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January 19, 2016, 06:02 

#21  
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Karl Lindqvist
Join Date: Jul 2012
Posts: 21
Rep Power: 12 
Canopus,
I can only refer to Sveningsson's thesis (http://publications.lib.chalmers.se/...passageflow): Quote:
Best regards, Karl 

February 20, 2016, 14:05 

#22 
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Ryan Tunstall
Join Date: Sep 2013
Posts: 10
Rep Power: 11 
The modifications made to the standard kepsilon by LaunderSharma mean that you are solving for a modified dissipation rate ( = epsilon  wall value of epsilon) rather than "pure" epsilon and thus unlike in most kepsilon models the wall boundary condition for this modified epsilon is exactly zero. That boundary condition is correct for that model but is incorrect for many others.


February 22, 2016, 04:56 

#23  
New Member
Ryan Tunstall
Join Date: Sep 2013
Posts: 10
Rep Power: 11 
Quote:
As others have reported there is a bug in epsilonLowReWallFunction, however I do not think that the published bug fix is fully correct. This wall function also applies a correction to the G field (corresponding to production of k). However in the published fix (here) the same correction is applied to G regardless of whether one is using a low or high y+ mesh; thus the wallfunction does not fully reduce to the lowRe approach when required. Note that we only need the wallfunction in a lowRe case to apply the correct value of epsilon at the wall, however it currently also modifies G leading to degraded results. The epsilonLowReWallFunction wallfunction formulation in version 3.0 is correct and in essence does not modify G when we are using a lowRe mesh. This formulation can easily be ported into earlier versions (see attached). It gives much better results, see attached plots, particularly for k. This wallfunction seems to be the most crucial factor in getting good results from this model. In terms of the BC's for k, epsilon, f, v2: seems to be minimal differences between using the suggested wallfunctions and fixedValue machine zero. For nut minimal differences between suggested wallfunctions and zeroGradient. 

March 10, 2017, 08:50 
epsilonLowReWallFunction in OFv16

#24 
Member
Join Date: Nov 2014
Posts: 36
Rep Power: 9 
Sorry to revive an old (but still very relevant thread). I have a question regarding the missing boundary condition epsilonLowReWallFunction in OFv16. OFv16 has only the epsilonWallFunction implemented. Does that mean that the epsilonWallFunction has a switch for the case where yPlus is near 1 (i.e. the low Re switch)? Has anyone tried it?
Now i see it is not that old thread. My mistake .. Last edited by Tscar; March 10, 2017 at 08:51. Reason: overlooked the date 

November 26, 2017, 05:32 

#25  
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Paul Palladium
Join Date: Jan 2016
Posts: 90
Rep Power: 8 
Quote:


May 20, 2018, 07:15 

#26  
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Karthick
Join Date: Oct 2016
Location: Munich
Posts: 18
Rep Power: 7 
Quote:
could you please clear my doubt? since v2f is a variant of 2 equation k epsilon model and the equations of k and epsilon in both the models are the same, is it logically right to use kLowReWallFunction and epsilonLowReWallFunction for handling of k and epsilon variables in k epsilon model. I hope you still remember Thanks, Karthick 

February 2, 2019, 11:38 

#27  
Senior Member
Guilherme
Join Date: Apr 2017
Posts: 181
Rep Power: 7 
Quote:
I liked your post and I have applied it to my case study. I'm simulating a pitzDaily geometry using the v2f model. You started the field (U) with a velocity profile that probably originates from another study, maybe a channel (similar to what I'm trying to do). Could you teach me how you did it? 

July 4, 2019, 04:21 
v2f: issues with boundary layer evolution

#28 
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Gerd Fade
Join Date: Jul 2015
Posts: 7
Rep Power: 9 
Dear Foamers,
I am struggling with applying the basic v2f model (v1806) to simple flows, e.g. backwardfacing step (lowRe) or Chow's wing testcase (highRe). Below you can see the upper wall w/o step of the backwardfacing step (BFS) and the suction side of Chow's wing both with SSTCC (Smirnov) and the v2f model. The problem is that the boundary layer does not develop properly with v2f. I tested a lot of different combinations of the boundary conditions without success. Here you see the BCs from the pitzDaily tutorial, with epsilon.lowReCorrection=on for the BFS case. backwardfacing step: SSTCC: v2f:  Chow's testcase: SSTCC: v2f:  Did you experience similar issues? And did you find a solution for it? Last edited by schiffbauer; July 4, 2019 at 08:48. 

November 19, 2019, 16:23 
v2f Boundary Condition

#29 
New Member
amir mofakham
Join Date: Feb 2011
Posts: 14
Rep Power: 13 
Hi Everyone,
I decided to use the v2f model of OpenFOAM since I heard the v2f model is able to correctly predict the quadratic nearwall variation of the wallnormal RMS velocity fluctuations (v). I had some difficulties to get the accurate results by this model, but fortunately in the end, I got promising results. I wanted to share my experience with others to probably help someone who wants to use the same model. Also, I wanted to make sure that I did it correctly. So please let me know your comments. First, I though without employing any wall functions we can get accurate results by the v2f model, but by running different simulations using different will functions for different variables, I found we need to impose the epsilonWallFunction on the wall to get accurate results for the nearwall regions, otherwise the wallnormal velocity fluctuation will be overestimated. Below are the boundary conditions that I imposed on the walls of a duct flow for different parameters: epsilon epsilonWallFunction; f uniform 1e10; k uniform 1e15; nut zeroGradient; v2 uniform 1e10; I appreciate if you let me know what epsilonWallFunction exactly does and it makes sense to impose the wall function on one variable? I do not understand why only epsilon needs the wall function! Thanks 

February 11, 2021, 13:41 

#30 
New Member
Join Date: Feb 2020
Posts: 29
Rep Power: 4 
Hello everyone,
I am trying to do modelling with buoyantBoussinesqSimpleFoam for incompressible flow simulations using v2f model. The above posts were helpful in preparing the case and my case ran well. Since the v2f model does not really need wall functions, I checked in a research paper that the nut was declared as zero gradient on the wall along with epsilon. I am doubtful about the value of alphat on the walls. What would be the most appropriate boundary condition for that? Would be be zerogradient or alphatJayatillekeWallfunction? I would really appreciate your help. 

February 16, 2021, 15:32 

#31 
New Member
Join Date: Feb 2020
Posts: 29
Rep Power: 4 
Hello everyone,
I am trying to do modelling with buoyantBoussinesqSimpleFoam for incompressible flow simulations using v2f model. The above posts were helpful in preparing the case and my case ran well. Since the v2f model does not really need wall functions, I checked in a research paper that the nut was declared as zero gradient on the wall along with epsilon. I am doubtful about the value of alphat on the walls. What would be the most appropriate boundary condition for that? Would be be zerogradient or alphatJayatillekeWallfunction? I posted this question in another thread as well but did not get reply. So, I am not sure if that thread is active any more or not. I would really appreciate your help. 

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boundary conditions, v2f, wall functions 
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