free-surface model

antonio · January 14, 2010, 07:01

Hi all.

I started recently to work with CFX. I am trying to implement a free-surface model.

I have already defined the geometry and the mesh. When I was defining the geometry I used the slice operation in order to have different types of meshes for air and water. However when I set the mesh I found that I could have a very good global mesh (for air and water) using exactly the same mesh (Tetrahedrons elements with Patch Independent Algorithm).

At the present moment I have launched the CFX-Pre. My main questions are (I am following the tutorial "free surface flow over a Bump"):
1) When I am creating the domain I`m giving the basic settings for air and basic settings and fluid models for water. However when I check their features in the "Automatic Default Domain " CFX assumes equal settings for air and water...

2) How can I define periodic boundary conditions?Basically I just want to give to the model the water height and the inclination of the bed and I want that the model compute the discharge...
Many thanks

stumpy · January 14, 2010, 09:48

1. Follow the tutorial again. You should only have 1 domain that contains 2 fluids, rather than 2 domains with 1 fluid each
2. The water height is part of the solution, you cannot specify it (expect at inlet boundaries).

antonio · January 14, 2010, 10:33

Dear Stumpy:

Thanks a lot for your suggestions. Just one more question. Should I review the mesh that I have created or can I transform in CFX-pre the mesh in order to have just a single domain?

Regards.

stumpy · January 14, 2010, 12:09

You can have a single domain containing both pieces. However, the mesh would need to match (i.e. not a GGI) since GGI's can have problems when aligned to a free surface.

fab · February 9, 2010, 17:40

hello everybody, i´m modelling the free surface too
i have the following problem:
the bottom should have 2 different temperatures! how i can make it with the if -function?
my bottom is 40 mm on the length.so how how can i declare it on the middel of the bottom without having a temperature-switch?it should be 25[C] left and 30[C] right from the middel!
maybe with a linear function?
thank u

zandi · February 16, 2010, 03:21

Quote:

Originally Posted by stumpy

2. The water height is part of the solution, you cannot specify it (expect at inlet boundaries).

but we can specify it
in cfx 11 see tutorial 7 bondary detail for inlet and Creating Expressions part
and instead of normal velocity in inlet select static pressure and put UpPress function for value
i think it works

January 14, 2010, 07:01	free-surface model	#1
antonio Senior Member Join Date: Jan 2010 Posts: 110 Rep Power: 5	Hi all. I started recently to work with CFX. I am trying to implement a free-surface model. I have already defined the geometry and the mesh. When I was defining the geometry I used the slice operation in order to have different types of meshes for air and water. However when I set the mesh I found that I could have a very good global mesh (for air and water) using exactly the same mesh (Tetrahedrons elements with Patch Independent Algorithm). At the present moment I have launched the CFX-Pre. My main questions are (I am following the tutorial "free surface flow over a Bump"): 1) When I am creating the domain I`m giving the basic settings for air and basic settings and fluid models for water. However when I check their features in the "Automatic Default Domain " CFX assumes equal settings for air and water... 2) How can I define periodic boundary conditions?Basically I just want to give to the model the water height and the inclination of the bed and I want that the model compute the discharge... Many thanks

February 9, 2010, 17:40	temperature on the botttom	#5
fab New Member Join Date: Jun 2009 Posts: 13 Rep Power: 5	hello everybody, i´m modelling the free surface too i have the following problem: the bottom should have 2 different temperatures! how i can make it with the if -function? my bottom is 40 mm on the length.so how how can i declare it on the middel of the bottom without having a temperature-switch?it should be 25[C] left and 30[C] right from the middel! maybe with a linear function? thank u

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January 14, 2010, 09:48		#2
stumpy Senior Member Join Date: Apr 2009 Posts: 417 Rep Power: 10	1. Follow the tutorial again. You should only have 1 domain that contains 2 fluids, rather than 2 domains with 1 fluid each 2. The water height is part of the solution, you cannot specify it (expect at inlet boundaries).

January 14, 2010, 10:33		#3
antonio Senior Member Join Date: Jan 2010 Posts: 110 Rep Power: 5	Dear Stumpy: Thanks a lot for your suggestions. Just one more question. Should I review the mesh that I have created or can I transform in CFX-pre the mesh in order to have just a single domain? Regards.

January 14, 2010, 12:09		#4
stumpy Senior Member Join Date: Apr 2009 Posts: 417 Rep Power: 10	You can have a single domain containing both pieces. However, the mesh would need to match (i.e. not a GGI) since GGI's can have problems when aligned to a free surface.