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

Turbulent and laminar conditions in one case

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

Like Tree1Likes
  • 1 Post By RobertHB

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 22, 2018, 08:49
Default Turbulent and laminar conditions in one case
  #1
New Member
 
David
Join Date: Oct 2018
Posts: 13
Rep Power: 2
Fool is on a distinguished road
Hi together,

I've just started to learn about CFD simulations, especially with OpenFOAM and I asked myself what happens if I use a turbulence module like simpleFOAM for a geometry where the flow isn't turbulent at every time. I'll probably get shitty results but how do I avoid it?

The case is that I have to simulate the distribution of water in a retention filter basin. The water comes to the filter basin by a special building where turbulent conditions exists but as soon as the water leaves this building and flows into the basin the conditions get laminar because of the larger area in that basin. Has anyone an idea how to handle situations like this?

Thanks
David
Fool is offline   Reply With Quote

Old   November 23, 2018, 04:54
Default
  #2
Senior Member
 
Robert
Join Date: May 2015
Location: Bremen, GER
Posts: 246
Rep Power: 6
RobertHB is on a distinguished road
The turbulence model and your solver, simpleFoam, are two different things. Using a certain solver, says nothing about whether you simulate turbulence or not, and more about if you are able to resolve the spacial and temporal scales of your flow.
simpleFoam is a steady-state solver, which is perfectly fine for flows which do not change over time, e.g. a laminar one, or large vortexes that achieve a steady motion. If you want to resolve the turbulences of your flow dependent on time, you might want to use a transient solver like pisoFoam or pimpleFoam. Solvers are chosen in the system/fvSchemes dictionary.

Each of the three solvers can use a turbulence model to calculate key variables like the turbulent kinetic enery k or the turbulence dissipation epsilon. This is where turbulence models come into play. Turbulence models are chose in the constant/turbulenceProperties dictionary and they require you to solver for different variables dependent on the model used.
Quote:
Originally Posted by Fool View Post
I asked myself what happens if I use a turbulence module like simpleFOAM for a geometry where the flow isn't turbulent at every time.
You can certainly run a simpleFoam simulation with a RANS turbulence model. No harm will come from solving a laminar flow with a turbulence model. But if you allready know that your flow will be laminar, why do so? You will solve for variables you don't need and will waste time doing so.

Quote:
I'll probably get shitty results but how do I avoid it?
Not if your flow is laminar and you use a turbulence model. But if your flow is turbulent and you do not use a turbulence model you will loose important information of your flow and, most likely, not see any turbulence.


Quote:
Has anyone an idea how to handle situations like this?
Transition of trubulent to laminar flow? The quickest solution: simpleFoam + RANS turbulence model. To get a first idea of your flow conditions, maybe its even enough to resolve some turbulence, but don't count on it.
Then use a pimpleFoam + RANS turbulence model. Map the velocity field, pressure and turbulence variables of your simpleFoam simulation to get a head start. Use an adjustable timestep to keep the maximum Courant number below 4.0. Give it alot of simulation runtime. Write timesteps regularily to check how and if your simulation changes from the simpleFoam solution.
Fool likes this.
__________________
If you liked my answer to your question, please consider leaving a "Like" in return
RobertHB is offline   Reply With Quote

Old   November 23, 2018, 09:28
Default
  #3
New Member
 
David
Join Date: Oct 2018
Posts: 13
Rep Power: 2
Fool is on a distinguished road
Thanks a lot!
Fool is offline   Reply With Quote

Reply

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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
CFX Treatment of Laminar and Turbulent Flows Jade M CFX 16 April 30, 2018 09:02
Running a turbulent case by using a laminar solution quarkz OpenFOAM Running, Solving & CFD 4 December 6, 2017 21:43
Why can i use a laminar solver for a turbulent flow? [Heat transfer problem] blackbow CFX 1 November 22, 2016 05:42
Ratio of eddy viscosity to molecular viscosity : Laminar or turbulent flow? JuPa CFX 7 September 9, 2013 08:45
pisoFoam turbulent case looks like laminar case inf.vish OpenFOAM Running, Solving & CFD 0 August 16, 2013 04:31


All times are GMT -4. The time now is 23:52.