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

setting pressure/velocity at different locations

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 6, 2012, 15:39
Default setting pressure/velocity at different locations
  #1
Member
 
Lauren Dransfield
Join Date: Jan 2012
Posts: 50
Rep Power: 14
ld1305 is on a distinguished road
I've set up a pulsatile flow through the aorta and coronary arteries which is currently driven by the pressures taken in the aorta and pressures taken in the arteries at the inlet and outlet respectively. The flow is set up using CSV files imported using the initialise profile data feature.

However, this means that the velocities or mass flow rates are not equal to those experienced normally in the heart, and I was wondering if it is possible to also add an extra plane which will not add or detract from the flow, but give it a velocity at the opening between the aorta and the arteries, just to make sure that the velocities stay more similar to those which are expected.

I have also run simulations without the aorta attached, in which I used the artery outlet velocity and inlet pressure as the driving force, which seemed to work with regards to keeping both fairly close to the expected values, though this method doesn't seem to work well with the aorta aswell.

Any help is much appreciated, thanks very much
ld1305 is offline   Reply With Quote

Old   March 6, 2012, 17:03
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
An implication of using the pressure inlet pressure outlet approach you are using is that you have no direct control over the flow rate, so small errors in the pressures, geometry or numerics can then become significant flow rate errors.

I do not understand exactly what you are asking for. If an extra plane does not add or subtract from the flow then it cannot do much.

You could do a source term which is zero if the velocity is in the range you are happy with, but slows (or speeds up) the flow if it goes outside your desired range. Is this what you want?
ghorrocks is offline   Reply With Quote

Old   March 6, 2012, 17:07
Default
  #3
Member
 
Lauren Dransfield
Join Date: Jan 2012
Posts: 50
Rep Power: 14
ld1305 is on a distinguished road
This could possibly work, though I'm not exactly sure how to implement it.

But doesn't add to or detract from I mean that I don't want a new flow to be introduced, but want to control what's already there.
ld1305 is offline   Reply With Quote

Old   March 6, 2012, 17:11
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Refer to source terms in the documentation. You could generate a source term which acts on the momentum equation (so no mass gain or loss) which does nothing except when the local velocity exceeds a defined value, then the source term clamps the flow velocity to that value, or maybe then has a resistance which slows the flow down. You will have to decide what the most appropriate approach is for your application.
ghorrocks is offline   Reply With Quote

Old   March 6, 2012, 17:15
Default
  #5
Member
 
Lauren Dransfield
Join Date: Jan 2012
Posts: 50
Rep Power: 14
ld1305 is on a distinguished road
This makes sense and could be useful, but as I said, the flow is pulsatile, so the velocity should be different at each given time-step, do you know if it's possible to have the maximum or minimum velocity change with respect to time if I were to use a source term?
ld1305 is offline   Reply With Quote

Old   March 6, 2012, 17:18
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
You can make it a function of anything you like. You have maximum flexibility with a source term.
ghorrocks is offline   Reply With Quote

Old   March 6, 2012, 17:26
Default
  #7
Member
 
Lauren Dransfield
Join Date: Jan 2012
Posts: 50
Rep Power: 14
ld1305 is on a distinguished road
Fantastic, I'll look it up and see what I can do, thanks very much

Mind if I mention you in my acknowledgements? You've helped with a few problems I've had with the software and you deserve recognition
ld1305 is offline   Reply With Quote

Old   March 6, 2012, 17:31
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
You may also wish to see the other thread currently active on the CFX forum which is also discussing source terms. It is discussing a few different approaches and that may help you understand what can be done.

Quote:
Mind if I mention you in my acknowledgements?
No problem, I am glad my comments have assisted you!
ghorrocks is offline   Reply With Quote

Old   March 6, 2012, 17:34
Default
  #9
Member
 
Lauren Dransfield
Join Date: Jan 2012
Posts: 50
Rep Power: 14
ld1305 is on a distinguished road
I'll have a look at that too, thanks
ld1305 is offline   Reply With Quote

Old   March 7, 2012, 13:07
Default
  #10
Member
 
Lauren Dransfield
Join Date: Jan 2012
Posts: 50
Rep Power: 14
ld1305 is on a distinguished road
I can find lots of information on what source terms are and what they're used for, but I can't find very much at all on how to implement a source term -I haven't used CFX long and wouldn't really know where to start
ld1305 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
Cells with t below lower limit Purushothama Siemens 2 May 31, 2010 22:58
Sover setting with TUI junbbung FLUENT 0 August 20, 2009 01:43
LiftDrag utility from v12 to v141 cfdphil OpenFOAM Running, Solving & CFD 2 December 5, 2007 06:49
Ultra high temperature? bk Siemens 2 July 19, 2005 01:01
Warning 097- AB Siemens 6 November 15, 2004 05:41


All times are GMT -4. The time now is 22:49.