Investigation and Optimization of Blade Tip Winglets Using an Implicit Free Wake Vortex Method

The Science of Making Torque from Wind 2014

Lawton, Stephen^1 ; Crawford, Curran^1

University of Victoria, Victoria, BC, Canada^1

关键词: Aerodynamic analysis;    Aerodynamic simulations;    Complex-step method;    Computational costs;    Fast multipole method;    Gradient-based optimization;    Objective functions;    Relative positions;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/524/1/012033/pdf
DOI  :  10.1088/1742-6596/524/1/012033

来源: IOP

【 摘 要 】

Novel outer-blade geometries such as tip winglets can increase the aerodynamic power that can be extracted from the wind by tailoring the relative position and strengths of trailed vorticity. This design space is explored using both parameter studies and gradient-based optimization, with the aerodynamic analysis carried out using LibAero, a free wake vortex-based code introduced in previous work. The starting design is the NREL 5MW reference turbine, which allows comparison of the aerodynamic simulation for the unmodified blade with other codes. The code uses a Prandtl-Weissinger lifting line model to represent the blade, and vortex filaments as the flow elements. A fast multipole method is implemented to accelerate the influence calculations and reduce the computational cost. This results in higher fidelity aerodynamic simulations that can capture the effects of novel geometries while maintaining sufficiently fast run-times (on the order of an hour) to allow the use of optimization. Gradients of the objective function with respect to design variables are calculated using the complex step method which is accurate and efficient. Since the vortex structure behind the rotor is being resolved in detail, insight is also gained into the mechanisms by which these new blade designs affect performance. It is found that adding winglets can increase the power extracted from the wind by around 2%, with a similar increase in thrust. It is also possible to create a winglet that slightly lowers the thrust while maintaining very similar power compared to the standard straight blade.