The mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and
generates high compensatory workload for pilots, degradation of the handling qualities and performance,
and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance
between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to
investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the
distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group
activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method,
and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the
ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a
“Large” and a “Wee” rotor near the ground and obstacle, and compared with the earlier experiments carried
out at the University of Glasgow. The results show that the predicted rotor induced inflow and flow field
compare reasonably well with the experiments. Furthermore, at certain conditions the tip vortices are pushed
up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover,
contrary to without the obstacle case, the peak and thickness of the radial outwash near the obstacle is
smaller due to the barrier effect of the obstacle, and an up-wash is observed. Additionally, as the rotor closes
to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the up-wash near the obstacle is
faster, indicating a stronger interaction between the rotor wake and the obstacle. Also, contrary to the case
without the obstacle, the fluctuations of the rotor thrust, rolling and pitching moments are obviously
strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the
obstacle is small