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

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Discussion Overview

The discussion centers around the concept of vortex breakdown, exploring its definition, relation to swirl number, and associated instabilities. Participants seek clarification on the theoretical and empirical aspects of vortex dynamics, particularly in the context of fluid mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant requests an explanation of vortex breakdown and its connection to swirl number, which is defined as the ratio of swirl to meridional motion strengths.
  • Another participant questions whether there are specific instabilities related to vortex breakdown beyond viscosity.
  • A participant mentions that vortex breakdown is characterized by a rapid change in the core radius of the vortex filament or tube, leading to a visible bubble or spiraling thread.
  • It is noted that the relationship between vortex breakdown and swirl number is established empirically, with various parameters such as capillary number, Reynolds number, and Rossby number potentially influencing this relationship.
  • One participant expresses unfamiliarity with the swirl number and references a resource, "Vortex Dynamics" by Saffman, while also highlighting the lack of a widely accepted theory for vortex breakdown.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding vortex breakdown and swirl number, with no consensus reached on the theoretical framework or empirical relationships involved.

Contextual Notes

Participants acknowledge the complexity of vortex dynamics and the potential for original contributions to the topic, indicating that existing literature may not fully address the empirical relationships or theoretical underpinnings.

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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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