|
[Sponsors] |
May 1, 2009, 01:17 |
Help with blood flow BCs
|
#1 |
New Member
Erick Johnson
Join Date: May 2009
Posts: 4
Rep Power: 16 |
I am probably missing something very simple, but I'm having a difficult time simulating a simplified, pulsatile flow.
I'm running a short and straight aneurysm model (no branching) to compare my meshes against literature. Using rough interpolations of the waveforms in Scotti (http://www.pubmedcentral.nih.gov/art...?artid=1298313 ... figure 2) I have inlet velocity and outlet pressure conditions with respect to time. My problem is, not knowing enough to set up the system?, the pressure outlet is causing backflow into the system and CFX terminates early. If I ignore the pressure, my wall shear stresses are two orders of magnitude off. What am I missing while setting up the BCs? Thanks for any help and feel free to tell me I'm doing it all wrong :/ Erick |
|
May 1, 2009, 02:41 |
|
#2 |
Member
Tristan Burton
Join Date: Mar 2009
Posts: 43
Rep Power: 17 |
Have you tried using an opening instead of an outlet at your downstream boundary? The opening will allow backflow into the domain.
Tristan |
|
May 1, 2009, 02:42 |
|
#3 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143 |
Hi,
Use an opening at the pressure boundary to allow back flow. Glenn Horrocks |
|
May 1, 2009, 09:32 |
|
#4 |
New Member
Erick Johnson
Join Date: May 2009
Posts: 4
Rep Power: 16 |
Unfortunately I've already switched to using an opening. It does allow blood back in at the outlet, which is what we'd expect to happen anyways, and lets me complete the run, but they way I have things set up is still causing backflow to such a degree that I essentially have a reversed flow (outlet to inlet).
If my setup isn't completely screwed up my next guess would be units, but I think those are in the ballpark too. For 1cm radius and 24cm length I have the inlet velocity between 0-30cm/s and the outlet pressure between 80-120mmHg. I'm currently using the laminar solver for speed with dt = 0.001s, but I've gotten similar results with a couple different turbulent models as well. |
|
May 1, 2009, 12:17 |
my mistakes
|
#5 |
New Member
Erick Johnson
Join Date: May 2009
Posts: 4
Rep Power: 16 |
I didn't say it before, but thanks for the suggestions.
Inlet velocity conditions and outlet (set as an opening) with the pressure conditions are correct. I was sampling the solution at just the wrong timesteps and seeing values I was not expecting. It also helped switching to a "local" min/max to get a better sense of the range. It did end up being all me. :P |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
FLUENT BLOOD FLOW RATE | Christoforos | FLUENT | 0 | September 18, 2008 11:08 |
modelling blood flow in arteries with starcd | sara | Siemens | 5 | April 10, 2007 10:17 |
Need help with BC's for a internal flow problem | ravi | FLUENT | 2 | March 16, 2005 01:45 |
Fluent blood flow BC | Michal | Main CFD Forum | 3 | February 17, 2005 04:17 |
Can reversed flow occur at velocity inlet Bcs. | kanok | FLUENT | 1 | September 30, 2003 12:54 |