Near wake hydrodynamics and structural design of a single foil cycloidal rotor in regular waves

We present a hydrodynamic and structural model to design a single foil wave cycloidal rotor in regular waves. The hydrodynamic part considers potential flow and represents the foil as a point vortex. The effect of the point vortices left on the wake of the foil and a correction for flow separation are considered. The structural part utilises beam theory to compute the bending moments and stresses on the foil of the cyclorotor. The validity of the hydrodynamic model is explored in attached and vortical flow conditions with the aid of CFD. Results show that the hydrodynamic model estimates the mean loading on the foil within 15% for attached flow conditions, whilst it underpredicts the loads in vortical flow conditions. Furthermore, large excursions from the mean load are found due to vortex shedding in the latter. Because the optimal structural operation of the rotor is in attached flow conditions, we utilise the coupled model to design a rotor that operates optimally for a range of different sea conditions. We find that with careful dimensioning of the radius and span, power extraction in regular waves can be optimised, whilst the structural penalty is kept constant at the allowable stress level.