Abstract
We derive the upper limit for power extraction from an open-channel flow with lateral bypass representing tidal power or run-of-river plants for the complete range of blockage , Froude number and turbine head . For this, a generic turbine model is used: a momentum and energy sink distributed over the geometric blocking of the channel allowing lateral bypass. It is indicated that existing models neglect important aspects of the free-surface deformation due to the energy extraction, yielding unphysical behaviour at high blockage, high Froude number or high turbine head. The asymptotic validity of existing theories for , , becomes evident: firstly, by comparing existing theories with the presented general theory; and secondly, by the experimental validation of the existing and presented theories. The accompanying systematic experimental study comprises a wide range of blockage ratios, , of downstream Froude numbers, , and of different turbine heads, , measured in multiples of the specific energy of the undisturbed flow. The subsequent model-based optimisation allows an indication of the optimal turbine head as well as the maximal obtainable coefficient of performance as a function of and or downstream water depth , respectively. The theory reveals points of operation in which there is a surge wave in the tailwater. The new physical insight and optimisation results may serve for plant design and operation, as well as for investment decisions.
Highlights
Low-head hydropower plants such as tidal power or run-of-river plants are a promising contribution to meeting the world’s rising electrical power demand, provided the technology becomes economically profitable (Rourke, Boyle & Reynolds 2010)
We first discuss the system behaviour for typical Froude numbers Fr2 0.5 and compare the predictions of model III presented in this paper with
The complete picture of model III is given in figures 18–21, in which the optimal operational strategy and the upper limit are discussed (§ 4.3)
Summary
Low-head hydropower plants such as tidal power or run-of-river plants are a promising contribution to meeting the world’s rising electrical power demand, provided the technology becomes economically profitable (Rourke, Boyle & Reynolds 2010). A reliable physical model for an energy-converting system capturing the relevant physical effects is necessary for investment decisions and optimal installation and operation. Adcock, Draper & Nishino (2015) pointed out that the maximal extractable power from tidal energy is of major interest and an adequate modelling is a crucial step.
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