A mathematic optimization model was presented to enhance the power coefficient of vertical-axis turbine for tidal current conversion by adjusting the blades' deflection angle. To do this, the blade deflection angle was expressed as a multinomial of Hicks-Henne functions. The coefficients of Hicks-Henne functions, which are design variables, were worked out by the revolving orientation method to achieve the maximal power coefficient. Example results indicate that the power coefficient of optimized turbine is evidently higher than that of cycloidal turbine. In addition, the features were described that the optimal deflection angle and attack angle change along with azimuth during a period. At last, the sample results were compared between moment-controlled model and the current model, and the theoretical basis of moment-controlled model was analyzed.
Vertical-axis straight blade turbine is an effective solution to utilize tidal stream kinetic energy as local energy source. To make the turbine be more practicable, researchers are struggling to enhance the power efficiency of the rotor. The investigations reveal that adopting variable-pitch blade can improve the rotor performance significantly in some aspects. The blade pitching mechanism can be passive or active. The active turbines being studied include cycloidal turbine (Zhu, 1980; Ma 1984) and cyclic pitch turbine (Schonborn and Chantzidakis, 2007). The passive turbines include spring-controlled turbine (Wang, 2006), moment-controlled turbine and kobold. The hydrodynamic performances of these turbines are different depending on respective pitch pattern. Therefore finding the optimized law of deflection angle is significant for the design of rotor performance and blade controlling mechanism. Wang, Zhang and Zeng (2004) takes the discrete deflection angle along the blade orbit as design variables, regard the weighted mean of power coefficient in a range of tip speed ratio(TSR) as objective function, adopt the conjugate gradient method to optimize the law of deflection angle
