Laminar Model

danillocafaldo · August 12, 2010, 21:54

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

ghorrocks · August 13, 2010, 07:13

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.

danillocafaldo · August 13, 2010, 09:24

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

Josh · August 13, 2010, 16:28

Off-topic, but I thought I'd let you know you have a very cool name, Mr. dos Reis.

ghorrocks · August 14, 2010, 08:36

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.

danillocafaldo · August 16, 2010, 11:43

Ok Ghorrocks.
Thank you very much for your answer.

Thanks Josh.

August 12, 2010, 21:54	Laminar Model	#1
danillocafaldo New Member Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 17	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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August 13, 2010, 07:13		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

August 13, 2010, 09:24		#3
danillocafaldo New Member Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 17	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

August 13, 2010, 16:28		#4
Josh Senior Member Joshua Counsil Join Date: Jul 2009 Location: Halifax, Nova Scotia, Canada Posts: 366 Rep Power: 18	Off-topic, but I thought I'd let you know you have a very cool name, Mr. dos Reis.

August 16, 2010, 11:43		#6
danillocafaldo New Member Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 17	Ok Ghorrocks. Thank you very much for your answer. Thanks Josh.