Analysis of a fluid structure interaction system under random gust
Paper in proceedings, 2013
In the design of wind turbine structures, aeroelastic stability is of utmost importance. It becomes even more crucial when there are uncertainties involved in it.A classical aeroelastic model with bending-torsion (plunge-pitch) oscillation having structural nonlinearity has been considered in the present study. The unsteady flow-field is assumed to be incompressible and inviscid and has been modeled both analytically and with a two dimensional vortex lattice code(UVLM). Analytical model is a linearized approach which approximates the airfoil as a thin flat plate with the unsteady wake rigidly attached to it. The vortex lattice code takes into account the shape of the airfoil and also evolution of the wake pattern which ultimately affects the aerodynamic loads. The system undergoes a horizontal random gust. Gust mean velocity and structural stiffness ratio are considered uncertain and are modeled using polynomial chaos expansion. This spectral technique gives considerable computational advantage over traditional Monte Carlo Simulation, especially for the higher fidelity UVLM model. PCE needs higher order of expansion to model the gust mean uncertainty compared to the structural stiffness uncertainty. Stresses from the bending torsion aeroelastic modes are used to calculate damage using an equivalent uniaxial stress. The stress and linear damage accumulation rule is used to estimate risk for the fatigue damage.Acomparison of damage is presented for both aeroelastic models for structural and aerodynamic uncertainties.