Hydrodynamic Design of Tidal Current Turbine and the Effect of Solidity on Performance

Abstract

Blade element momentum (BEM) flow model in conjunction with pattern search optimization algorithm embedded in the National Renewable Energy Laboratory (NREL) tool HARP_Opt was used to design a horizontal axis tidal current turbine (HATCT). The numerical method was validated with the experimental data and a good agreement was achieved. The designed turbine has a 3 bladed rotor of 4 meters diameter and rated mechanical power of 20 kW. Performance metrics of the rotor for steady and uniform flow was simulated at flow speeds from 0.5-3.5 m/s. The turbine achieved its rated power at a tip speed ratio (TSR) 5.7 with a peak CP value of 0.47 and peak thrust of 16.7 kN-m. Additionally, a series of simulations were performed at TSR from 1-10 to obtain performance curve for the turbine at a design current velocity of 1.5 m/s. Effect of solidity on performance was quantified by varying the number of turbine blades. The value of CP increased by 1.5% with increasing the number of blades from 2 to 3. The value of CP further increased by only 0.2% with increase in number of blades from 3 to 4. The value of turbine thrust was minimally effected by increase in the number of blades. However, the value of thrust per blade increased with a reduction in number of blades. The increase in flap moment and thrust per blade with reduction in number of blades could have serious consequences for the structural integrity of the turbine.