Abstract
Among the various devices developed to extract energy from tidal and wind energies, the vertical-axis turbines (VATs) and horizontal-axis turbines (HATs) are one of the dominant technologies. In addition, VATs are considered advantageous over HATs in certain regions, for example, canals and estuaries. While the blade section of VATs continues to command considerable research for turbine efficiency, the humpback whale tubercles have also been explored recently as one of the means to enhance the lift-to-drag ratio using wavy leading-edge blades. Published work on static airfoils and VATs yield mixed results, which are favorable or adverse, depending on flow conditions, airfoil shape and leading-edge waviness, and VAT solidity and tip-speed ratio (TSR). In this research, the effect of sinusoidal leading-edge blade son turbine performance is explored numerically using an ultra-high solidity (36.67%) hydrokinetic VAT whose blade section is comprised of a cambered NACA 633-018 airfoil. The study focuses on VAT performance characterization as a function of TSR, amplitude and wavelength of leading-edge blade. To this aim, COMSOL Multiphysics solver is used as a computational fluid dynamics (CFD) package to model the flow through a VAT with either straight or sinusoidal blades. The CFD model is based on single-phase and incompressible fluid, unsteady flow, segregated, implicit and second-order scheme in time and space, along with the k-ω turbulence model. The turbulent model, meshing scheme, mesh independence, and boundary conditions are evaluated collectively by validating numerical results of VAT coefficient of performance with experimental data using a two-dimensional configuration. The numerical study of straight leading-edge blade is extended in three dimensions, with appropriate boundary conditions, and validated experimentally. It also sets the stage for three-dimensional numerical simulation of a VAT whose leading-edge blades are sinusoidal, over a wide range of wavelengths and amplitudes. The results show that at the same TSR, the VAT's coefficient of performance with a wavy-edge blade dropped by approximately 40% in comparison to a VAT with straight-edge blade. Keyword: Sinusoidal leading edge; Vertical axis turbine; NACA 633-018; COMSOL Multiphysics; Meshing schemes; Turbulent models; Frozen rotor.