CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > STAR-CD

Star-CD transient simulation, problem of loss of mass

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 12, 2010, 11:07
Default Star-CD transient simulation, problem of loss of mass
  #1
kit
New Member
 
ychen
Join Date: Apr 2010
Posts: 2
Rep Power: 0
kit is on a distinguished road
I have tried several times to simulate a transient turbulent flow through a duck with conjugated heat transfer.
I tried two kinds of BCs, 1) pressure inlet, fixed mass flux as outlet; 2) fixed velocity inlet, flow split (1.0) as outlet.
For both case, the time step was set in the range of micoseconds, thus the maximum Courant number was less than 10. In each simulation, I check the mass conservation, and found out that the mass flux at both inlet and outlet decrease after each time step, therefore, after a long simulation (thousands or hundred of thousand), the mass flux goes to ZERO!!

I am so disappointed with Star-CD. How can it be?

Did anyone here encountered the similar problem with Star-CD transient simulations?
kit is offline   Reply With Quote

Old   April 12, 2010, 12:35
Default
  #2
Senior Member
 
Pauli
Join Date: Mar 2009
Posts: 181
Rep Power: 8
Pauli is on a distinguished road
The user manual states "it is particularly important to avoid" a combination of prescribed pressure and flow-split outlet conditions.

Try a fixed mass flux inlet & flow split (1.0) outlet.
Pauli is offline   Reply With Quote

Old   April 13, 2010, 08:51
Default
  #3
kit
New Member
 
ychen
Join Date: Apr 2010
Posts: 2
Rep Power: 0
kit is on a distinguished road
Thanks Pauli. Actually I have tried every possible BC, including the fixed inlet mass flux (provide velocity components, density & inlet temperature) and split outlet. It failed!

For a lower velocity or incompressible case, the calculations seem also acceptable. My problem is compressible with a peak velocity of about 400 m/s.

I run the same problem with CFX, it works quite well and much much faster.

For the steady-state, Star-CD runs well. Since in this case the tiny imbalance of mass flux between inlet & outlet is not important.

I have tried to find similar studies or comments on star-cd transient simulations, and found nothing important to me.
kit is offline   Reply With Quote

Old   April 13, 2010, 11:34
Default
  #4
Senior Member
 
Pauli
Join Date: Mar 2009
Posts: 181
Rep Power: 8
Pauli is on a distinguished road
Two things to check.

1) For the inlet boundary condition, do you have the flow switch set to mass or velocity. If you want a specific mass flux, it should be mass. Velocity will be adjusted based upon the pressure/density required by the domain.

2) Where is the reference pressure cell & what is it's value. This is very important for compressible flow problems. I don't remember what is the official "correct" method. I tend to place my reference pressure cell close to the outlet. That way I can peg the outlet boundary's pressure to a known value (usually ambient for my work).
Pauli is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
DPM mass problem Henrik Ström FLUENT 8 December 14, 2014 12:44
Synthetic (pulsatile) jet transient simulation aero CFX 0 November 6, 2009 02:10
Mass Diffusion: Transient and Steady State BC rval CFX 3 November 19, 2008 01:52
Mass loss! So what? jinwon park Main CFD Forum 13 May 22, 2008 09:29
Transient simulation Error information Li CFX 0 July 25, 2007 11:27


All times are GMT -4. The time now is 07:06.