A non-linear unsteady vortex-lattice method for rotorcraft applications

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 rotorcraft applications. With this aim, a numerical element was implemented in the solver obtained by a coupling between the potential unsteady vortex lattice method and viscous aerodynamic data of aerofoil sections available from two-dimensional high-fidelity computational fluid dynamics (CFD) simulations or experimental wind-tunnel tests. The paper describes the mathematical formulation of the method as well as a validation of the implementation performed by comparison with both high-fidelity CFD simulation results and experimental data obtained over aerodynamics and aeroelastic fixed-wing benchmarks. Then, the method was used for the evaluation of the aerodynamic performance of two rotorcraft test cases, i.e. the full-scale proprotor of the XV-15 tiltrotor operating in different flight conditions and two propellers in tandem with overlapping disks. Simulation results comparison with high-fidelity CFD and data from wind tunnel tests highlighted the potentialities and advantages of the implemented approach to be used for the design and investigation of rotorcraft configurations characterised by consistent viscosity effects.