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-   -   inviscid 2d computation for M=0.3 flow past cylinder on fine mesh can not converge (http://www.cfd-online.com/Forums/main/86235-inviscid-2d-computation-m-0-3-flow-past-cylinder-fine-mesh-can-not-converge.html)

boubalos March 17, 2011 10:16

inviscid 2d computation for M=0.3 flow past cylinder on fine mesh can not converge
 
I try to use very fine mesh to test my Euler solver, however I get the following surprising results. I wish someone can give me a explain.

Both my solver and Fluent can get a correct result on a coarse mesh. The Mach contour shows symmetrical. wake is very weak.

Both my solver and Fluent can not get a correct result on a fine mesh. The Mach contour shows unsymmetrical, and wake is strong and long. Fluent even can not get a converged result!

The diameter of the cylinder is 2.0. The mesh is structured. The first layer mesh is 0.001 for fine mesh; and 0.02 for coarse mesh. Far field boundary is 40 times of the diameter away. And I am quite sure that my solver and Fluent is correctly setted.

boubalos March 20, 2011 02:27

Can't any one help me, on such a simple problem ...? :(

praveen March 20, 2011 03:41

Describe the numerical scheme, post pictures of grid, solution. Then somebody might be able to help.

Martin Hegedus March 20, 2011 05:26

The issue may be that a subsonic Euler solution has very little dissipation. When the solution starts up a high pressure compression zone will occur at the front and a low pressure expansion zone occurs at the back side. The solution will then oscillate between the front and the back. Eventually these oscillations may die down. Maybe. The solution methodology may keep it going. If you are just testing out your code by comparing it to Fluent you can run it at a Mach number high enough to get a shock. Maybe Mach 0.7. The shock will isolate the back from the front. But it still may take time to converge.


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