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Supersonic flow over flate plate

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Old   August 12, 2014, 10:03
Default Supersonic flow over flate plate
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Sazid Zamzl Hoque
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Hi everyone,
I am trying to model supersonic flow over flat plate in ansys fluent. I am using fluent for last two months only. I am finding difficult to give the outlet boundary condition in fluent. I applied the outflow boundary condition to outlet. but, it gives an error as I am using ideal gas as fluid.
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Old   August 12, 2014, 10:25
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Originally Posted by SAz_ID View Post
Hi everyone,
I am trying to model supersonic flow over flat plate in ansys fluent. I am using fluent for last two months only. I am finding difficult to give the outlet boundary condition in fluent. I applied the outflow boundary condition to outlet. but, it gives an error as I am using ideal gas as fluid.
Hey!
Outflow boundary condition is a special model!
It can not be used for compressible flow and you know every supersonic flow is compressible!
It can not be used with pressure inlet boundary condition!
You can find more details in ansys fluent user guide!
Good luck!
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Old   August 12, 2014, 11:12
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Thanks Mr. amin.z,
yeah I just got the information about outflow boundary condition. But I cannot figure out what are the actual boundary conditions that should be used in compressible flow over flat plate. The boundary conditions I have used are:
inlet : pressure inlet
outlet : pressure outlet
free stream : pressure far field
flat plate : wall
But the solution is not converging, are these boundary conditions correct?
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Old   August 12, 2014, 11:34
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Originally Posted by SAz_ID View Post
Thanks Mr. amin.z,
yeah I just got the information about outflow boundary condition. But I cannot figure out what are the actual boundary conditions that should be used in compressible flow over flat plate. The boundary conditions I have used are:
inlet : pressure inlet
outlet : pressure outlet
free stream : pressure far field
flat plate : wall
But the solution is not converging, are these boundary conditions correct?
For a supersonic flow is better to use "pressure inlet" or "mass flow inlet" for inlet faces and "pressure outlet" and "pressure far field" for outlet faces!
When you using "pressure far field", the outlet face must be far enough!
The convergence for supersonic flows usually need great iterations!
If divergence happens for your model, you must change the under relaxation factors (in pressure based solver) or Courant number (in density based solver) for stabling the solution!

Last edited by amin.z; August 12, 2014 at 13:22.
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Old   August 12, 2014, 14:11
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I tried changing the courant number and under ralaxation factor, but still the solution is diverging. If you give me a fluent file of the flow upto convergent it will be very helpfull for me.

Thank you
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Old   August 12, 2014, 14:46
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I don't understand your meaning dear!

Are your sure quality of your grid is ok and it's enough fine...!? It can be reason of divergence!
Also you must ensure that your initalization be close to your final results! It's very important for converging!

For 1 year, I worked on supersonic flow and convergent-divergent nozzles! I'm suggesting you: "For supersonic flow analysis you must be very patient! Because somitimes a small change in solution setup and B.Cs can diverge the solution!"
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Old   August 12, 2014, 14:56
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I used instructions to mesh the flow region from "Computational fluid dynamics: a practical approach" and I think the quality is fine. Anyway thanks a lot for your help.
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Old   August 17, 2014, 04:40
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I don't understand your meaning dear!

Are your sure quality of your grid is ok and it's enough fine...!? It can be reason of divergence!
Also you must ensure that your initalization be close to your final results! It's very important for converging!

For 1 year, I worked on supersonic flow and convergent-divergent nozzles! I'm suggesting you: "For supersonic flow analysis you must be very patient! Because somitimes a small change in solution setup and B.Cs can diverge the solution!"
h,
the solution is converged for the supersonic flow. But the solution is not correct. what will be the temperature for the plate? I know the Tinf (288.16 K).
And should I have to give back flow temperature in pressure outlet boundary condition?
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Old   August 17, 2014, 04:54
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h,
the solution is converged for the supersonic flow. But the solution is not correct. what will be the temperature for the plate? I know the Tinf (288.16 K).
And should I have to give back flow temperature in pressure outlet boundary condition?
Hey
What is the solution residuals? Supersonic flows usually need at least 1e-7 for convergence!
And do you increase courant number and under relaxation factors after solution convergence with small values of their!??

And if it's ok,check and ensure that BCs been ok! Be careful about "total" input values!
,
If you have backflow in outlet, of course it's better to set a logical value for its!
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Old   August 17, 2014, 14:09
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Hey
What is the solution residuals? Supersonic flows usually need at least 1e-7 for convergence!
And do you increase courant number and under relaxation factors after solution convergence with small values of their!??

And if it's ok,check and ensure that BCs been ok! Be careful about "total" input values!
,
If you have backflow in outlet, of course it's better to set a logical value for its!
My solution residuals are 1e-6. I think the total input values are not correct. Now the results are fine.
Thanks a lot amin.z .
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