Investigation On The Performance Of Classical Blade (NACA4418) And Magnus Effect Based Chiral Blade In Planetary Boundary Layer

Nowadays, most of the Horizontal Axis Wind Turbines(HAWTs) are designed under the implicit hypothesis of a uniform incoming flow. Such hypothesis is far from relevant when immersing HAWTs in Planetary Boundary Layer(PBL) of few hundred meters’ height. Due to the viscosity and terrain roughness, there is a large wind gradient near ground inside the PBL, which will result in the torque variation and the pitching moment of the blade, thus in the reduction of power output.The goal of this study was to investigate the possibility of Magnus effect based device(Chiral blade) to generate lift and its ability to retrieve energy inside the PBL. For the whole study a reference model NACA4418 was chosen as the classical blade and the Chiral blade was simplified as rotating cylinder. This study consists of two separate parts:(1) Quantify the loss of efficiency that comes from the use of classical blade inside PBL, and(2) Estimate the gain in efficiency when substituting the classical blade by Chiral blade. For preliminary estimation, BEM method was used to build blade aerodynamic model and a Python code was written to design a classical blade based on this model. Then the power loss of a classical blade inside the PBL was calculated based on EXCEL, afterwards, an optimized blade(Chiral blade) by assuming that each blade element could work at optimal lift was developed to compare with the previous one. To get a more accurate result, the Computational Fluid Dynamics(CFD) software FLUENT was used to compare these two cases under the pseudo-rotating condition, in which the rotation of the blade inside the PBL was simulated by simply changing the setting of incoming relative wind velocity. A full cycle was simulated for each blade.Results in BEM method showed the loss of efficiency of classical blade due to PBL was estimated to 10% and the gain in efficiency when substituting the classical blade by Chiral blade reached to nearly 70%.While in numerical simulation, the loss of efficiency is estimated to 4~5% and the gain in efficiency reaches to around 60%.Therefore, Chiral blade had advantage over classical blade NACA4418 turbine in retrieving energy inside the PBL, which is of great importance for future wind turbine blade design.