"Rotor Tip Vortex / Airframe Collision Effects on the Vortex and Airframe".
Mahalingam, R., Komerath, N.M.
AIAA Paper 96-2013, 27th AIAA Fluid Dynamics Conference, New Orleans,
LA, June 1996.
This paper describes progress towards understanding the interaction between
a vortex-dominated wake from a two-bladed rotor, and a solid cylinder
surface. Prior work had taken this problem to the level where the flow was
predictable except for the details of the collision between the tip vortex
and the surface. The substantial role of the core axial velocity, postulated
from pressure data on the airframe, is now confirmed by direct velocity
measurements. Both the tip vortex core and the inboard vortex sheet, with
opposite vorticity, have substantial wake-like velocities:
further evidence that the axial velocity is due to the no-slip condition.
The vortex shows interior structure: Outside the core, there are
multiple thin regions of jet-like velocity, attributed to the induced
effect of the rolling-up vortex sheets. This appears to resolve
the contradiction between Euler results (jet-like axial velocity) and experiments
(wake-like core). During the collision, the axial
velocity at the top of the airframe persists even after the flow has stagnated
on the Advancing Blade Side, further evidence of the blade-wake
genesis of this flow. Suction peaks on the RBS stay for a long duration.
The levels of suction observed are far above what can be explained using
potential flow theory alone.
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