"FOREBODY VORTEX CONTROL AT HIGH INCIDENCE USING A MOVEABLE NOSE STAGNATION
Darden, L.A. and Komerath, N.M.
AIAA 95-1775, Applied Aerodynamics Conference, June 1995
A direct causal relationship is shown between lateral displacement of the
nose stagnation point and lateral asymmetry of the vortex system over a wing-body
configuration at angle of attack. Steady asymmetry is created and eliminated
by moving the nose tip for angles of attack up to 40 deg. Rapid movement
of the nose tip is then used to induce and eliminate dynamic vortex asymmetry.
Video images of smoke in laser sheets in two cross-flow planes, and of the
shadow of the nose, are analyzed to construct time series representations
of the vortex asymmetry and compared with the simultaneous nose position.
The intersection point of the zero-vorticity contour (ZVC) with the body
surface serves as a metric of vortex asymmetry. The dynamics of the vortex
asymmetry are analyzed in the frequency domain using these series. Correspondence
between nose movement and degree of asymmetry shows that forebody asymmetry
is a deterministic phenomenon directly related to the location of the nose
stagnation point. The assumption of linear response is valid upstream of
the wing vortices, but deteriorates downstream. The frequency-domain transfer
function between nose movement and asymmetry is used to extract the steady-state
sensitivity of the vortex in response to nose deflection, the time lag, and
the rate dependence of sensitivity. The lag in the vortex response is an
order of magnitude larger than the freestream convection time, and increases
with downstream distance. The moving nose tip is shown to be a simple method
for creating, studying, modifying, and eliminating forebody vortex flow asymmetry,
statically and at high rates.
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