Evaluating the effect of blade surface roughness in megawatt wind turbine performance using analytical and numerical approaches

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Past experiences show that the blade surface roughness can affect negatively on the performance of a wind turbine and consequently a reduction in its annual energy production (AEP). In this work, we use the computational fluid dynamics (CFD) tool, model the roughness at wind turbine blade surface, obtain the blade aerodynamics coefficients, and calculate the output power for megawatt wind turbine blade. In these procedures, we also validate our CFD results against the available experimental data reported for a megawatt wind turbine airfoil section. Similar to past experiences, our CFD solutions approve that the blade roughness can effectively reduce both and coefficients as well as the stall angle of a clean airfoil. Normally, any reduction in aerodynamics performance of an airfoil would inversely affect the performance of its corresponding wind turbine blade. To achieve a better understanding of the inverse effect of blade surface roughness on the performance of a megawatt wind turbine blade, we carefully simulate the blade sections for a megawatt wind turbine considering both clean and rough surface situations. In this regard, we use the blade element momentum (BEM) theory to calculate the power for the chosen megawatt wind turbine blade. To enrich our study, we consider both the Reynolds number variation along the blade span and the three-dimensional flow effects in our BEM calculations. The achieved results show that a megawatt wind turbine with a rough surface would noticeably perform less power generation than an equivalent wind turbine with a clean airfoil surface. Our calculations show that the megawatt wind turbine can be faced with 25% reductions in its AEP in a wind velocity about 11-16 ⁄.