"FOREBODY VORTEX CONTROL AT HIGH INCIDENCE USING A MOVEABLE NOSE STAGNATION POINT"
Darden, L.A. and Komerath, N.M.

AIAA 95-1775, Applied Aerodynamics Conference, June 1995

ABSTRACT
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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