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

compresible flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 25, 2003, 02:50
Default compresible flow
  #1
Martin
Guest
 
Posts: n/a
Hi! Iam begginer user STAR-CD. I dont know, how defining boundry condicion for compresible flow for fluid flow though pipe on end nozzle, (diameter is not constant). Flow is transsonic. Inlet is 50m/s, Preasure 10Mpa and Teperature 2500K. I use Inflow-preasure, but it divergent. Plese help me. Thanks
  Reply With Quote

Old   March 25, 2003, 02:58
Default Re: compresible flow
  #2
Stefan
Guest
 
Posts: n/a
You should try "stagnation - pressure", this worked for me (I had to deal with this problem lately, too)
  Reply With Quote

Old   March 25, 2003, 03:05
Default Re: compresible flow
  #3
Martin
Guest
 
Posts: n/a
termophyzical models->Liguid gases->initi->default?

monitorin -> deffault?
  Reply With Quote

Old   March 25, 2003, 03:12
Default Re: compresible flow
  #4
Stefan
Guest
 
Posts: n/a
Well, I guess you have to try this. I put in my initial temperatur and an estimate for the velocity. It would make sense to place your monitoring cell at a point of great changes (throat,...). In compressible flow there is an important connection the reference cell location. I do not know what the best thing location is, I put my reference cell at my outlet and defined my oulet pressure, and therefore all pressure data is relative to that location. Hope that helps.
  Reply With Quote

Old   March 25, 2003, 03:23
Default Re: compresible flow
  #5
Martin
Guest
 
Posts: n/a
I try it,init 1000K estimate vel 50m/s ,Stagnation (DU 1, 10Mpa,1000K)- Prasure(0.1Mpa, 293K) but -> negative density #076
  Reply With Quote

Old   March 25, 2003, 03:29
Default Re: compresible flow
  #6
Stefan
Guest
 
Posts: n/a
This might be a problem due to the large difference in pressure (two orders of magnitude). I read somewhere that this might lead to problems, and one should place the reference cell accordingly. But actually I just had this one problem, so I might not be a valuable help. Maybe you should place your reference pressure in an area where pressure is around 1 MPa ?
  Reply With Quote

Old   March 25, 2003, 04:03
Default Re: compresible flow
  #7
Martin
Guest
 
Posts: n/a
This solution divergent. initial 2000K 50m/s reference 1MPa T 600K stagnation (relative) 10MPa, Tem 2000K, preasure 1Mpa 600K *** WARNING #061 *** RATIO OF STAGNATION PRESSURE AND STATIC PRESSURE AT REGION 1

CELL 5107 LESS THEN 1. TEMPORARILY SET TO 1. *** WARNING #060 *** DENSITY OUT OF BOUND DUE TO PRESSURE CORRECTION AT CELL 16 DENSITY= -1.8100E+03 LIMITER APPLIED
  Reply With Quote

Old   March 27, 2003, 05:41
Default Re: compresible flow
  #8
Nicola
Guest
 
Posts: n/a
Hi Martin,

I had once a similar problem, I started with a higher density than expected, tried to get convergence, then took this solution as a starting point for the next calculation where I reduced the density a bit. I suppose this should work also with pressure. You have to play also with the residuals to get convergence. It is not at all a scientific way of getting a solution, but if it works...
  Reply With Quote

Old   March 27, 2003, 22:28
Default Re: compresible flow
  #9
cjtune
Guest
 
Posts: n/a
My 'beginner's problem' was to not use the 'pseudo-transient' soultion method... after enabling that, although the simulation never really converged, it at least did not diverge. Got to play around with the time step sizes.

  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
DNS for compresible flow Shuo Main CFD Forum 2 February 21, 2008 10:00
results for flow past flat plate normal to flow lisa Main CFD Forum 2 August 30, 2005 16:36
Navier stokes compresible viscid flow fea, somebody can help? Jose Choy Main CFD Forum 3 October 24, 2003 02:28
External Flow-compressible flow solver-lift/drag Tom Brown Main CFD Forum 7 December 29, 2000 14:41


All times are GMT -4. The time now is 14:22.