Experimental and Numerical study of a vertical axis tidal current turbine

One of the renewable energy sources is the vast energy present in sea and tidal currents. Tidal turbines can be classified as either vertical or horizontal based on their rotation axis. The present investigation concerns parameters that affect flow hydrodynamics in a vertical-axis tidal turbine. A 1:20 Hunter turbine model was manufactured and investigated in a laboratory followed by transient solution CFD simulations. The simulation was carried out for both rigid lid surfaces and free surface assumptions while SST k-ω turbulence model was used for both cases and volume of fluid method was employed for the free surface model. Simulations results verified by Empirical data which showed a good agreement. Power coefficient reached 0.23 at the best case scenario and the maximum power coefficient occurs at a flow coefficient between 0.4 and 0.43 for all investigated flows. The rigid lid CFD results demonstrated that for the rigid lid cases increasing blockage ratio also increases power coefficient such that the power coefficient at blockage ratio 0.32 is 13.2 which is 8.4 percent higher than the power coefficient for the 0.2 blockage with a 4.8 value. Furthermore the free surface simulations showed that the flow deflection on turbine region leads to a greater torque exerted on turbine blade. While the maximum mean torque coefficient for the rigid lid cases is 0.18, for the free surface cases the said coefficient reaches 0.4 showing a 120 percent increase. Additionally the free surface cases power coefficient increased 10 percent.