Research On Optimal Design Of Airfoil For Horizontal-axis Wind Turbines

Blade is an essential component of wind turbine which induces the lift and drag. Airfoil,which is blade’s cross section, has significant influences on aerodynamic characteristic of theblade. High performance airfoil with multi-objective and multi-constraint is the researchhotspots at present.According to each requirement of preliminary stage and modification stage, there weretwo solving programs of flow fields around a airfoil which were executed in airfoil design. Atthe later stage, XFOIL was used to obtain the aerodynamic parameters. It was proved thatXFOIL was able to achieve the specified high accuracy by comparing with NASA’sexperimental data. At the first stage, the lift coefficient and pressure coefficient weredetermined by the three panel methods(vortices, doublets, linear strength vortexes), whichbased on incompressible potential flow equation and Prandtl-Glauert compressibilitycorrection. And then the panel methods’ results were validated with XFOIL.Three parameterization methods that including disturbing function method, such aspolynomials and Hicks-Henne, control point method, such as Bezier, Spline and B-spline, andconformal mapping method, such as shape function, were used to describe an airfoil. Thensome comparisons with these methods were drawn on the aspects of controllability andcompleteness. It can be found from the results of grey evaluation analysis that the firstmethod’s accuracy is the highest, the second has the strongest stability and the last one is hardto extend.Finally, the inverse design model based on SQP algorithm and direct design based onGA algorithm were established in turn. If the lift coefficient was specified, the former woulddesign two different airfoils which can satisfy the pressure distribution of each other. One wasreflex airfoil which was applicable to both higher strength and stability conditions for rotor.The other was rooftop airfoil, which made it adapt to variable low velocity wind or highrunning efficiency. The last model was applied to the optimal problem about wind turbineairfoil within the multiple operation conditions. The results indicate that the optimized airfoilhas a wider and more effective working range by comparing with NACA0015.5with the samethickness. In the example taking account of aerodynamic and aeroacoustic performance, theredesigned airfoils have higher lift to drag ratios and lower levels of noise emission.