Nonlinear aeroelastic study for folding wing structures

A folding wing structure consisting of three components (a fuselage, an inboard wing, and an outboard wing) is modeled computationally using a geometrically nonlinear structural dynamics theory based upon van Karman strains and a three-dimensional vortex lattice aerodynamic model with an exact tangent flow boundary condition and planar wake assumption. The structural dynamic equations of motion are discretized in space using a discrete Ritz basis derived from finite element analysis and component synthesis. Results from the computational model are compared with those from experiments designed and tested in the Duke University wind tunnel for three folding wing configurations. Stable limit cycle oscillations at flow velocities beyond the linear flutter velocity are measured in wind-tunnel experiments and predicted using the computational model. Overall, the limit cycle oscillation magnitude and dominant response frequency results from theory show good agreement with those measured in the experiment. Qualitatively, both the experimental and theoretical limit cycle oscillation curves for the inboard wing show limited nonlinear stiffening with flow velocity for the range of velocities tested. The theoretical model also predicts that the outboard wing limit cycle oscillation tip displacements for the folding wing configuration with the largest outboard folding angle is significantly higher than the two other configurations. Unlike the inboard wing, for each configuration, the outboard wing theoretical limit cycle oscillation curves do show a trend that is reminiscent of a stiffening nonlinearity. DOI: 10.2514/1.44868