Flow field around vertical axis cross-flow hydrokinetic turbines

Renewable energy sources, most notably, wind energy, solar energy and small scale hydropower schemes have undergone major development lately. However the intermittency and weather dependency of solar and wind energies pose a challenge. Another form of renewable energy which has attracted great interest in recent times is hydrokinetic energy. Hydrokinetic energy is harnessed from flow waters of river streams, tidal flows or ocean currents. This energy resource has a great potential to be exploited on a large scale because of its predictability and intensity. It is most likely to be one of the new and clean energy alternatives for the 21st century. In this study, a vertical axis cross-flow hydrokinetic turbine, namely a modified form of Lucid Energy Technology (LET) Gorlov Helical Turbine (GHT) was investigated. The working principles of vertical axis cross-flow hydrokinetic turbines are different from those of commonly used horizontal axis ones. The advantages of this type of turbines are; independency from the current direction including reversibility, stacking and self-starting without complex pitching mechanisms. The turbine has been simulated in a three dimensional and fully developed rectangular open channel flow. Computational fluid dynamics (CFD) simulation of the hydrokinetic turbine was performed by computationally solving the Reynolds-Averaged Navier-Stokes Equations (RANS). In computational studies ANSYS FLUENT, commercially available software was employed. The flow field was studied with the turbine being positioned at two different depths, while the depth and the velocity of the open channel flow were kept constant. The results have shown that placing the turbine closer to the bed of channel causes an increase in water velocity near the free surface. Although the water velocity near the channel bed seems to be decreasing, the turbulence flow takes place just behind the turbine and the burst of the flow directlybelow the turbine are expected to cause scouring and increase turbidity levels. Keywords: Computational Fluid Dynamics, Hydrokinetic Turbines, Kinetic Energy, Renewable Energy, ANSYS FLUENT