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CEL expession for Cp in CFX-Pre

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Old   February 28, 2008, 14:18
Default CEL expession for Cp in CFX-Pre
  #1
Farid
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Is it possible to write a CEL function or create a variable in CFX- Pre to get Cp distribution on any suface or body?
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Old   February 28, 2008, 17:25
Default Re: CEL expession for Cp in CFX-Pre
  #2
Glenn Horrocks
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Hi,

Yes. You can do it during the simulation by sending it to a additional variable or in post processing in CFX-Post. You would only do it in the simulation if you needed to use the variable in the simulation.

Glenn Horrocks
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Old   February 29, 2008, 09:54
Default Re: CEL expession for Cp in CFX-Pre
  #3
Farid
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Thanks Glenn.

I am trying to write CEL expression as areaInt(p)@airfoil. but it will give me just one value of pressure on the surface. i need pressure on each point of the airfoil.
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Old   February 29, 2008, 10:48
Default Re: CEL expession for Cp in CFX-Pre
  #4
CycLone
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areaInt(p)@airfoil returns the area integrated pressure over the entire airfoil region. If you want the local pressure, just use 'p' or 'Pressure'. Also keep in mind that this pressure is relative to the reference pressure you defined in your domain object.

-CycLone
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Old   February 29, 2008, 11:13
Default Re: CEL expession for Cp in CFX-Pre
  #5
Farid
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Thanks Cyclone.

I tried to write an expression as "Pressure@AIRFOIL" but the following error message was shown:

"Deprecated syntax detected at position 9 of expression:

"Pressure@AIRFOIL" Missing function call parentheses. This will be an error in future releases of the software. Successfully read 8 characters:

Pressure then error detected at:

@AIRFOIL"

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Old   February 29, 2008, 12:39
Default Re: CEL expession for Cp in CFX-Pre
  #6
CycLone
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When you write an expression, it is evaluated where it is used. Cp is the change in local pressure relative to the inlet dynamic pressure:

Cp = (p-p_inf)/(Dynamic_inf)

p_inf is the far field pressure and v_inf is the velocity of the wing. In CEL, just write:

Pinf = areaAve(p)@inlet Dynamic inf = massFlowAve(ptot-p)@inlet Cpres = (p-Pinf)/Dynamic inf

The above can be done in CFX-Post. To display Cp distribution on the airfoil, you first need to create a variable and set it equal to "Dynamic inf". Once you have your variable, plot it wherever you please.

-CycLone

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Old   February 29, 2008, 12:40
Default Re: CEL expession for Cp in CFX-Pre
  #7
CycLone
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(sorry, forgot the line breaks)

When you write an expression, it is evaluated where it is used. Cp is the change in local pressure relative to the inlet dynamic pressure:

Cp = (p-p_inf)/(Dynamic_inf)

p_inf is the far field pressure and v_inf is the velocity of the wing. In CEL, just write:

Pinf = areaAve(p)@ Dynamic inf = massFlowAve(ptot-p)@inlet Cpres = (p-Pinf)/Dynamic inf

The above can be done in CFX-Post. To display Cp distribution on the airfoil, you first need to create a variable and set it equal to "Dynamic inf". Once you have your variable, plot it wherever you please.

-CycLone

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Old   February 29, 2008, 17:51
Default Re: CEL expession for Cp in CFX-Pre
  #8
marco
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RANS modelling had its days and now LES is taking over. CFX is not a very good software for serious LES work. Considering the cost and limited features that CFX offers, is it still worth to work on such a software?

On the other hand OpenFOAM offers much more than CFX for both RANS and LES modelling and its absolutely free of charge. OpenFOAM results have proven to be much more accuarte than CFX results. When OpenFOAM is the future then why work on CFX. Why are you guys still using CFX and have you considered switching to OpenFOAM? comment please cyclone and Others.

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Old   February 29, 2008, 18:25
Default Re: CEL expession for Cp in CFX-Pre
  #9
Rogerio Fernandes Brito
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Caro Marco, eu estou tendo problemas no cfx para a simulação da transferencia de calor por condução. Esse programa que voce citou é bom para a solução da equação da difusão de calor?

Dear Marco, I am having problems in cfx for the simulation of the conduction heating transfer . Is this program that you mentioned good for the solution of the equation of the heat diffusion?
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Old   February 29, 2008, 18:27
Default Re: CEL expession for Cp in CFX-Pre
  #10
Rogerio Fernandes Brito
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Where is the link on the internet to make the download of OpenFOAM? Gracias!
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Old   February 29, 2008, 19:03
Default Re: CEL expession for Cp in CFX-Pre
  #11
marco
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Yes its excellent. www.openfoam.org is the link. It works much better on Linux though. I would recommend you burn an ISO image on a CD and install Linux first and then you can install OpenFoam. You will be amazed how good its solvers and other features are! You will end up regretting the time you wasted on CFX.

marco
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Old   February 29, 2008, 21:37
Default Re: CEL expession for Cp in CFX-Pre
  #12
Rogerio Fernandes Brito
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Are there the same features as cfx ???
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Old   March 1, 2008, 08:43
Default Re: CEL expession for Cp in CFX-Pre
  #13
marco
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Much better features.

marco
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Old   March 1, 2008, 10:28
Default Re: CEL expession for Cp in CFX-Pre
  #14
Hekler
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Because openfoam is a convoluted uninteligible piece of crap. Have you looked at the source code lately? Besides LES is not an industrial strength tool anyways.
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Old   March 1, 2008, 10:34
Default Re: CEL expession for Cp in CFX-Pre
  #15
Hekler
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like what? It doesn't even have a decent GUI, and you have to compile it yourself, and it has zero testing, there is nothing positive about it.
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Old   March 1, 2008, 10:37
Default Re: CEL expession for Cp in CFX-Pre
  #16
Hekler
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what problems do you have? I solve heat conduction problems in cfx all the time. It works great.
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Old   March 1, 2008, 16:13
Default Re: CEL expession for Cp in CFX-Pre
  #17
Rogerio Fernandes Brito
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Could you show me your problem? Did u make a comparison with experimental data? what kind of mesh do u use?
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Old   March 1, 2008, 16:15
Default Re: CEL expession for Cp in CFX-Pre
  #18
Rogerio Fernandes Brito
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There is no version of openfoam for Windows. What a shame!
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Old   March 5, 2008, 22:09
Default Re: CEL expession for Cp in CFX-Pre
  #19
HekLeR
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Try 1d conduction in a solid box. The answer is analytic. Is that not what you solve? Hopefully you do not need my setup for this.
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Old   March 5, 2008, 22:13
Default Re: CEL expession for Cp in CFX-Pre
  #20
HekLeR
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That's right.

Why don't you do it yourself. It's open source after all, therefore it must be the best thing ever.

If your lucky, someone may even pay you money to do it for them. To bad your income stream is gone when you merge your changes back to the central version.

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