Design and Analysis of a Novel Ocean Current Two-Coupled Crossflow Turbine Energy Converter

In this study, a novel ocean current energy converter is proposed. The energy converter is composed of two crossflow turbines. The two turbines rotate at the same speed but in opposite directions; therefore, the summation of the hydrodynamic torques applied to the two turbines is equal to zero, which can make the converter self-stabilizing. A channel is designed to guide a large amount of water flowing through the turbine, thereby increasing the incident velocity, power, and efficiency of the turbine. The guide vanes are positioned in front of the turbine to guide the ocean current, producing the optimal flow incident angle and thereby increasing the performance of the turbine. A novel empirical formula for determining the power and efficiency of the converter is derived. Moreover, a computational fluid dynamics (CFD) analysis of the energy converter is conducted using the commercial software Star CCM+ in the standard κ-ω turbulence model with wall functions. The accuracy of the empirical formula is verified by comparing the theoretical results with those obtained using the CFD method. Finally, the effects of several parameters on the performance of the energy converter are investigated. The optimal parameters are obtained as follows: (1) The optimal setting angles of vanes γ 1 = 78°, γ 2 = γ 1 + 10 ° , and γ 3 = γ 1 − 5 ° . (2) The optimal blade angle β = 44°. (3) The optimal rotating speed N = 2.6 ( V cur /1.6) rpm. (4) The optimal ratio of turbine center distance r L 4 ≥ 2.50. (5) The optimal ratio of turbine shaft length is approximately 5.5 < ( r shaft = W shaft /D tur ) opt < 5.7. (6) The performance of each turbine with N blade = 31 blades is significantly better than that with N blade = 23 blades.