AIAA 97-1785, 28th Fluid Dynamics Conference, June 1997
VORTEX-SURFACE COLLISION: 3-D CORE FLOW EFFECTS
Mahalingam, R. and Komerath, N.M. Georgia Institute of Technology
Radcliff, T. , Burggraf, O.R. , and Conlisk, A.T The Ohio State University
The interaction of a strong vortex with a curved surface is a basic
problem in fluid mechanics, whose solution is crucial to predicting the flow
around a rotorcraft. In past work, the initial stages of the interaction
between a rotor tip-vortex and a cylindrical airframe were successfully measured
and predicted using potential flow concepts, followed by boundary layer calculations.
The interaction during and after the collision phase is asymmetric. The axial
velocity in the core of the vortex plays a major role in the final stages
of collision. Lateral velocity measurements are matched with lateral vorticity
contours on the top of the cylinder. The eruption of the reverse-flow boundary
layer upstream of the primary vortex is captured from lateral velocity contours.
Effects of vortex age and blade passage on the core axial velocity are documented.
In the computations, the core is modelled as a family of helical vortices,
whose strength and position are based on experimentally measured core axial
velocities. The analytical predictions are compared with experimentally measured
vortex propagation and surface pressure over a hemisphere/cylinder airframe.
Initiation of vortex core flattening during collision, is seen from the experiments.
The geometry of the vortex-wake is described using the surface pressure contours
and tip-vortex geometry from flow-visualization.
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