High speed flow with LaunderSharmakepsilonModel
Dear All,
I need to run a compressible high speed nozzle flow in OF on a lowRe mesh (y+<1). So far I did my calculations with the kOmegaSST turbulence model and it worked quite nice. Now I have to use the kEpsilon turbulence model on the same mesh. The only lowRe kepsilon turbulence for a compressible case available in OF is the one by Launder and Sharma. I compared the code of the LaunderSharmaKE with the standard kEpsilon model and found some differences as additional sourceterms as well as some turbulent Reynoldsnumber functions. So I have some questions, hoping anybody can answer these:
Thanks in advance! Sebastian 
Hi sebastian,
Did you find something? I have to simulate a flow in a nozzle and I would like to use this turbulence model. Other question: Could you post your boundary condition for the komega case? To compare with my boundary conditions. Thanks Valentin 
hello Sebastian
Did you find out the proper answers? And how did you find out which method is suitable for lowRe compressible? 
hi Valentin
do you want to simulate a lowRe turbulence too?could you send your case to me? Thanks. 
3 Attachment(s)
Hi eshan :)
Yes I would like to make a lowReynolds simulation in a nozzle. I attached a case with komegaSST model with boundary conditions for lowReynolds simulations (I think). 
thanks Valentine
could you tell me about how choose and which formulas(if they are any) you used for obtaining omega value on walls and also inlet values? and why didn't you assign mut to be calculated on walls also? thanks so much. 
omega on walls: although for a keps model you have to set k = 0 and eps=0 on walls. According to my understanding for a komega omega isn't 0 on walls. If you use the omega WallFunction it will assign the correct condition on walls (omega = omegavis + omegalog. Omegalog will be zero as you use a lowRe mesh).
for the inlet: first I impose a uniform value that I calculated with an approximate solution. But I don't think the profile has to be uniform. So I impose condition for k wich calculates the value for k depending on U (k = 3/2 (I U)^2). After that I choose an inlet function for omega wich uses the formula omega = sqrt(k) / (Cmu^0.25 * l). So wich depends on k. To be consistent with the value of k. For mut: Set mut as calculated would be ok. But I prefer to set mut = 0 as you are in the laminar part of the turbulent boundary layer. 
thanks so much valentine.was very useful.
a question occurred to me.should internalField better to be equal to inflow values or be equal to values have set on walls? and how can do about highRe study?how should set the values on the walls(and also internalField)? thanks. 
dear Sebastian
have a look into it:http://www.openfoam.org/mantisbt/view.php?id=835#c2167 it looks there isn't yet an lowRe kOmegaSST model in OF as Dr.Weller told me. 
for high Reynolds, you have to choose wallfunction for k, epsilon (or omega). The choice of wallFunction is made in the mut file. You can choose spaldingWallFunction which allows mesh with y+< 30 (for my case it was useful)
For internalField I set a approximate value. It's not very important as it is just a value to initialize your case. 
Quote:

thanks.
3 questions: 1)in lowRe as you said omega should not be zero(1e10) but how can specify an appropriate value there?is it approximate? 2)what do you mean by using wallFunction for omega in lowRe case while in lowRe maybe we don't have to use wall functions afaik Quote:

1) & 2) omegaWallFunction assigns the good value for omega at the wall regardless the type of turbulence model (low or high)
3) Where? (inlet, outlet, wall)? 
in 1 question I wonder how can set an omega value on wall?(what value?a value around inflow?)
in 3 I mean on the wall too. thank you for help. 
and do you mean that main setting for wall function is done in mut not other variables?and no need to set other variables (k/omega/epsilon) to spaldingWallFunction?
Quote:
 also this error occurred whan I used spaldingWallFunction.maybe it has removed in 2.2.0 version I use? Code:
[1] > FOAM FATAL IO ERROR: another trouble I had for you is that could you please describe me a bit whats the differences between mutUwallFunction and mutkWallFunction? thanks so much.:) 
In my opinion, typically for high Reynolds number model with the use of the spalding wallFunction: kwall = kqRWallFunction
eps wall: epsilonWallFunction muwall: mutUSpaldingWallFunction When you use a komega model, regardless you use a lowRe or highRe model, you have to put omegaWallFunction in the file 0/omega 
thanks.:)
when I was using mutkWallFunction,and by yPlusRAS compressible in highRe simulation I obtained y+ values in a range of 2045.is it OK in your opinion? if y+ be lower than 30 does the accuracy decrease? and what does spalding method do? 
According to the Fluent user guide, the performance of a highRe model decreases when you have y+<30. So I think it is the same with OpenFOAM.
Spalding wallFunction allows y+<30. In my case it is interisting because we have a big range of y+ and we have to ensure that y+ < 200 (so some y+ comes smaller than 30) 
All times are GMT 4. The time now is 19:18. 