CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Stirred tank Using MRF

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

Like Tree1Likes
  • 1 Post By ghost82

Reply
 
LinkBack Thread Tools Display Modes
Old   November 11, 2013, 05:55
Default Stirred tank Using MRF
  #1
New Member
 
Gurpreet
Join Date: Sep 2013
Posts: 16
Rep Power: 3
gurpreet89 is on a distinguished road
[LEFT]hi friends,
i am working on stirred tanks (baffled) with rushton turbine using multiple reference frame for my project work. I am very new to the fluent. i have made the geometry of stirred tank in designmodeler ,i have created an interface between the rotor(moving region) and fluid(stationary region). Now when i am rotating the fluid in contact with the impeller at 180 rpm, keeping the impeller and the outer fluid stationary i am getting the vector plots as given in pictures




as the fluid crosses the interface it changes its direction, why is it happening?? plz help
gurpreet89 is offline   Reply With Quote

Old   November 11, 2013, 08:09
Default
  #2
Senior Member
 
ghost82's Avatar
 
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 918
Rep Power: 15
ghost82 will become famous soon enough
Hi,
check your cell zones; assign to rotor zone absolute rotational velocity of xxx rpm; make stator zone stationary; in boundary conditions set shaft+impeller walls rotating at a relative rotational velocity of 0 rpm and to baffles/tank absolute velocity of 0 rpm.

PS: positive rotational velocity means conterclockwise rotation

Daniele
ghost82 is offline   Reply With Quote

Old   November 14, 2013, 03:26
Default thanks for the reply
  #3
New Member
 
Gurpreet
Join Date: Sep 2013
Posts: 16
Rep Power: 3
gurpreet89 is on a distinguished road
Actually there are many walls in my case in the 'boundary conditions' i dont understand which one is for rotor and which one is for baffle. i used display option to show those walls but it is not showing any. dont know whether there is any mistake in my geometry.

i iterated it for 1500 iterations but after around 1000 graph becomes constant.do i need to iterate more to get better results?

can you send me one of your example so that i can compare?
gurpreet89@gmail.com
gurpreet89 is offline   Reply With Quote

Old   November 14, 2013, 04:14
Default
  #4
Senior Member
 
ghost82's Avatar
 
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 918
Rep Power: 15
ghost82 will become famous soon enough
Then, turn back on your geometry and fix it.
An example of mrf is from Mr. Bakker,

Stirred tank flow field model

http://www.bakker.org/dartmouth06/engs199/

Daniele
ghost82 is offline   Reply With Quote

Old   November 16, 2013, 09:46
Default
  #5
New Member
 
Gurpreet
Join Date: Sep 2013
Posts: 16
Rep Power: 3
gurpreet89 is on a distinguished road
thanks for replying, i visited bakker's website. He is a very well known personality in the field of stirred tanks and CFD. i downloaded his one of the homework file 'pbt.msh.gc' . i imported that file then putted the same boundary and cell conditions as you told
in cell zone conditions - gave fluid-impeller the 'absolute' volcity of 30 rpm and kept fluid tank as stationary.
in boundary conditions - gave relative velocity 0 to the impeller and shaft, and 'absolute' velocity 0 to baffles and tank wall.

i used 'coupled' discretisation method and did hybrid initialization, result i am getting as below


above image is streamline view


contours (top view)


vectors

as in my case, the vectors inside the rotating zone are moving in opposite direction to the stationary zone. plz help
gurpreet89 is offline   Reply With Quote

Old   November 16, 2013, 09:52
Default
  #6
Senior Member
 
ghost82's Avatar
 
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 918
Rep Power: 15
ghost82 will become famous soon enough
Hi,
can you plot velocity in stn frame in cfd post?

Daniele
ghost82 is offline   Reply With Quote

Old   November 16, 2013, 10:41
Default
  #7
New Member
 
Gurpreet
Join Date: Sep 2013
Posts: 16
Rep Power: 3
gurpreet89 is on a distinguished road
yes ,now i am getting in the same direction
thank you very much
gurpreet89 is offline   Reply With Quote

Old   November 16, 2013, 10:54
Default
  #8
Senior Member
 
ghost82's Avatar
 
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 918
Rep Power: 15
ghost82 will become famous soon enough
Just for your info, when you plot velocity in stn frame you have velocity with regard to a stationary frame.
When you plot velocity you have velocity with regard to the moving frame.

