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Thank you for your concern. I did not work on it for past 4 days, as I had examinations. Today I tried again with your mesh. But it did not work. In your mesh what is the cylinder wall? The innermost circle should be cylinder, right? But the outermost concentric circles are taken as wall by FLUENT as your boundary conditions states that. You named them as "geom". Please clarify on that. Also I have very limited experimental data with me at reynolds number 30, 40 etc. I am comparing drag coefficient to validate my results. Experimental value of cd at Re=40 is 1.8, but I am getting 6.5. I am going terribly wrong with my circular domain (244X200). Any suggestions on how to get out this situation. I am using all default settings in solver while simulating this. Also, I never got vortices behind cylinder. Regards Mahindra |
That mesh has problems, you have just highlighted. Use the latest mesh http://www.4shared.com/rar/R7dSz2kw/...21_2012_2.htmlthere are no such walls in interior.
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But the problem I am facing is on convergence criteria. When I ran FLUENT with default value of 0.0001 as criteria, I did not get vortices. Then I changed it to 0.00001 to all residuals, which have me some encouraging results with vortices in wake region. When I disabled check convergence criteria, solution never converged even after 8000 iterations. But cd value got converged to 1.5329. Can you tell me how to approach this convergence criteria, I mean how to arrive at correct value?? Thank you |
For laminar flows I set the convergence criteria as (just out of habit)
1. If using absolute convergence criteria then 1e-18 2. Relative convergence (for transient flows) 1e-5 Quote:
My advise would be to study the convergence behavior and plot Cd as function of this criteria (make a graph in excel) so that you get idea what should be convergence criteria in your case. You are getting Cd as 1.5329 and experimental value is 1.8 (14% error), you need to refine the mesh further (in addition to above discussion) or some other parameters e.g. extent of domain on downstream side. PS. In Fluent 13 I usually setup the case for similar problems as : 1. Coupled pressure solver with Courant number 1e5 to 1e06 2. All schemes with 2nd order accuracy 3. Hybrid initialization or some times patch initialization (for transient case) |
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Thank you for your quick reply. I did all these simulations using your mesh and I think you made it in ICEM. Also I would like to know whether I can open that mesh in Gambit to make necessary changes. |
No. You can not edit this in gambit, you need ICEM for this.
But I can guide you to build similar mesh in gambit. Or if you need I can further refine this mesh and extend the domain and upload again. |
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Thanks |
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Also I can refine in steps of 1. Is it necessary to refine whole mesh or only selected elements? Thank You |
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Thanks |
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After making these chagnes, 1. go to pre mesh (left pan) 2. right click and update 3. Convert to unstructured mesh 4. Output mesh. |
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First going to blocking tab--> Pre Mesh Parameters--> Refinement There I am selecting the 8 blocks you have made around cylinder wall. Selecting refinement directions all. Still mesh is not getting refined, but I am getting result refinement done. Help me. Also while writing .msh file, what are options I have to choose, I mean Scaling factors, Write binary file etc Thanks |
since pre mesh is not visible in left pan, therefore you can not see the effect of refinmnet command. Turn on pre mesh and turb off shells in mesh. After refining the mesh, right click on premesh and update and convert to unstructured mesh. After that you can out put the mesh.
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1 Attachment(s)
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Also I am selecting the blocks around cylinder for refinement. Is it correct to do? Thanks |
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http://www.4shared.com/rar/dwx89ip_/...an29_2012.html
Download above files. I am facing this problem in icem: 1. I created two additional circles of dia 3 and 7 in order to make the blocking in the boundary layer and important flow regions (got highly orthogonal mesh) and associate two o-block edges to these circles and got pretty good mesh. But I got the walls in interior. Is there any method so that the temporary circles (wall) do not include in the final mesh? 2. When removed these circles, the above problem was resolved but when edited by mahi007 (later checked by myself) the pre-mesh is distorted. This is logical since there is no geometry where edges can be projected. 3. Again I have recreated the circles to associate two O-blocks and this time I set the boundary condition for these circles (walls) as interior in ICEM and did not get any wall in Fluent. But this time I got two interior zones. Is there any method so that I neither get the walls nor two interior zones. |
yeah this shows that results are still sensitive to mesh. Refine mesh further.
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Will it make any difference to results? Can you provide me with the mesh with above correction made? Thanks |
What is problem having two interior zones instead of one?
No problem, but this should not happen Will it make any difference to results? No Can you provide me with the mesh with above correction made? It is already uploaded in my previous post |
Mesh file is here. Same as previous one, no refinement.
http://www.4shared.com/rar/7Q6zQBgQ/fluent.html |
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Sorry, I mean I want entire project files, not only mesh. In previous post you attached does not have .uns files and most others. It has only 3 files which has all edges. I mean when I opened that in ICEM, I can only see edges you made. I want entire package after you made correction (Pre mesh distortion). Thanks |
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