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praveen June 13, 2012 01:03

Carbuncle phenomenon for blunt body flow on unstructured grid
Roe scheme is known to suffer from carbuncle phenomenon for blunt body flows like hypersonic flow over a cylinder. I have seen numerical results on structured grids that exhibit carbuncle. But has anybody found this occurring on unstructured grids. I am trying mach=10 flow over a cylinder on triangular grids with first order Roe scheme without any entropy fix, and am unable to get any carbuncle. I know that it may not occur all the time; changing the grid can make it go away. But is there a reliable way to induce it on triangular grids.

SangeethCFD July 30, 2015 05:38

Carbuncle on unstructured - a gray area
Dear Praveen,

I have been studying numerical shock instabilities for over an year now. As such I have not come across any papers reporting or even attempting to produce carbuncle on unstructured grid. [1] suggests that carbuncle forms only on grids with preferred direction and any anisotropic grids (like unstructured) may not form it at al. However, [2] shows that a triangulated structured grid may produce carbuncle.

Sorry that the reply is so late. I happened to see you post only recently. Did you come across any such reports of carbuncle on unstructured grid since you posted?

[1] = 'Dissipative mechanism in Gudonov type schemes', IJNMF, 2001, vol 37
[2] = ' Nearly all speed, stabilized, time accurate upwind schemes on unstructured grid', AIAA, 2010, vol 48.

praveen July 30, 2015 10:11

I could not get carbuncle on purely unstructured grids. If you use structured grids which are triangulated, you may get carbuncle. As you said, the shock has to be aligned with the grid lines to see this.

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