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Engineering Approach to Predicting Free Surface Vortices at Low-Head Hydropower Intakes

Author(s): Frank Suerich-Gulick; Susan Gaskin; Marc Villeneuve; Etienne Parkinson

Linked Author(s): Marc Villeneuve, Susan Gaskin

Keywords: Hydropower intakes; Free surface vortex; Physical scale modeling; Scale effects; Particle entrainment

Abstract: Hydropower development is driven globally by an increased emphasis on the development of renewable energy resources. An increased concern for the environmental impacts has led to an increasing number of project that are low-head run-of-the river installations with their much smaller associated reservoirs. The low head and often more complex flows at the intakes of these plants make them more prone to problems associated with the formation of free surface vortices at the intakes. Free surface vortices thus formed can lead to unsteady or non-uniform flow at the turbines or result in entrainment of air or debris. The impact can range from lower power output to premature degradation of the turbines or other mechanical components. Prediction of the occurrence of free surface vortices is typically made during the early design phase using empirical correlations based on scale laboratory experiments. However predictive accuracy is limited by the sensitivity of vortex characteristics to intake geometry and velocity distributions (which can vary considerably in run-of-the river plants), and hence physical scale model testing for large projects is common. For smaller projects, it would be useful to predict the strength of possible vortices based on the geometry and flow conditions at an intake. Uncertainties remain in the interpretation of these results from the laboratory scale to the prototype scale. In the current work, experimental measurements made in a small scale laboratory model are used to understand free surface vortex formation and to develop a semi-empirical model to predict vortex characteristics at intakes. This model extends Burger ’s model to allow vortex characteristics (characteristic radius, bulk circulation and air entrainment) to be linked to the geometry and flow conditions of an intake. The processes contributing to the formation of free surface vortices at intakes are discussed. As vortices often entrain floating debris, reducing turbine efficiency, the processes controlling particles entrainment and their relative magnitudes are investigated.


Year: 2013

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