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

Large Eddy Simulation of turbulent channel flow

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

Like Tree1Likes
  • 1 Post By daroz

Reply
 
LinkBack Thread Tools Display Modes
Old   March 14, 2017, 12:41
Default Large Eddy Simulation of turbulent channel flow
  #1
New Member
 
Join Date: Mar 2011
Posts: 6
Rep Power: 8
daroz is on a distinguished road
I am trying to reproduce the well known turbulent channel flow simulation of Kim, Moin and Moser (1987) where they provide a DNS solution of the problem.

In my case, I am trying approach the problem with the available LES in ANSYS Fluent R.17.2. I am using Smagorinsky-Lilly (Dynamic Stresses) for the SGS modelling and periodic conditions in both stream and spanwise directions. The flow is driven by a constant mass flow rate.

The problem is that I am getting a laminarized solution after several flowthrough times. I have tryied to use RANS and URANS solutions as initital flow fields as well as a perturbated field via an UDF.

The space and time discretization requirements are being fullfiled, at least I guess they are (CFL < 1, y+ < 1, etc)...

Does anyone have any idea of what I am doing wrong or have experienced the same problem?

Thank you.
daroz is offline   Reply With Quote

Old   March 30, 2017, 12:23
Default
  #2
New Member
 
钱权
Join Date: Mar 2017
Posts: 5
Rep Power: 2
qianquan is on a distinguished road
recently i do circle cylinder flow with les , smagorinsky-lily (dynamic), re=140000, boundry layers are 40. at first, using ke turbulent model with steady , when it converged, tap 'solve/initialize/init-instantaneous-vel' in GUI , and then switch to les , spatial discretion is bound central differing , max cfl around 2, the results looks ok


Sent from my iPhone using CFD Online Forum mobile app
qianquan is offline   Reply With Quote

Old   March 30, 2017, 13:23
Default
  #3
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 707
Blog Entries: 17
Rep Power: 21
sbaffini will become famous soon enough
The plane channel flow is quite tough to get started, especially if your discretization is adding dissipation (yes, the bounded central scheme might still be too much diffusive). Also, the spectral synthesizer as implemented in Fluent is not the best tool out there. It all depends from the scale at which energy is supplied in your turbulent velocity field. In plane channel this happens to be very small and numerics dominated. For the cylinder it is much more large and manageable in Fluent.

Long story short, check out my initialization routine here:

https://www.cfd-online.com/Forums/bl...nt-part-1.html

and use the unbounded central scheme at least for the first few hundred iterations. Obviously, I assume that everything else is ok with your setup.
sbaffini is offline   Reply With Quote

Old   March 30, 2017, 14:18
Default
  #4
New Member
 
Join Date: Mar 2011
Posts: 6
Rep Power: 8
daroz is on a distinguished road
Thank you for the support!

I have handled the simulation of the plane channel flow since the post.

I've used a steady solution obtained with the SST model as initial field.

I am trying to employ the same methodology for the turbulent duct flow. I will let you know if I succeeded.

Thank you "sbaffini" for the routines you provided. I am sure they will be very useful.
sbaffini likes this.
daroz is offline   Reply With Quote

Old   March 30, 2017, 15:06
Default
  #5
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 1,851
Rep Power: 26
LuckyTran will become famous soon enoughLuckyTran will become famous soon enough
I never encountered consistent relaminarization, but I also do not typically use the bounded schemes. I.e. I used second order Euler and not bounded second order, and plain central instead of bounded central.

For me the problem was the initial perturbation. It could be reasonably turbulent for a few flow through times but because of the streamwise periodic BC, it relaminarizes after say 3 or 4 flow-thru times (but not 1 because it takes a flow-thru to recycle the initial flow). However, this was entirely my fault because I gave a bad initial perturbation. For example uniform random perturbations everywhere had a tendency to relaminarize. Sometimes I messed up my script and put perturbations on only the upper-half of the channel. An interesting flow develops which is turbulent on the upper side but laminar on the lower side!

I haven't tried the "solve/initialize/ init-instantaneous-vel" option in Fluent for channel flow, but I would think that it should work reasonably well. Unfortunately, this option requires you to have a current RANS solution so that you cannot re-do the perturbations in the middle of your LES run.

So yeah, maybe the solution is to give a good perturbation and run with unbounded schemes.

Last edited by LuckyTran; March 30, 2017 at 18:47.
LuckyTran is online now   Reply With Quote

Old   March 30, 2017, 16:38
Default
  #6
New Member
 
Join Date: Mar 2011
Posts: 6
Rep Power: 8
daroz is on a distinguished road
I haven't encountered any problem in obtaining the RANS solution. Actually it reaches convergence very quickly.

The only things I have changed from the time I was having problems is that I reduced the time-step and switched the pressure-velocity coupling to the COUPLED method. I am still using bounded central differencing for momentum but in the next time I will follow the advises and use an unbounded scheme for the first few hundred iterations.
daroz is offline   Reply With Quote

Reply

Tags
channel flow, fluent, les

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
Velocity profile is not turbulent (OPEN CHANNEL FLOW) roi247 FLUENT 2 March 15, 2017 08:30
Accuracy of LRR and SSG in turbulent channel flow dradenkovic OpenFOAM Running, Solving & CFD 1 August 23, 2016 13:03
LES database for turbulent channel flow at Re_tau=590 sbaffini Main CFD Forum 10 May 27, 2014 10:55
About Some Concepts:Laminar flow, turbulent flow, steady flow and time-dependent flow Jing Main CFD Forum 5 March 2, 2013 15:02
a symposium about large eddy simulation dictatore_bozorg FLUENT 1 April 29, 2012 10:47


All times are GMT -4. The time now is 01:38.