Ahmed Abd El-Rahman
Professor of Fluid Mechanics
17304 Faculty of Engineering, Cairo University Rd., Giza 12613, Egypt (email)
17304 Faculty of Engineering, Cairo University Rd., Giza 12613, Egypt (email)
The geometry of airfoil sections in small wind turbine blades affect the boundary layer separation, promote the flow transition to turbulence and consequently influence the performance of many types of small wind turbines. However, few optimization results are available for typical small wind turbine blades. Here, we report a particular shape optimization study of the standard SG6043 airfoil that applies the genetic algorithm along with the low-Re XFOIL solver. The numerical model is first validated against available experimental values for the SG6043 airfoil at a Reynolds number of 100, 000. The predicted lift and drag profiles are qualitatively found in good agreement with the experimental values, particularly in the pre-stall regime, provided that the XFOIL’s transition exponent is adjusted to 11. The simulation is then extended to a lower Reynolds number of 60, 000 that is consistent with an average tip-speed-ratio λ = 4.0. Four specific scenarios seeking different objective functions are proposed for optimization. While the first two scenarios focus on typical optimum configurations at which the maximum lift-to-drag ratios are realized, the objective function of the latter scenarios considers the maximum arithmetic-mean over multiple consecutive degrees of the corresponding angle of attacks. The preliminary results show remarkable improvement in the range from 24% to 10% in the predicted lift-to-drag ratios in comparison with the original configuration at the expense of the corresponding airfoils’ stiffness. This is followed by an elaboration on the entire blade design along with the specification of the resulting power coefficient and annual energy production.
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