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Old   August 12, 2010, 20:54
Default Laminar Model
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Danillo Cafaldo dos Reis
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Hi,

I want to know if when I set the turbulence model to laminar CFX will solve exactly the Navier Stokes Equations.
CFX user guide says:

"Laminar flow is governed by the unsteady Navier-Stokes equation. The laminar option does not apply a turbulence model to the simulation and is only appropriate if the flow is laminar"

So, the fact thar it doesn't apply a turbulence model means that the equation that is solved is the NSE?
It seems true, but could be false I think.

What I want to simulate is a Mixing Layer. I will start with a tangent hyperbolic profile and analyse its development until it gets turbulent, so I have a laminar flow.

I want to know what CFX does solve for this case.

Thanks
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Old   August 13, 2010, 06:13
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Glenn Horrocks
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Sounds like you need to read a basic CFD textbook. The laminar model is the Navier Stokes Equations, when you apply a turbulence model you then are talking about the Reynolds (or Fauve) averaged Navier Stokes equations. I recommend you read a CFD textbook to understand what the previous sentence is saying.

If your flow is laminar or just getting transitional a laminar model is probably OK. Sometimes you need the turbulence transition model, depends on the case. CFX supports both approaches.
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Old   August 13, 2010, 08:24
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Danillo Cafaldo dos Reis
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Thank you ghorrocks.

I'm starting my CFD study now I have a lot to learn.

I asked this because one told me that in CFX solver the laminar model was not implemented with the NSE but also with a RANS with such parameters that approximate the NSE.
Theoretically I know that laminar means NSE, without turbulence, but me question was how do the solver see this.

Regards
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Old   August 13, 2010, 15:28
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Joshua Counsil
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Off-topic, but I thought I'd let you know you have a very cool name, Mr. dos Reis.
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Old   August 14, 2010, 07:36
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Glenn Horrocks
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Quote:
I asked this because one told me that in CFX solver the laminar model was not implemented with the NSE but also with a RANS with such parameters that approximate the NSE.
I don't understand what you are saying here but when the laminar flow model is selected CFX does a numerical simulation of the Navier Stokes equations. When you select a Reynolds or Fauve averaged model it fires up the RANS. I have no idea what your friend is talking about.
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Old   August 16, 2010, 10:43
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Danillo Cafaldo dos Reis
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Ok Ghorrocks.
Thank you very much for your answer.

Thanks Josh.
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