List of papers presented Francis-99 workshop
The second Francis-99 workshop was held on 14 and 15 December 2016. Total 10 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.
 Peter Mössinger, Roland Jester-Zürker and Alexander Jung, 2017, "Francis-99: Transient CFD simulation of load changes and turbine shutdown in a model sized high-head Francis turbine," Journal of Physics: Conference Series, 782(1), p. 012001. doi:10.1088/1742-6596/782/1/012001.
Abstract: With increasing requirements for hydropower plant operation due to intermittent renewable energy sources like wind and solar, numerical simulations of transient operations in hydraulic turbo machines become more important. As a continuation of the work performed for the first workshop which covered three steady operating conditions, in the present paper load changes and a shutdown procedure are investigated. The findings of previous studies are used to create a 360° model and compare measurements with simulation results for the operating points part load, high load and best efficiency. A mesh motion procedure is introduced, allowing to represent moving guide vanes for load changes from best efficiency to part load and high load. Additionally an automated re-mesh procedure is added for turbine shutdown to ensure reliable mesh quality during guide vane closing. All three transient operations are compared to PIV velocity measurements in the draft tube and pressure signals in the vaneless space. Simulation results of axial velocity distributions for all three steady operation points, during both load changes and for the shutdown correlated well with the measurement. An offset at vaneless space pressure is found to be a result of guide vane corrections for the simulation to ensure similar velocity fields. Short-time Fourier transformation indicating increasing amplitudes and frequencies at speed-no load conditions. Further studies will discuss the already measured start-up procedure and investigate the necessity to consider the hydraulic system dynamics upstream of the turbine by means of a 1D3D coupling between the 3D flow field and a 1D system model.
 Ken-Robert G. Jakobsen and Martin Aasved Holst, 2017, "CFD simulations of transient load change on a high head Francis turbine," Journal of Physics: Conference Series, 782(1), p. 012002. doi:10.1088/1742-6596/782/1/012002.
Abstract: Motivated by the importance of better understanding the structural integrity of high-head hydraulic turbines operating at intermittent conditions, complete 360º steady-state and transient simulations of a Francis turbine are presented in this paper. The main target of the work has been to investigate different numerical approaches such as mesh deformation for different operating conditions. Steady-state simulations were performed at the best efficiency point (BEP) and used as initial conditions for the transient simulations considering load rejection from BEP to part load (BEP2PL) and during load acceptance from BEP to high load (BEP2HL). Simulation results were compared with experimental data available for the Francis-99 project where close agreement was found for the mesh independent solution. The transient load analyses showed general trends in accordance with the measurement reports, especially for the pressure in vaneless space that is of high importance regarding RSI effects. Some deviations were identified for the net head at load rejection for which further investigations will be conducted. All CFD simulations were performed at model scale with ANSYS CFX v. 17 at either 96 or 120 cores (2.60 GHz). The immersed boundary technique was tested during the initial stages of the project, but had to be abandoned due to severe memory requirements. Pressure amplitudes and other instantaneous results were not considered.
 Yuvraj Dewan, Chad Custer and Artem Ivashchenko, 2017, "Simulation of the Francis-99 Hydro Turbine During Steady and Transient Operation," Journal of Physics: Conference Series, 782(1), p. 012003. doi:10.1088/1742-6596/782/1/012003.
Abstract: Numerical simulation of the Francis-99 hydroturbine with correlation to experimental measurements are presented. Steady operation of the hydroturbine is analyzed at three operating conditions: the best efficiency point (BEP), high load (HL), and part load (PL). It is shown that global quantities such as net head, discharge and efficiency are well predicted. Additionally, time-averaged velocity predictions compare well with PIV measurements obtained in the draft tube immediately downstream of the runner. Differences in vortex rope structure between operating points are discussed. Unsteady operation of the hydroturbine from BEP to HL and from BEP to PL are modelled. It is shown that simulation methods used to model the steady operation produce predictions that correlate well with experiment for transient operation. Time-domain unsteady simulation is used for both steady and unsteady operation. The full-fidelity geometry including all components is meshed using an unstructured polyhedral mesh with body-fitted prism layers. Guide vane rotation for transient operation is imposed using fully-conservative, computationally efficient mesh morphing. The commercial solver STAR-CCM+ is used for all portions of the analysis including meshing, solving and post-processing.
 A Minakov, A Sentyabov and D Platonov, 2017, "Numerical investigation of flow structure and pressure pulsation in the Francis-99 turbine during startup," Journal of Physics: Conference Series, 782(1), p. 012004. doi:10.1088/1742-6596/782/1/012004.
Abstract: We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at startup regimes. Numerical technique for calculating of low frequency pressure pulsations in a water turbine is based on the use of DES (k-ω Shear Stress Transport) turbulence model and the approach of "frozen rotor". The structure of the flow behind the runner of turbine was analysed. Shows the effect of flow structure on the frequency and intensity of non-stationary processes in the flow path. Two version of the inlet boundary conditions were considered. The first one corresponded measured time dependence of the discharge. Comparison of the calculation results with the experimental data shows the considerable delay of the discharge in this calculation. Second version corresponded linear approximation of time dependence of the discharge. This calculation shows good agreement with experimental results.
 A Minakov, D Platonov, A Sentyabov and A Gavrilov, 2017, "Francis-99 turbine numerical flow simulation of steady state operation using RANS and RANS/LES turbulence model," Journal of Physics: Conference Series, 782(1), p. 012005. doi:10.1088/1742-6596/782/1/012005.