Daniele
villager likes this.
ghost82 is offline   Reply With Quote

Old   May 14, 2014, 11:36
Default
  #9
New Member
 
solmaz aryafar
Join Date: Feb 2013
Posts: 11
Rep Power: 4
solmaz aryafar is on a distinguished road
Hello Daniele and gurpreet89,

First orf all thanks for the useful topic!

I have a question!!
I tried the same example as you were talking about above (pbt.msh.gz) , and I don't get the convergence at all. I used the same cell zone conditions and boundary conditions, and just one thing I'm not really sure about is the "direction of rotation" which I selected it to be (1 0 0), is that correct?
So why my solution doesn't converge???

Actually I tried this example, because I have the same problem with my own example, which is a stirred tank as well.
Please help me, I'm running out of time!

Thanks in advance,
Solmaz.
solmaz aryafar is offline   Reply With Quote

Old   May 17, 2014, 23:20
Default
  #10
New Member
 
Gurpreet
Join Date: Sep 2013
Posts: 16
Rep Power: 3
gurpreet89 is on a distinguished road
hi,

(1 0 0) means rotation about x-axis, similarly (010) fr rotation about y-axis and (001) about z-axis. If the shaft of the impeller is in X direction then take (100) but i think in that example the it was (001).

Gurpreet
gurpreet89 is offline   Reply With Quote

Old   May 20, 2014, 08:32
Default
  #11
New Member
 
solmaz aryafar
Join Date: Feb 2013
Posts: 11
Rep Power: 4
solmaz aryafar is on a distinguished road
Hello Gurpreet,

Thanks a lot for your answer! I guess now it's getting better, but no in that example the shaft was in the direction of x-axis

Look, I have a question here from you, because as I saw in the forum you work (or worked) on stirred tank simulations, am I right? So here I have a problem!

I created a mesh in Ansys Meshing for my stirred tank which have pitched blade impellers, and I used MRF approach, but I had issues in convergence, I mean the solution did not converge! As I showed the mesh to an expert (which I couldn't reach anymore unfortunately) he said that the quality of mesh is not good, and that I need to try Sliding Mesh approach. Then I researched a little bit in forumes, and also teh website of Prof. Bakker, and now it seems to me that I need to mesh the part arround the impellers with structured cells as the rest of the tank, am I right? so does it mean that I have to use sweep mesh for this part? I imagined like that, so I tried to mesh this part with sweep methos but the Ansys Meshing complains and says: "this part is not sweepable. So my question is that, I need to use ICEM instead of Ansys Meshing? I mean it's not possible to make sweep meshes arround a complex geometry (like the impellers) with Ansys Meshing?

I will appreciate your (or any one else's) help!

Solmaz.
solmaz aryafar is offline   Reply With Quote

Old   May 26, 2014, 10:33
Default
  #12
New Member
 
Gurpreet
Join Date: Sep 2013
Posts: 16
Rep Power: 3
gurpreet89 is on a distinguished road
hi,
what convergence criteria you are following, 10^-3 or 10^-4 ?
In my case, i was able to converge it to 10^-3 using ansys meshing and went closer to 10^-4. i made my rotor and baffles as structured but for fluid zone i used tetrahedral (unstructured).
may be your results are not converging due to some geometry issues, if you want your results to be very accurate with error less than 10- 5 % or so,then you can go for ICEM.
Results don't vary much either you use MRF or SM, lot of journals are there on the same.
gurpreet89 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
[GAMBIT] geometry and griding a stirred tank prec ANSYS Meshing & Geometry 12 May 22, 2014 12:46
[Design Modeler] Stirred Tank using MRF gurpreet89 FLUENT 2 October 6, 2013 14:02
Monitoring Convergence in Stirred Tank using MRF method GOPINATH87 Main CFD Forum 0 August 19, 2011 23:45
Stirred tank using MRF dishengbin FLUENT 14 March 13, 2011 23:11
CFX 5.5.1 stirred tank and LES problem Nishant CFX 2 September 13, 2002 07:11


All times are GMT -4. The time now is 09:00.