Abstract:The Savonius wind turbine is a type of vertical axis wind turbine (VAWTs) that is simply composed of two or three arc-type blades which can generate power even under poor wind conditions. A modified Savonius wind turbine with novel blade shapes is introduced with the aim of increasing the power coefficient of the turbine. The effect of blade fullness, which is a main shape parameter of the blade, on the power production of a two-bladed Savonius wind turbine is investigated using transient computational fluid dynamics (CFD). Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations with a renormalization group turbulent model. This numerical method is validated with existing experimental data and then utilized to quantify the performance of design variants. Results quantify the relationship between blade fullness and turbine performance with a blade fullness of 1 resulting in the highest coefficient of power, 0.2573. This power coefficient is 10.98% higher than a conventional Savonius turbine.

Three-dimensional transient Computational Fluid Dynamics (CFD) simulations are performed to study the hydrodynamic performance of an ocean current turbine with a 3.0 m diameter 3-bladed rotor. Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations and the shear stress transport k-ω turbulent model is utilized. The influence of yaw angle and upstream turbulence intensity (TI) on the turbine performance is studied. The CFD method is first validated using existing experimental data and good agreement is obtained. The performance of the turbine, including power, thrust and wake characteristics are then studied at different tip speed ratios (TSR). The turbine obtains a maximum coefficient of power (Cp) of 0.4642 at TSR=6 and the coefficient of thrust (Ct) increases over the entire evaluated TSR range to a value of 0.8788 at a TSR=10. Simulations are also performed at four different yaw angles, 0°, 5°, 10° and 15° which show that both Cp and Ct decrease as yaw angle increases. Finally simulations of three different TIs, 3%, 6% and 9%, are performed and analyzed. Results show that TI minimally affects Cp and Ct for the considered TI range, but greatly influences the downstream wake structure.

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This paper investigates the possibility of using active individual blade pitch control for positioning moored ocean current turbines within an array. Using a numerical simulation of a representative ocean current turbine it is shown that harmonic blade oscillations with amplitudes of 1.5° can be used to displace an ocean current turbine laterally by a distance equal to one rotor diameter, when the mooring cable length is approximately 30 times the diameter of the rotor blade. For current flow directions that would result in a downstream turbine operating in the wake of an upstream system at a distance of 10 diameters, this technique could be used to reduce the power loss of the downstream system from about 50% (caused by the reduced flow speed available in the turbine wake) to the 1.2% power loss associated with the suggested control approach.

Technological advances in marine renewable energy allow for various methods of extracting energy in the form of electrical power from the ocean. One method is through the process of ocean thermal energy conversion (OTEC). This study assesses the distributions of electrical power that can be extracted from the ocean around the state of Florida. The OTEC resource is analyzed with the combination of a state-of-the-art ocean circulation model, the Hybrid Coordinate Ocean Model, along with a state-of-the-industry OTEC plant model in order to predict the attainable power values offshore Florida. The power predictions are then constrained by local cold deep sea water replenishment to provide an upper limit to the sustainable OTEC resource. The thermal resource is used as input to the plant model to predict the potential power production. The resource data is then validated through the comparison against in situ oceanic measurements to safeguard the quality of the predicted power values.

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