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-   -   CFX gravity driven free surface flow tutorial (http://www.cfd-online.com/Forums/cfx/66502-cfx-gravity-driven-free-surface-flow-tutorial.html)

mechovator July 17, 2009 02:33

CFX gravity driven free surface flow tutorial
 
Dear friends

I am working on water flow through dam. I want to simulate gravity driven free surface flowin the dam. but i am not able to find any tutorial related to the topic this is my email
mechovator@yahoo.com
can you kindly send me a tutorial about how to model a gravity driven free surface flow. It will be of great help to me.

Regards

Mechovator

michael_owen July 17, 2009 13:49

What about the free surface flow over a bump tutorial?

rogbrito July 17, 2009 22:01

The meshes are here:

http://www.4shared.com/file/65772301..._Mr_Brito.html

http://www.4shared.com/file/65770211..._Mr_Brito.html


Quote:

Originally Posted by michael_owen (Post 223062)
What about the free surface flow over a bump tutorial?


mechovator July 19, 2009 12:53

yes but that is not a gravoty driven flow... how will I model a multiphase gravtiy driven free surface that tutorial I need..... and to be more specific I have to add sedimentation effects... i.e. soil flow..... so kindly do tell me if you have any such tutorial. related to just gravity driven flow or sedimentation

Sher July 19, 2009 19:16

Free surface modeling
 
Hi mechovator,
I am also solving a similar problem as your on CFX 11. I am modeling a rectangular tank (a mini dam).

I am wondering how to model its free surface. If you have solved your problem then please advise me and also help me how to model its free surface, please

Rui July 20, 2009 09:08

Once again, see Tutorial 7 (Free Surface over a Bump).

If you have done this tutorial, I still don't understand where you are having difficulties! What don't you know how to do???
Try to ask more precise questions.

flattie July 20, 2009 18:45

Quote:

Originally Posted by mechovator (Post 223198)
yes but that is not a gravoty driven flow... how will I model a multiphase gravtiy driven free surface that tutorial I need..... and to be more specific I have to add sedimentation effects... i.e. soil flow..... so kindly do tell me if you have any such tutorial. related to just gravity driven flow or sedimentation

Being polite would help! Why is it so hard for the text-message generation to write a clearly written, polite question?

Remember,you are talking to engineers. Poor grammar, spelling and not even taking the time to capitalize a sentence shows you probably haven't taken the time to think the problem through either.

mechovator July 21, 2009 12:28

Ok i will when i will get the solution

mechovator July 21, 2009 12:54

Dear Rui. I went through your thesis. Learned alot from it. I have decided to model steady state water flow first. I have no interest in simulating the free surface, neither do I need its behavior. I just want to give free atmostpheric boundary condition (ambient pressure of 1 pa)to upper surface of the water like there are for inlet, outlet and wall etc. I went through the free surface tutorial.

mechovator July 21, 2009 12:58

Solution will be more appretiated than comments
 
Quote:

Originally Posted by Rui (Post 223310)
Once again, see Tutorial 7 (Free Surface over a Bump).

If you have done this tutorial, I still don't understand where you are having difficulties! What don't you know how to do???
Try to ask more precise questions.

Quote:

Originally Posted by flattie (Post 223374)
Being polite would help! Why is it so hard for the text-message generation to write a clearly written, polite question?

Remember,you are talking to engineers. Poor grammar, spelling and not even taking the time to capitalize a sentence shows you probably haven't taken the time to think the problem through either.

Dear flat

It would have been gr8 if u had a solution 2 the problem. Just :( commenting on the grammar without understanding the problem and giving no solution is like .....

Rui July 21, 2009 15:11

Ok.
I'm sorry to say this, if it is not your case, but recently there are a few people posting here that, to be honest, they seem to me to be just joking.
And, to be honest again, for their own good ... I hope they're.

ckleanth July 21, 2009 16:28

Quote:

Originally Posted by mechovator (Post 223504)
Ok i will when i will get the solution

mechovator, your tone is disgusting especially when trying to ask help from people for free. if one check your posts you have not contributed at all to this community and in most of your posts you continuously asking for someone to send you data/files/tutorials etc. You say you are a student and started an MS course, your university should had provided you with the software together with lectures/tutorials for you to study. I simply dont believe you and and I especially dont have time to spend for the likes of you, so I can tell you form now dont expect any help at least from me...

ghorrocks July 21, 2009 18:46

Ok everybody, let's get back to the topic. I think the point has been made so let's move on.

