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

Single Rotating Domain

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 22, 2009, 07:24
Default Single Rotating Domain
  #1
Member
 
DT
Join Date: May 2009
Location: Lisbon
Posts: 37
Rep Power: 16
fluentnoob is on a distinguished road
Hi everyone!

I was trying to model a rotating domain shaped like the region in between two concentric cylinders. Here is a picture of the domain.
http://picasaweb.google.co.in/lh/pho...eat=directlink

I tried setting the inlet boundary condition as mass flow inlet and outlet as pressure outlet. And I'm rotating the domain about an axis along the +ve Y direction, and passing through the center of the cylinders. And the pressure distribution I expected was concentric isobaric lines throughout the domain. But I cannot seem to get this distribution from the boundary conditions I have set. Can you please help me out with the kind of boundary conditions I am supposed to use?

I specified the fluid domain as rotating reference frame with and angular velocity of 0.1 rad/s, specified the mass flow rate as 4.01e+06 kg/s. The rotation axis origin as X=-100, Y=0, Z=0. Rotations axis direction as X=-100, Y=1, Z=0.The dimensions of the inlet and the outlet are 20mx20m.
And specified the static pressure as zero at the pressure outlet.

Can you please tell me what am I doing wrong?

Thank you very much.
fluentnoob is offline   Reply With Quote

Old   June 22, 2009, 13:34
Default
  #2
Member
 
DT
Join Date: May 2009
Location: Lisbon
Posts: 37
Rep Power: 16
fluentnoob is on a distinguished road
OK. I found that I was specifying the rotation axis direction incorrectly. I specified it as [0 1 0] and got the isobaric pressure lines as expected. But something is still wrong. The velocity profile on the side walls is as expected, highest on the wall with the smaller radius, and more on the wall with the larger radius. But away from the walls, the velocity profile goes awry. Have a look at this please...
http://picasaweb.google.co.in/lh/pho...eat=directlink
Can you please please help me out? What am I doing wrong? Why is the velocity profile on the Inlet so different? Why doesnt it vary like (omega*R)? That is, increase as the radius increases (It is increasing, but as you can see in the pic, in a very strange fashion)? Please please please help me out. Thank you.
fluentnoob is offline   Reply With Quote

Old   June 23, 2009, 07:20
Default
  #3
Member
 
DT
Join Date: May 2009
Location: Lisbon
Posts: 37
Rep Power: 16
fluentnoob is on a distinguished road
Ok. I have another doubt now. When the whole domain is rotating, should there be concentric iso-velocity lines, or both iso-velocity and isobaric lines(both concentric)?

What should be the boundary conditions? Please please help me out..
fluentnoob is offline   Reply With Quote

Old   June 23, 2009, 11:20
Default
  #4
Member
 
DT
Join Date: May 2009
Location: Lisbon
Posts: 37
Rep Power: 16
fluentnoob is on a distinguished road
Ok, So I got that part sorted out. Could anyone please just help me with the following? I'd be extremely grateful to the person who can give me advice on the following, any advice. Thank you.

I am trying to simulate a sphere rotating about a point, submerged in water. I have defined a domain around the sphere as fluid. Now I proceeded to solve for the forces etc. on the sphere in the following two ways:

Approach 1:
At the Inlet, defined the fluid velocity as angular, of the appropriate magnitude, and with the apt rotation axis. All this in absolute terms.

Approach 2:
At the Inlet, defined the fluid velocity as angular, of the appropriate magnitude, and with the apt rotation axis. Also, defined the sphere as rotating about the rotation axis. All this in absolute terms.

Could you please help me out over here and tell me which approach is correct? Would all the extra terms due to the circular motion (centrifugal force etc) be included in approach 2 and not 1? Please can anyone help me out with this?

Thank you..
fluentnoob is offline   Reply With Quote

Old   June 23, 2009, 11:48
Default
  #5
Member
 
DT
Join Date: May 2009
Location: Lisbon
Posts: 37
Rep Power: 16
fluentnoob is on a distinguished road
By approach 2, wouldnt the viscous force increase? Because the velocity of the fluid relative to the sphere will increase and become the (velocity of the sphere + Tangential velocity of the fluid) right? So does that make the first approach correct?
fluentnoob is offline   Reply With Quote

Reply

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
Problem with rotating SOLID domain Roland R CFX 0 May 8, 2009 04:38
Single Rotating Domain Sans CFX 3 October 26, 2007 03:33
Difference b/t rotating wall and rotating domain? Juno Kim CFX 2 February 20, 2007 21:08
rotating domain in rotating domain, different axis Robert Stringer CFX 3 December 4, 2006 08:04
Size of rotating domain Adam CFX 4 November 28, 2006 11:28


All times are GMT -4. The time now is 07:36.