How to apply a function as boundary condition

coompressor · January 13, 2009, 04:48

Dear Foamers,
I'm a newbie here. For my question, I want to add a function with time and circumferential position as the variables for the inlet boundary condition.
The study object is a circular ring and the inlet radius is R2 while the outlet one is R3. The inlet condition should be V2=V_mean+sin(Omega*t+phi), in which the Omega is the angular velocity and a constant in this expression. V_mean and phi (initial position) are also constants, t is the time for unsteady calculation. Can such kind of boundary condition be given? For fluent, this is very easy through using the UDF.
Thanks all.

vijayakumar · January 15, 2009, 04:49

i need to run a combustion problem.... i used XI-foam as solver, while running some errors are coming... i need to know which solver is good for combustion problem.. and few guidelines for solving combustion problem.

gschaider · January 15, 2009, 06:07

OK. Let's see: http://openfoamwiki.net/index.php/Ho..._Message_Board

You hit the points 1,2,3,5 and 7. Not a bad score. But it means it is very unlikely that you'll get an answer. No offense.

coompressor · January 15, 2009, 06:53

Ok, I'd like to use the DNS solver in OpenFoam 1.5.
Is this information clear?

ngj · January 15, 2009, 07:14

Hi Chuang

I am certain that Bernhard's comment was not minded on you, but on the person who hijacked the thread.

As a answer to your question, I cannot see any spatial variation in your boundary condition, thus you might be able to achieve what you are after by applying "timeVarying<something>". I am not at a OF-machine at the present, but you should be able to find it using the search function.

Best regards

Niels

gschaider · January 15, 2009, 15:47

Hi Chunag!

Niels is right. I meant the other poster. Sorry if I upset you

Bernhard

coompressor · January 15, 2009, 22:26

Hi, Niels and Bernhard,
If you plot the function I posted, it has nonuniform distribution along the circumferential direction. for a function, such as sin(n*theta) is a kind of flower function. theta is the circumferential coordinate. I've noticed a poster which talked about parabolic inlet boundary condition. But there do existed some differences. Can anybody give me a hint?

ngj · January 18, 2009, 16:03

Hi Chuang

There is not problem in specifying boundary conditions, which are varying both in space and time.

I you want to give a Dirichlet condition, then I would recommend you to find parabolicInlet-BC, which you will be able to find on this forum. This you should be able to modify to the purpose you are considering.

When you have implemented your own conditions just compile the BC using the wmake-procedure, link the BC to the solver of your choice, and you should be well off.

Good luck,

Niels

coompressor · January 19, 2009, 19:45

Hi Niels,
Thx for your kind help! I'll try it and post my results here.

Best Regards,
Chuang Gao

andrea · February 12, 2009, 11:22

Hi everybody,
I'm dealing with boundary condition as function of a calculated scalar fields. I think to derive it from a fixedValue bc. Someone have already done something similar?

January 13, 2009, 04:48	Dear Foamers, I'm a newbie	#1
coompressor New Member Chuang Gao Join Date: Mar 2009 Posts: 12 Rep Power: 17	Dear Foamers, I'm a newbie here. For my question, I want to add a function with time and circumferential position as the variables for the inlet boundary condition. The study object is a circular ring and the inlet radius is R2 while the outlet one is R3. The inlet condition should be V2=V_mean+sin(Omega*t+phi), in which the Omega is the angular velocity and a constant in this expression. V_mean and phi (initial position) are also constants, t is the time for unsteady calculation. Can such kind of boundary condition be given? For fluent, this is very easy through using the UDF. Thanks all.

January 15, 2009, 04:49	i need to run a combustion pro	#2
vijayakumar New Member VIJAYAKUMAR R Join Date: Mar 2009 Location: BANGALORE, KARNATAKA, INDIA Posts: 20 Rep Power: 17	i need to run a combustion problem.... i used XI-foam as solver, while running some errors are coming... i need to know which solver is good for combustion problem.. and few guidelines for solving combustion problem.

