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

Treatment of RANS-LES boundary in Embedded LES

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 6, 2018, 09:11
Default Treatment of RANS-LES boundary in Embedded LES
  #1
New Member
 
Clarice du Plessis
Join Date: Aug 2017
Location: Stellenbosch University
Posts: 9
Rep Power: 6
clarice is on a distinguished road
I'm modeling an axial fan in Fluent with the goal of determining the acoustics using Ffowcs-Williams Hawkings. I have an upstream duct, then the fan, followed by a downstream duct. The solution is steadily converged using k-epsilon realizable, and now I want to enable embedded LES in the fan cell zone with the purpose of activating the acoustics model when the flow has reached a statistically steady state.

​I read that using solve/initialize/init-instantaneous-vel generates an instantaneous velocity field out of the steady state results, which I did, but now I am struggling to figure out how to specify a spectral sythesizer / random vortex approach at the RANS to LES interface boundary. Does anyone have any advice on how I would go about doing that? Or does the solve/initialize/init-instantaneous-vel command take care of the creation of turbulence at the RANS/LES interface?
clarice is offline   Reply With Quote

Old   September 7, 2018, 12:26
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,447
Rep Power: 53
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
The init-instantaneous-vel command adds perturbations onto your RANS field to generate a suitable initial condition. If you don't add perturbations, you tend to get a flow that remains laminar rather than producing any turbulence.


You of course need to also specify the perturbations at domain boundaries, otherwise your flow will likely become laminar if the incoming flow does not have any perturbations. Since it's rare that anyone has time-accurate velocity, temperature, and pressure profiles at boundaries some tools are needed. The spectral synthesizer is one such tool. However, here we are talking about inlets at the domain, not the RANS|LES interface.


Unfortunately, I don't recall what is the treatment at the RANS-LES interface. I haven't used e-LES in a long long time.
LuckyTran is offline   Reply With Quote

Old   September 12, 2018, 10:25
Default
  #3
New Member
 
Clarice du Plessis
Join Date: Aug 2017
Location: Stellenbosch University
Posts: 9
Rep Power: 6
clarice is on a distinguished road
Thanks! I found some documentation and guidelines on the use of the Vortex Method that Fluent recommends for the treatment of the RANS-LES interface, but I can't find it anywhere in Fluent in order to activate/use it.
clarice is offline   Reply With Quote

Old   September 12, 2018, 11:54
Default
  #4
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,447
Rep Power: 53
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Did you miss it in the Fluent manual? There's step by step instructions.

Fluent Manual


Which part are you stuck on? Do you have embedded LES already activated?
LuckyTran is offline   Reply With Quote

Old   September 27, 2018, 04:38
Default
  #5
New Member
 
Clarice du Plessis
Join Date: Aug 2017
Location: Stellenbosch University
Posts: 9
Rep Power: 6
clarice is on a distinguished road
I have seen the instructions, and I have activated embedded LES in a certain zone, but the interfaces between the LES and RANS regions do not give me the option to change the boundary condition from interface to rans-les interface. All the usual options are there, except the rans-les interface option.
clarice is offline   Reply With Quote

Old   September 27, 2018, 16:06
Default
  #6
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,447
Rep Power: 53
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Since you said interface... do you have more than 1 cell zone condition? The RANS and LES region need to be in the same cell zone. And that surface will should not be an interface.
LuckyTran is offline   Reply With Quote

Reply

Tags
embedded les, large eddy simulation, les, rans les interface, spectral synthesizer

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Error - Solar absorber - Solar Thermal Radiation MichaelK CFX 12 September 1, 2016 06:15
Low torque values on Screw Turbine Shaun Waters CFX 34 July 23, 2015 09:16
Difficulty In Setting Boundary Conditions Moinul Haque CFX 4 November 25, 2014 18:30
Low Mixing time Problem Mavier CFX 5 April 29, 2013 01:00
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 05:05


All times are GMT -4. The time now is 15:53.