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-   -   Need help on Boundary Condition (http://www.cfd-online.com/Forums/openfoam-pre-processing/94201-need-help-boundary-condition.html)

CNT9 November 9, 2011 02:07

Need help on Boundary Condition
 
Hello,
I'm still learning about OpenFoam, and I need some helps.
I want to model a converging flow, so there are two inlets coming in and
a single outlet.
However, instead of assigning velocity differences at inlets and outlets,
I want to make this a pressure-driven flow (thus assigning only pressure values and possibly assigning velocity values as zeroGradients) - and two inlets should have different initial pressure values.
So any suggestions for good boundary conditions for two inlets and an outlet?

Thank you in advance.

chegdan December 8, 2011 18:27

Quote:

Originally Posted by CNT9 (Post 331306)
Hello,
I'm still learning about OpenFoam, and I need some helps.
I want to model a converging flow, so there are two inlets coming in and
a single outlet.
However, instead of assigning velocity differences at inlets and outlets,
I want to make this a pressure-driven flow (thus assigning only pressure values and possibly assigning velocity values as zeroGradients) - and two inlets should have different initial pressure values.
So any suggestions for good boundary conditions for two inlets and an outlet?

Thank you in advance.

Try looking at

http://www.cfd-online.com/Forums/ope...-inlet-bc.html

and

http://www.cfd-online.com/Forums/ope...-openfoam.html

and then search the forum a little more for "pressure inlet"

I do remember that specifying pressure at the inlet, it is very easy to create hypersonic flow (not sure where I read that)...so be careful. Also, remember that if you use solvers like simpleFoam, the value you are specifying is actually pressure divided by fluid density.

Cheers,

sundark28 April 26, 2012 08:15

Need help boundary conditions using groovyBC
 
Hi guys,

Im pretty new in OpenFoam (i m using Openfoam2.1). I consider the geometry of a cylinder and i would like to simulate a swirling turbulent flow (LES Simulation). I want to change the entry condition for the velocity field with the following expression: (i want a tangetial velocity profil which depends on radius)

" variables: Ur (radial velaocity), Ut (tangential velocity), r_vc (radius of the vortex), v_max (maximal velocity)

expression:
for 0 < radius < r_vc Ur = V_max * radius / r_vc

for r_vc < radius < R (radius of the cylinder) Ur = V_max *r_vc / radius"

Thanks in advance for your help !!

chegdan April 26, 2012 09:42

Quote:

Originally Posted by sundark28 (Post 357175)
Hi guys,

Im pretty new in OpenFoam (i m using Openfoam2.1). I consider the geometry of a cylinder and i would like to simulate a swirling turbulent flow (LES Simulation). I want to change the entry condition for the velocity field with the following expression: (i want a tangetial velocity profil which depends on radius)

" variables: Ur (radial velaocity), Ut (tangential velocity), r_vc (radius of the vortex), v_max (maximal velocity)

expression:
for 0 < radius < r_vc Ur = V_max * radius / r_vc

for r_vc < radius < R (radius of the cylinder) Ur = V_max *r_vc / radius"

Thanks in advance for your help !!


This is usually my go to answer on these, but why not try groovyBC (http://openfoamwiki.net/index.php/Contrib_groovyBC) or go ahead and install swak4foam (http://openfoamwiki.net/index.php/Contrib/swak4Foam) to get even more tools, and look at

http://www.cfd-online.com/Forums/ope...locity-bc.html

that will cover it for you. As always, use your search skills on the forum. Good luck.


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