"Recent Experiments On Vortex Collisions With A Cylinder".
Mahalingam, R., Peterson, K.G., Funk, R.B., Komerath, N.M. and Conlisk,
AIAA 95-2236, Fluid Dynamics Conference, June 1995.
Abstract: The detailed interaction process of a vortex with a solid body
is important in the unsteady aerodynamics of maneuvering aircraft, especially
rotorcraft. This paper extends previous experimental work. The interaction
of the tip vortices in the wake of a two-bladed rotor with a circular cylinder
is studied. The cylinder dimensions are large in comparison to the vortex
core. Attention is focused on the interaction at the top of the cylinder,
where the vortex filament is nominally perpendicular to the cylinder axis.
Previous work has shown that the pre-collision vortex trajectory and surface
pressure extrema can be predicted from potential flow analysis. Experimental
results are presented on the collision phase. A time history of the collision
event in a vertical plane along the top of the cylinder is constructed from
rotor-synchronized flow images and correlated with pressure traces assembled
from several locations along the top. These results show the sequence of
development of secondary vortical structures upstream of the main vortex,
separation of the reverse-flow boundary layer, and the final stages of core
collision with the surface. Results from a dual-camera system are presented
to show temporal evolution at some selected phases. While some evidence
is presented on the postulated sudden eruption of the reverse flow boundary
layer, this event is yet to be captured from the dual-camera system.