A Computational Fluid Dynamics Based Viscous Vortex Particle Method for Coaxial Rotor Interaction Calculations

The coaxial rotor in hover and forward flight experiences complex unsteady aerodynamic interaction effects. Standard methods used for isolated rotor analysis are not adequate for obtaining the unsteady loads and wake. More accurate and computationally efficient approaches are required. The viscous vortex particle approach based on the Lagrangian formulation of the incompressible Navier-Stokes equations is a grid free method suitable for capturing the vortex wake interaction over long distances. The rational function approximation of unsteady airfoil loads from a CFD database is used to reduce computational effort and improve accuracy of load calculations. The vortex particle method and the rational function approximation are combined and applied to evaluate performance, wake evolution and loads for a coaxial rotor system in hover. The isolated and coaxial rotor thrust and torque performance were accurately predicted. The unsteady hub loads in hover were calculated using this technique. The blade passage frequency was a dominant source of oscillations in aerodynamic loading. The effect of the rotor wake system was determined and a comparison of the aerodynamic loading models was conducted.