Mahalingam, R., and Komerath, N. M., “ Characterization of the Near-Wake of a Helicopter Rotor”, AIAA Paper 98-2909, 29th AIAA Fluid Dynamics Meeting,
June 1998, Albuquerque, NM.

Vortex characteristics in the near wake of a 2-bladed teetering rotor in steady forward flight are measured using a laser velocimeter. The vortex passage at a measurement point is seen to be repeatable to within 1degree of rotor revolution. Velocity was measured in the planes intersected by the rotor-blade tip at the rotor azimuths of 0, 90, 180 and 270 degrees. Variations in tip-vortex characteristics such as core-radius, circulation and axial velocity were obtained as functions of rotor azimuth. Empirical curve fits are described for these variations. The core axial velocity is of the order of the peak tangential velocity at all locations. It is higher than peak tangential velocity over part of the advancing blade side of the rotor.  The axial velocity in all cases is wake-like, being directed towards the blade of origin. Wake geometries obtained from the LDV data are also presented here.

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