A Non-Linear Unsteady Vortex Lattice Method for Aeroelastic Rotor Loads Evaluation

The present work aims to extend the capabilities of DUST, a mid-fidelity aerodynamic solver developed at Politecnico di Milano, for the aerodynamic simulation of flight conditions characterised by flow separations. With this aim, a novel numerical element was implemented in the solver obtained by a coupling between the potential unsteady vortex lattice method and viscous aerodynamic data of airfoil sections available from two-dimensional high-fidelity CFD simulations or experimental wind-tunnel tests. The paper describes the mathematical formulation of the method and the results of a comprehensive validation of the novel numerical element performed by comparison with both high-fidelity CFD simulations results and experimental data. In particular the validation test cases included the evaluation of the airloads of a fixed rigid wing, the flutter speed of a wedged wing and the aerodynamic performance of the full scale proprotor of the XV-15 tiltrotor operating in hover condition, forward flight in helicopter mode and airplane mode.