January 15, 2009, 06:07	OK. Let's see: http://openfoam	#3
gschaider Assistant Moderator Bernhard Gschaider Join Date: Mar 2009 Posts: 4,225 Rep Power: 51	OK. Let's see: http://openfoamwiki.net/index.php/Ho..._Message_Board You hit the points 1,2,3,5 and 7. Not a bad score. But it means it is very unlikely that you'll get an answer. No offense. __________________ Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

January 15, 2009, 06:53	Ok, I'd like to use the DNS so	#4
coompressor New Member Chuang Gao Join Date: Mar 2009 Posts: 12 Rep Power: 17	Ok, I'd like to use the DNS solver in OpenFoam 1.5. Is this information clear?

January 15, 2009, 07:14	Hi Chuang I am certain that	#5
ngj Senior Member Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Copenhagen, Denmark Posts: 1,903 Rep Power: 37	Hi Chuang I am certain that Bernhard's comment was not minded on you, but on the person who hijacked the thread. As a answer to your question, I cannot see any spatial variation in your boundary condition, thus you might be able to achieve what you are after by applying "timeVarying<something>". I am not at a OF-machine at the present, but you should be able to find it using the search function. Best regards Niels __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

January 15, 2009, 15:47	Hi Chunag! Niels is right.	#6
gschaider Assistant Moderator Bernhard Gschaider Join Date: Mar 2009 Posts: 4,225 Rep Power: 51	Hi Chunag! Niels is right. I meant the other poster. Sorry if I upset you Bernhard __________________ Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

January 15, 2009, 22:26	Hi, Niels and Bernhard, If	#7
coompressor New Member Chuang Gao Join Date: Mar 2009 Posts: 12 Rep Power: 17	Hi, Niels and Bernhard, If you plot the function I posted, it has nonuniform distribution along the circumferential direction. for a function, such as sin(n*theta) is a kind of flower function. theta is the circumferential coordinate. I've noticed a poster which talked about parabolic inlet boundary condition. But there do existed some differences. Can anybody give me a hint?

January 18, 2009, 16:03	Hi Chuang There is not prob	#8
ngj Senior Member Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Copenhagen, Denmark Posts: 1,903 Rep Power: 37	Hi Chuang There is not problem in specifying boundary conditions, which are varying both in space and time. I you want to give a Dirichlet condition, then I would recommend you to find parabolicInlet-BC, which you will be able to find on this forum. This you should be able to modify to the purpose you are considering. When you have implemented your own conditions just compile the BC using the wmake-procedure, link the BC to the solver of your choice, and you should be well off. Good luck, Niels __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

January 19, 2009, 19:45	Hi Niels, Thx for your kin	#9
coompressor New Member Chuang Gao Join Date: Mar 2009 Posts: 12 Rep Power: 17	Hi Niels, Thx for your kind help! I'll try it and post my results here. Best Regards, Chuang Gao

February 12, 2009, 11:22	Hi everybody, I'm dealing wit	#10
andrea Member Andrea Petronio Join Date: Mar 2009 Location: Trieste, Italy Posts: 43 Rep Power: 17	Hi everybody, I'm dealing with boundary condition as function of a calculated scalar fields. I think to derive it from a fixedValue bc. Someone have already done something similar?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to apply a function as boundary condition	coompressor	OpenFOAM Running, Solving & CFD	0	January 13, 2009 04:50
How can apply mass flow rate boundary condition?	Sima	Phoenics	1	December 1, 2007 19:55
Apply boundary condition functions	billy	OpenFOAM Pre-Processing	7	December 18, 2005 22:22
How to set a boundary condition as a function respect to time	chnrdu	OpenFOAM Running, Solving & CFD	2	June 17, 2005 05:18
Random function UDF for boundary condition	Chris	FLUENT	4	March 28, 2003 16:38