Michel Sabourin

New parameters influencing hydraulic runner lifetime

Traditionally, hydraulic runner mechanical design is based on calculation of static stresses. Today, validation of hydraulic runner design in terms of reliability requires taking into account the fatigue effect of dynamics loads. A damage tolerant approach based on fracture mechanics is the method chosen by Alstom and Hydro-Quebec to study fatigue damage in runners. This requires a careful examination of all factors influencing material fatigue behavior. Such material behavior depends mainly on the chemical composition, microstructure and thermal history of the component, and on the resulting residual stresses. Measurement of fracture mechanics properties of various steels have demonstrated that runner lifetime can be significantly altered by differences in the manufacturing process, although remaining in accordance with agreed practices and standards such as ASTM. Carbon content and heat treatment are suspected to influence fatigue lifetime. This will have to be investigated by continuing the current research.

Hydraulic Runner Design Method for Lifetime

Quest for reliability of hydraulic runners is a concern for all mature electricity producers. The fatigue damage caused by dynamics loads is frequently the root cause of runner failure. This paper presents the damage tolerance approach based on fracture mechanics as the method chosen by Alstom and Hydro-Quebec to predict effects of damage on runner lifetime and consequently to be use as a design method. This is sustained by a research on fracture mechanics properties of runner materials and by recommendations on the strategy to define a safety margin for design. The acquired knowledge permits to identify potential improvement of the runner lifetime without significant cost increase, like being more specific on some chemical composition or heat treatment.

Optimal blank design based on finite element method for blades of large Francis turbines

Abstract Metal pressing process that is widely used in industries has advantages over casting process for producing large Francis turbine blades from thick plates. Prior to the pressing process, blank design is firstly performed to determine flat blanks. The traditional trial and error approach is not applicable to blade design for Francis turbines that are not standard due to hydraulic characteristics of power plant sites. The rapid development of computing technology makes it possible to obtain optimal flat blanks by numerical modelling and simulation. In this paper, inverse finite element approach is investigated for blank design and an elasto-plastic model has been built using the well-known commercial software ANSYS. Numerical simulations for blade unfolding models with thick shell elements, solid elements and shell elements have given results with negligible differences. Unfolding tests with simple geometries have been carried out and the numerical results agree well with the analytical solutions. A large and thick shape of a Francis turbine blade for a hydropower plant has been successfully unfolded by inverse FE model. Sensibility analysis shows that the middle surface of the flat blank is independent of blade thickness. For ensuring the machining of the blade after the pressing process, a new contour is obtained by extending the boundary of the flat blank provided by the numerical model. This research may provide a useful tool for optimal blank design of Francis turbine blades.

Modeling and simulation of optimal blank design and hot pressing process for manufacturing large francis turbines blades from very thick plates

Hot pressing process is widely used in automotive, shipbuilding, energy production and civil engineering. However, the trial and error technique that is intensive time and energy consuming is still used. Particularly, the design of Francis turbines of hydropower plants is not standard, but variable from site to site due to hydraulic conditions and cost of energy. As a result, the blade hydraulic profile of each Francis turbine is different. The blades, one of the key components of Francis turbine runners, are produced in small batches and the setup of the dedicated punch and die increases significantly the unit production costs. In this paper, the blade unfolding process for optimal blank design will be firstly presented, and then a hot pressing process for very thick plates is proposed. The pressing process of high strength steel at hot temperature is characterized by thermo-mechanical behaviors, three-dimensional unsteady deformation, high nonlinearity, continuous local forming. The analyses of residual stress distribution and applied forces are carried out.Copyright