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

ABSTRACT:

 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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