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Search: Posts Made By: Amir
Forum: OpenFOAM July 17, 2014, 10:28
Replies: 70
Views: 28,239
Posted By Amir
Well, this was a concept we were talking about...

Well, this was a concept we were talking about all the time. The viscous term includes both normal and in-plane components, but the pressure term only contains normal component. So if anyone would be...
Forum: OpenFOAM July 16, 2014, 16:51
Replies: 70
Views: 28,239
Posted By Amir
Hi, Reasonably, the total traction force...

Hi,

Reasonably, the total traction force would be originated from the total stress tensor consisted of both pressure and viscous terms; however, it has a typo and needs to be modified like this:
...
Forum: OpenFOAM April 10, 2013, 18:18
Replies: 70
Views: 28,239
Posted By Amir
Yes, this is correct. It's called the deviation...

Yes, this is correct. It's called the deviation tensor because it causes deviation from the isometric pressure tensor.

Bests,
Forum: OpenFOAM April 10, 2013, 17:59
Replies: 70
Views: 28,239
Posted By Amir
Yep, something like that. You have to change...

Yep, something like that.

You have to change it to "(sigma_ij . n).n = 2 * mu * partial(u,x)"

No, in your notation it is (sigma.n)!

Bests,
Forum: OpenFOAM April 6, 2013, 07:17
Replies: 70
Views: 28,239
Posted By Amir
No, this is not correct! We are talking about...

No, this is not correct! We are talking about deviation tensor (T) not the whole stress tensor. The pressure is not a part of deviation tensor. The normal component is originated from the strain rate...
Forum: OpenFOAM April 5, 2013, 16:16
Replies: 70
Views: 28,239
Posted By Amir
If your flow field is turbulent, they shouldn't...

If your flow field is turbulent, they shouldn't be the same. It's better to use the same definition for the stress tensor as it's done in the official utility. (It's more general)

Bests,
Forum: OpenFOAM April 5, 2013, 14:11
Replies: 70
Views: 28,239
Posted By Amir
The real wall shear stress would be lower since...

The real wall shear stress would be lower since it's just one of the component of the wall traction. (The wall traction has 2 perpendicular components, the real wall shear stress and the normal one)...
Forum: OpenFOAM April 5, 2013, 10:51
Replies: 70
Views: 28,239
Posted By Amir
Dear Albert, That's my question too! :) ...

Dear Albert,

That's my question too! :)



Regarding my own experience, and as a part my master thesis, I found around 10% deviation between these 2 relations for my case, which was a...
Forum: OpenFOAM April 4, 2013, 05:42
Replies: 70
Views: 28,239
Posted By Amir
Hi, None of the implemented statements are...

Hi,

None of the implemented statements are real wall shear stress but in many cases their differences are really negligible; i.e., it depends on the wall curvature and the velocity gradients.
In...
Forum: OpenFOAM March 15, 2013, 12:38
Replies: 70
Views: 28,239
Posted By Amir
Reasonably, it's consisted of laminar and...

Reasonably, it's consisted of laminar and turbulent parts; you can find that from the solver code and regarded libraries.

Dear Mojtaba,
This is not correct to put the "tau" file to "0" folder!...
Forum: OpenFOAM March 15, 2013, 09:45
Replies: 70
Views: 28,239
Posted By Amir
Hi, For this purpose, if it's really...

Hi,

For this purpose, if it's really necessary according to your solver, take a look over the attachment.
It's Better to see this post...
Forum: OpenFOAM August 15, 2012, 15:43
Replies: 70
Views: 28,239
Posted By Amir
Because it's the constitutive equation! Take a...

Because it's the constitutive equation! Take a look over basic fluid mechanic equation in a continuum media.
(T=2*mu*D) for incompressible flow
D : symmetric part of grad(U)

Bests,
Forum: OpenFOAM August 15, 2012, 11:47
Replies: 70
Views: 28,239
Posted By Amir
The resolution is not the concern but the mesh...

The resolution is not the concern but the mesh grading is. If you have equal-size faces, you'll achieve the same result. But generally, your formulation doesn't lead to the average value physically...
Forum: OpenFOAM August 15, 2012, 09:55
Replies: 70
Views: 28,239
Posted By Amir
Have you taken a look over patchAverage utility?...

Have you taken a look over patchAverage utility? (postProcessing->patch->patchAverage)
As you can see; you'll need to compute patch area there (not the numbers!):

scalar area =...
Forum: OpenFOAM August 14, 2012, 07:26
Replies: 70
Views: 28,239
Posted By Amir
No, as I said it leads to wall traction instead...

No, as I said it leads to wall traction instead of wall shear stress. (you can easily check the formulation)

Of course it is! the tau parameter depends on your model. (actually I prepared it for...
Forum: OpenFOAM August 13, 2012, 15:37
Replies: 70
Views: 28,239
Posted By Amir
Oh, sorry about previous post, that was a forum...

Oh, sorry about previous post, that was a forum conflict! :o
But in openFoam it seems that the original utility compute wall traction instead of wall shear stress and I posted the revised form you...
Forum: OpenFOAM August 13, 2012, 10:17
Replies: 70
Views: 28,239
Posted By Amir
Hi, Try this: solve->monitor->surface .......

Hi,

Try this:
solve->monitor->surface .... wall fluxes (wall shear stress)

Bests,
Forum: OpenFOAM September 23, 2011, 10:15
Replies: 70
Views: 28,239
Posted By Amir
Dear Guifan, First of all, note that this...

Dear Guifan,

First of all, note that this relation for shear stress we discussed about is valid just for incompressible flow; for compressible cases, another term should be added.
As you know, in...
Forum: OpenFOAM September 19, 2011, 23:14
Replies: 70
Views: 28,239
Posted By Amir
Dear Guifan, Your definition is wrong; here,...

Dear Guifan,

Your definition is wrong; here, viscosity is a function of shear rate, it's not a multiplication term! :eek:
T=2 \eta (\gamma\dot{} ) D
The differences maybe due to coarse grid near...
Forum: OpenFOAM September 18, 2011, 09:42
Replies: 70
Views: 28,239
Posted By Amir
There are few errors in this part of code: ...

There are few errors in this part of code:
First of all: I'm not sure that inner product is overloaded for 2 variables which one of them is scalar and another is vector, so it's better to use:...
Forum: OpenFOAM September 17, 2011, 08:37
Replies: 70
Views: 28,239
Posted By Amir
Dear Guifan, T is stress tensor and n is...

Dear Guifan,

T is stress tensor and n is unit normal vector, according to openFOAM definitions:
n=-mesh.Sf().boundaryField()[patchi] / mesh.magSf().boundaryField()[patchi]
and, ...
Forum: OpenFOAM September 16, 2011, 06:08
Replies: 70
Views: 28,239
Posted By Amir
Dear Guifan, In many solvers such as FLUENT...

Dear Guifan,

In many solvers such as FLUENT and OpenFOAM wall traction is considered as wall shear stress and I don't know why!
If we assume T as stress tensor and n as unit normal vector of...
Forum: OpenFOAM September 16, 2011, 03:38
Replies: 70
Views: 28,239
Posted By Amir
Dear Bernhard, I think this utility needs some...

Dear Bernhard,
I think this utility needs some modifications because it computes wall traction instead of wall shear stress, right?
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