" 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, June 1991.

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.