CHALLENGE - Although much work has been reported on design of winglets on airplane wings, , the volume of published efforts to design bladelets (winglets at the tips of the wind turbine blades) for rotating lifting surfaces is still very limited. This is especially true for mathematical optimization of bladelets for propeller type wind turbine blades. This work investigated the effectiveness of bladelets on the tips of wind turbines on increasing wind turbine rotor power output.
SOLUTION - Each blade + bladelet configuration was analyzed using the OpenFOAM solver MRFSimpleFoam. Multi-objective optimization was performed on the bladelet configuration only (not on the blade configuration) using modeFRONTIER software. The shape of each bladelet configuration was defined by the span, sweep angle, dihedral angle, twist angle and the taper ratio. The three simultaneous objectives were to maximize the coefficient of power, while minimizing the coefficients of thrust and blade twisting moment. A multi-dimensional response surface based on radial basis functions was created for each of the three objectives and coupled with the NSGA-II optimization algorithm to arrive at a Pareto frontier. Four virtual Pareto designs were selected at random from the Pareto frontier and validated in OpenFOAM. Out of the four selected designs, the Pareto design least sensitive to geometric defects is presented.
BENEFITS - It was demonstrated that bladelets can increase power output of the wind turbine rotor and that the proposed multi-objective optimization framework is capable of identifying several candidate blade + bladelet configurations in multi-dimensional design space.