Abstract
Over the years most studies on wake characteristics have been devoted to wind turbines, while few works are related to hydrokinetic turbines. Among studies applied to rivers, depth and width are important parameters for a suitable design. In this work, a numerical study of the wake in a horizontal-axis hydrokinetic turbine is performed, where the main objective is an investigation on the wake structure, which can be a constraining factor in rivers. The present paper uses the Reynolds Averaged Navier Stokes (RANS) flow simulation technique, in which the Shear-Stress Transport (SST) turbulent model is considered, in order to simulate a free hydrokinetic runner in a typical river flow. The NREL-PHASE VI wind turbine was used to validate the numerical approach. Simulations for a 3-bladed axial hydrokinetic turbine with 10 m diameter were carried out, depicting the expanded helical behavior of the wake. The axial velocity, in this case, is fully recovered at 12 diameters downstream in the wake. The results are compared with others available in the literature and also a study of the turbulence kinetic energy and mean axial velocity is presented so as to assess the influence of proximity of river surface from rotor in the wake geometry. Hence, even for a single turbine facility it is still necessary to consider the propagation of the wake over the spatial domain.
Highlights
There is no doubt that Brazil has an enormous watershed and relevant river connections, which provide an important hydraulic energy source for its territory, ensuring hydraulic energy as the most representative power source of the country
The numerical investigation on the wake characteristics of hydrokinetic turbines presented in this work constitutes an important tool for efficient analysis of power systems in isolated regions, such as are typically found in the Amazon
All simulations were performed using a precise numerical technique frequently used in computational fluid dynamics, as described by several authors available in the literature Huang et al 2011, Mo and Lee 2012, Sorensen et al 2002
Summary
There is no doubt that Brazil has an enormous watershed and relevant river connections, which provide an important hydraulic energy source for its territory, ensuring hydraulic energy as the most representative power source of the country. Hydrokinetic turbines have recently been used as converters of river, tidal and marine currents into electrical energy. This technology has become significant due to the use of renewable energy sources with. Mesquita et al 2014 present a general methodology for the efficient design of horizontal-axis hydrokinetic turbines with variable rotation. Their model includes the effect of multiplier, electric generator, inertia of whole system, and frictional resistances of a turbine with a 10 m diameter and producing electric power of around 500 kW. Churchfield et al 2013 describes an important application of the six marine turbine with 5 m diameter placed in an array in the East River in New York City and a dual rotor in Strangfordlough in Nothern Ireland converting 1,2 MW
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