|
[Sponsors] |
April 23, 2013, 07:47 |
Flat Terrain ABL problem
|
#1 |
Member
Davide
Join Date: Dec 2012
Posts: 33
Rep Power: 13 |
Hi all,
i'm new to openFoam; i have read the userguide and i've done the tutorials. I have started with a small simulation of a 2D flat terrain; i've managed to setup the Atmospheric Boundary Layer inlet condition. Basically i have modified the simpleFoam/turbineSiting tutorial, and i've reduced the turbulentKE because my simulation domain is small (1.65 m long, 0.24 m height). I'm puzzled about the results; as you can see in the picture, i've plotted the velocity profile at the inlet (dark red), mid section (green), outlet (cyan). In the horizontal axis there is velocity magnitude [m/s], in the vertical axis there is Height [m]. The velocity profile is somehow modified along the terrain, and i'm pretty sure it is wrong. What can i do to correct this issue? PS: In this link you can find the simulation... it is too big to upload it in the attachment. |
|
April 25, 2013, 03:08 |
|
#2 |
Member
Davide
Join Date: Dec 2012
Posts: 33
Rep Power: 13 |
please, anyone can help me?
|
|
April 30, 2013, 11:29 |
|
#3 |
New Member
ze
Join Date: Jan 2013
Posts: 1
Rep Power: 0 |
hi
I’ve just seen your thread and I've checked your case. I'm not sure, because i'm also new to openFoam, but i think your top conditions shouldn't be those of a symmetry plane...they should be equal to the inlet conditions...but that's my opinion and like I’ve said, I’m also new to openFoam. best regards |
|
April 30, 2013, 16:10 |
|
#4 |
Senior Member
Lieven
Join Date: Dec 2011
Location: Leuven, Belgium
Posts: 299
Rep Power: 22 |
Dear Davide,
What you see in the graph is the result of two things: 1. The log-profile is only the solution to the equations for a particular set of BC. E.g. at the top of the BC you should set a fixed shear stress and not a symmetry plane. 2. (the main reason) At ground level, the gradient of the velocity behaves strongly non-linear. When you apply e.g. linear interpolation to the velocity field, you will make a large numerical error. At higher altitudes, the gradient is smaller and this is less of a problem. Hence, the profile is mainly distorted at ground level. I would recommend you to read the following papers. The first one discusses (1) and the second one (2). If you implement the content of both papers in OF and rerun your simulation, you will get a perfectly logarithmic velocity profile. http://www.sciencedirect.com/science...6761050600136X http://onlinelibrary.wiley.com/doi/1...nticated=false Enjoy ;-) Lieven |
|
May 6, 2013, 08:52 |
|
#5 |
Member
Davide
Join Date: Dec 2012
Posts: 33
Rep Power: 13 |
Thank you guys.
@Lieven, those are really interesting papers, thank you!!! |
|
August 6, 2013, 09:11 |
|
#6 | |
Senior Member
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
Rep Power: 13 |
Quote:
Could you explain how do you implement a fixed shear stress on the top boundary condition in OpenFoam? Is is sufficient to impose a constant velocity (Ux equal to the inlet velocity at corresponding height)? Regards, Eloïse |
||
August 6, 2013, 09:15 |
|
#7 |
Senior Member
Lieven
Join Date: Dec 2011
Location: Leuven, Belgium
Posts: 299
Rep Power: 22 |
Hi Eloïse,
The fixedShearStress boundary condition is available in OF ;-). Imposing the velocity might work, and is physically "correct" in case of an open field with perfect numerics. But as soon as you have objects in your domain and numerical errors (due to discretization), it is not the right way to go. Cheers, Lieven |
|
October 20, 2019, 17:03 |
|
#8 | |
New Member
marco velazquez
Join Date: Aug 2019
Posts: 4
Rep Power: 6 |
Quote:
Hello Davide, I'm interested in your simulation, could you share it?, I'm trying to use turbine siting but after running "Allrun" script in paraview it doesn't work, velocity is always zero. thank you. Marco |
||
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
conduction problem | venkataramana | OpenFOAM | 3 | December 1, 2013 07:30 |
UDF compiling problem | Wouter | Fluent UDF and Scheme Programming | 6 | June 6, 2012 04:43 |
Problem Importing Geometry ProE to CFX | fatb0y | CFX | 3 | January 14, 2012 19:42 |
natural convection problem for a CHT problem | Se-Hee | CFX | 2 | June 10, 2007 06:29 |
Adiabatic and Rotating wall (Convection problem) | ParodDav | CFX | 5 | April 29, 2007 19:13 |