FT-PV plus - Francis turbine test rig virtual +

As electricity market parameters are undergoing major changes, cost optimisation regarding the planning and realisation as well as the revitalisation of hydro power plants becomes mandatory – especially as far as turbine design, durability forecast and component quality management are concerned – aiming at an increase of the annual output and/or the return of investment. At present, 100% reliability of statements on the efficiency, the annual output, cavitation and vibrations of Francis turbines can only be provided by means of model tests. However, model test are complex, time-consuming and expensive, and only pay off for turbine performances of approximately 10 MW and more. In the field of small hydro power model tests are merely realised in exceptional cases. Thus, the hydraulic design of the turbine is often based on considerably less expensive CFD (Computational Fluid Dynamics) calculations. However, in this case numerous assumptions are made that lead to differing data on the annual output, the influences on the durability and the behaviour of systems (vibrations, cavitation) and to non-reliable water hammer calculations. Additionally it has to be pointed out, that the CFD-simulation is still not capable of a reliable prediction of the part load behaviour, which is very important for Francis-Turbines. Finally, the CFD-approach bears unrateable technical and economic risks. However, future developments and optimisations of Francis turbines will increasingly be based on CFD calculations (without model tests) in order to save costs. Whereas prediction accuracy of CFD simulations for the optimum operation range of a turbine is excellent, calculations for part load and overload are still subject to numerous uncertainties as of occurring flow separations. Their simulation setup has to meet highest requirements regarding model design and modelling of turbulences. In addition, usually within the scope of CFD calculations the runner side gaps are not taken into account thus allowing for a considerable reduction of the already extensive simulation efforts. However, this approach requires simplified analytic calculation tools, the application of which often leads to misinterpretations resulting in necessary optimisations. Furthermore, water hammer calculations are also only possible based on turbine data defined by means of 4-quadrant characteristics diagrams whereas CFD calculation of these – so far – provide merely very inaccurate figures. As of these uncertainties plant components have to be oversized, thus causing unjustified increases of construction costs. The target of the present research project is the development of a “Virtual Test Rig” for Francis turbines. Based on experimental tests realised in parallel on a model test rig, BEST PRACTICE standard procedures for the reliable calculation of the performance and the characteristics of Francis turbines throughout the ENTIRE operating range (part load, optimum, overload) will be defined, which are not existent in this form yet. As a result, the accuracy of CFD calculations will be increased and thus water hammer calculation based on CFD will become possible. Additionally, reliable assessments of the potential of refurbishment projects as far as possible efficiency levels and the amelioration of part load behaviour by means of new runner designs can be provided.