How to calculate pressure drop

Gearb0x · March 8, 2010, 08:34

Hello,

I have a channel solved with simplefoam and I would like to calculate the pressure drop ... How can I do that?

Thanks for the help

LVDH · March 8, 2010, 09:28

Hi,
after the calculations you have you calculate the total pressure.
Then you should calculate the average over the boundaries you are analyzing. I do not know how to automatically calculate the difference using openfoam utilities, so you will either have to write your own program to do this or use your calculator (or brain).
Here are the commands you need:

Code:

ptot
patchAverage ptot inlet
patchAverage ptot outlet

I assumed you named our boundaries "inlet" and "outlet".

Gearb0x · March 8, 2010, 10:01

Ok!!

Thanks a lot for the help

Gearb0x · March 10, 2010, 11:37

How does the patchAverage utily work? Is it mass flow weighted? Area weighted?

Thanks for the information

LVDH · March 11, 2010, 04:00

I am not sure.
but as far as I know the massflow is the phi-field. When you execute yPlus it calculates phi. When you execute patchAverage it does not. So I think one can say that the patchAverage utility does not use the massflow.

You could take a look into the source code. I do not have the time for that right now but it should be easy to understand.

LVDH · March 11, 2010, 04:34

Ok,
I took a look.
Its averaged over the area.

Gearb0x · March 13, 2010, 07:44

A big big thanks for the help!!
I've found something interesting on the wiki :

http://openfoamwiki.net/index.php/Co...unctionObjects

But I can't make it work. I don't know how to use it. Maybe I have to run the case to make it work and you cannot use a command tu run it after solving the problem ...

LVDH · March 15, 2010, 04:01

Hi,
that does sound very interesting indeed.
I will check it out later today.

March 8, 2010, 08:34	How to calculate pressure drop	#1
Gearb0x Member Jérémy Bulle Join Date: Nov 2009 Posts: 93 Rep Power: 5	Hello, I have a channel solved with simplefoam and I would like to calculate the pressure drop ... How can I do that? Thanks for the help

March 8, 2010, 09:28		#2
LVDH Member Andre Z Join Date: Dec 2009 Posts: 32 Rep Power: 5	Hi, after the calculations you have you calculate the total pressure. Then you should calculate the average over the boundaries you are analyzing. I do not know how to automatically calculate the difference using openfoam utilities, so you will either have to write your own program to do this or use your calculator (or brain). Here are the commands you need: Code: ptot patchAverage ptot inlet patchAverage ptot outlet I assumed you named our boundaries "inlet" and "outlet".

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March 8, 2010, 10:01		#3
Gearb0x Member Jérémy Bulle Join Date: Nov 2009 Posts: 93 Rep Power: 5	Ok!! Thanks a lot for the help

March 10, 2010, 11:37		#4
Gearb0x Member Jérémy Bulle Join Date: Nov 2009 Posts: 93 Rep Power: 5	How does the patchAverage utily work? Is it mass flow weighted? Area weighted? Thanks for the information

March 11, 2010, 04:00		#5
LVDH Member Andre Z Join Date: Dec 2009 Posts: 32 Rep Power: 5	I am not sure. but as far as I know the massflow is the phi-field. When you execute yPlus it calculates phi. When you execute patchAverage it does not. So I think one can say that the patchAverage utility does not use the massflow. You could take a look into the source code. I do not have the time for that right now but it should be easy to understand.

March 11, 2010, 04:34		#6
LVDH Member Andre Z Join Date: Dec 2009 Posts: 32 Rep Power: 5	Ok, I took a look. Its averaged over the area.

March 13, 2010, 07:44		#7
Gearb0x Member Jérémy Bulle Join Date: Nov 2009 Posts: 93 Rep Power: 5	A big big thanks for the help!! I've found something interesting on the wiki : http://openfoamwiki.net/index.php/Co...unctionObjects But I can't make it work. I don't know how to use it. Maybe I have to run the case to make it work and you cannot use a command tu run it after solving the problem ...

March 15, 2010, 04:01		#8
LVDH Member Andre Z Join Date: Dec 2009 Posts: 32 Rep Power: 5	Hi, that does sound very interesting indeed. I will check it out later today.