If you want a simple model of the free surface then won't a opening set at atmospheric pressure do the trick? A bit of flow will go in and out but if you don't care about that then it sounds pretty simple. It might be a convergence issue as pressure boundaries don't like flow going in/out at angles - I think the entrainment condition may help here but I have never used that option so can't be sure.

Glenn Horrocks

Sher July 21, 2009 19:48

Free surface modelling IN CFX 11
 
Hi everybody and specially RUI,

First of all I would like to thanks Rui for his/her great contribution to this community on this forum.

I am modeling a free surface problem and according to the suggestion of most of the ppl on this forum I tried Tutorial 7 But I could not successfully apply to my rectangular tank which I am modelling on CFX 11.

My Boundary conditions are as:
Inlet = Inlet with VolFair = 0, VolFwater=1

outlet= outlet with static pressure = uppres=
density of water*g*VolFwater(upH-y)
Top=opening with VolFair=1 and VolFwater=0 and static pressure=0
others BC are walls.

If I model outlet as a outlet, then solver gives a message that 100% area at outlet is covered by a wall and if I model outlet as opening then the flow becomes reverse (from outlet towards inlet.).

Please somebody help me in this regards.

Specially I would expect to hear from Rui.
Cheers

ckleanth July 21, 2009 21:08

sher, without posting the domain and expressions ccl thre's little to say really. for example you didnt define what is your physical representation of your inlet and outlet perhaps a drawing and the model ccl?.

from what you wrote one would assume that for your inlet you have only water.. obviously the model depends on what your geometry is, however if I was to model a dam, air velocity and the effect of air to the water flow would be negligible therefore can be regarded as zero. if this is the case you have, you need to think how to express this relations as an inlet boundary

the top boundary can also be modeled as a simple free slip condition.

from what you said the outlet definition is wrong, you have forgotten to include the air in your hydrostatic relations. check again the said tutorial, most of your answers are there.

Sher July 22, 2009 01:50

Free surface modeling in CFX
 
Thanks ckleanth for your reply on my problem,
Can you please advise me how to post the .ccl file and the geometry. Actually I am new on this forum and need your help to know how I will make attchments.

Thanks

mechovator July 22, 2009 01:58

My tone will be like that if some one does not help and just comment. Not helping is one thing and commenting and being personal is another and you should also avoid that mr. You did the same thing. Elders should behave like elders. It's not that you can help or not or you don't want to. It's the way you are talking to a person. Morality and self respect is much more to me than grammar and profession.

mechovator July 22, 2009 02:01

Thank you ghorrocks. Am trying to refine mesh these days and will surely contact you when i again get back to boundary conditions.

ckleanth July 22, 2009 04:34

Quote:

Originally Posted by Sher (Post 223580)
Can you please advise me how to post the .ccl file and the geometry...

in pre click on file>export and choose the parameters you want to export (for example the domain physics, expressions, initial conditions and any other information that you think it would be necessary for people to know so they can help)
in this forum you could also attach pictures or screenshots and zip files (in which you could attach a small 2D cfx or def file - I think there is a limit on the size you can attach though)

Sher July 22, 2009 07:20

1 Attachment(s)
Quote:

Originally Posted by ckleanth (Post 223609)
in pre click on file>export and choose the parameters you want to export (for example the domain physics, expressions, initial conditions and any other information that you think it would be necessary for people to know so they can help)
in this forum you could also attach pictures or screenshots and zip files (in which you could attach a small 2D cfx or def file - I think there is a limit on the size you can attach though)

Hi Ckleanth,
So many thanks for your help.I have uploaded the .CCL file of my CFD problem. Actually I am modelling a rectangular pond which have circular Inlet and Outlet at opposit ends. I am using CFX11 to model its hydrodynamics and want its top to model as free surface. I have again studied tutorial 7 and it seems that my expressions are according to that tutorial. But the flow pattern that I got is amazing and beyond the true pattern. Can you please advise me that what should i change in my .ccl file to get a good result. Also, I will appreciate your help if you please advise me how can I make my mesh a structural mesh. The previous mesh which I use is the mesh which CFX11 give us bydefault.

I again thanks for your so nice advice and help.

Cheers


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