" Interaction Between a Vortex Dominated Wake and a Separated Flowfield".
Komerath, N.M., Kim, J-M., Liou, S-G., School of Aerospace Engineering,
Georgia Institute of Technology, Atlanta Georgia 30332-0150
AIAA Paper 91-1819, 22nd Fluid Dynamics, Plasmadynamics and Lasers Conference,
Abstract: The interaction between a rotor wake and the separated flow downstream
of an axisymmetric back-step is considered, as a basic representation of
higher-order aerodynamic interactions around rotorcraft. The velocity and
surface pressure fields are related to previous flow visualization results.
The major visualized features are confirmed by azimuth-resolved velocity
data and vorticity contours which are phase-linked to the rotor. Vortex
interaction features are also seen clearly in the azimuth-resolved surface
pressure. A secondary, counter-rotating vortical structure appears downstream
of the tip vortex. While the blade frequency is the primary temporal descriptor
of the problem, multiple time scales do occur, with pressure spectra showing
peaks at the shear layer natural frequencies, the rotor frequency, and their
harmonics. Instability of the tip vortex trajectories causes a large spectral
peak at the rotor frequency. Vortex interaction with the boundary layer
generates local unsteadiness, as seen from histograms of velocity taken
during 0.5-degree azimuth intervals.