Vortex Wake Development and Aircraft Dynamics
The written paper describes and augments material delivered semiformally in Session III of the Symposium, as commentary to a movie. The computed aircraft response results were reported at the end of Session VI of the Symposium.
Calculations of the sinuous instability of a trailing pair are extended, using a nonlinear vortex modeling technique, and the effects of initial parameters are examined, particularly the initially assumed wavelength. Realistic-looking tresses obtained were demonstrated using computer graphics.
More complex modes of vortex decay may be demonstrated by flow visualization in water, using the hydrogen bubble technique. Vortex bursting is shown to be possible before and/or after the “wavy” mode. These small-scale measurements are shown to be consistent with flight measurements.
In another series of experiments, smoke injected into the core of the trailing vortex behind a 13-foot-span C-130 wind-tunnel model, mounted in a 23-foot by 16-foot working section, showed remarkable coherence until the adverse pressure gradient in the wind-tunnel diffuser caused vortex bursting. The effects, on vortex burst position in the diffuser, of auxiliary blowing into or near the vortex core are discussed qualitatively.
The results of a computer simulation are discussed concerning the dynamic response and loads induced on an aircraft which enters the trailing vortex of a lead aircraft of large size. In the study, McCormick’s or Owen’s semi-empirical theories were judged as preferable for vortex decay estimates with distance behind the aircraft. However, the simulation results were only available using vortex core magnitudes from classical theory. The calculated normal load factors and maximum angular motions (with and without control) were close to those reported for recent FAA and NASA tests with a CV-990 or DC-8 flying into the wake of a DC-9 or a jumbo jet.
KeywordsVortex Ring Vortex Core Lift Coefficient Roll Angle Vortex Pair
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