CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLOW-3D

set the outflow curve at downstream

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 20, 2012, 23:34
Default set the outflow curve at downstream
  #1
Member
 
Yi-Lang Chen
Join Date: May 2009
Posts: 58
Rep Power: 8
Andy Chen is on a distinguished road
Dear experts:

When I set the outflow curve(B.C. use volume flow rate) at downstream. Then water flow toward upstream. That is not right. It Should toward downstream by gravity. How did I set Boundary condition if I want to set the outflow curve at downstream.

Thanks your help!!
Andy Chen is offline   Reply With Quote

Old   May 21, 2012, 10:34
Default
  #2
Senior Member
 
Jeff Burnham
Join Date: Apr 2010
Posts: 204
Rep Power: 8
JBurnham is on a distinguished road
Set the velocity component to a positive or negative vector that points out of the domain. By default, the volumetric-flow boundary vector points into the domain, normal to the boundary, and you have to specify it if you want a different direction. Note that a downstream Vfr boundary will only remove the fluid which is in contact with the boundary. If dry spots appear, the flow rate will oscillate. Why not use a Vfr upstream instead?
JBurnham is offline   Reply With Quote

Old   May 21, 2012, 21:09
Default
  #3
Member
 
Yi-Lang Chen
Join Date: May 2009
Posts: 58
Rep Power: 8
Andy Chen is on a distinguished road
First of all, thanks your reply, JBurnham.
I simulated the reservoir case. It should be controlled by gate at downstream. But I don't know how did use gate in FLOW-3D. So, our team consider that will set outflow curve(volume flow rate of B.C.) at downstream to solve the problem. Do you have any suggest can provide our team?

Thanks!!
Andy Chen is offline   Reply With Quote

Old   May 24, 2012, 22:05
Default
  #4
Senior Member
 
michael barkhudarov
Join Date: Mar 2009
Posts: 331
Rep Power: 9
MuxaB is on a distinguished road
Quote:
Originally Posted by Andy Chen View Post
First of all, thanks your reply, JBurnham.
I simulated the reservoir case. It should be controlled by gate at downstream. But I don't know how did use gate in FLOW-3D. So, our team consider that will set outflow curve(volume flow rate of B.C.) at downstream to solve the problem. Do you have any suggest can provide our team?

Thanks!!
Andy, just like Jeff said, set the flow rate vs. time curve and define the flow direction vector pointing OUTWARDS. By default it points inwards.
MuxaB is offline   Reply With Quote

Old   May 25, 2012, 10:19
Default
  #5
Member
 
Yi-Lang Chen
Join Date: May 2009
Posts: 58
Rep Power: 8
Andy Chen is on a distinguished road
Quote:
Originally Posted by MuxaB View Post
Andy, just like Jeff said, set the flow rate vs. time curve and define the flow direction vector pointing OUTWARDS. By default it points inwards.
Yes, I already solved about flow direction vector problem. I just reply that Jeff said "the flow rate will oscillate. Why not use a Vfr upstream instead?". I simulated the resvoir and it was controlled by gate at downstream(I set Vfr at upstream). So, our team consider that could set Vfr at downstream. Maybe it can solve about "the resvoir was controlled by gate" problem. That was I do why I set Vfr at downstream
Andy Chen is offline   Reply With Quote

Old   May 25, 2012, 11:21
Default
  #6
Senior Member
 
Jeff Burnham
Join Date: Apr 2010
Posts: 204
Rep Power: 8
JBurnham is on a distinguished road
I assume that 'the reservoir is controlled by a downstream gate' means that there is gravity-fed overflow through (over or under) a gate, and that the flow is critical (Fr = 1) somewhere on the gate. Is the gate inside of the domain? If it's not, then you might as well use Vfr at the downstream boundary. If the gate is in the domain, however, you will want to let the flow go over the gate under the control of gravity, and be solved by the Navier-Stokes equations. In that case, it would be over-specifying the problem to define a flowrate at the downstream boundary. If I'm correct in my assumption (that Fr = 1 at the gate) then the downstream boundary will not have an effect on the reservoir level itself (no information propagates upstream from the critical transition point, and you could use an Outflow-type boundary downstream instead). You can use the Vfr boundary downstream - it will remove fluid at the rate you specify. I was just suggesting that you think carefully about whether that's a physical representation of the problem or not.
JBurnham 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
Installation problems indy OpenFOAM Installation 7 April 3, 2009 09:40
Propeller Fan Curve Simulation Teng_YJ FLUENT 2 February 16, 2009 20:37
Problem installing on 64bit with ver13 jonititan OpenFOAM Installation 0 April 28, 2006 05:45
Problems with installation jonititan OpenFOAM Installation 4 November 6, 2005 05:16
CFX4.3 -build analysis form Chie Min CFX 5 July 12, 2001 23:19


All times are GMT -4. The time now is 16:38.