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-   -   units after multipl. with phi (https://www.cfd-online.com/Forums/openfoam/107412-units-after-multipl-phi.html)

 Tobi September 26, 2012 11:01

units after multipl. with phi

Hi all,

I have an equation like that:

Code:

`div(phi, H) + Q`
Solver that is used is rhoSimpleFoam - compressible. The unit of H is [J/kg]. Q has the unit [W/m³].

I had a look at the phi file and the file has the unit [kg/s]. Also I had a look at the createCompressiblePhi.H file and there is phi defined as the mass flow.

So after div(phi, H) I should get the unit [J/s] = [W] ...
Or am I wrong?

If phi = rho then everything would be nice :)
I am a bit confused.

Tobi

 meindert September 26, 2012 13:07

Could it be that you are missing the cell volume from the finite volume integration in your Q term?

phi = rho would still not solve your problem, because you're still missing [1/s] in that case.

 Tobi September 26, 2012 13:12

Hi,

no its implemented in the flamelet tool from alberto.
He added an enthalpy defect like that:

Code:

``` div(phi, H) - laplacian(turbulence->mut/sigmat, H) + Qrad```

Code:

`Qrad = 4 * sigma_B * (T_cell^4 - T_env^4) * as`

H [J/kg]

Well - but you `re right. There is still a s missing :/
I a m confused with taht code.

 meindert September 28, 2012 05:52

Hi Tobi,

Have a look at equation 2.29 in the Programmer's Guide.

 Tobi September 30, 2012 08:11

Quote:
 Originally Posted by meindert (Post 384024) Hi Tobi, Have a look at equation 2.29 in the Programmer's Guide.
Hi,
do you mean the libOpenSmoke Guide or what programmers guide do you mean?

 elvis October 1, 2012 10:30

Hi Tobias,
the folks at OpenCFD have discontinued Programmers Guide that is correct

but you can still find

 Tobi October 1, 2012 13:32

HI,

thanks very much.
Thats that what I need :) integration over a volume V - now I know how that works.

Thought that the programmers-guide is only the doxygen-code :)
Nice to know.

Tobi

 meindert October 3, 2012 17:24

Perhaps it's good to know that you can also find it in your \$WM_PROJECT_DIR/doc/Guides-a4 directory.

 Tobi October 4, 2012 15:55

Quote:
 Originally Posted by meindert (Post 384783) Perhaps it's good to know that you can also find it in your \$WM_PROJECT_DIR/doc/Guides-a4 directory.

Nice to know.
Working with OF for 3 years now and be in that directory some times but never realized that :)

stupid!

but thanks!
tobi

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