbulence models and accurate numerical schemes. Efficiency, pressure, and velocity measurements were conducted on the Francis-99 test case at the Waterpower laboratory, Norwegian University of Science and Technology (NTNU), Norway. Many questions were raised during the workshop concerning the challenges related to accurate simulations of high-head Francis turbines. One of the main challenge was the optimization of the numerical models without compromising the numerical accuracy. It was also highlighted that the numerical model many times mislead and results in incorrect prediction of the flow field.

Main objective of the workshop was to evaluate the numerical techniques applied to investigate the hydraulic turbines and prove open platform to the researchers for conducting numerical studies in high head turbines. For that geometry and mesh were proposed to the participants. Many participants also created their own meshes to improve the quality and investigate in detail specific issues such as near-wall modeling. The complexity of the turbine model geometry and high Reynolds number imply compromises by the mesh. A quality assessment of the mesh is necessary for a proper assessment of the simulations. A mesh sensitivity analysis is not always possible due to computational limitations. Systematic information about the mesh quality parameters, minimum angle, volume change, aspect ratio, etc. is a first step but not sufficient per se. In addition to the mesh, the numerical schemes and type of code should also be stipulated. The same mesh will not provide the same results for different codes; it is also a function of the code used, and each code operates differently.

The hydraulic efficiency obtained by the different participants is very close to the experimental ones. The overestimation at part load is attributed to the omission of the seal leakage losses. Often, numerical results are misleading because the torque and head are over-predicted with an inlet flow boundary condition; see Lenarcic et al. Because the torque generated by the turbine and the available head are related to each other, the hydraulic efficiency is fairly well predicted. Using the head as the inlet boundary condition provides a higher flow rate, decreasing the hydraulic efficiency. The reason is an under-prediction of the viscous losses. The use of a wall function assuming equilibrium between the production and dissipation of turbulence is widely used in the simulation of hydraulic turbines. The boundary layer of hydraulic turbines is never fully developed because of the continuously changing geometry and rapid change in pressure gradients. Resolving the boundary layer up to y⁺ = 1 is not feasible, even with RANS models. There is a need to develop wall functions that enable the estimation of viscous losses under boundary development if accurate simulations are to be developed. Improved simulations and results enable reliable estimation of the blade loading.

In a high-head Francis turbine, pressure amplitudes generated by the rotor-stator interactions are a major concern. A recently developed flow modeling technique was applied to investigate the rotor-stator interaction in the model Francis turbines for the first time. This technique obtained good agreement with the measured values. It has provided a compromise between numerical accuracy and the required computational power for simulating the complete turbine.

At the Francis-99 workshop, numerical simulations were conducted using three modeling approaches: (1) modeling of a complete turbine, (2) modeling of the components, and (3) passage modeling. The simulation of a complete turbine is more expensive than the other two approaches. No significant difference was found between the results obtained with the complete turbine and component modeling approaches. It was considered that the component modeling approach would provide the optimum solution when accurate boundary conditions are prescribed. Further, one can select a passage modeling approach and create a fine mesh near the boundaries to reduce the necessary computational power and time. This approach provides good results but does not consider the influence of the neighboring passages. However, using recently developed techniques of passage modeling can provide reliable results, including dynamic pressure loading generated by rotor-stator interaction.

Input to the second workshop

To minimize the error due to the use of different mesh types and densities, it was noted that a mesh with a uniform density would be provided. The simulations would be conducted using the provided mesh only and validated with the provided experimental data. The mesh would be provided with different y+ values to accommodate different turbulence models. At the second Francis-99 workshop, both steady-state and transient operating conditions will be investigated. Numerical models will be validated with the steady-state experimental results, and the same model will be used for transient conditions. Load variations and start-stop conditions will be investigated under transient operations. The primary focus will be numerical modeling and investigation of the hydraulic turbine during transient conditions.

Publications

Total 14 research paper were presented in the workshop. All the papers were peer-reviewed before the publication in the workshop. The published papers in the workshop are available online at Journal of Physics: Conference Series. and the papers may be freely available.

