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-   -   CEL expession for Cp in CFX-Pre (http://www.cfd-online.com/Forums/cfx/25332-cel-expession-cp-cfx-pre.html)

Farid February 28, 2008 14:18

CEL expession for Cp in CFX-Pre
 
Is it possible to write a CEL function or create a variable in CFX- Pre to get Cp distribution on any suface or body?

Glenn Horrocks February 28, 2008 17:25

Re: CEL expession for Cp in CFX-Pre
 
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

Farid February 29, 2008 09:54

Re: CEL expession for Cp in CFX-Pre
 
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.

CycLone February 29, 2008 10:48

Re: CEL expession for Cp in CFX-Pre
 
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

Farid February 29, 2008 11:13

Re: CEL expession for Cp in CFX-Pre
 
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"


CycLone February 29, 2008 12:39

Re: CEL expession for Cp in CFX-Pre
 
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


CycLone February 29, 2008 12:40

Re: CEL expession for Cp in CFX-Pre
 
(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


marco February 29, 2008 17:51

Re: CEL expession for Cp in CFX-Pre
 
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.


Rogerio Fernandes Brito February 29, 2008 18:25

Re: CEL expession for Cp in CFX-Pre
 
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?

Rogerio Fernandes Brito February 29, 2008 18:27

Re: CEL expession for Cp in CFX-Pre
 
Where is the link on the internet to make the download of OpenFOAM? Gracias!

marco February 29, 2008 19:03

Re: CEL expession for Cp in CFX-Pre
 
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

Rogerio Fernandes Brito February 29, 2008 21:37

Re: CEL expession for Cp in CFX-Pre
 
Are there the same features as cfx ???

marco March 1, 2008 08:43

Re: CEL expession for Cp in CFX-Pre
 
Much better features.

marco

Hekler March 1, 2008 10:28

Re: CEL expession for Cp in CFX-Pre
 
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.

Hekler March 1, 2008 10:34

Re: CEL expession for Cp in CFX-Pre
 
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.

Hekler March 1, 2008 10:37

Re: CEL expession for Cp in CFX-Pre
 
what problems do you have? I solve heat conduction problems in cfx all the time. It works great.

Rogerio Fernandes Brito March 1, 2008 16:13

Re: CEL expession for Cp in CFX-Pre
 
Could you show me your problem? Did u make a comparison with experimental data? what kind of mesh do u use?

Rogerio Fernandes Brito March 1, 2008 16:15

Re: CEL expession for Cp in CFX-Pre
 
There is no version of openfoam for Windows. What a shame!

HekLeR March 5, 2008 22:09

Re: CEL expession for Cp in CFX-Pre
 
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.

HekLeR March 5, 2008 22:13

Re: CEL expession for Cp in CFX-Pre
 
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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