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problem with wallShearstress at interFaom

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Old   March 20, 2012, 02:45
Default problem with wallShearstress at interFaom
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Jignesh
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Hi everyone

Can you tel me how to write the value of wallShearstress in laminar pipe flow.

Actually i gave the command of wallShearstress but it cant write the value of shearstress but it gave me some error like
Create time

Create mesh for time = 0

Time = 0
Reading field U

Reading/calculating face flux field phi



--> FOAM FATAL IO ERROR:
keyword transportModel is undefined in dictionary "/home/turbo3/Desktop/jignesh/1inchpipe/pref0sample/constant/transportProperties"

file: /home/turbo3/Desktop/jignesh/1inchpipe/pref0sample/constant/transportProperties from line 20 to line 34.

From function dictionary::lookupEntry(const word&, bool, bool) const
in file db/dictionary/dictionary.C at line 400.

FOAM exiting


so what can i do?
can anybody help me?

Jignesh
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Old   March 20, 2012, 04:51
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Andrea Ferrari
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Hi Jignesh,

i think wallShearStress utility is not suitable for multiphase. I have a similar problem with force calculation (have a look here Force calculation in multiphase simulations). So if you want to use it in your multiphase cases you have to write your own code and read the correct "transportProperties" dict.

best

andrea
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Old   March 20, 2012, 09:15
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Arne Stahlmann
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In case you are only interested in the stresses e.g. for the water-phase, you could simply copy one of the one-phase dictionaries (with values for water) into your case and temporarily use that one for the utility.

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Old   March 21, 2012, 02:38
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Quote:
Originally Posted by Arnoldinho View Post
In case you are only interested in the stresses e.g. for the water-phase, you could simply copy one of the one-phase dictionaries (with values for water) into your case and temporarily use that one for the utility.

Arne
thanx for ur reply but when i will used only water phase, is it gave me correct value? because in my pipe water and air both are flowing at the same time and my flow pattern is stratified. so is it possible to use this in two phase flow?

thanx
jignesh
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Old   March 21, 2012, 03:55
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Arne Stahlmann
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That depends on what you are interested in.
If its only the water, then yes, if its both, then no. In the latter case you indeed have to modify the utility to account for both phases. I thought you could only be interested in one phase, therefore my hint.
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Old   March 21, 2012, 04:32
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Andrea Ferrari
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Hi all.
i think just multiply by nu_1 is not correct. In wallShearStress.C you have:

wallShearStress.boundaryField()[patchi] =
(
-mesh.Sf().boundaryField()[patchi]
/mesh.magSf().boundaryField()[patchi]
) & Reff.boundaryField()[patchi];
and

Reff is defined, if for example you are running laminar, as:
-nu()*dev(twoSymm(fvc::grad(U_))).


In my opinion you have to multiply somewhere by alpha to eliminate the contribution from the zones where there is fluid 2. or not?

best

andrea


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Old   March 21, 2012, 04:54
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Quote:
Originally Posted by Andrea_85 View Post
Hi all.
i think just multiply by nu_1 is not correct. In wallShearStress.C you have:

wallShearStress.boundaryField()[patchi] =
(
-mesh.Sf().boundaryField()[patchi]
/mesh.magSf().boundaryField()[patchi]
) & Reff.boundaryField()[patchi];
and

Reff is defined, if for example you are running laminar, as:
-nu()*dev(twoSymm(fvc::grad(U_))).


In my opinion you have to multiply somewhere by alpha to eliminate the contribution from the zones where there is fluid 2. or not?

best

andrea



Thanx sir

but i am solving two phase laminar flow pattern.

so if possible then please tel me how i modified wallShearstress.C?

i used two fluid air and water.

so how can i calculate wallShearstress.C?
Thanx
jignesh
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Old   March 30, 2012, 08:43
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Michael Stiehm
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Hello jignesh,

do you define the transportModel in your constant/transportProperties-file? If not just add the line:

transportModel Newtonian;

when you have a newtonian fluid.

Greetings
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