Abstract
The research and application of marine renewable energy have received much attention due to its potential to generate power with less emissions than traditional sources. Among various types of wave energy converters (WECs), research is still in its infancy for Vertical-Axis Wave Turbines. While the concept has been well adopted in the wind energy industry, the use of this technology for wave energy harvesting could meet challenges due to the reciprocal motion of surface waves. When previously tested, the wave turbine design showed promising spin-up and sustained rotation of the rotor in regular waves. This test encouraged detailed assessment of the self-starting process of the rotor in the present work.
For numerical simulation, a Computational Fluid Dynamics (CFD) model following the Reynolds-Averaged Navier-Stokes framework was established. The model took various aspects into account, such as the influence of the numerical waves, the highly unsteady initial self-starting process, and the appropriate gridding strategy needed to suit a wide range of rotational speeds from near-zero to the quasi-steady, terminal speed of the rotor. The CFD model was applied to reveal detailed characteristics of the flow field and to evaluate the sensitivity of the self-starting process to different inertial properties and damping coefficients of the rotor. The simulation showed that the inertial properties of the rotor would only affect the efficiency of the self-starting process. In contrast, the damping coefficient could have a profound effect on the attained steady-state rotational speed, which has strong implication for the design of power-take-off.
The methodology established in the present work will be invaluable for design optimization as the self-starting process is an important stage of the device operating in an ever-changing environment. The methodology is also transferrable to other types of renewable energy devices that are equipped with a self-started rotor.