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

small density change for isothermal flows

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 6, 2013, 11:02
Default small density change for isothermal flows
  #1
Senior Member
 
Join Date: Nov 2012
Posts: 171
Rep Power: 14
hz283 is on a distinguished road
Hi All,

When I simulate the isothermal flows, I used the rhoPimeplFoam. I also made some modification on that solver (1) comment the statements for solving the enthalpy equation but retain therm.correct() (2) use Low Ma number assumption, pressure for the EoS is fixed to be 101325 Pa. However, when I use this solver to simulate the isothermal flows, the density shows very small change.

I attached an example: an isothermal air jet, uj=7m/s, temperature is always 294K in the initial field and during the simulation. However, as I said, the density in the domain varies between 1.197 and 1.188. This is the density for air. In Openfoam, the density is updated through rho=p*psi, where psi=1/(R*T). Along this line, it seems that the density change should be from R because in this case p and T are fixed. But I do not know why R is changed since I use pureMixture , which should be also fixed. The complete options for thermalphysical models I used are:
thermoType hPsiThermo<pureMixture<sutherlandTransport<specieT hermo<hConstThermo<perfectGas>>>>>;

Another possible explanation is that this small variation of density is completely caused by numerical error, which should be tolerable.

I am a little confused about this problem. Thank you in advance if someone can give me comments on this.

Thanks.
hz283 is offline   Reply With Quote

Old   April 6, 2013, 11:05
Default
  #2
Senior Member
 
Join Date: Nov 2012
Posts: 171
Rep Power: 14
hz283 is on a distinguished road
Attach a contour of density here. Thanks.

Quote:
Originally Posted by hz283 View Post
Hi All,

When I simulate the isothermal flows, I used the rhoPimeplFoam. I also made some modification on that solver (1) comment the statements for solving the enthalpy equation but retain therm.correct() (2) use Low Ma number assumption, pressure for the EoS is fixed to be 101325 Pa. However, when I use this solver to simulate the isothermal flows, the density shows very small change.

I attached an example: an isothermal air jet, uj=7m/s, temperature is always 294K in the initial field and during the simulation. However, as I said, the density in the domain varies between 1.197 and 1.188. This is the density for air. In Openfoam, the density is updated through rho=p*psi, where psi=1/(R*T). Along this line, it seems that the density change should be from R because in this case p and T are fixed. But I do not know why R is changed since I use pureMixture , which should be also fixed. The complete options for thermalphysical models I used are:
thermoType hPsiThermo<pureMixture<sutherlandTransport<specieT hermo<hConstThermo<perfectGas>>>>>;

Another possible explanation is that this small variation of density is completely caused by numerical error, which should be tolerable.

I am a little confused about this problem. Thank you in advance if someone can give me comments on this.

Thanks.
Attached Images
File Type: jpg air_jets.jpg (20.6 KB, 8 views)
hz283 is offline   Reply With Quote

Reply


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
Incompressible and compressible flow. Confused student. Main CFD Forum 27 March 18, 2017 13:25
Change density; reynolds number thiez03 CFX 4 April 5, 2012 18:04
Lagrangian particles (change density and diameter) kel85uk OpenFOAM 1 July 22, 2011 05:01
Large volume and small flows Astrid CFX 5 April 26, 2002 06:47
Multiphase Flows Elliot Schwartz Main CFD Forum 6 May 28, 1999 03:11


All times are GMT -4. The time now is 00:47.