The effects of uncertainty in flow conditions, namely angle of attack, Reynolds number, and freestream Mach number, on airfoil characteristics in the low-Reynolds-number regime are evaluated. The Ishii airfoil, a thin–cambered airfoil known to have high aerodynamic performance in this regime, is analyzed. The NACA0012 airfoil is also analyzed as a comparative study. The results for two sets of nominal flow conditions are compared to comprehensively characterize performance in the low-Reynolds-number regime. Statistical quantities of aerodynamic coefficients are computed by coupling the stochastic spectral projection method based on polynomial chaos expansion with two-dimensional flow simulations. The relative contribution of the uncertainty of each flow parameter to the variance of outputs is computed using Sobol's global sensitivity analysis. It is shown that, for the Ishii airfoil, the lift coefficient is highly sensitive to the uncertainty, while the lift-to-drag ratio has a high statistical mean and the pitching moment coefficient has low sensitivity. This indicates that, for thin–cambered airfoils, attention should be given to rapid degradation due to unexpected variation in the angle of attack.
View full abstract