CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Pressure BC for compressible flow

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By dancfd

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 4, 2013, 13:57
Default Pressure BC for compressible flow
  #1
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
Hey lads,

i need an outletInlet bc for pressure in my compressible case,for my farfield. I used outletInlet but it doesn't work. I need something like inletOutletTotalTemperature, which i use for temperature. Anything in mind? I already used totalPressure but it works like fixedValue,i need an outletInlet.

Thanks
VSass is offline   Reply With Quote

Old   April 4, 2013, 16:17
Default
  #2
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
use waveTransmissive or now pressureTransmissive i think.there is examples in tutorials.
immortality is offline   Reply With Quote

Old   April 5, 2013, 06:09
Default
  #3
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
Well, here are my case files.

p

GEOM
{
type zeroGradient;
}
FARFIELD
{
type waveTransmissive;
value uniform 1e+05;
gamma 1.4;
phi phi;
rho rho;
psi psi;
lInf 1;
fieldInf 1e+05;
}

T
GEOM
{
type zeroGradient;
}
FARFIELD
{
type inletOutletTotalTemperature;
U U;
phi phi;
psi psi;
gamma 1.4;
T0 uniform 306.534;
}

U
GEOM
{
type fixedValue;
value uniform (0 0 0);
}
FARFIELD
{
type pressureInletOutletVelocity;
value uniform (100 0 0);
}

I'm a little stuck here,so thanks for your advise.
VSass is offline   Reply With Quote

Old   April 5, 2013, 13:17
Default
  #4
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
does this settings of BC's work?you could set T also in waveTransmissive form.whats your doubt about?
immortality is offline   Reply With Quote

Old   April 5, 2013, 13:29
Default
  #5
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
No,they don't work. I want to find the correct combination of those in order for my farfield not to be reflective. I could use something like inletOutletTotalPressure but it doesn't exist. I need something like pressure Farfield in Fluent, which i've seen you are familiar within an other post.
VSass is offline   Reply With Quote

Old   April 5, 2013, 15:12
Default
  #6
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
in my opinion you should make FarField BC divided into two parts.one for inlet part and one for outlet part.on inlet part you should specify p and T(U be in any kind of zeroGradient BC's) or U and T(p be of zeroGradient kind)
I don't know what do your case and geometry like.do you have an airfoil or something like that?
immortality is offline   Reply With Quote

Old   April 5, 2013, 15:57
Default
  #7
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
I have a sphere geometry in a sphere farfield. What you say sounds great but i will need some guidance in making and applying it.

(Thanks a lot for your interest!)
VSass is offline   Reply With Quote

Old   April 5, 2013, 16:11
Default
  #8
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
oh i remembered you wanted to simulate vortex shedding in a sphere thats in a flow.can't you change farField patch to a cylindrical form that has an inlet and an outlet?
immortality is offline   Reply With Quote

Old   April 5, 2013, 20:31
Default
  #9
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
Yes,that's me.No, 'cause i've already completed the incompressible simulation and i want the compressible results to have a complete comparison.So,any ideas for the combination of p/T/U at farfield?
VSass is offline   Reply With Quote

Old   April 5, 2013, 22:16
Default
  #10
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
set T as waveTransmissive as i told you before.if it didn't work set it simply zeroGradien.if this also didn'p work you should set farfield as a cylinder to have certained inflow and outflow patches.do these 3 ones and let me know the results.
immortality is offline   Reply With Quote

Old   April 6, 2013, 07:51
Default
  #11
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
Ok, but can you explain to me why zeroGradient at farfield? I thought we need something like inlet/outlet or wave transmissive like you've said.
VSass is offline   Reply With Quote

Old   April 6, 2013, 08:36
Default
  #12
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
zeroGradient have to be set for variables that we have to set a value for them for starting numerical calculations and not required by fluid dynamics itself.
inletOutlet is a kind of zeroGradient.when flow is going into domain it has the value we specified ourselves as external value(becomes like fixedValue) and when the flow flows outward! solver read the values of variable in domain and put it on boundary(and becomes zeroGradient).
immortality is offline   Reply With Quote

Old   April 10, 2013, 10:06
Default
  #13
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
A brief report:
the boundary conditions were just fine.The reason why i couldn't see the desired vortices was because rhoCentralFoam is inviscid. I came to this conclusion due to the fact that i get the same and desired distributions of p,T,U with different ( but relative when it comes to their nature) boundary conditions, but i don't see any vortices.

So,next step was to change solver. I now use rhoPimpleFoam with laminar simulation, and i can see clearly the desired vortices. The problem know is that the solution crashes after some time, saying something like : Max Number of Iterations Exceeded, which i think is a problem with temperature.

Also, i think that the solution is highly dependable from the maxDeltaT and that CFL condition alone is not enough.

So,you recommend the same bcs for reaching convergence?
VSass is offline   Reply With Quote

Old   May 19, 2014, 23:03
Default
  #14
Senior Member
 
Daniel
Join Date: Jul 2009
Location: Montreal, Canada
Posts: 156
Rep Power: 16
dancfd is on a distinguished road
Hello Vasileios,

Could you please expand upon why changing boundary conditions and obtaining the same results suggests that rhoCentralFoam is inviscid? I have been using it to model airfoil flow, and I have found that it does develop a boundary layer and a wake with significant vortices.

Maybe something else is wrong with your simulation. I have had different results with rhoPimpleFoam, rhoCentralFoam, and sonicFoam; not sure why, but it seems as though they are suited to different applications.

Daniel
immortality likes this.
dancfd is offline   Reply With Quote

Old   May 26, 2014, 13:39
Default
  #15
Member
 
VS
Join Date: Nov 2012
Posts: 86
Rep Power: 13
VSass is on a distinguished road
Daniel,

I supposed that rhoCentralFoam is inviscid because, provided that Reynolds is sufficient and the boundary conditions of the farfield do not create numerical reflections that wouldn't allow the flow to separate and the vortices to detach, I came to the hypothesis that this solver solves the Euler formulation of the equations.

Kind regards
VSass is offline   Reply With Quote

Reply

Tags
outletinlet, pressurebc, rhocentralfoam

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pressure Outlet Guage pressure Mohsin FLUENT 36 April 29, 2016 18:16
Non-steady flow simplified for use in Vissim steamerandy Main CFD Forum 0 October 31, 2011 22:08
Pressure outlet in two-phase flow in horizontal 2D channel AlmostSurelyRob Main CFD Forum 0 November 17, 2010 08:32
pressure distribution in water flow, differences in icoFoam and COMSOL deniggo OpenFOAM Running, Solving & CFD 14 September 30, 2010 04:48
Flow not moving - Supersonic/Initial Pressure problem? shankara.2 FLUENT 0 June 9, 2009 21:49


All times are GMT -4. The time now is 03:40.