A typical fighter aircraft performs maneuvers at high angle of attack. Separated vortical flows originating from delta wings, leading-edge extensions, and forebodies interact with fins and tails. Experimental evidence suggests that several unsteady flow phenomena may excite fins depending on angle of attack. Vortex breakdown phenomenon is the most important source of fin buffeting, causing large structural vibrations and severe fatigue damage. The interaction of vortex breakdown with a fin is a complicated process affected by 1) the time-averaged breakdown location, which is determined by the pressure gradient set by the fin; 2) helical mode instability of the flow downstream of breakdown; 3) quasi-periodic oscillations of breakdown location, 4) distortion of incident vortex and vortex splitting; 5) unsteady flow separation from the leading edge of the fin, 6) possible coupling between the flow separation and vortex breakdown (with a feedback effect); and 7) aeroelastic deflections of the fin. Different aspects of fin buffeting have been previously investigated. However, the effect of aeroelastic deflections of the fin has not been investigated before. The interaction of vortex breakdown with an oscillating fin was investigated by flow visualization and velocity measurements to understand the effects of aeroelastic deflections on fin buffeting. For frequencies lower than a cutoff frequency, the response of vortex breakdown location is quasi periodic, and the amplitude of the variations of breakdown location decreases with increasing frequency. For frequencies higher than the cutoff frequency, vortex breakdown does not respond to the fin oscillations. These observations suggest that the dynamic response of breakdown location to an oscillating fin is similar to that of a low-pass filter. For different locations of the fin with respect to the vortex, similar amplitude responses were found. This result can be used in the design of fins to prevent a feedback effect and coupling between the vortex breakdown and fin structure. A theoretical explanation of the experimental observations based on the wave propagation characteristics of the vortex flows is presented.
Interaction of vortex breakdown with an oscillating fin
Beeinflussung der zusammenbrechenden Wirbelröhre auf der Saugseite eines Deltaflügels durch die Schwingungen einer Heckflosse
AIAA Journal ; 39 , 3 ; 438-446
2001
9 Seiten, 12 Bilder, 29 Quellen
Article (Journal)
English
Interaction of vortex breakdown with an oscillating fin
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