Gust loads with uncertainty due to imprecise gust velocity spectra

Gust loads on a rigid, flat-plate airfoil at zero angle-of-attack were simulated given imprecise knowledge of atmospheric turbulence spectra. Aerodynamic loads were computed with an unsteady vortex lattice model, which includes temporal variations in wake vorticity and the associated downwash on the airfoil. The non-intrusive formulation of the polynomial chaos expansion in terms of the multivariate Hermite polynomials was employed to quantify the predicted uncertainty in the unsteady lift. Expansion coefficients were estimated through Latin hypercube sampling of the parameters in the vertical and streamwise gust spectra. The first-order chaos expansion in terms of the uncertain spectral parameters was found to be sufficient for representing the stochastic aerodynamic lift and the stochastic lift was found to be most sensitive to imprecision in the standard deviation of the vertical turbulence component. These conclusions were found to be unaffected by ignoring the effects of gusts on the locations of the shed vortices in the airfoil's wake.