1. Aakti, B., Amstutz, O., Casartelli, E., Romanelli, G., and Mangani, L., 2015, "On the performance of a high head Francis turbine at design and off-design conditions," Journal of Physics: Conference Series, 579(1), p. 012010. doi: 10.1088/1742-6596/579/1/012010.
2. Amstutz, O., Aakti, B., Casartelli, E., Mangani, L., and Hanimann, L., 2015, "Predicting the performance of a high head Francis turbine using a fully implicit mixing plane," Journal of Physics: Conference Series, 579(1), p. 012009. doi: 10.1088/1742-6596/579/1/012009.
3. Bergan, C., Amiri, K., Cervantes, M. J., and Dahlhaug, O. G., 2015, "Preliminary measurements of the radial velocity in the Francis-99 draft tube cone," Journal of Physics: Conference Series, 579, p. 012014. doi: 10.1088/1742-6596/579/1/012014.
4. Buron, J. D., Houde, S., Lestriez, R., and Deschenes, C., 2015, "Application of the non-linear harmonic method to study the rotor-stator interaction in Francis-99 test case," Journal of Physics: Conference Series, 579(1), p. 012013. doi: 10.1088/1742-6596/579/1/012013.
5. Celic, D., and Ondracka, H., 2015, "The influence of disc friction losses and labyrinth losses on efficiency of high head Francis turbine," Journal of Physics: Conference Series, 579(1), p. 012007. doi: 10.1088/1742-6596/579/1/012007.
6. Jost, D., Skerlavaj, A., Morgut, M., Meznar, P., and Nobile, E., 2015, "Numerical simulation of flow in a high head Francis turbine with prediction of efficiency, rotor stator interaction and vortex structures in the draft tube," Journal of Physics: Conference Series, 579(1), p. 012006. doi: 10.1088/1742-6596/579/1/012006.
7. Lenarcic, M., Eichhorn, M., Schoder, S. J., and Bauer, C., 2015, "Numerical investigation of a high head Francis turbine under steady operating conditions using foam-extend," Journal of Physics: Conference Series, 579(1), p. 012008. doi: 10.1088/1742-6596/579/1/012008.
8. Minakov, A. V., Sentyabov, A. V., Platonov, D. V., Dekterev, A. A., and Gavrilov, A. A., 2015, "Numerical modeling of flow in the Francis-99 turbine with reynolds stress model and detached eddy simulation method," Journal of Physics: Conference Series, 579(1), p. 012004. doi: 10.1088/1742-6596/579/1/012004.
9. Mossinger, P., Jester-Zurker, R., and Jung, A., 2015, "Investigation of different simulation approaches on a high-head Francis turbine and comparison with model test data: Francis-99," Journal of Physics: Conference Series, 579(1), p. 012005. doi: 10.1088/1742-6596/579/1/012005.
10. Nicolle, J., and Cupillard, S., 2015, "Prediction of dynamic blade loading of the Francis-99 turbine," Journal of Physics: Conference Series, 579(1), p. 012001. doi: 10.1088/1742-6596/579/1/012001.
11. Stefan, D., and Rudolf, P., 2015, "Proper orthogonal decomposition of pressure fields in a draft tube cone of the Francis (tokke) turbine model," Journal of Physics: Conference Series, 579(1), p. 012002. doi: 10.1088/1742-6596/579/1/012002.
12. Stoessel, L., and Nilsson, H., 2015, "Steady and unsteady numerical simulations of the flow in the tokke Francis turbine model, at three operating conditions," Journal of Physics: Conference Series, 579(1), p. 012011. doi: 10.1088/1742-6596/579/1/012011.
13. Wallimann, H., and Neubauer, R., 2015, "Numerical study of a high head Francis turbine with measurements from the Francis-99 project," Journal of Physics: Conference Series, 579(1), p. 012003. doi: 10.1088/1742-6596/579/1/012003.
14. Yaping, Z., Weili, L., Hui, R., and Xingqi, L., 2015, "Performance study for Francis-99 by using different turbulence models," Journal of Physics: Conference Series, 579(1), p. 012012. doi: 10.1088/1742-6596/579/1/012012.

Group photograph

Download data

 Table 5. Click on the corresponding hyperlink to download the file.