Numerical Investigation on the Effects of Diffuser Inlet Opening Angles on the Performance of a Drag-Based Hydrokinetic Turbine

The potential of ocean energy as a renewable source is widely acknowledged. Ocean currents energy is one of the ocean energies, which is harnessed by using hydrokinetic turbines (HKTs). Despite continuous efforts on the optimization of HKTs’ energy conversion performance, challenges remain in regions with slow flow velocities. This study aims to investigate the effects of incorporating a diffuser into a HKT design on the power output performance. Numerical simulations using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and renormalized group (RNG) k-ε turbulence model is conducted by varying the diffuser inlet opening angles (θi = 15°, 20°, 25°, 30°, and 35°). The results show that the highest flow velocity is measured at the diffuser throat for all angles, which a deceleration flow effect is also observed here. This decelerated flow zone is found to be extended from the diffuser wall to its midline. The optimal configuration for power and torque coefficients is found in inlet opening angle of 20°. Overall, incorporating a diffuser with the optimum inlet opening angle in the HKT design improves the power generation efficiency compared to the HKT configurations without a diffuser.