Abstract: We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at three regimes, using two eddy-viscosity- (EVM) and a Reynolds stress (RSM) RANS models (realizable k-epsilon, k-ω SST, LRR) and detached-eddy-simulations (DES), as well as large-eddy simulations (LES). Comparison of calculation results with the experimental data was carried out. Unlike the linear EVMs, the RSM, DES, and LES reproduced well the mean velocity components, and pressure pulsations in the diffusor draft tube. Despite relatively coarse meshes and insufficient resolution of the near-wall region, LES, DES also reproduced well the intrinsic flow unsteadiness and the dominant flow structures and the associated pressure pulsations in the draft tube.
 A Gavrilov, A Dekterev, A Minakov, D Platonov and A Sentyabov, 2017, "Steady state operation simulation of the Francis-99 turbine by means of advanced turbulence models," Journal of Physics: Conference Series, 782(1), p. 012006. doi:10.1088/1742-6596/782/1/012006.
Abstract: The paper presents numerical simulation of the flow in hydraulic turbine based on the experimental data of the II Francis-99 workshop. The calculation domain includes the wicket gate, runner and draft tube with rotating reference frame for the runner zone. Different turbulence models such as k-ω SST, ζ-f and RSM were considered. The calculations were performed by means of in-house CFD code SigmaFlow. The numerical simulation for part load, high load and best efficiency operation points were performed.
 E. Casartelli, L. Mangani, O. Ryan and A. Del Rio, 2017, "Performance prediction of the high head Francis-99 turbine for steady operation points," Journal of Physics: Conference Series, 782(1), p. 012007. doi:10.1088/1742-6596/782/1/012007.
Abstract: Steady-state numerical investigations are still the reference computational method for the prediction of the global machine performance during the design phase. Accordingly, steady state CFD simulations of the complete high head Francis-99 turbine, from spiral casing to draft tube have been performed at three operating conditions, namely at part load (PL), best efficiency point (BEP), and high load (HL). In addition, simulations with a moving runner for the three operating points are conducted and compared to the steady state results. The prediction accuracy of the numerical results is assessed comparing global and local data to the available experimental results. A full 360°-model is applied for the unsteady simulations and for the steady state simulations a reduced domain was used for the periodic components, with respectively only one guide vane and one runner passage. The steady state rotor-stator interactions were modelled with a mixing-plane. All CFD simulations were performed at model scale with an in-house 3D, unstructured, object-oriented finite volume code designed to solve incompressible RANS-Equations. Steady and unsteady solver simulations are both able to predict similar values for torque and head in design and off-design. Flow features in off-design operation such as a vortex rope in PL operation can be predicted by both simulation types, though all simulations tend to overestimate head and torque. Differences among steady and unsteady simulations can mainly be attributed to the averaging process used in the mixing plane interface in steady state simulations. Measured efficiency agrees best with the unsteady simulations for BEP and PL operation, though the steady state simulations also provide a cost-effective alternative with comparable accuracy.
 Y Zeng, L X Zhang, J P Guo, Y K Guo, Q L Pan and J Qian, 2017, "Efficiency limit factor analysis for the Francis-99 hydraulic turbine," Journal of Physics: Conference Series, 782(1), p. 012008. doi:10.1088/1742-6596/782/1/012008.
Abstract: The energy loss in hydraulic turbine is the most direct factor that affects the efficiency of the hydraulic turbine. Based on the analysis theory of inner energy loss of hydraulic turbine, combining the measurement data of the Francis-99, this paper calculates characteristic parameters of inner energy loss of the hydraulic turbine, and establishes the calculation model of the hydraulic turbine power. Taken the start-up test conditions given by Francis-99 as case, characteristics of the inner energy of the hydraulic turbine in transient and transformation law are researched. Further, analyzing mechanical friction in hydraulic turbine, we think that main ingredients of mechanical friction loss is the rotation friction loss between rotating runner and water body, and defined as the inner mechanical friction loss. The calculation method of the inner mechanical friction loss is given roughly. Our purpose is that explore and research the method and way increasing transformation efficiency of water flow by means of analysis energy losses in hydraulic turbine.
 N Tonello, Y Eude, B de Laage de Meux and M Ferrand, 2017, "Frozen Rotor and Sliding Mesh Models Applied to the 3D Simulation of the Francis-99 Tokke Turbine with Code_Saturne," Journal of Physics: Conference Series, 782(1), p. 012009. doi:10.1088/1742-6596/782/1/012009.
Abstract: The steady-state operation of the Francis-99, Tokke turbine [1-3] has been simulated numerically at different loads using the open source, CAD and CFD software, SALOME  Code_Saturne . The full 3D mesh of the Tokke turbine provided for the Second Francis-99 Workshop has been adapted and modified to work with the solver. Results are compared for the frozen-rotor and the unsteady, conservative sliding mesh approach over three operating points, showing that good agreement with the experimental data is obtained with both models without having to tune the CFD models for each operating point. Approaches to the simulation of transient operation are also presented with results of work in progress.
 Petter T.K. Østby, Jan Tore Billdal, Bjørn Haugen and Ole Gunnar Dahlhaug, 2017, "On the relation between friction losses and pressure pulsations caused by Rotor Stator interaction on the Francis-99 turbine," Journal of Physics: Conference Series, 782(1), p. 012010. doi:10.1088/1742-6596/782/1/012010.
Abstract: High head Francis runners are subject to pressure pulsations caused by rotor stator interaction. To ensure safe operation of such turbines, it is important to be able to predict these pulsations. For turbine manufacturers it is often a dilemma whether to perform very advanced and time consuming CFD calculations or to rely on simpler calculations to save development time. This paper tries to evaluate simplifications of the CFD model while still capturing the RSI phenomena and ensuring that the calculation does not underpredict the pressure amplitudes. The effects which turbulence modeling, wall friction, viscosity and mesh have on the pressure amplitudes will be investigated along with time savings with each simplification. The hypothesis is that rotor stator interaction is manly driven by inviscid flow and can therefore be modelled by the Euler equations.Go to top