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Search: Posts Made By: sbaffini
Forum: FLUENT August 13, 2015, 17:58
Replies: 34
Views: 2,236
Posted By sbaffini
I mean, there is no node implied, just cells. ...

I mean, there is no node implied, just cells.

However, for the record, in a finite difference setting you would have used the source term for each of the nodes you are actually solving for.
Forum: FLUENT August 13, 2015, 17:54
Replies: 34
Views: 2,236
Posted By sbaffini
Well, in finite volume, the source term is...

Well, in finite volume, the source term is applied on a cell by cell basis, just like the pressure gradient. This means that it is simply applied to all the cells.
Forum: FLUENT August 13, 2015, 17:43
Replies: 34
Views: 2,236
Posted By sbaffini
Dear Ahmed, what do you mean by something wrong...

Dear Ahmed, what do you mean by something wrong in the unsteady part?

You just need to add this as classical source term
(Fluent knows how to do that) under cell zone conditions.

I am on the...
Forum: Main CFD Forum July 22, 2015, 04:09
Replies: 14
Views: 260
Posted By sbaffini
At this point, i suggest using both approaches...

At this point, i suggest using both approaches (k-eps+WF and k-w) to evaluate the differences, unless you have a very specific reason to use k-eps. I insist on this because,
nowadays, there are...
Forum: Main CFD Forum July 21, 2015, 15:13
Replies: 14
Views: 260
Posted By sbaffini
If you want to add additional terms to the wall...

If you want to add additional terms to the wall function formulation, you can consider this simple model:
...
Forum: Main CFD Forum July 21, 2015, 15:06
Replies: 14
Views: 260
Posted By sbaffini
Yes, i meant the gravity and unsteady terms. ...

Yes, i meant the gravity and unsteady terms.

Consider a full 3D computation; wall functions are used on a minimum part of the domain. Still, they are gratly influencing your results. When i look...
Forum: Main CFD Forum July 21, 2015, 11:59
Replies: 14
Views: 260
Posted By sbaffini
This is not wrong per se (also, the k-eps model...

This is not wrong per se (also, the k-eps model actually requires the wall function as it cannot be integrated down to the wall).

What is problematic, in my opinion, is that your whole model is a...
Forum: Main CFD Forum July 21, 2015, 11:17
Replies: 14
Views: 260
Posted By sbaffini
This is a non linearity, just like for nu_t. You...

This is a non linearity, just like for nu_t. You either perform outer iterations or simply use previous values (for Up). As i said, you can use an implicit approach with no wall function and add the...
Forum: Main CFD Forum July 21, 2015, 03:52
Replies: 14
Views: 260
Posted By sbaffini
1) No 2) The typical approach for implicit...

1) No

2) The typical approach for implicit cases is to discretize implicitly as if no wall function is used and explicitly for the difference between the wall function and the implicit...
Forum: Main CFD Forum July 20, 2015, 11:30
Replies: 14
Views: 260
Posted By sbaffini
Multiply your first equation by u_* and subtract...

Multiply your first equation by u_* and subtract U_p. You will end up with something like f(u_*)=0, which needs to be solved iteratively for u_* (e.g., by Newton-Raphson).
Forum: Main CFD Forum July 17, 2015, 05:39
Replies: 11
Views: 241
Posted By sbaffini
You can find attached some routines i wrote some...

You can find attached some routines i wrote some time ago. They are part of a larger piece of code, so some parts might not look clear (i.e., the data structures), but the logic
is there.

The...
Forum: Main CFD Forum July 16, 2015, 03:38
Replies: 11
Views: 241
Posted By sbaffini
Usually, for convex polyhedral(polygonal) cells...

Usually, for convex polyhedral(polygonal) cells in 3D(2D), a much faster test is the triangle(segment)/segment intersection test between:

1) The segment connecting the given point and the cell...
Forum: Main CFD Forum July 10, 2015, 05:25
Replies: 1
Views: 112
Posted By sbaffini
You probably mean 'unstructured'. However, the...

