Recent theoretical and experimental work has suggested that placing a vertical-axis wind turbine near a similar turbine that is rotating in the opposite direction may improve the efficiency of both turbines. A high-order Implicit Large Eddy Simulations (ILES) method is used to confirm these results by modeling a 2D cross-section of the wind turbines. In order to account for the moving domain, an element flipping technique is employed. This approach flips elements and uses an L 2-projection on the interfaces between the rotating turbines and the static outer mesh region. An Arbitrary-Lagrangian-Eulerian method is used to solve for the dynamic pressure and shear stress on the turbine blades using an isentropic formulation of the compressible Navier-Stokes equation. Our preliminary results seem to confirm those of the recently published experiments for straight-bladed, counterrotating turbines. When the turbines are oriented such that a line connecting their centers of rotation is perpendicular to the incident wind direction, the power coefficient of each turbine can increase by more than 10%. In fact, when the turbines are oriented in a doublet-like configuration, where the blades travel upwind in the interior region between the turbines, our simulations show that the power coefficient of each turbine is increased by 15%. However, unlike the experimental results, when the incident wind is oriented parallel to this line, the power coefficient of the shadowed turbine is reduced significantly. We show snapshots of the fluid velocity and hypothesize why the power of the turbines may be increased due to blockage effects. That is, at certain azimuthal angles the relative wind speed that the blade encounters is larger than in the isolated case.
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