Impact of Downstream Myring Body on Tidal Turbine Performance Characteristics

This study explores the effect of downstream bodies on the performance characteristics of a tidal turbine operating at both design and off-design tip-speed ratios (TSRs). Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations are performed using a 12 million-cell mesh, which is previously validated and confirmed to provide mesh-independent and experimentally consistent results for a bare turbine. The downstream body is positioned 0.25D_t downstream of the turbine with a diameter of 0.5D_t, where D_t is the turbine diameter of 5.5 m. Our previous work demonstrated that placing a cylindrical object without a nose or tail in close proximity (0.25 D_t) results in approximately 24% and 12% reductions in the power (C_P) and thrust (C_T) coefficients, respectively, at the optimal efficiency point of the bare turbine (TSR = 5). To mitigate this performance deterioration, a nose and tail with a streamlined Myring profile were added to the cylinder, reducing the performance loss to approximately 2%. Building on these findings, the present study evaluates turbine performance over a wide range of TSR values for both the bare turbine and the turbine with a downstream body equipped with a nose and tail. This analysis highlights the influence of downstream bodies on turbine power output under off-design conditions, enabling the determination of the best efficiency point and the turbine characteristic curves (C_p vs. TSR and C_T vs. TSR) when a downstream body is attached. This comprehensive analysis aims to operate the turbine with downstream bodies most efficiently at varying flow conditions in both wet and dry seasons.