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

Rotation flow calc. II. Andy

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 8, 2003, 01:54
Default Rotation flow calc. II. Andy
  #1
Christian
Guest
 
Posts: n/a
I hope I am not out of line. This tread is a copy from 03-04 Andy, in case you want to comment the mail, but haven't seen it Otherwise I apologise.

Hi Andy.

I am sorry for the delay. I needed time to think about your answer, and to check the calc. I do appreciate your time.

There not much swirl in the physical model. I have not measured it, only a visually evaluation. The calc however, the tangential component are as much as 10%. I don't think that is correct.

I cannot see why a certain amount of solid body rotation is wrong. I thought that it was "normal" close to the axis to have a "solid core". However, it does not seem to be the case in my calc. If the calc shows too mush solid core what will be your recommendation?

The velocity vectors are all pointing in the rotational direction, so I guess that is ok. No funny directions of the flow.

I am curious. What do you mean by more expensive procedures? The k-e cannot capture a rotational flow very well, and is inexpensive. RSTM is more expensive (and more unstable) but should be able to capture the rotational characteristics (well that's what I thought until last week Do you mean LES or are you thinking of modifications to the RSTM?

Do you have any recommendations to steps making the calculation work.

Ps. Funny thing is that I have made an calc for about 1 year ago that is very similar to this one, and it worked fine. I have looked it over to find any differences in setup, but cannot see any. I guess that I was lucky the last time, and that my knowledge of rotating flow needs an upgrade.
  Reply With Quote

Old   April 9, 2003, 08:49
Default Re: Rotation flow calc. II. Andy
  #2
andy
Guest
 
Posts: n/a
Many of the previous comments were based on the assumption you were solving a strongly swirling flow which is difficult for the solution procedure (stiff equations) and difficult for the turbulence model (curvature can greatly stabilize or destabilize the turbulent motion in a shear layer). "As much as 10% tangential velocity" is well below what would trigger swirling flow treatments.

Solid body rotation is correct at the core of a vortex. In a free vortex (but not a forced) this region is very small.

More expensive solution procedures will solve solution variables in blocks, pre-condition matrices, perform inner iterations and the like. Such solution procedures tend to be more robust and can work with smaller amounts of "numerical fixes" like pressure smoothing. However, they require more memory and more computer time per iteration. I was not refering to turbulence modelling.

If you have an old prediction which works and a current one that does not then studying the differences will tell you where the problem lies. I doubt luck has much to do with it but experience helps.

I would recommend either talking to someone local experienced with CFD or talking to your CFD supplier. I think we have just demonstrated the difficulties of getting this type of help from a forum such as this.

  Reply With Quote

Old   April 10, 2003, 04:06
Default Re: Rotation flow calc. II. Andy
  #3
Christian
Guest
 
Posts: n/a
Thank you Andy.
  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
Fully Developed Flow in Star-cd SMM STAR-CD 0 September 5, 2011 22:08
Compressible flow, no data at the outlet mireis FLUENT 1 July 28, 2010 05:22
Can 'shock waves' occur in viscous fluid flows? diaw Main CFD Forum 105 November 20, 2009 04:19
Rotation flow calculation Christian Main CFD Forum 5 April 3, 2003 12:19
Rotation flow calculation. Hans FLUENT 0 March 31, 2003 05:03


All times are GMT -4. The time now is 10:13.