# Numerical Simulations of Novel Conning Designs for Future Super-Large Wind Turbines
## 4 Conclusions  
In future designs of super-large wind turbines, the question of being upwind or downwind will be an important one for the wind energy industry. The present paper put forward a conceptual design consisting of an actively load-aligned blade tip and a fixed load-aligned blade root. In order to evaluate the advantages and disadvantages of these concepts, it is of vital importance to carefully select appropriate tools. Different conning configurations, including special cones with three segments, were simulated and analyzed based on a 10 MW reference rotor. The results provide knowledge regarding the complex force distributions of these configurations, and could serve to improve the traditional BEM on traditionally or specially coned rotors. Up- and down- wind coning approaches yield different aerodynamic performance, e.g., in their total integrated loading, distributed force, and flow fields. The force distributions and their differences may be explained by the concept of the angle of attack. It was found that parameters which have the greatest influence on the angle of attack are the position of blade tip and the cone angle. The blade tip position determines the induction velocity contour, and subsequently, the inflow velocity at the blade sections. With the upstream movement of the blade tip, blade sections away from the tip will be immersed more heavily in the tip vortex trace. Then, the blade sections will suffer from stronger axial induction, smaller axial inflow velocity, a lower angle of attack, and consequently, a lower force distribution. The downstream movement of the blade tip has the opposite effect. The cone angle determines the velocity and force projecting process from the axial to the normal direction, which influences the thrust and tangential forces in the normal and axial directions. The correct inflow velocity decomposition, which connects the axial and normal directions, is indispensable. The same relative blade tip position and cone angle will result in the same force; however, applying the same tip position or cone configuration alone does not guarantee the same aerodynamic performance. The aerodynamic performance discrepancy between an upwind cone and its downwind counterpart is significant. In the present study, the most upwind and downwind cones had a thrust difference up to 8% and a torque difference of up to 5%. Nevertheless, the traditional BEM method could not differentiate an upwind cone from its downwind counterpart under the same chord, twist and airfoil distributions. Many studies on load-aligned concepts or comparing upwind/downwind designs have utilized tools based on traditional BEM, which arguably makes their conclusions disputable. A correction to the traditional BEM method must be made before it can be used to assess new cone concepts. Such an improved BEM should consider the influence of blade tip position and cone angle, and adopt the corrected inflow velocity decomposition. To date, debate over  
Figure 13: Distributions of angle of attack: (**a**) \(\alpha_{z}\); (**b**) \(\alpha_{n}\). up- or down-wind coning is ongoing. The design and optimization of super-large coned rotors still has a long way to go. Conceptualization, Z.S. and W.Z. ; methodology, Z.S. and W.Z. ; software, W.S. and W.Z. ; validation, Z.S., W.Z. and W.S. ; formal analysis, Z.S., W.Z., W.S. and Q.T. ; investigation, Z.S. ; resources, W.Z. and W.S. ; data curation, Z.S., Q.T., J.C., X.L. and W.S. ; writing--original draft preparation, Z.S., W.Z. and W.S. ; writing--review and editing, Z.S., W.Z. and W.S. ; visualization, Z.S. ; supervision, W.Z. and W.S. ; project administration, W.Z. ; funding acquisition, Z.S. and W.Z. All authors have read and agreed to the published version of the manuscript.