No abstract

In this work, we proposed an upscaling methodology to extrapolate results from wind tunnel experiments with small-scale model to the full-size hydrokinetic turbine. Small-scale 1:20 wind tunnel experiments (Re ∼ 10 4), with a three-blade horizontal axis turbine, were carried out looking to identify the characteristic curves of a full-size turbine operating in water (Re ∼ 10 6). The lack of dynamic similarity due to unmatched Reynolds numbers is analyzed in the framework of blade element momentum theory arguments. A new semi-empirical power-law equation is achieved, uniquely based on the BEM theory which relates the power coefficients of model and full-size turbine to the Reynolds numbers and a power factor, specific to each turbine. Computational fluid dynamic CFD simulations for the same rotor geometry, simulating different runners with varying diameters from small-scale model to full-scale turbine are carried out to validate the upscaling arguments, and to verify the accuracy of the power coefficient curves predicted by proposed methodology.

No abstract

The evolution of wind and hydrokinetic turbines stimulated the development of several tools to evaluate and to predict horizontal axis rotor behavior. From this perspective, the Blade Element Momentum methods stand out as one of the most common approaches due to its reliability and computing speed. In the classical Blade Element Momentum, the axial induction factor is a crucial variable to compute correctly the turbine parameters. Usually, the axial induction is determined by an interactive process that balances the forces at blade sections with momentum equations. The forces are computed based on the airfoil polars evaluated at each blade section with local inlet velocity. This procedure assumes that the swirl terms are linearized, where the lateral pressure forces is neglected. In order to evaluate these tri-dimensional effects on Blade Element Momentum method, the present work introduces a different methodology to determine the axial induction factor employing Computational Fluid Dynamics simulations. The method was applied for a full-scale horizontal axis rotor with 3 blades and 1 meter of diameter, with wind tunnel experiments for validation. The axial induction factor obtained with the new technique was compared to the classical Blade Element Momentum method. The results show axial induction factor variations along the radial and axial coordinates. An analogy with Glauert power coefficient limit was made, finding a specific limit curve for the tested turbine and, moreover, a correlation between turbine firing speed and induction factor.

No abstract