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Date of Award
Master of Science (MS)
The accurate simulation of thick-airfoils is of great importance for the design of efficient wind turbines. Simulation of these airfoils is difficult for a number of reasons. The low operational speed and therefore low Reynolds number results in a laminar to transitional to turbulent flow over the airfoil. The use of empirical methods to predict transition has been shown to introduce large uncertainty in the transition location which necessitates a more conservative design. High angles of attack cause some trailing edge separation which conventional eddy viscosity models cannot accurately predict. Additionally, once in operation, a leading edge grit roughness forms on the airfoils. These irregularities are caused by the accumulation of insect debris, ice, and erosion. The effect of surface roughness on these airfoils is of importance because the surface conditions directly affect the efficiency of the of the wind turbines. Accurate simulation of the transition and roughness effects will directly aid in the design of more efficient wind turbines.
This paper employs the four-equation Shear-Stress-Transport (SST) k-ω transition turbulence model to simulate the flow over smooth and rough airfoils. The SST k-ω turbulence model is modified to account for boundary layer transition and surface roughness. The four-equation SST k-ω transition model and equivalent sand grain approach surface roughness modification is used. Implementation of the transition model is first verified by computing the flow over the T3 series of flat plates. Implementation of the surface roughness model is verified by computing the flow over a series of rough flat plates. Next, the modifications are combined into SST k-ω-transition-roughness model. The flows over smooth and rough S809 airfoils, which are commonly used in horizontal-axis wind turbines, are computed. Results are compared with the experimental data. The results show that both transition and surface roughness must be resolved for the accurate prediction of this family of airfoils.
David Peters, Qiulin Qu
Available for download on Monday, February 22, 2044