|
[Sponsors] |
Please explain steady turbulence for simpleFoam |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
August 31, 2010, 11:28 |
Please explain steady turbulence for simpleFoam
|
#1 |
Member
Join Date: Dec 2009
Posts: 33
Rep Power: 16 |
In layman terms could someone please explain what the steady-state means for simpleFoam solver with turbulent flow?
I mean I always thought turbulent flow was unsteady? Thanks |
|
August 31, 2010, 12:42 |
|
#2 |
Senior Member
Marco A. Turcios
Join Date: Mar 2009
Location: Vancouver, BC, Canada
Posts: 740
Rep Power: 28 |
Though I have never used simpleFoam myself, looking at the solver code it appears that steady state would refer to the mean flow, as the monitored residuals are calculated after the momentum equation is solved (in UEqn.H). At least this makes sense to me with RAS turbulence models, not sure how it would apply to LES.
Obviously it depends on your particular case whether or not a steady mean flow even makes sense or says anything useful. Your choice of timescale is would also be important. |
|
August 31, 2010, 20:46 |
|
#4 |
Member
Join Date: Dec 2009
Posts: 33
Rep Power: 16 |
Well my case involves modelling the time-averaged solution. If that makes any sense?? In terms of turbulent flow, all I know is that it comprises of mean flow and fluctuating flow.
|
|
September 1, 2010, 15:36 |
|
#5 |
New Member
Matt James
Join Date: Jun 2010
Location: Marinette,WI, USA
Posts: 25
Rep Power: 16 |
I would say the steady-state refers to a mean, fully developed flowfield. While a pipe flow may be turbulent, you can expect it to reach a state where the mean flow profile doesn't change with time.
Am I understanding your question correctly? |
|
September 1, 2010, 21:19 |
|
#6 |
Member
Join Date: Dec 2009
Posts: 33
Rep Power: 16 |
Hi mdjames. Thanks for your help. Yeah that seems to make sense to me. But how do you discern whether it has reached fully developed flow? Is it a simple case of observing your post-processing flow or does it fully develop when the solution converges?
|
|
September 2, 2010, 12:56 |
|
#7 |
New Member
Matt James
Join Date: Jun 2010
Location: Marinette,WI, USA
Posts: 25
Rep Power: 16 |
is your flow oscillatory or time-independent as t -> Infinity? Also, is there an analytical solution?
Just a thought, you might get some more help from the General CFD forum as I'm not sure if this is strictly an OpenFOAM question. |
|
September 3, 2010, 22:32 |
|
#8 | |
Member
Join Date: Dec 2009
Posts: 33
Rep Power: 16 |
Quote:
I am doing this on OpenFOAM. I'm not quite sure what you mean by 'is there an analytical solution?'. But as far as I understand, my flow needs to converge to steady-state within the turbulent flow. Does that make any sense? Basically I'm just curious as to how turbulent flow can be steady-state when I'm constantly reading in fluid dynamics books that turbulent flow is time dependant? It seems somewhat contradictory to use simpleFoam. |
||
September 7, 2010, 17:01 |
|
#9 |
New Member
Matt James
Join Date: Jun 2010
Location: Marinette,WI, USA
Posts: 25
Rep Power: 16 |
The flow will be steady-state when the mean flow stops developing. The fluctuations(turbulence) are kind of superimposed on the steady state flow.
Think of a river. If you had to describe the flow to someone, you might say that its velocity peaks in the middle and decays to zero at the banks. However, the river is almost certainly turbulent. Would you call a steadily flowing river time-dependent just because it's turbulent? No, the time dependent part of the flow (eddies) are just along for the ride on the mean flow. It's all a matter of what part of the flow you're interested in. |
|
September 8, 2010, 00:14 |
|
#11 | |
Member
Join Date: Dec 2009
Posts: 33
Rep Power: 16 |
Quote:
|
||
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
High turbulence intensity | wenfengxie | FLUENT | 1 | April 16, 2010 13:00 |
question about turbulence model selection and sensitivity | karananand | Main CFD Forum | 1 | February 26, 2010 05:41 |
Centrifugal Pump and Turbulence Model | Michiel | CFX | 12 | January 25, 2010 04:20 |
Turbulence Intensity Vs CFD Simulation | Apple L S Chan | Main CFD Forum | 3 | December 15, 1998 18:28 |
turbulence modeling questions | llowen | Main CFD Forum | 3 | September 11, 1998 05:24 |