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Search took 0.00 seconds. Search: Posts Made By: ghorrocks
Forum: CFX September 28, 2011, 08:45
Replies: 33
Views: 5,573
Posted By ghorrocks
You need to do a mesh refinement study to...

You need to do a mesh refinement study to determine if your mesh is adequate. You cannot tell by simply looking at it.

Lots more detail is here:...
Forum: CFX September 28, 2011, 07:11
Replies: 33
Views: 5,573
Posted By ghorrocks
As I said in the other post you do not need to...

As I said in the other post you do not need to make porous domains different domains. You can make them sub-domains of the entire fluid domain. It probably won't make any difference but it is worth a...
Forum: CFX September 25, 2011, 20:39
Replies: 33
Views: 5,573
Posted By ghorrocks
I was not aware of the difference in porosity...

I was not aware of the difference in porosity models. You learn something evey day.

If I was you I would trial the momenum source approach anyway. Maybe set up a simple benchmark simulation and...
Forum: CFX September 25, 2011, 20:26
Replies: 33
Views: 5,573
Posted By ghorrocks
If you are doing it right you will probably get...

If you are doing it right you will probably get some non-steady turbulent scale fluctuations starting up. This is effectively LES.



My preferred approach would be to fix the problem. You have...
Forum: CFX September 25, 2011, 19:29
Replies: 33
Views: 5,573
Posted By ghorrocks
The gamma-theta transitional model was developed...

The gamma-theta transitional model was developed for transition on airfoils. Your thing looks nothing like an airfoil so I do not think it will work very well for you.

I agree that the SST model...
Forum: CFX September 24, 2011, 06:37
Replies: 33
Views: 5,573
Posted By ghorrocks
Correct. Yes, definitely. In fact I...

Correct.



Yes, definitely. In fact I know there is an update in V13 to improve the convergence of porous regions. This may fix your entire problem if you are not using the current version.
Forum: CFX September 22, 2011, 18:28
Replies: 33
Views: 5,573
Posted By ghorrocks
Depends on what you are modelling. There are no...

Depends on what you are modelling. There are no simple answers in CFD. If you are modelling a flow where boundary layer effects are not very important then this sounds fine. Also if you are in the...
Forum: CFX September 21, 2011, 06:51
Replies: 33
Views: 5,573
Posted By ghorrocks
The forum still has posts from 10 years back. It...

The forum still has posts from 10 years back. It is just a little hard to find things with so many posts.

1a) The default k-e model only works for mid to high turbulence. It is not good at low...
Forum: CFX September 20, 2011, 19:23
Replies: 33
Views: 5,573
Posted By ghorrocks
I learnt all that stuff on the forum years ago....

I learnt all that stuff on the forum years ago. There was a guy called "Robin" who posted some very informative posts here years ago, if you do a search you might find some of his posts from years...
Forum: CFX September 20, 2011, 18:26
Replies: 33
Views: 5,573
Posted By ghorrocks
1) I suspect both cases (low and high Re) are...

1) I suspect both cases (low and high Re) are transient from what you have said.

2) The steady state simulation eliminates many of the terms which come about in the transient Navier Stokes which...
Forum: CFX September 20, 2011, 06:32
Replies: 33
Views: 5,573
Posted By ghorrocks
Some comments: I see you have specified...

Some comments:

I see you have specified water properties in some detail. If you want accurate water properties then just use the built-in IAPWS water properties. This is the best source for water...
Forum: CFX September 20, 2011, 06:09
Replies: 33
Views: 5,573
Posted By ghorrocks
Thanks. Have you read the documentation about...

Thanks. Have you read the documentation about "Obtaining Convergence"? Also some more tips are here:...
Forum: CFX September 19, 2011, 19:09
Replies: 33
Views: 5,573
Posted By ghorrocks
This flow is definitely laminar and therefore you...

This flow is definitely laminar and therefore you should be using the laminar flow model. If you cannot get this to converge then fix it rather than using a turbulence model. As previously mentioned...
Forum: CFX September 15, 2011, 18:43
Replies: 33
Views: 5,573
Posted By ghorrocks
The eddy viscosity in the k-e model is...

The eddy viscosity in the k-e model is proportional to k^2/e (http://www.cfd-online.com/Wiki/Standard_k-epsilon_model). Epsilon gets small in laminar flows so the eddy viscosity does not degenerate...
Forum: CFX September 14, 2011, 18:56
Replies: 33
Views: 5,573
Posted By ghorrocks
No it does not. If you use the k-e model in a...

No it does not. If you use the k-e model in a laminar flow it will give you more dissipation then is really there, so is a significant source of error. The SST and related models are better here...
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