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

twoPhaseEulerFoam - weird behaviour

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 23, 2012, 07:13
Default twoPhaseEulerFoam - weird behaviour
  #1
Member
 
Join Date: Nov 2010
Posts: 41
Rep Power: 15
grjmell is on a distinguished road
To check some funcitonality of twoPhaseEulerFoam, I went back to basics and tried to do something really "simple". What i wanted to do is a box, with a layer of solids at the bottom, and above that just water. No inflow/outflow, just fluid at rest with sediment at the bottom of the box. I was expecting to see nothing happening. But velocities developed in the flow, out of nowhere.
I then tried removing the sediment, having just water in a box, no inflow/outflow. And again, some weird velocities develop. I have turned all turbulence etc.. off. I have tried buoyantPressure and zeroGradient BCs for pressure, and although the results are different, both result in some velocity in the box (see image, for t=1s). Have also tried an open boundary at the top but that didnt help either.
I have attached the case without sediment (however you can use the setFields file to add solids to the domain). I don't understand why the model is performing that way , I couldnt find a problem in my set-up, but if someone could check or explain i'd be very grateful.
Attached Images
File Type: jpg 1_visAll.jpg (26.1 KB, 77 views)
Attached Files
File Type: zip Box0a.zip (16.9 KB, 7 views)
grjmell is offline   Reply With Quote

Old   February 23, 2012, 09:10
Default
  #2
Member
 
Rob
Join Date: Sep 2011
Posts: 55
Rep Power: 14
robbirobocop is on a distinguished road
Having a look at your boundary conditions it can be seen that the top is opened by assigning a pressure with a fixedValue there.

Thus, a pressure field is calculated as can be seen in the second picture of the first line. Consequently, a flow movement occurs and velocity is build.

In a nutshell, with your assigned fixedValue for the pressure at the top you initialise the velocity field and thus, it does not come out of the blue for no reason.

In order to change that, you might work with a reference pressure inside your box and assign buoyantPressure to the top. I do not know if it will change anything since I usually do not simulate closed boxes
robbirobocop is offline   Reply With Quote

Old   February 23, 2012, 09:47
Default
  #3
Member
 
Join Date: Nov 2010
Posts: 41
Rep Power: 15
grjmell is on a distinguished road
Ok I understand what you mean now. Can you explain what in a little more detail the bit with reference pressure please, and how id try to set it up...?
grjmell is offline   Reply With Quote

Old   February 23, 2012, 10:07
Default
  #4
Member
 
Rob
Join Date: Sep 2011
Posts: 55
Rep Power: 14
robbirobocop is on a distinguished road
Inside the fvSolution file that is inside your case/system directory, there are two entries for the reference pressure.

pRefCell and
pRefValue

For the first entry you must enter coordinates in x,y and z direction, the second one specifies the value, e.g. 1e05 for ambient pressure.

Thus, the entries would be like:

pRefCell (0 1 0);
pRefValue 1e05;
robbirobocop is offline   Reply With Quote

Old   February 28, 2012, 07:42
Default
  #5
Member
 
Join Date: Nov 2010
Posts: 41
Rep Power: 15
grjmell is on a distinguished road
Hi Rob,
Thanks for your help so far. I have implemented the pressure as suggested (i've attached the case with updated bcs), and it works (see 1st pic) probably as good as it ever will, only very small velocities is developed. it also works well for a flow-condition, e.g. moving lid. the same set-up however does not work once i add solids fraction, again weird things happen (see pic 2).
I'm not sure whether the BCs with a solid fraction need to be different then when you run it without solids? but it doesnt seem logical for that to be the case. anyway, i have tried with various different boundary conditions and i cant get it to work. any ideas?
Attached Images
File Type: png noFlownoSed.png (37.6 KB, 40 views)
File Type: jpg noFlowSed.jpg (28.6 KB, 49 views)
Attached Files
File Type: zip Box2.zip (19.8 KB, 6 views)
grjmell is offline   Reply With Quote

Old   May 22, 2012, 05:07
Arrow reference to similar post
  #6
New Member
 
Lydia Schulze
Join Date: Jan 2012
Location: Karlsruhe, Germany
Posts: 20
Rep Power: 14
Lydia is on a distinguished road
Hello Foamers,

I just found this post, which is pretty similar to the one i recently started. If someone has similar problems, i recommend to have a look at the following post:

http://www.cfd-online.com/Forums/ope...behaviour.html

Alberto Passalacqua has given some good references for this topic here.

Best regards,
Lydia
Lydia is offline   Reply With Quote

Reply

Tags
twophaseeulerfoam

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
strange pressure behaviour with symmetricPlane boudary condition - interFoam duongquaphim OpenFOAM Running, Solving & CFD 10 August 20, 2013 15:00
Something wrong in UEqns.H within twoPhaseEulerFoam cheng1988sjtu OpenFOAM 2 June 24, 2011 11:48
twoPhaseEulerFoam freemankofi OpenFOAM 0 May 23, 2011 17:24
Unstable behaviour after long period of stablility plunge11 FLUENT 1 April 6, 2011 10:15
Modelling Industrial cyclone behaviour Günther Hasse Main CFD Forum 3 October 12, 1999 20:34


All times are GMT -4. The time now is 07:46.