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-   -   setting pressure/velocity at different locations (http://www.cfd-online.com/Forums/cfx/98248-setting-pressure-velocity-different-locations.html)

ld1305 March 6, 2012 14:39

setting pressure/velocity at different locations
 
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 :)

ghorrocks March 6, 2012 16:03

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?

ld1305 March 6, 2012 16:07

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.

ghorrocks March 6, 2012 16:11

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.

ld1305 March 6, 2012 16:15

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?

ghorrocks March 6, 2012 16:18

You can make it a function of anything you like. You have maximum flexibility with a source term.

ld1305 March 6, 2012 16:26

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

ghorrocks March 6, 2012 16:31

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!

ld1305 March 6, 2012 16:34

I'll have a look at that too, thanks :)

ld1305 March 7, 2012 12:07

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


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