CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   Porous artery and SST turbulence model (http://www.cfd-online.com/Forums/cfx/117586-porous-artery-sst-turbulence-model.html)

kmgraju May 11, 2013 07:19

Porous artery and SST turbulence model
 
Dear friends
I am simulating a flow in a artery having 80 % area reduction. The artery wall I considered as a porous medium. I have introduced different flow rate from 50 ml/min to 150 ml/min. When I use 150 ml/min , I am expecting low Reynolds turbulence may occur. Since the intensity of turbulence is very less, I use SST turbulence model. But the maximum pressure I got 600 mm Hg. But this cannot happen. If I use a laminar flow condition I cannot capture the flow instability.

When I specify fluid porous interface ,

I put fluid model as SST turbulence.

Please help me
How to specify in the porous domain ?In porous domain the velocity of the fluid is very less and it cannot be turbulence through the wall?

Please help me

Thank you

kmgraju May 12, 2013 10:59

Dear friends any help?

Regards

kmgraju May 12, 2013 12:38

[QUOTE ]I'm having a problem to set my problem involving a fluid domain and a porous domain (artery model) in the CFX pre.

I would like set a model of the turbulent (SST) for fluid domain and laminar (Darcy) for the porous domain.

I have created the two domains (porous and fluid) in the CFX Pre and a interface porous fluid in Domain interface, I configured option in the model Additional Interface Model of mass transfer and momentum-type Conservative Interface Flux, the method used was the GGI Connection.

With the domains and the interface created, I'm able to simulate with the same turbulence model in the two domains, but want to know how to separate the models.

Getting separates the two models using the Enable Beta Features in Case Options > General Options and disabled Constant Domain Physics. Thus, achieving enable a model the turbulent to fluid domain and laminar to porous domain, the problem is that in CFX-solver error appears before the first interaction "Stopped in routine error.

I think that is missing enable a feature, or am I skipping a step, and do not know which, can anyone help me?


Thank you

Regards[/QUOTE]

ghorrocks May 12, 2013 19:28

I am no expert in blood modelling, but I would expect the particles and other non-Newtonian bits in blood to make traditional turbulence models quite inaccurate. So if you are not getting accurate results then I am not surprised. There is a whole science of describing the rheology of blood.

With regard to different turbulence models in different domains - you cannot do this. The boundary of the turbulence domain has several undefined variables (all the turbulence variables). Anyway, have you checked that you need to? The SST model often returns results essentially the same as a laminar flow model anyway when the k is almost zero, so you might find running SST everywhere is good enough. You would nee dto check this.

kmgraju May 24, 2013 10:56

Dear all
In my model, the turbulence may be expected to happen 2 cm away from the inlet. I use SST fluid model. Kindly give an idea , how to solve this problem.
I use medium intensity 5% when I set at the inlet.

Please help me to complete my task as soon as possible.

Thank you

ghorrocks May 24, 2013 19:22

Did you read my previous post? It suggests an important reason why you are getting errors.

5% turbulence is reasonably high turbulence. You could consider lowering this. And I think the SST turbulence model is the bets choice until we know otherwise. But as previously stated I would not expect high accuracy from this model. You are not taking into account many of the complex blood rheology so I would expect your results to be miles off.

kmgraju May 24, 2013 22:14

Quote:

Originally Posted by ghorrocks (Post 429893)
Did you read my previous post? It suggests an important reason why you are getting errors.

5% turbulence is reasonably high turbulence. You could consider lowering this. And I think the SST turbulence model is the bets choice until we know otherwise. But as previously stated I would not expect high accuracy from this model. You are not taking into account many of the complex blood rheology so I would expect your results to be miles off.

Thank you Glenn.

I set now default intensity and auto compute length scale.
Is it necessary to set equation class setting in cfx pre.

I would like to say something about you. I really appreciate your valuable guidance.If I get some feedback from you and others I am so confident in my task.
Thank you again

Govind

ghorrocks May 25, 2013 05:05

Thanks for the compliment :)

What do you mean by "equation class setting".

kmgraju May 25, 2013 09:42

Quote:

Originally Posted by ghorrocks (Post 429934)
Thanks for the compliment :)

What do you mean by "equation class setting".

Dear Mr Glenn
I mentioned here the solver control settings.

I got the answer if I set default intensity and auto compute length scale.

Thank you

Regards

Govind

kmgraju May 25, 2013 20:31

Dear all , can any one please clarify the following terms

I have chosen SST model and I have selected Turbulence control which is in solver control>advanced options . But the solver return with error.
Thank you




"Turbulence Control

This option allows specification of a different turbulence model to be used from the first iteration through to the transition iteration. The idea is to solve a simpler and more robust turbulence model for the first few iterations. In the order of increasing complexity, the turbulence models are laminar, zero equation, dispersed phase zero equation, k epsilon, and then RNG k epsilon. You should use this option when startup with the desired turbulence model is not possible."

ghorrocks May 26, 2013 07:17

I never use this turbulence control parameter. I find it always hides a more fundamental problem. So I would return this to default and look for the more fundamental problem.

Can you post your CCL, an image of what you are modelling and a cross section of your mesh?

kmgraju June 8, 2013 05:33

1 Attachment(s)
Dear all
(Mr Glenn Sorry for the late response due to my personal)

please find the attached cross section of artery model. I consider the wall as porous. The blood flow taking place narrow stenosis
I would like to capture low Re turbulence I use SST model and I set TURBULENCE:
Fractional Intensity = 0.01
Option = Intensity and Auto Compute Length

after the simulations I got the error message as shown below . Is this error message important?
+--------------------------------------------------------------------+
| ERROR #002100004 has occurred in subroutine Out_Scales_Flu. |
| Message: |
| The Reynolds number is outside of the range expected based on the |
| Option selected for the TURBULENCE MODEL. Check this setting, |
| the values of the properties, mesh scale, consistency of units |
| and solution values in the input file. Execution will proceed. |
+--------------------------------------------------------------------+


Thank you

ghorrocks June 10, 2013 22:27

This is a warning, not an error. If you are happy the flow is laminar you can ignore it.

kmgraju June 11, 2013 00:50

Quote:

Originally Posted by ghorrocks (Post 433241)
This is a warning, not an error. If you are happy the flow is laminar you can ignore it.

Thank you so much


All times are GMT -4. The time now is 16:12.