
[Sponsors] 
June 21, 2012, 09:30 
Boundary Conditions for Flow Problem

#1 
Member
Join Date: Mar 2012
Location: Munich, Germany
Posts: 67
Rep Power: 6 
Hello,
I´ve some questions about how to implement boundary conditions. I have a domain, where something flows through, in my case I´m using rhoCentralFoam. At the inlet I´ve a fixed velocity, a fixed temperature and a fixed pressure. At the outlet I want to set a fixed pressure and give no defaults to velocity and temperature. These should be calculated from the neighbour cells in the timestep before. I hope, you know what I mean How can I do this in OpenFoam? Is there a possiblity with the standard bc or groovyBC? regards treima 

June 21, 2012, 09:39 

#2  
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,934
Rep Power: 41 
Quote:


June 21, 2012, 09:52 

#3 
Member
Join Date: Mar 2012
Location: Munich, Germany
Posts: 67
Rep Power: 6 
Thanks.
I´ve tried fixedValue and zeroGradient. If I set these outlet conditions, U  zeroGradient p  fixedValue T  zeroGradient the case gives a floating exeption and problemes with the courantnumber. If I set U  zeroGradient p  zeroGradient T  zeroGradient the case works, but doesn´t match to my ideas. The best think would be, if it´s possible to set a "new" boundary condition for every timestep. But if this isn´t possible i´ve to setup a new case with other physical relations. I´m just wondering that this case haven´t discussed before regards treima 

June 21, 2012, 10:07 

#4  
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,934
Rep Power: 41 
Quote:


June 22, 2012, 07:20 

#5 
Member
Join Date: Mar 2012
Location: Munich, Germany
Posts: 67
Rep Power: 6 
My inlet conditions are
p  fixedValue, value uniform 1, T  fixedValue, value uniform 1, U  fixedValue, value uniform (3 0 0). And my outlet conditions just should be p  fixedValue, value uniform 1, T and U should be calculated from the domain in the timestep before. 

June 22, 2012, 15:11 

#6  
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,934
Rep Power: 41 
Quote:


June 25, 2012, 02:34 

#7 
Member
Join Date: Mar 2012
Location: Munich, Germany
Posts: 67
Rep Power: 6 
Thank you for your advice.
I´ve tried to fix the pressure at the outlet and set zeroGradient at the Inlet, but I still can´t calculate a solution because of a "floating execption"... Perhaps this is caused by my geomety, which you can see below. My idea was to set at inlet: p  fixedValue, T  fixedValue, U  fixedValue outlet: p  fixedValue Gamma_free and Gamma_fixed: slip condition (u*n=0). I was searching for good choices for the remaing conditions. I want to use these conditions, because they are just the first step in a bigger calculation. The aim is to do a very simple shapeoptimization with adjoint equations for this case. On Gamma_free should be a given pressuredistribution. 

June 25, 2012, 05:34 

#8 
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 3,934
Rep Power: 41 

July 2, 2012, 05:21 

#9 
Member
Join Date: Mar 2012
Location: Munich, Germany
Posts: 67
Rep Power: 6 
I´ve solved this problem.
If you take a very low temperature, you have a machnumber > 1, so you have to set just inletconditions and no condition at the outlet. Now I´m taking a appropriate proportion between velocity and temperature, so that Ma = (U^2)/T < 1 for all timesteps and every cell. Now it works very well. Now, in my next step, I want to implement the adjoint equation. I have calculated the adjoint equations and boundary conditions. In the subsonic case, for example, I have just one boundary condition, a function dependent of all adjoint variables. A small example is, with a the adjoint variables, a1 + 2 a2 + 3 a3 + 4 a4 = 0. Is it possible to implement this in OpenFoam? I´ve a underdetermined equation system as a boundary condtion... 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
non reflective boundary conditions for incompresible flow  Pascal_doran  OpenFOAM Programming & Development  16  August 25, 2015 05:35 
Water subcooled boiling  Attesz  CFX  7  January 5, 2013 04:32 
Import problem  ARC  Open Source Meshers: Gmsh, Netgen, CGNS, ...  0  February 27, 2010 11:56 
CG, BICGSTAB(2) : problem with matrix operation and boundary conditions  moomba  Main CFD Forum  2  February 17, 2010 04:37 
mass flow in is not equal to mass flow out  saii  CFX  2  September 18, 2009 08:07 