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ld1305 February 1, 2012 12:52

CFX Coronary Flow Simulation
 
Hi, I have a coronary artery that I am running through CFX to try and find the pressure at certain points, mainly before and after a blockage, but elsewhere would be useful too.

I'm having a couple of problems, though:

1. I can't seem to make the flow go through all the outlets, there is one inlet, and 4 outlets and just by using a quick velocity streamline it's obvious the flow only goes one way.

2. I can't seem to find a way to find the pressure at given locations anyway

3. The main problem: I'm not too sure how to make the flow pulse, as would be natural in the human body, I'd need it to be every 0.75 seconds, though not too sure otherwise. I also have mass flow rate and properties of blood etc if that's any use


Thanks very much,
Lauren

ld1305 February 1, 2012 12:53

Some printscreens of the crude mesh (it's to be improved later) and some other things I've managed are here

ghorrocks February 1, 2012 18:25

Your questions:
1) Then you boundary conditions or simulation is wrong. Are you sure the pressures are correct? I suspect some of the outlets really do have back flow at some stages of the pumping cycle.

2) The easiest way is to colour the outer wall by pressure in CFD-Post. Or you can put points and get the pressure at those points. In the solver you can define monitor points and get the pressure during simulation.

3) This is simple to implement, use a CEL expression (or interpolation function) to define the mass flow rate versus time.

Also I suspect you will find the deformation of the vessels significantly affects the results.

FrankW February 2, 2012 03:30

Hi Lauren,

is your model scale right? I can see a ruler with a lenght of 20-30 meters on 2 pictures.

Frank

ghorrocks February 2, 2012 05:43

Good point. Is this a scan of the arteries from Godzilla?

ld1305 February 2, 2012 10:48

Yeah... I need to change the scale, I'll sort that out afterwards. For now I have it to go through all the different parts of the artery though, just need to work on the pulsatile flow a little, though this seems to be the trickier bit to be honest :/

ld1305 February 2, 2012 10:50

As it is I can#t comment on the deformation of the vessels as I have no way to accurately predict their movement. This has been done before using a different imaging technique, but I don't have access to more advanced images yet

ghorrocks February 2, 2012 17:26

You should get the scale right straight away. It will change the Re number of the flow, and separations and lots of other flow features. Therefore the resistance balance will be totally different and hence the flow split will be totally different.

It is easy to do and you do not need to remesh. Just do a mesh transform using a scaling function in CFX-Pre with your existing mesh.

ld1305 February 4, 2012 14:14

I've changed the scale, but the major problems I'm having now are with finding the correct values for the blood, which is obviously causing issues with getting the correct results... don't happen to know anywhere do you? I have most of the basic numbers, just a few more needed for the analysis

ghorrocks February 5, 2012 18:19

There is lots of papers in the literature on this, do a google search.

ld1305 February 5, 2012 19:14

I have done and can't fine many of the numbers I'm looking for, mostly with regards to how to set it up in CFX as a material, I can't model it as a pure substance (because it isn't) and because there is no molar mass, and the other ways don't seem much help either...

ghorrocks February 6, 2012 20:14

Blood rheology is a whole field of research in itself. It sounds like you better do some research on it before proceeding - as you point out blood is a very complex fluid and there is many different levels of simplification you can use to model it.

ghorrocks February 6, 2012 20:14

Blood rheology is a whole field of research in itself. It sounds like you better do some research on it before proceeding - as you point out blood is a very complex fluid and there is many different levels of simplification you can use to model it.

ld1305 February 7, 2012 04:17

I know I don't need any of the thermal properties of blood, only those which could effect pressure and mass flow rate, I don't know that the shear stresses etc are even important to be honest.

I'm going to go and see a tutor about it later and see if he can help, but thanks :)


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