Can someone please explain to me the concept of vortex breakdown?

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Vortex breakdown is a phenomenon characterized by a rapid change in the core radius of a vortex filament, often resulting in a bubble or spiraling thread. It is related to the swirl number (SN), which is the ratio of swirl to meridional motion strengths, and its disappearance occurs as the SN decreases. The concept of helicity in vortices suggests that vortex lines form axial screw patterns, which can lead to instabilities. Despite its experimental discovery, there is no widely accepted theoretical framework for vortex breakdown, indicating a gap in understanding that presents opportunities for further research. The relationship between vortex breakdown and various parameters like swirl number and Reynolds number is primarily established empirically.
sashankhrao
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Can someone please explain to me the concept of vortex breakdown?
 
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Other than viscosity? Is there a particular instability you are thinking about?
 


Hi Andy,

Thanks for your reply.Actually I don't understand the concept of vortex breakdown and its relation to Swirl Number (SN) which is defined as the ratio of swirl to meridianol motion strengths. I have read that vortex breakdown diappearance occurs as the SN decreases.
 
Yikes... I've never heard of a swirl number. My only resource is "Vortex Dynamics" by Saffman.

I found a link here (http://www.enme.umd.edu/combustion/underwater_propulsion.htm) with some information that helped.

If I understand your context, you are referring to a "vortex with helicity", which I think means that the vortex lines form axial screw patterns. The swirl number seems to be related to the pitch angle of the vortex lines, but I can't tell for sure. A vortex with helicity has moving vortex lines, which are then subject to instabilities.

"Vortex breakdown" is a rapid change in the core radius of the vortex filament or tube- it was an experimentally-discovered phenomenon, and is characterized by a rapid increase in the core radius, which appears as a bubble or spiraling thread. Saffman claims there is no widely accepted theory for this phenomenon yet.

In practical terms, it means that the relationship between the two is established empirically- by varying the swirl number (and other relevant parameters, for example capillary number, Reynolds number, Rossby number...)- this is glaringly missing from the above webpage. There's probably a lot of opportunity for original contributions to the topic.
 


Hi Andy,

Thank you for your interest in my doubt. If you could assist me with your email address i could send you the document that i am trying to understand. Its on Vortex Breakdown. A pdf file.
 


Sashankhrao,

I just sent you a personal message with my address. Hope I can help!
 
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