Test case

Experiments have been conducted on the Francis-99 turbine model used for the first Francis-99 workshop. Both steady state (constant guide vane angle) and transient (time dependent guide vane angle) measurements were performed. Three operating points were selected for the steady state measurements; part load (PL), best efficiency point (BEP), and high load (HL). These operating points are different from the first workshop. The transient measurements include load acceptance from PL to BEP, load reduction from BEP to PL, turbine startup and shutdown. Pressure and velocity data at different locations of the turbine were acquired simultaneously during the measurements. Several repetitions of the measurements have been carried out to estimate the random uncertainty in the measurements. Below you will find:

• Locations of pressure and velocity measurements in the turbine which are same for all the operating points.
• Steady state test case which describes the investigated operating points and corresponding experimental data for numerical validation.
• Transient test case which describes the investigated operating conditions and corresponding experimental data for numerical validation. Additional data on variation of head, discharge, torque, runner angular speed, and guide vane movement in time domain are provided. This information will be needed to setup numerical model for the load variation and start-stop.

Information on the Francis-99 webpage is limited. A number of references are listed at the end of this page to get further insights into the test rig, Francis-99 model and some experimental conditions. However, the articles are not related to the measurements available for the second workshop.

Locations of pressure and velocity measurements in the turbine

For the pressure measurements, a pressure sensor VL2 was mounted at the vaneless space, and three pressure sensors DT5 and DT6 were mounted at the draft tube cone. Exact locations of the sensors and observed uncertainties are provided in Table 1. The reference coordinate system is shown in Figure 1. The pressure data along with other flow variables were acquired at the sampling rate of 5 kHz and velocity data were acquired at the sampling rate of 40 Hz.

Coordinate locations of velocity measurement- line 1

Coordinate locations of velocity measurement- line 2

Coordinate locations of velocity measurement- line 3

Figure 1. Global coordinates for the measurement locations, geometry, and mesh.

Figure 2. Sections of PIV measurement in the draft tube cone. Dimensions are not scaled.

Steady state measurements

Table 3 shows the acquired flow parameters during PL, BEP and HL operating points. It should be noted that the uncertainties provided in the table are correspond to BEP condition. The uncertainty in hydraulic efficiency is the total uncertainty. This includes random and systematic uncertainty in the basic parameters used to compute hydraulic efficiency. Procedure available in IEC 60193 was followed to estimate the uncertainty and hydraulic efficiency. Cross sectional areas at the inlet and outlet pressure measurement are 0.0962 m² and 0.236 m², respectively. The outlet cross sectional area corresponds to the experimental pressure measurement section which is located at 1.58 m before the actual draft tube outlet in the numerical model. The height difference (z) between inlet and outlet pressure measurement is 1.0715 m. Uncertainty in the area measurements is ± 0.1%. Hydraulic torque output from the runner is the sum of toque to the generator and friction torque.

Transient measurements

Total four transient conditions have been investigated experimentally and several repetitions were performed at the same conditions to investigate the random uncertainty in the acquired data. The four transient conditions are:

1. Load acceptance: Increase turbine output power from BEP to HL by opening the guide vanes from 9.84°, i.e., increasing discharge.
2. Load reduction: Decrease turbine output power from BEP to PL by closing the guide vanes from 9.84°, i.e., decreasing discharge.
3. Turbine startup: Guide vane opening from 0.8° to BEP.
4. Turbine shutdown: Guide vane closing from BEP angle to 0.8°.

During the transient conditions the runner angular speed was constant, i.e., 333 rpm. For the load variation runner was operating at 333 rpm. For the startup, 333 rpm of the runner was achieved at 0.8° and it was synchronized to the corresponding load. During the shutdown, when guide vanes reached to 0.8°, the generator was decoupled from the load and set to speed-no-load condition. Data acquired during guide vane movement between 0.8° and 9.84° are provided. As a matter of fact, air bubbles were present in the model below 0.8° and the PIV data were inaccurate. Flow parameters observed at the load coupling/decoupling point are shown in Table 5. Further, Figures 3 and 4 show variation of head discharge, torque and guide vane angle during the transient conditions. The minimum and maximum values are scaled between 0 and 1 to extract the trend of the corresponding parameters during the transients. At time t = 1 s, the guide vanes were set to open/close to perform transient conditions. After certain time, the guide vanes reached to set value of angle (i.e., 6.72° or 12.43°) then steady state condition was followed. Attached data provides all necessary information required to perform numerical simulations. Discharge values during the transient conditions of load acceptance, rejection and start-stop are not accurate since the flowmeter response time was low. However, dicharge variation was the function of guide vane movement. The guide vanes movement was straight line therefore, initial and final discharge values can be taken from the steady state data at the corresponding guide vane position/ operating point and the linear variation can be considered. For the transient measurements, there is some delay in the flowmeter and inlet pressure transducer. Therefore, these values will not match exactly with the start/stop time of the guide vanes.

 

Figure 3. Variation of flow parameters during load rejection from BEP to PL

Figure 4. Variation of flow parameters during load acceptance from BEP to HL

Table 6. Acquired time, pressure, velocity, guide vane angle, runner angular speed, head, and discharge data during load variation and start-stop measurements. Click on the corresponding name to download.

