# crow instability

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 October 24, 2000, 02:44 crow instability #1 A.Jaafar Guest   Posts: n/a Could anyone explain to me what is crow instability and the relation to the flow past bluff bodies.. thanx in advance..

 October 30, 2000, 06:06 Re: crow instability #2 Vidyadhar Mudkavi Guest   Posts: n/a dear jaafar, i am only aware of crow instability in the context of aircraft wake vortices. i am not sure if this has anything to do with bluff body flows! -vidyadhar mudkavi october 30, 2000

 October 30, 2000, 07:03 Re: crow instability #3 A.Jaafar Guest   Posts: n/a could you then explain to me what it is in the context of aircraft wake vortices. thank you very much for the response.

 October 30, 2000, 07:19 Re: crow instability #4 Vidyadhar Mudkavi Guest   Posts: n/a aircraft wake consists, usually, of two counter rotating vortices known popularly as tip vortices. they have filament-like structure. when they are immersed in the ambient atmosphere, they receive perturbation from their equilibrium position (which is a straight line). these purturbations grow and they become sinusoidal. so, each vortex looks like a sine wave which are confined in a plane. however the plane containing the perturbed vortices make an angle of about 45 degrees to the vertical. eventually, in symmetric mode, the opposite vortices touch each other and form rings. there exists photographic observations of such instabilities in real life. the instability is mostly linear for most part of its evolution. it becomes nonlinear towards the end phase of the instability when the opposite vortices touch each other. -vidyadhar mudkavi october 30, 2000

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