On the upscaling approach to wind tunnel experiments of horizontal axis hydrokinetic turbines
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(2020) 42:539
TECHNICAL PAPER
On the upscaling approach to wind tunnel experiments of horizontal axis hydrokinetic turbines Marianela M. Macias1 · Rafael C. F. Mendes1 · Taygoara F. Oliveira1 · Antonio C. P. Brasil Jr.1 Received: 28 March 2020 / Accepted: 3 September 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020
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 ∼ 104 ), 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 ∼ 106 ). 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. Keywords Hydrokinetic turbines · Wind tunnel experiments · Upscaling · CFD simulations
1 Introduction Presently, private entities and governments are increasing investments in the power sector, leading to development of technological advances and improvements in the efficiency of wind turbines. Studies based on aerodynamic and structural improvements, using computer simulation methods and wind tunnel experiments, have the goal of making technology more competitive with traditional sources such as fossil fuels [13]. Based on the same principles as wind energy, the hydrokinetic energy contained in rivers, estuaries, channels and ocean currents is considered as a renewable energy source that can produce electricity [19]. The use of water flow in hydrokinetic turbines is becoming an attractive source of energy due to the high energy density of water movement, good predictability and the low environmental impact [20]. Technical Editor: Erick Franklin, Ph.D. * Marianela M. Macias [email protected] 1
Energy and Environmental Laboratory, Mechanical Engineering Department, University of Brasilia, Brasília, DF 70910‑900, Brazil
The hydrokinetic conversion has grown over the last couple of years in several countries that have implemented these systems [22, 46]. In most cases, wind and hydrokinetic turbines are large machines and consequently, real-scale tests are extremely complex and expensive. Tests with full-scale turbines offer more realistic results but these are rare. To the best of the authors’ knowledge, the largest turbine tested in a controlled laboratory condition had a diameter of 10 m [17]. Consequently, the wind
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