Oscillating wings animated by concurrent pitching and heaving motion components can be used to extract energy from an oncoming fluid flow, such as that associated with tidal currents. The hydrodynamics of these renewable energy devices is inherently unsteady and depends significantly both on kinematic parameters such as the wing trajectory, its pitching and heaving amplitudes and its reduced frequency, and the wing geometry. We are using our in-house Navier-Stokes research code COSA to quantitatively assess the dependence of the energy conversion efficiency of oscillating wings for tidal energy applications on the detailed 3D geometry of the wing. The top and bottom figures below show respectively a view of the surface mesh of an oscillating wing with end-plates and a view of the surface mesh of an oscillating wing without end-plates. In both cases, the depicted grid has been coarsened for graphical clarity.
The grids above have been used to calculate with the COSA code the unsteady flow past the wings with different tip geometry and also the reference ideal flow field associated with the infinite wing. Acronyms AR, EP, and ST stand for Aspect Ratio, End-Plate and Sharp Tip respectively. The figure below shows a snapshot of flow vorticity contours for a particular position of the periodic oscillation.