You probably mean 'unstructured'. However, the following paper:

http://www.dept.ku.edu/~cfdku/papers/1999-AIAAJ.pdf

has the answer for arbitrary convex polygons/polyhedra.
Forum: Main CFD Forum July 9, 2015, 03:47
Replies: 4
Views: 171
Posted By sbaffini
I don't know how much debate there is on this...

I don't know how much debate there is on this topic but, in my opinion, there are serious advantages in NOT using ghost cells:

1) Ghost cells require extrapolation. The state in the extrapolated...
Forum: Main CFD Forum July 8, 2015, 13:04
Replies: 2
Views: 138
Posted By sbaffini
Long story short: 1) Most DNS use a fixed...

Long story short:

1) Most DNS use a fixed mass flow rate (instead of pressure gradient), that' s why the pressure gradient is not specified.

2) If your channel has height H=2, rho=1,...
Forum: Fluent UDF and Scheme Programming July 7, 2015, 11:09
Replies: 2
Views: 162
Posted By sbaffini
Why do you expect the mass flow rate at the...

Why do you expect the mass flow rate at the pressure outlet to be different from the inlet one?

However, the task is more difficult than the way you approached it. Both inlet and outlet surfaces...
Forum: Main CFD Forum June 20, 2015, 13:06
Replies: 29
Views: 7,040
Posted By sbaffini
Look for the works of Capizzano or De Tullio, i...

Look for the works of Capizzano or De Tullio, i don't remember now the titles (just add IBM to their names).

The group working on the code NASCART-GT has also produced in this field.

However, ...
Forum: Main CFD Forum June 19, 2015, 17:30
Replies: 29
Views: 7,040
Posted By sbaffini
Well, there are a number of reasons for which the...

Well, there are a number of reasons for which the IBM is more suitable at low Re. However, high Re applications are possible as well. It is important to choose the most suitable IBM flavor for the...
Forum: Main CFD Forum June 19, 2015, 07:24
Replies: 29
Views: 7,040
Posted By sbaffini
Roughness effects can only be included in wall...

Roughness effects can only be included in wall function models, independently from the specific approach (IBM, body fitted, etc.). The underlying reasoning is that if you cannot resolve the wall...
Forum: Main CFD Forum June 7, 2015, 15:39
Replies: 6
Views: 172
Posted By sbaffini
Do you have any feel of a sensible overhead (some...

Do you have any feel of a sensible overhead (some might be unavoidable)?
Forum: FLUENT June 2, 2015, 16:58
Replies: 2
Views: 141
Posted By sbaffini
The wall function is just a Black box which is...

The wall function is just a Black box which is invoked for a cell face which is a wall in order to obtain the wall stress to use as boundary condition.

Thus, for a given cell, it is invoked...
Forum: Main CFD Forum May 29, 2015, 17:05
Replies: 7
Views: 181
Posted By sbaffini
On a uniform grid, a courant equal to 1 should...

On a uniform grid, a courant equal to 1 should give you the exact solution for an explicit euler-1st order upwind scheme, at least in the linear case. Maybe there is some problem in your scheme. Can...
Forum: Main CFD Forum May 29, 2015, 14:19
Replies: 7
Views: 181
Posted By sbaffini
I might be wrong (so please double check me) but...

I might be wrong (so please double check me) but i think that you cannot evaluate an order of accuracy correctly if your reference exact solution is discontinuous
Forum: Main CFD Forum May 29, 2015, 14:09
Replies: 10
Views: 233
Posted By sbaffini
Be aware that when the 'transitional' label is...

Be aware that when the 'transitional' label is attached to a RANS like model it usually means that it has a sort of 'smart' switcher to predict the trsndition location for, say, attached flows over...
Forum: Main CFD Forum May 29, 2015, 03:51
Replies: 6
Views: 172
Posted By sbaffini
This guy: https://github.com/szaghi/OFF ...

This guy:

https://github.com/szaghi/OFF

has developed a basic solver trying to follow the most modern Fortran features. I don't remember the exact details but i remember he complaining about...
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