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

simulation results for k-w model and SST model

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 15, 2007, 05:01
Default simulation results for k-w model and SST model
  #1
Li
Guest
 
Posts: n/a
Hi, guys. I am learning CFX10.0 and now I encountered a problem. My case is simple with the air supply from the left top and air discharge from the right bottom, but I got weild simulation results of streamline and velocity distribution. I mean I found a reference in which he got similar results of k-w model with that of k-e model and different results from SST model. But I got similar results of k-w model with that of SST modle. I don't know why, would you help me to look at it and give me some suggestions. Thank you very much! (1)streamline of k-w model http://imageshack.dk//viewimage.php?...e/M2k94389.jpg (2)streamline of SST model http://imageshack.dk//viewimage.php?...e/tYn97524.jpg (3)velocity distribution at x=3m http://imageshack.dk//viewimage.php?...e/alh97900.jpg

  Reply With Quote

Old   June 17, 2007, 16:25
Default Re: simulation results for k-w model and SST model
  #2
Gert-Jan
Guest
 
Posts: n/a
Need more info:

- How does your grid look like? Is it appropriate for the models you use?

- Reynolds number?

- What do you specify for turbulence at the inlet?

- How well is it converged? Should not be of any problem if your grid is ok. Do you have monitor points? Imbalance?

Gert-Jan

www.bunova.nl

  Reply With Quote

Old   June 18, 2007, 02:51
Default Re: simulation results for k-w model and SST model
  #3
Li
Guest
 
Posts: n/a
Gert-Jan, thank you very much for your response. The grid file is here,http://imageshack.dk//viewimage.php?...e/IVK49154.png

Reynolds number is about 5000, and I set the turbulence intensity as 4% and turbulent length scale as 0.0168 which is one-tenth of the inlet height. Actually, I set the residual type as RMS, residual target as 1E-05. Finally, the monitor residual graph shew it arrived at the residual target. But I didn't set monitor points.

With kind regards, Li
  Reply With Quote

Old   June 18, 2007, 02:51
Default Re: simulation results for k-w model and SST model
  #4
Michael B
Guest
 
Posts: n/a
I've noticed a velocity at the inlet of 0.5 m/s. Are your calculation laminar or turbulent?
  Reply With Quote

Old   June 18, 2007, 02:54
Default Re: simulation results for k-w model and SST model
  #5
Li
Guest
 
Posts: n/a
Michael, thank you very much for your response. The Reynolds number is about 5000. I am just doing some practice to learn CFX through comparing the simulation results with the measurements. And my supervisor hopes me to compare the simulation result for different turbulent models with the measurements.
  Reply With Quote

Old   June 20, 2007, 01:21
Default Re: simulation results for k-w model and SST model
  #6
Jens
Guest
 
Posts: n/a
Hi,

I can seen taht you are working on the Annex 20 case.

You should expect quite good results.

First check you mesh. It seems like that the mesh is not very good. Take a look at the profile. You can seen a large jump in the jet core velocity. The core of the flow much resolved.

The turbulence models can be sensitive to the mesh close to the walls. Furthermore check the convergence.

Have you ensure that the residual are below 10-4 and the imbalance is small ???

Take look at the following homepage: http://www.cfd-benchmarks.com/

It has a lot on benchmarking for this kind of flow etc.

Regards

Jens
  Reply With Quote

Old   June 20, 2007, 03:49
Default Re: simulation results for k-w model and SST model
  #7
Li
Guest
 
Posts: n/a
Hi Jens. Thank you very much for your response. Yeah, I am doing the simulation according to Annex 20. Maybe there is a problem with the mesh file. But I am just wondering it would cause the streamline so different? I also asked one of my friend to simulate it with k-w model in Phoenix, he got the similar streamline as that of k-e model even he adopted very coarse mesh.
  Reply With Quote

Old   June 29, 2007, 04:19
Default Re: simulation results for k-w model and SST model
  #8
Kumar
Guest
 
Posts: n/a
K-w solves well for near wall flows compared to k-w. SST is just an addition of turb shear stress to k-w,but it will use k-w near wall and k-e away from wall. Again wall functions like std and scalable solve for y+ below 20 with less efforts than automatic which requires arbitrary fine mesh. But automatic wall functions will capture laminar sublayer, and the log layer if you have around 10 nodes in that region.

So it's of no use if u r using sst/k-w and auto wall functions with coarse grid and comparison will give u no idea abt their inequalities with k-e.

Kumar.
  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
Use of k-epsilon and k-omega Models Jade M Main CFD Forum 12 June 2, 2015 13:16
Low Reynolds Number SST Model Josh CFX 39 February 19, 2014 09:47
Water subcooled boiling Attesz CFX 7 January 5, 2013 04:32
k-omega SST simulation of turbulent flow around a circular cylinder DanM OpenFOAM Running, Solving & CFD 16 December 12, 2012 14:39
Low Reynolds k-epsilon model YJZ ANSYS 1 August 20, 2010 13:57


All times are GMT -4. The time now is 11:41.