The power extraction by flapping foil hydrokinetic turbine in swing arm mode

In the present study the power extraction capability by flapping foil hydrokinetic turbine is investigated. The heaving motion of the foil is considered in two different motion patterns including the simple linear translational motion and the rotation of swing arm on which the foil is mounted. The laminar and incompressible flow around a NACA0012 foil is conducted using Computational Fluid Dynamics (CFD) method. It is shown that the power extraction is possible and more desirable in the lower reduced frequencies. Additionally, the swing arm mode may increase the amount of extracted power and improve the performance of hydrokinetic turbine. Changes in kinematics of flapping foil alter the angle of attack profile and the local Reynolds number on the surface of the foil. These two sensitive changes influence on the sub-layer flow near to surface of the foil and make the vortex structure to be complex during flapping cycle. In the other words, in swing arm mode the vortex creation, growth, separation and shedding occur with an alternative pattern compared to simple mode. Finally, it is shown that the importance of the swing arm mode is in a certain range of swing arm lengths.