Fluid-structure simulations of the stochastic behaviour of a medium head Francis turbine during startup

• Published in: IOP conference series. Earth and environmental science 2019-03, Vol.240 (2), p.22026
• Main Authors: Morissette, J F, Nicolle, J
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics; Dynamic loads; Finite element method; Fluid flow; Fluid-structure interaction; Head (fluid mechanics); Hydraulic turbines; Interaction models; Labyrinth seals; Life expectancy; Life span; Load; Mechanical properties; Modelling; Pressure dependence; Simulation; Stochasticity; Stresses; Transient operation
• ISSN: 1755-1307; 1755-1315; 1755-1315
• DOI: 10.1088/1755-1315/240/2/022026

The use of dynamic CFD and FEA simulations of hydraulic turbines for steady operation is now widespread for fatigue analysis. However, machines will undergo a major role change from the traditional base load operation in the coming years. This can have a significant impact on life expectancy. In this regard, a lot of research efforts have been recently devoted to improve understanding of hydraulic turbines transient operations such as startup and runaway. Our recent experiences have shown that almost all turbines present unique behaviour from a stochastic point of view during transient operation, and we consider there is still a lot to learn about how to correlate load patterns to life expectancy. In past work, startup simulations and no-load stochastic predictions were presented separately. To our knowledge, no one has attempted to combine them to predict stochastic stresses by simulations in the case of turbine startup. The challenge is thus to capture much more physics while respecting fluid-structure interaction modelling requirements. This paper presents specifically transient CFD and FEA simulations of a medium head Francis turbine startup aimed at getting stochastic dynamic loads on the runner. The CFD simulations involve, among other things, variable rotating speed, mesh deformation, labyrinth seals, resistive torque, roughness, SAS turbulence modelling. 1-way fluid-structure simulations with time-dependent pressure loads are used to determine the stochastic stresses. The stochastic loads are challenging, and only a part of them were captured. Encouraging results are obtained at the leading edge, but the trailing edge deformations lack most of the content. Simulations and experiments might indicate that a stronger coupling is required to get both the fluid load and the mechanical answer right.