Abstract
To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.
Highlights
In recent decades, the prospect of the depletion of fossil fuels has directed attention toward renewable energy sources
It can be seen that the curve of the Helical blade is smoother than that of the Straight blade. This is due to the fact that the Straight blade has an optimal angular position with respect to the relative wind corresponding to 30◦, while the Helical blade always presents a section in the optimal position with respect to the relative wind
Dynamic two-dimensional simulation data have been collected at different tip speed ratio values, and the results show the torque, lift and drag coefficient behavior of the rotor blade over a revolution with respect to the azimuthal position
Summary
The prospect of the depletion of fossil fuels has directed attention toward renewable energy sources. Carrigan et al [15], fixing the tip speed ratio (TSR) of the wind turbine, developed an iterative design system to maximize the torque for different airfoil cross-sections and solidities in two-dimensional CFD simulations. A 2.5D model [16] is presented in the literature, which differs from a 3D simulation, because only a segment of the airfoil blades is modeled with periodic boundaries at the extremities of the domain The limitation of this model is that it can only be used with Darrieus-type straight-bladed VAWT. This modeling approach produces a more realistic three-dimensional vortex diffusion after flow separation, it cannot capture the effect of tip vortex and vertical flow divergence in VAWT.
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