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Title: Effect of ambient turbulence on vortex instability

Description: Physical modeling of the effect of ambient turbulence on wing-tip vortices was conducted in a towing tank, which measured 18 m long, 1.2 m wide and 0.9 m deep. The towing system was capable of towing two oil-bearing carriages independently or simultaneously. The carriages rode on thin oil films released from four pads supporting the carriages on two tracks, one round and one flat. The tracks were aligned such that the vertical displacement of the instrumentation carriage was within 2 mm in the 12-m working section [2]. Trailing vortices were generated by towing a rectangular wing with a span 5.1 cm and a chord of 2.5 cm at several negative angles of attack [1]. Ambient turbulence was generated by towing upstream of the wing 3 grids with different mesh sizes [2]. In the absence of ambient turbulence (left column), sinusoidal linking is the only form of instability, as predicted by Crow [3].In weak turbulence, both sinusoidal and bursting instabilities are observed (middle column); the dominant wavelength of the sinusoidal instability deceases with increasing turbulence intensity. In strong turbulence, the vortex instability is predominantly of the bursting type (right column).

Credits: Dr. (Pete) H.-T. Liu

References: [1] Liu, H.-T. (1992) "Effects of Ambient Turbulence on the Decay of a Trailing Vortex Wake," AIAA J. of Aircraft, 29, 255-263.

[2] Liu, H.-T. (1995) "Energetics of Grid Turbulence in a Stably Stratified Fluid," J. Fluid Mech. 296, 127-157. [3] Crow, S. C. (1970) "Stability Theory for a Pair of Trailing Vortices," AIAA Paper 70-53.

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