CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Atmospheric boundary layer

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   June 13, 2010, 06:55
Default Atmospheric boundary layer
  #1
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Hi
I try to simulate an atmospheric boundary layer, on bottom I use wall function, but if i use nutRoughWallFunction, epsilon has a overshooting in last cells why?

Best Regards
Attached Files
File Type: pdf eps.pdf (3.8 KB, 316 views)
Daniele111 is offline   Reply With Quote

Old   June 14, 2010, 05:57
Default
  #2
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
Hi,

the overshooting is a known problem! Look for example here:
http://www.openfoamworkshop.org/2009...ner_slides.pdf

What Version of OpenFOAM are you using? I think, there have been some problems with the nutRoughWall-Condition in OpenFOAM 1.6! So, you should use OpenFOAM 1.6.x!!

Hope, that helps!
farbfilm is offline   Reply With Quote

Old   June 14, 2010, 06:05
Default
  #3
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Hi
I read this paper, useful. But the problem is openfoam 1.6! I use now wall function of 1.6.x and I haven't overshooting problem,thanks you
Daniele111 is offline   Reply With Quote

Old   June 14, 2010, 11:58
Default
  #4
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
using openfoam 1.6.x the overshooting there isn't; but I Have another problem: in atmospheric boundary layer simulation, th wall value of epsilon and k would be costant? In my simulation these value are constant only after some cells along x axis Why?
Attached Files
File Type: pdf fig.pdf (3.8 KB, 162 views)

Last edited by Daniele111; June 15, 2010 at 05:16.
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 05:04
Default
  #5
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Hi
What are the correct boundary conditions for p field in these simulation?

Thanks
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 05:05
Default
  #6
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
What is x?? Is it the height of your domain or the main flow direction??
farbfilm is offline   Reply With Quote

Old   June 15, 2010, 05:13
Default
  #7
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Main flow direction, change inlet p condition:
Attached Files
File Type: pdf wss.pdf (3.5 KB, 197 views)
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 05:29
Default
  #8
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
Sorry, I don't understand what Wss means...
I've chosen a "zeroGradient"-condition for my ABL-Simulations at the inlet for p!

To achieve a homogenous ABL (constant values in flow direction), you have to calculate the right Ks (and Cs) in subject to your z0 (conversion of z0 to Ks due to your roughWallBC)!

Hope, that helps...
farbfilm is offline   Reply With Quote

Old   June 15, 2010, 05:32
Default
  #9
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Wss, is wall shear stress, my z0 is 0.001, Ks=0.02, Cs=0.5 it's wrong?

Thanks you!
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 05:36
Default
  #10
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
My Bc. Thanks you again
Attached Files
File Type: gz bc.tar.gz (1.0 KB, 149 views)
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 05:42
Default
  #11
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
I'm getting a value of 0.019586! Almost the same...

I've used the formula:
Ks = E*z0/Cs where E=9.793 is a constant of the wall function!
farbfilm is offline   Reply With Quote

Old   June 15, 2010, 05:47
Default
  #12
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
My Ks=20*y0, but where is th mistake? Your Cs=0.5? E in your simulation epsilon, k are constant in the first cell along main flow direction, my x-axis?
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 05:52
Default
  #13
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
I think, the velocity at the bottom should be zero (no slip condition)!

Unfortunately, I don't have any experiences with the timeVaryingMappedFixedValue-BC! So, I can't help with this! I used the GroovyBC for the analytical profiles!

Maybe, you should define the constants of the wall function in the nut-file! Just to be sure, you use the same like in your conversion from z0 to Ks! Actually, Cs is 0.327 in your BC's and not 0.5 like you mentioned before!
farbfilm is offline   Reply With Quote

Old   June 15, 2010, 06:01
Default
  #14
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
I just use groovyBc, timeVaryingMappedFixedValue-BC is not the problem, it's the same thing. I don't understand when you say that I would define the constants of the wall function in the nut-file. What do i do this? The velocity at the bottom has a value becouse I use like reference a paper that imposed it, but I pose it 0 and the problem there is. The p bc is the same that you have?
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 06:48
Default
  #15
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
Yes, p BC is the same!!
farbfilm is offline   Reply With Quote

Old   June 15, 2010, 15:02
Default
  #16
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Hi
Bah I try to use absurd values of Ks and Cs, but the result is always the same; I copied the turbulenceModels folder of OpenFOAM 1.6.x and I copy it in src folder of OpenFOAM 1.6 and the I compile it. It's wrong? Because if I change ks and cs not change the result?
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 16:01
Default
  #17
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Can i see your bc?
Daniele111 is offline   Reply With Quote

Old   June 15, 2010, 17:36
Default
  #18
Member
 
Michael
Join Date: Mar 2009
Posts: 48
Rep Power: 8
farbfilm is on a distinguished road
Hi,

sure! Here are my BC's! I definitely get a change when I use different values for Ks (see the picture)!

Hope that helps! Why do you want to simulate an ABL? What is the topic of your project??
Attached Images
File Type: png velocity.png (4.1 KB, 182 views)
Attached Files
File Type: gz BC.tar.gz (12.0 KB, 145 views)
farbfilm is offline   Reply With Quote

Old   June 15, 2010, 17:53
Default
  #19
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
Thank you! I must simulate sand dune evolution. So I would calculate shear stress at bottom. Thank you again
What are these fields in your groovy bc?

refValue uniform 0;
refGradient uniform 0;
valueFraction uniform 1;
value uniform 0.1;
valueExpression "para";
gradientExpression "0";
fractionExpression "1";

Last edited by Daniele111; June 15, 2010 at 18:18.
Daniele111 is offline   Reply With Quote

Old   June 16, 2010, 05:08
Default
  #20
Senior Member
 
Daniele
Join Date: Feb 2010
Posts: 134
Rep Power: 7
Daniele111 is on a distinguished road
I try to use your bc setup, but the velocity field along main flow is these. It's correct? What is your first cell higth? My domain is higth 100m
Attached Files
File Type: pdf U.pdf (5.2 KB, 171 views)

Last edited by Daniele111; June 16, 2010 at 07:20.
Daniele111 is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wind turbine simulation Saturn CFX 34 October 16, 2014 05:27
Turbulent Boundary Layer on a Flat Plate Hoshang Garda FLUENT 1 November 27, 2013 11:24
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 05:05
Combining BCs: wall - outlet. Boundary layer disappears MartinaF OpenFOAM Running, Solving & CFD 1 July 20, 2009 18:14
Convective Heat Transfer - Heat Exchanger Mark CFX 6 November 15, 2004 16:55


All times are GMT -4. The time now is 06:41.