Pressure distribution on a surface, numerical data

Bollonga · February 10, 2014, 09:47

Hi everybody,

I'm simulating the flow over an inclined flat plate and I would like to get the pressure distribution over the surface in numerical data, to work with it in Matlab.

How can I do it? Do I have to use a UDF to write the pressure data and each point coordinates at the desired timesteps? Is there any fluent tool to do that?

Thank you guys!

flotus1 · February 10, 2014, 10:11

Under "Calculation activities" in the Fluent GUI you can set up an automatic export.
Here you can choose the format of the exported file, the location of the data to be exported and the variables.
You can also specify a time step interval if you dont need the data from every time step.

Or you could record a macro where you export the data you want to transfer to matlab manually. Find this option in "calculation activities" -> "execute commands" -> "define macro".
Then you can record something like file -> export -> solution data

Bollonga · February 10, 2014, 10:19

Thanks a lot. I'll try the automatic export option as I'm not very used to macros.

How could I select the surface in which I want to get the pressure using the macro option?

flotus1 · February 10, 2014, 10:26

In the automatic export window, you get to select the surfaces for which you want to export the data. You will see what I mean once you opened the window.

Bollonga · February 10, 2014, 10:31

Quote:

Originally Posted by flotus1

In the automatic export window, you get to select the surfaces for which you want to export the data. You will see what I mean once you opened the window.

I was talking about the macro option, I guess a macro is like some text line commands recorded, right? And I would like to know how to select the surface following this approach, the automatic report approach is clear to me.

Thanks!

flotus1 · February 10, 2014, 10:51

I misread, sorry about that.

Giving it a second thought, I dont think that a macro is the best option for your application since it will overwrite the previous results.

Bollonga · February 11, 2014, 04:33

Just a question, Alex.

As I posted on this thread http://www.cfd-online.com/Forums/flu...o-surface.html I would like to compute forces on an iso-surface or a clip-surface which are not a named part. Is there a way to compute that force?

Thanks!

flotus1 · February 11, 2014, 05:06

I gave this a try, and apparently you can apply an automatic export to isosurfaces aswell.
Not sure how you want to define a force on a surface inside a fluid. Actually that seems to be the tricky part here.

Bollonga · February 11, 2014, 05:10

Quote:

Originally Posted by flotus1

I gave this a try, and apparently you can apply an automatic export to isosurfaces aswell.
Not sure how you want to define a force on a surface inside a fluid.

Okay, but it seems I cannot do it in the results/reports/forces option. I can only choose named selections there and it would be really usefull to be able to check forces on some unnamed areas.

flotus1 · February 11, 2014, 05:15

I am quite sure that the force on any surface element inside a fluid has to be zero because pressure and shear stress on both sides of the surface have to be equal.

Bollonga · February 11, 2014, 05:19

Quote:

Originally Posted by flotus1

I am quite sure that the force on any surface element inside a fluid has to be zero because pressure and shear stress on both sides of the surface have to be equal.

I mean forces on a wall surface that is part of a body. These shouldn't be zero.

flotus1 · February 11, 2014, 05:23

These are the forces on one side of the surface.
And if they are part of a boundary, you should be able to do any postprocessing you like within fluent.

Maybe we need a more concrete example on what you are trying to do.

Bollonga · February 11, 2014, 05:28

Quote:

Originally Posted by flotus1

These are the forces on one side of the surface.
And if they are part of a boundary, you should be able to do any postprocessing you like within fluent.

Maybe we need a more concrete example on what you are trying to do.

I have an inclined flat plate near the ground in an atmospheric flow. I'm computing Cd and Cl for the whole plate, but I would like to check the force or coefficient on just a corner or a specific area of the panel.

I guess this should be done in a post-process stage but I don't know how.

flotus1 · February 11, 2014, 05:41

I dont know how to get these forces from the force reports in fluent directly.
But what you can do is calculate the surface integral of shear stresses and pressure. This can be applied to clipped surfaces or isosurfaces.

February 10, 2014, 09:47	Pressure distribution on a surface, numerical data	#1
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	Hi everybody, I'm simulating the flow over an inclined flat plate and I would like to get the pressure distribution over the surface in numerical data, to work with it in Matlab. How can I do it? Do I have to use a UDF to write the pressure data and each point coordinates at the desired timesteps? Is there any fluent tool to do that? Thank you guys!

February 11, 2014, 04:33		#7
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	Just a question, Alex. As I posted on this thread http://www.cfd-online.com/Forums/flu...o-surface.html I would like to compute forces on an iso-surface or a clip-surface which are not a named part. Is there a way to compute that force? Thanks! Last edited by Bollonga; February 11, 2014 at 04:47. Reason: language correction

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February 10, 2014, 10:11		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	Under "Calculation activities" in the Fluent GUI you can set up an automatic export. Here you can choose the format of the exported file, the location of the data to be exported and the variables. You can also specify a time step interval if you dont need the data from every time step. Or you could record a macro where you export the data you want to transfer to matlab manually. Find this option in "calculation activities" -> "execute commands" -> "define macro". Then you can record something like file -> export -> solution data

February 10, 2014, 10:19		#3
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	Thanks a lot. I'll try the automatic export option as I'm not very used to macros. How could I select the surface in which I want to get the pressure using the macro option?

February 10, 2014, 10:26		#4
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	In the automatic export window, you get to select the surfaces for which you want to export the data. You will see what I mean once you opened the window.

February 10, 2014, 10:51		#6
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	I misread, sorry about that. Giving it a second thought, I dont think that a macro is the best option for your application since it will overwrite the previous results.

February 11, 2014, 05:06		#8
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	I gave this a try, and apparently you can apply an automatic export to isosurfaces aswell. Not sure how you want to define a force on a surface inside a fluid. Actually that seems to be the tricky part here.

February 11, 2014, 05:15		#10
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	I am quite sure that the force on any surface element inside a fluid has to be zero because pressure and shear stress on both sides of the surface have to be equal.

February 11, 2014, 05:23		#12
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	These are the forces on one side of the surface. And if they are part of a boundary, you should be able to do any postprocessing you like within fluent. Maybe we need a more concrete example on what you are trying to do.

February 11, 2014, 05:41		#14
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,428 Rep Power: 49	I dont know how to get these forces from the force reports in fluent directly. But what you can do is calculate the surface integral of shear stresses and pressure. This can be applied to clipped surfaces or isosurfaces.