Inviscid fluid flow past a square cylinder.

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Discussion Overview

The discussion revolves around the flow of an inviscid incompressible fluid past a square cylinder, exploring the challenges and characteristics of such flow compared to more commonly studied cases like circular cylinders. The scope includes theoretical considerations, simulation challenges, and the implications of sharp edges on fluid behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that while inviscid flow around a circular cylinder is well-studied, the flow around a square cylinder presents unique challenges due to sharp corners.
  • One participant mentions a forthcoming paper on viscous flow past a square cylinder, indicating that vortex shedding is more complex in that scenario compared to inviscid flow.
  • Another participant expresses concern that inviscid flow may produce vortices at the corners of a square cylinder, which contradicts the expectation that inviscid flow should not develop rotation spontaneously.
  • It is suggested that truly inviscid flow around sharp corners leads to nonphysical infinite acceleration, complicating the analysis and simulation of such flows.
  • A participant questions the relevance of studying inviscid flow around corners, suggesting it is far from physically realizable.
  • One participant seeks clarification on the concept of a square cylinder, indicating a need for further explanation of the topic.

Areas of Agreement / Disagreement

Participants express differing views on the implications of inviscid flow around sharp corners, with some highlighting the theoretical challenges and others questioning the relevance of the study. There is no consensus on the behavior of inviscid flow in this context.

Contextual Notes

Participants acknowledge limitations in current understanding, particularly regarding the behavior of inviscid flow at sharp edges and the potential for nonphysical results in simulations. The discussion does not resolve these complexities.

tarnhelm
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The flow of an inviscid incompressible fluid around a circular cylinder is commonly studied in fluid dynamics courses. There's a wikipedia article about it here: http://en.wikipedia.org/wiki/Potential_flow_around_a_circular_cylinder.

However, what about a square cylinder? There seem to be issues with simulating such flow across sharp edges or boundaries like the corners of squares. Can somebody tell me what you expect with such a scenario?
 
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Actually a colleague of mine is about to publish a paper in the Journal of Fluid Mechanics on the viscous flow past a square cylinder. It is a very similar flow field to a circular cylinder but te vortex shedding is more complex. I'd say keep an eye on JFM for it, but it will probably be a year before it is actually published.
 
Thanks for that. I think there's a lot of stuff out there about viscous flow past a square cylinder. However, inviscid flow presents a problem because it may be the case that vortices are produced at the corners, which I don't think should be the case in inviscid flow. At the very least, finite difference simulations seem to produce this effect. As I understand it, steady incompressible inviscid flow shouldn't spontaneously develop rotation like this. I'm wondering if anybody has any more info about it, because google isn't turning up much!
 
The problem is that a truly inviscid flow can turn around an arbitrarily sharp corner, which causes infinite acceleration of the fluid. This is clearly nonphysical. There isn't really a solution to this, which is why it is mostly ignored. If you decide to allow infinite acceleration, it would be qualitatively similar to the circular cylinder in terms of streamlines, but the corners would effectively be singularities in the flow. As for simulations, they have to have some inherent damping in order to converge, so they will never simulate truly inviscid flow.

Out of curiosity, why the interest in inviscid flow around corners? It's quite far from any physically realizable flow.
 
A square cylinder? Someone will have to explain what that means to me.
 

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