"Summary of the Interaction of a Rotor Wake with a Circular Cylinder".
J.M. Kim, N.M. Komerath.
AIAA Journal Vol. 33, No. 3, March 1995, p. 470-478.
Abstract: To compute the aerodynamics of a rotorcraft in low-speed flight,
the interaction of the strong vortices in the rotor wake with the airframe
must be modeled. Using a hemisphere-cylinder airframe and a 2-bladed rotor
for reference, the various phenomena encountered during such interactions
are summarized, combining previous results on various configurations with
recent experimental results. Differences between the interaction at the front
and aft portions of the wake are discussed. The pre-collision phase conforms
to expectations from potential flow, and includes distortion of the vortex
trajectory determined by the sense of rotation of the vortex. The collision
phase involves complex boundary layer interactions. The axial velocity in
the vortex core causes substantial asymmetry, and influences the surface
pressure distribution on the airframe side under the advancing rotor blade,
where the axial flow stagnates. The post-interaction vortex is much weaker,
but still contains some swirl energy. Where flow separation occurs due to
airframe shapes, the interaction is not modified significantly, because the
vortex dominates the interaction with separated shear layers for parameter
values of practical interest. Areas of remaining uncertainty are discussed.
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