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September 29, 2014, 05:34 |
residual for naca 4412 seem wrong
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#1 |
New Member
Daniel
Join Date: Sep 2014
Posts: 12
Rep Power: 11 |
hi
im doing a simulation for flow around airfoil NACA 4412. but the residual seem not going to be stable.it keeps going up and down. the residual for angle of attack -5,0 and 5 is stable.but for the -10,10 and 15 is like the pic given. is anyone can help me with this? |
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September 29, 2014, 17:48 |
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#2 |
Senior Member
Join Date: Nov 2010
Location: USA
Posts: 1,232
Rep Power: 24 |
While your residuals in magnitude seem high (this is probably related to the grid), the oscillations you see are probably the result of a transient phenomenon. Are you running steady-state? If so, residuals like this for a high angle of attack may be expected. Can you post images of your grid and give some information on the physics regime?
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September 30, 2014, 01:18 |
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#3 | |
New Member
Daniel
Join Date: Sep 2014
Posts: 12
Rep Power: 11 |
Quote:
-gradients -2D -segregated flow -steady -ideal gas -inviscid do you mean grid as the mesh?if so,here it is.. |
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October 1, 2014, 16:43 |
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#4 |
Senior Member
Join Date: Nov 2010
Location: USA
Posts: 1,232
Rep Power: 24 |
You're running the physics inviscid but it looks like you have a nice boundary layer mesh? Why is that?
What mach number is this at? |
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October 8, 2014, 05:01 |
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#5 |
Member
David
Join Date: Nov 2011
Posts: 39
Rep Power: 14 |
First of all, are the results good enough? say Cd,CL.
If the results are good than have a look at the absolute residuals value. If the absolute residuals value is small enough then don't pay too much attention to the residuals. |
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October 8, 2014, 06:32 |
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#6 | |
New Member
Daniel
Join Date: Sep 2014
Posts: 12
Rep Power: 11 |
Quote:
it was running with 3,000,000 reynolds number and that makes it as 43.81m/s as the velocity.. any suggestion?maybe i should do something else in physics or something.. |
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October 8, 2014, 06:35 |
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#7 |
New Member
Daniel
Join Date: Sep 2014
Posts: 12
Rep Power: 11 |
the results are not good enough apart from angle of attack -5,0 and 5.others than those are not.
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October 8, 2014, 06:44 |
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#8 |
Member
David
Join Date: Nov 2011
Posts: 39
Rep Power: 14 |
reduce your URF and see what happens.
BTW, did you use the same mesh for different AOA? Judging by your mesh, I suppose that you used the same mesh and changed the direction of incident wind, right? There is a tutorial in ccm+ help file which tells you how to use overset mesh to test the effect of AOA. (You do have to use overset mesh, however, you will have a brief idea about where you need more meshes.) Since you can get good result for some AOA, I would say it is caused by mesh most probably. |
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October 8, 2014, 07:26 |
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#9 | |
New Member
Daniel
Join Date: Sep 2014
Posts: 12
Rep Power: 11 |
Quote:
yes i am using the same mesh for different aoa.is it something wrong with it? where i can find the help file?if i may ask that |
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October 8, 2014, 07:32 |
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#10 |
Member
Join Date: May 2014
Posts: 30
Rep Power: 12 |
URF = Under Relaxation Factor
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October 13, 2014, 02:22 |
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#11 |
New Member
Daniel
Join Date: Sep 2014
Posts: 12
Rep Power: 11 |
i got the lift coefficient right, but why the drag coefficient seem wrong and quite different from the theoretical?
i used the direction in the report as (1,0,0) or should i change to another value? |
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