Thirty years of numerical flow simulation in hydraulic turbomachines

The application of computational fluid dynamics (CFD) in the design of water turbines and pumps started about 30 years ago. This paper reviews the main steps and breakthroughs in the methods that were made during this period, through the eyes of one particular water turbine company which spear-headed some of the first developments for practical applications. Practical examples are used to illustrate the developments of the tools from 1978 to 2008 and to give an overview of the complete revolution in hydraulic turbine design that has occurred over this time. Several periods with distinct levels of complexity, and hence accuracy of the physical models and of the simulation methods can be distinguished. The first steps coincided with the introduction of the Finite Element Method into CFD, and were characterized by simplified Quasi-3D Euler solutions and Fully 3D potential flow solutions. Over the years the complexity continuously increased in stages: via 3D Euler solutions, to steady RANS simulations of single blade passages using finite volume methods, extending to steady simulations of whole machines, until today unsteady RANS equations are solved with advanced turbulence models. The most active areas of research and development are now concerned with including the effects of 2-phase flows (free surface flow in Pelton turbines and cavitation) and fluid–structure interaction.