
[Sponsors] 
November 14, 2013, 05:21 
Adding gravity in rotating domain

#1 
New Member
Join Date: Oct 2013
Posts: 21
Rep Power: 4 
Hello,
in my Oil/Air multiphase flow calculation with a rotating domain (only 1° is modeled) i want to add gravity in the radial direction z. The rotating axes is x. If I set the buoyancy model and use x=0 [m/s^2] y=0 [m/s^2] z=9.81 [m/s^2] the solver automatically counterrotates the relative Frame gravity vector and so the vector components y and z Change with the Rotation angle. How can i avoid this? Could i use a subdomain and define a momentum source in order to model the gravity? What do i have to add there? The unit is [Nm] best regards Thomas 

November 14, 2013, 07:01 

#2 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,545
Rep Power: 97 
If the domain in rotating in the X axis and gravity is along z then I cannot see how a 1° segment with periodic or symmetry conditions can model that. You are going to have to model the full 360°.
But to keep gravity pointing the same direction, you could use a momentum source, or you could just make the gravity vector a function of time. They both sound like they would work. 

November 14, 2013, 07:34 

#3 
New Member
Join Date: Oct 2013
Posts: 21
Rep Power: 4 
Hello Glenn,
i think gravity is the wrong word. In my rotational domain (which could be imagined as a rotational couette flow) I get a state where oil droplets are surrounded by air, so they hover in space with no velocity. With the additional body force I want to get them out of the Domain in the radial z direction. I still tried to make the gravity (buoyancy) vector as a function of time but the calculation is not exact because my rotational speed also changes with time. So what I have to add in the momentum source term to apply a Body acceleration in z? regards 

November 14, 2013, 17:35 

#4 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,545
Rep Power: 97 
I do not understand how gravity can be used to help in the strange situation you explain. But I do not need to understand, I will just answer your question
If your rotation changes with time then simply link the rotation of the gravity vector to the rotation speed. Isn't that the easiest approach? I think some tutorials use source terms  not sure which ones, have a look. 

November 21, 2013, 03:49 

#5 
New Member
Join Date: Oct 2013
Posts: 21
Rep Power: 4 
Thanks for your help! I will figure it out.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Not rotation of free surface in a rotating domain  matte_fole  Main CFD Forum  0  October 24, 2012 08:50 
rotating domain  mach000  CFX  2  April 19, 2010 10:52 
Counter rotating wall for rotating domain  melvin  CFX  0  February 4, 2008 05:51 
Difference b/t rotating wall and rotating domain?  Juno Kim  CFX  2  February 20, 2007 21:08 
A rotating solid domain in CFX551?  rotlin  CFX  2  January 7, 2003 06:59 