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

Transient combustion

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 18, 2004, 02:16
Default Transient combustion
  #1
kris
Guest
 
Posts: n/a
I want to solve the combustor of dump type.

Geometry in combustion process has combustion instability in arbitrary equivalent ratio.

In steady state analysis with STAR-CD, mass residual value,of course, Not reduced .

In transient analysis approach,

case1) combustion model is EBU. Turbulent model is k-epsilon model.

case2) combustion model is PPDF. Turbulent model is k-epsilon model.

Problem of case2: 1. when I solve in the case2, Temperature increase with time step but In case1, Temperature Not change. I think this is because of ignition setting problem.

How does I determine ignition time step

2.Is it possible to see the Growth of a combustion instability following transient calculation with STAR-CD?
  Reply With Quote

Old   August 18, 2004, 22:12
Default Re: Transient combustion
  #2
Mike
Guest
 
Posts: n/a
Kris,

I think dump combustors are usually premixed, which means the PPDF model is not an appropriate choice.

The approach you are describing is an unsteady RANS calculation. For premixed combustion in Star, you can choose from the flame front models (i.e., Weller and CFM) or ebu models. I believe that flame front models are more appropriate for premixed combustion, but they are also more difficult to use.

Getting successful numerical ignition often requires some experimentation. You should probably turn on ignition early in the calculation and leave it on for at least a residence time or some other characteristic timescale for your problem. Then you should run the unsteady analysis for at least several residence times beyond ignition. Typical ignition temperature (in Star) is 1800K and the burnt fraction might be set at 0.25.

Good luck - Mike

  Reply With Quote

Old   August 21, 2004, 01:23
Default Re: Transient combustion
  #3
kris
Guest
 
Posts: n/a
Thank you very much, Mike.

Actually, I used ummixed gas, inlet1(coannulus=fuel),inlet2(center=oxidant),in my geometry.

Recently, two kinds of model is used. those is PPDF and EBU.

The problem of EBU is ignition time step.

So, I first applied PPDF for my model. then that time in which combustion start was decided as starting ignition for EBU.

Of course, I condsidered characteristic timescale but combustion is NOT occured.

Now, I am going on calculation using PPDF.

For High order Temporal Discretization, I used Crank-Nicholson, applied for UD scheme execept density.

At this point there were another problem.

that is unstable. :<

actually, in this case, time step interval is a little long.

Original objective is to get Pressure oscillation

  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
combustion model in premixed combustion chamber wuyu FLUENT 6 March 26, 2014 14:58
Transient Flow, Transient Pressure in Work Bench Erich CFX 1 May 8, 2007 11:55
transient combustion and mesh adaption Peter CFX 4 April 20, 2006 18:23
Transient Combustion Jan Erik FLUENT 0 November 15, 2001 08:44


All times are GMT -4. The time now is 02:54.