Computational study on multi-objective optimization of the diffuser augmented horizontal axis tidal turbine

The result from a multi-objective optimization on the outlet diffuser angle of the tidal turbine is presented with a focus on the turbine efficiency and cavitation. This study is the first to investigate the impact of the diffuser angle on the diffuser augmented tidal turbine in performance and cavitation inception. The 1/2 scale model was designed with three blades based on NACA 4616 airfoil. Seven diffuser angles were varied from 10.43° to 35.97° in tidal current velocity around 0.7 m/s. The standard k−e turbulence model and the multiple reference frame motion were conducted in steady-state for the computational analysis with Tip Speed Ratio (TSR) ranged from 1 to 5. It was shown that the diffuser angle strongly influences the turbine performance and cavitation inception. The maximum power coefficient was found at the largest diffuser angle as more space for the turbine to rotate leads to a higher pressure drop, which involves the current velocity change extracted to the torque of the rotor. However, the highest cavitation was also found at the largest diffuser angle since a higher-pressure drop increases the cavitation number. By multi-objective optimization using the GA-ANN method supported by TOPSIS, it was concluded that the optimum design of the tidal turbine was owned by a diffuser angle of 20.04°.