CFD predictions have been carried out to study the aerodynamic behavior of wind turbine airfoils with distributed roughness over their surface. Wind turbines blades work in variable roughness surface conditions during their operational life, new or washed blades with very low roughness levels and blades that are contaminated by insects, dirt, dust or erosion. The existence of roughness over the blade surface generates a performance loss in the airfoil aerodynamics which understanding and accurate prediction is very important for wind turbine blade designers. In this paper, CFD calculations using the in-house compressible code WMB for several Reynolds numbers and roughness sizes are presented. Numerical data are compared to OSU experimental results for the NREL S809 wind turbine airfoil with locally distributed roughness over the airfoil leading edge. The study is completed with computations for the NACA0012 airfoil and a study of the boundary layer evolution with distributed roughness over the airfoil surface. WMB (Wind Multi Block) is a CFD method developed and validated by CENER and the University of Liverpool for wind turbine aerodynamics analysis (2D and 3D). It is capable of analysing compressible, RANS or URANS equations. In this study RANS equations have been solved. In addition, distributed roughness can be simulated using WMB. WMB has the capacity to simulate distributed roughness elements spread over a chosen area of the airfoil surface (upper or lower area, the whole airfoil or only an isolated zone). Nevertheless, this work is focused on airfoils with leading edge roughness calculations with turbulent flows. Roughness is included in WMB using two different approaches: Hellsten-Laine model and Knopp et al model. In Hellsten-Laine model the boundary condition for the specific dissipation rate is modified to account for the roughness layer that replaces the viscous sublayer. On the other hand in Knopp model a law of the wall is used to obtain values for k (turbulent kinetic energy) and ω at the wall. The main goal of this work is to calculate airfoil aerodynamics when roughness elements are distributed over its surface for different types of airfoils at high Reynolds numbers and including a sensitivity study to roughness parameters. Special attention will be paid to stall area prediction. In this work global airfoil magnitudes and local boundary layer magnitudes are studied numerically with WMB and compared with experiments. The final conclusion obtained from the study presented in this paper is that WMB is a valid tool to study airfoil aerodynamics when there are rough elements distributed over its surface.
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机译：已经进行了CFD预测，以研究在其表面分布有粗糙度的风力涡轮机翼型的空气动力学性能。风力涡轮机叶片在其使用寿命期间会在变化的粗糙度表面条件下工作，新的或经过清洗的叶片的粗糙度水平极低，并且叶片会受到昆虫，污垢，灰尘或侵蚀的污染。叶片表面粗糙度的存在会影响翼型空气动力学性能，这对于风力涡轮机叶片设计者而言，理解和准确预测非常重要。在本文中，介绍了使用内部可压缩代码WMB对几个雷诺数和粗糙度大小进行的CFD计算。将数值数据与NREL S809风力涡轮机机翼的OSU实验结果进行了比较，该结果在机翼前缘上局部分布了粗糙度。研究完成了对NACA0012机翼的计算，并完成了在机翼表面分布粗糙度的边界层演变研究。 WMB（Wind Multi Block）是一种由CENER和利物浦大学开发并验证的CFD方法，用于风轮机空气动力学分析（2D和3D）。它能够分析可压缩的RANS或URANS方程。在本研究中，已经解决了RANS方程。此外，可以使用WMB模拟分布粗糙度。 WMB具有模拟分布在机翼表面选定区域（上部或下部区域，整个机翼或仅一个孤立区域）的分布粗糙度元素的能力。尽管如此，这项工作还是集中在机翼上，该机翼具有在湍流中进行前缘粗糙度计算的功能。使用两种不同的方法将粗糙度包括在WMB中：Hellsten-Laine模型和Knopp等模型。在Hellsten-Laine模型中，修改了特定耗散率的边界条件，以考虑代替粘性子层的粗糙度层。另一方面，在克诺普（Knopp）模型中，壁的定律用于获得壁处的k（湍动能）和ω的值。这项工作的主要目的是计算当雷诺数较高时，不同类型的翼型上的粗糙度元素分布在其表面上时的翼型空气动力学特性，包括对粗糙度参数的敏感性研究。将特别注意失速区域的预测。在这项工作中，利用WMB对整体翼型量级和局部边界层量级进行了数值研究，并与实验进行了比较。从本文提出的研究中得出的最终结论是，当表面上分布着粗糙的元素时，WMB是研究机翼空气动力学的有效工具。
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