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-   -   Boundary conditions - OpenFoam (http://www.cfd-online.com/Forums/openfoam/73068-boundary-conditions-openfoam.html)

sankarv February 25, 2010 14:01

Boundary conditions - OpenFoam
 
I am a new user of OpenFoam and I am trying to set-up an under-expanded supersonic jet issuing into an open atmosphere.
I am using the rhoCentralFoam and it has an example for the a similar jet.
Even though I can just copy the b.c. files (p,T and U) from the tutorial, I would like to better understand the various keywords in these files.

For example,
Jet_inlet
{
type totalPressure;
value uniform 300000.0;
p0 uniform 300000.0;
U U;
phi phi;
rho none;
psi psi;
gamma 1.4;
}
I do not understand all the keywords here. what does p0, phi, and psi stand for ?
I saw another example where all of the above keywords are not used ?
Is there any documentation for what kind of keywords must be specified for what
kind of boundary conditions ? Somebody please help.

Thanks
Vaidya

sankarv February 26, 2010 06:50

Under-expanded jets - Boundary conditions help
 
Hello OpenFoamers

I need some help with the boundary conditions desperately. As I have mentioned in my previous post, I am trying to simulate an under-expanded jet. I have successfully simulated the same problem using Fluent. Now
I am trying to use OpenFoam to compare the two solvers. (BTW,
This is my first ever OpenFoam simulation.....)
I am using rhoCentralFoam. It is a 2D grid I imported from Fluent using fluentMeshtoFoam.

Here is the configuration.
_________________________________
| free-stream |
| |
| wall_inlet |
| |Outflow
| |
! |
! jet_inlet axis |
!-------------------------------------|


Here is my 'p' file
dimensions [1 -1 -2 0 0 0 0];
internalField uniform 10000.0;
boundaryField
{
Jet_inlet
{
type totalPressure;
value uniform 300000.0;
p0 uniform 300000.0;
U U;
phi phi;
rho none;
psi psi;
gamma 1.4;
}
wall_inlet
{
type zeroGradient;
}
axis
{
type zeroGradient;
}
outflow
{
type pressureTransmissive;
value 10000.0
}
top_boundary
{
type pressureTransmissive;
value 10000.0
}
}
// ************************************************** *********************** //

For the outflow and top_boundary (freestream) I have tried wave transmissive, zeroGradient,pressureTransmissive boundary conditions.
But the simulation always crashes when the initial transient shock reaches the outflow.

Here is my 'U' file
dimensions [0 1 -1 0 0 0 0];
internalField uniform (0 0 0);
boundaryField
{
Jet_inlet
{
type fixedValue;
value uniform (319.2 0 0);
}
wall_inlet
{
type fixedValue;
value uniform (0 0 0);
}
axis
{
type zeroGradient;
}
outflow
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}
top_boundary
{
type zeroGradient;
}
}

Here is my 'T' file
{
Jet_inlet
{
type totalTemperature;
value uniform 300;
T0 uniform 300;
U U;
phi phi;
rho none;
psi psi;
gamma 1.4;
}
wall_inlet
{
type zeroGradient;
}
axis
{
type zeroGradient;
}
outflow
{
type zeroGradient;
}
top_boundary
{
type totalTemperature;
value uniform 300;
T0 uniform 300;
U U;
phi phi;
rho none;
psi psi;
gamma 1.4;
}
}

I must admit I am using the boundary conditions by looking at similar files in the rhoCentralFoam. I would sincerely appreciate if someone can
tell me what is wrong with my set-up and also if possible tell me the
meaning of the various keywords in the b.c files 'p','U' and 'T'. I can
make an educated guess about some of them, but I would be more comfortable hearing that from experts out there...


Please help

Thanks
Vaidya

koichi March 19, 2010 05:05

did you find a solution for the definition of psi, phi and U in totalPressure bc?

sankarv April 4, 2010 18:02

Creating New solver: for particle laden compressible jets
 
1 Attachment(s)
Hello OpenFoamers

I am a new user of OpenFoam and I am trying to set-up a particle-laden
under-expanded supersonic jet issuing into an open atmosphere.
Note, before I started OpenFoam, I ran fluent and got a converged
solution for this problem

Here are details of OpenFoam simulation:
---------------------------------------
Solver: rhoCentralFoam
Grid: axi-symmetric grid imported from Fluent using fluentMeshtoFoam
I.C: I used the converged Fluent solution as initial condition for openFoam
I managed to get a converged steady state solution for this
problem without particles


Particle laden jets:
!----------------------------------
Now I am trying to run a particle-laden jets. Since the solver
rhoCentralFoam does not have Lagrangian Particle Tracking in it, I realized
that I have to create a new solver.
I came across the icoLagrangianFoam solver which is basically a particle
tracking solver for an incompressible flow.

I found a nice tutorial "Tutorial icoLagrangianFoam/SolidParticle" by
Auerlia Vallier
(google for file name: Tutorial_icoLagrangianFoam_reviewed.pdf).
I used that and managed to implement particle tracking
in the rhoCentralFoam solver.
I called this new solver rhoCentralParticleFoam

This works well. But the problem is that the drag model in the original
icoLagrangianFoam is a very simple constant drag model.
I want to implement the standard drag model which is a function of
particle Reynolds number based on the stokesian drag for spherical particles.

Chapter 5 in the tutorial describes how to implement this drag model.
When I did these changes I get compilation errors that I cannot comprehend. I admit that I don't know c++ and I am not able to figure out the exact problem.

Can someone help me to fix these compilation errors ?
I have attached a tar file which contains the codes I am using for
this solver

karthick October 22, 2010 02:58

underexpanded jets
 
halo mr. sankarv

i am a new user of fluent! from ur post i learnt that u ve successfully simulated underexpanded jets in fluent. presently i am tryng to simulate the same!!! but i don get the results at alll


can u just help me with the same!!!! could u say me wat sort of profile ahs to be put and the necessary boundary conditions to be specified in gambit and the NPR values to be put in the fluent!!!!


i am desperately in nedd of ur help !!!

sankarv October 22, 2010 09:29

Karthick

There is a paper by K. Senesh & V.Babu titled Numerical Simulation of Subsonic and supersonic jets, AIAA 2005-3095. In this paper they talk about the models, grids, initial conditions and boundary conditions for fluent. I followed this paper to setup my case in fluent. Please try to look up this paper.



Quote:

Originally Posted by karthick (Post 280279)
halo mr. sankarv

i am a new user of fluent! from ur post i learnt that u ve successfully simulated underexpanded jets in fluent. presently i am tryng to simulate the same!!! but i don get the results at alll


can u just help me with the same!!!! could u say me wat sort of profile ahs to be put and the necessary boundary conditions to be specified in gambit and the NPR values to be put in the fluent!!!!


i am desperately in nedd of ur help !!!


edinmichael February 14, 2012 07:18

Hi i am just starting in cfd... and am trying to simulate under-expanded jet using fluent. but my solution is not converging. can you please help me with it.


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