Pressure	BEP to PL	BEP to HL	Startup	Shutdown
Velocity	BEP to PL	BEP to HL	Startup	Shutdown

Numerical modeling

Geometry and mesh of the investigated model Francis turbine are provided (can be downloaded from Table 7) to perform numerical simulations. You are also most welcome to make your own mesh. The provided numerical model includes spiral casing, 14 stay vanes, 28 guide vanes, 15 blades, 15 splitters, and a draft tube. The global coordinate system is the same as the one provided for the experimental data (Figure 1). Geometry files are available in legacy format (igs and parasolid). The guide vane mesh is provided for the three steady operating points, i.e., PL, BEP and HL. The provided meshes are for high Reynolds number therefore y+ value would be above 30 at BEP. Mesh in the spiral casing is hybrid including 3 million cells, 65% hexahedral, 27% prism, 4.5% pyramid, and 3.5% tetra. Meshes in the other components are purely hexahedral or hex dominated. Mesh nodes in the distributor and runner passage are 0.3 and 0.8 million, respectively. Mesh nodes in the complete draft tube are one million. Maximum aspect ratio, maximum expansion ratio and minimum angle of mesh in the runner are 56.3, 1.7 and 36.8, respectively. The provided meshes are tested at BEP using ANSYS CFX and OpenFOAM solvers, and for all operating points using NUMECA solvers. However, not all the configurations are tested. Mesh in the distributor domain may be used to perform transient simulations by mesh deformation technique as long as solver supports. Table 7 shows the mesh configurations and download link.
The mesh download link is here.

Following nomenclatures shall be followed to understand the table:
SC+SV: Mesh in the entire spiral casing with 14 stay vanes.
GV_PL: Mesh in a guide vane passage at PL angle.
GV_BEP: Mesh in a guide vane passage at BEP angle.
GV_HL: Mesh in a guide vane passage at HL angle.
RU: Mesh in a runner blade passage.
DT: Mesh in the complete draft tube.
1SV+2GV: Mesh in one stay vane passage and two guide vane passage.
RU+Cone: Mesh in a runner blade passage with extended cone.
DT_uns: Unstructured mesh in the draft tube.
AUTOMESH files are provided for NUMECA software users, if any.
.msh and .cgns both formats are supported by ANSYS CFX and FLUENT.
Mesh for the OpenFOAM code is tested. Moreover, input files for OpenFOAM extend 3.2 are available in the same folder with example case. Details regarding mesh can be found here.

Disclaimer: The provided data, geometry and mesh under Francis-99 workshop series are free for research and education. Upon the usage of the data and the geometry, acknowledgement must be given. “We/I used the test-case provided by NTNU – Norwegian University of Science and Technology under the Francis-99 workshop series.”

References

1. Goyal, R., Bergan, C., Cervantes, M.J., Gandhi, B.K., Dahlhaug, O.G., 2016, “Experimental investigation on a high head model Francis turbine during load rejection,” 28th IAHR Symposium, Grenoble, France, July 4-8, 2016.
2. Bergan, C, Goyal, R., Cervantes, M.J., Dahlhaug, O.G., 2016, “Experimental investigations of a high head model Francis turbine during steady-state operation at off-design conditions,” 28th IAHR Symposium, Grenoble, France, July 4-8, 2016.
3. Trivedi, C., Cervantes, M., and Dahlhaug, O. G., 2016, “Numerical Techniques Applied to Hydraulic Turbines: a Perspective Review,” ASME Applied Mechanics Reviews, 68(2), p. 26. http://dx.doi.org/10.1115/1.4032681.
4. Trivedi, C., Cervantes, M., and Dahlhaug, O. G., 2016, “Experimental and Numerical Studies of a High-Head Francis Turbine: A Review of the Francis-99 Test Case,” Energies, 9(2), p. 74. http://dx.doi.org/10.3390/en9020074.
5. Trivedi, C., Gandhi, B. K., Cervantes, M., and Dahlhaug, O. G., 2015, “Experimental Investigations of a Model Francis Turbine during Shutdown at Synchronous Speed,” Renewable Energy, 83, pp. 828-836. http://dx.doi.org/10.1016/j.renene.2015.05.026.
6. Trivedi, C., Cervantes, M., Dahlhaug, O. G., and Gandhi, B. K., 2015, “Experimental Investigation of a High Head Francis Turbine During Spin-No-Load Operation,” ASME Journal of Fluids Engineering, 137(6), p. 061106. http://dx.doi.org/10.1115/1.4029729.
7. Trivedi, C., Cervantes, M., Gandhi, B. K., and Dahlhaug, O. G., 2015, “Transient Pressure Measurements on a High Head Model Francis Turbine during Emergency Shutdown, Total Load Rejection, and Runaway,” ASME Journal of Fluids Engineering, 136(12), p. 121107. http://dx.doi.org/10.1115/1.4027794.
8. Trivedi, C., Cervantes, M., Gandhi, B. K., and Dahlhaug, O. G., 2014, “Experimental Investigations of Transient Pressure Variations in a High Head Model Francis Turbine during Start-up and Shutdown,” Journal of Hydrodynamics, 26(2), pp. 277-290, 2013. http://dx.doi.org/10.1016/S1001-6058(14)60031-7.
9. Trivedi, C., Cervantes, M., Gandhi, B. K., and Dahlhaug, O. G., 2014, “Pressure Measurements on a High Head Francis Turbine during Load Acceptance and Rejection,” Journal of Hydraulic Research, 52(2), pp. 283-297, 2014. http://dx.doi.org/10.1080/00221686.2013.854846.
10. Trivedi, C., Cervantes, M., Gandhi, B. K., and Dahlhaug, O. G., 2013, “Experimental and Numerical Studies for a High Head Francis Turbine at Several Operating Points,” ASME Journal of Fluids Engineering, 135(11), p. 111102. http://dx.doi.org/10.1115/1.4024805.
11. Trivedi, C., Cervantes, M., Gandhi, B. K., 2016, “Numerical investigation and validation of a Francis turbine at runaway operating conditions,” Energies, 9(3), p. 22. http://dx.doi.org/10.3390/en9030149.