Launder-Sharma Low-Re epsilon boundary condition

thomas. · June 30, 2016, 09:39

Hello all,

in the need of more detailed understanding of the model that I am using in my simulation-case (Launder Sharma Low Re-model), I got into Wilcox' book, Lars Davidson's lecture notes and Moukalled's text book.

In both texts, the boundary conditions at the wall for an modified epsilon are defined to zero, while the boundary conditions for the "normal"-epsilon are defined to the expression *2 (two times) the "epsilon_wall" expression seen for the Nagano-Tagawa-model in the CFD-wiki: http://www.cfd-online.com/Wiki/Low-Re_k-epsilon_models . Hence: the epsilon_wall boundary conditions for the Launder-Sharma and the Chien models would be wrong, if the "epsilon_wall" expression is related to the "normal"-epsilon. BUT, if you read the Launder-Sharma original paper, they give a boundary condition for epsilon = 0... So, which one should I take?

I am using OpenFOAM. And my question is: how can I calculate a boundary condition for epsilon, since I don't have an expression for "k" in order to apply sqrt on it and then differentiate in perpendicular direction of the wall? Or does OF use the modified expression for epsilon as "epsilon" in the 0-case folder?

On the other side, according to Moukalled's text book (which focuses mainly on OF), the boundary condition for epsilon would be the one for the Chien low-Re model. And since this book focuses on OF, I could suppose that the given boundary conditions in this book are the ones to be applied in OF. Am I wrong?

I would really appreciate your help.

Best regards.

thomas. · June 30, 2016, 10:08

I answered the question myself. According to "http://www.tfd.chalmers.se/~hani/pdf_files/PiroozMoradnia.pdf" , OF solves the epsilon_modified equation. The 0/epsilon file should be actually be called "epsilon_mod" in order to avoid confusion.

I would also then suppose that the epsilon-values at the wall in the CFD-wiki are the "epsilon_modified" values and NOT the actual epsilon values.

If I am wrong, please correct me.

June 30, 2016, 09:39	Launder-Sharma Low-Re epsilon boundary condition	#1
thomas. Member thomas Join Date: Jul 2014 Posts: 50 Rep Power: 12	Hello all, in the need of more detailed understanding of the model that I am using in my simulation-case (Launder Sharma Low Re-model), I got into Wilcox' book, Lars Davidson's lecture notes and Moukalled's text book. In both texts, the boundary conditions at the wall for an modified epsilon are defined to zero, while the boundary conditions for the "normal"-epsilon are defined to the expression *2 (two times) the "epsilon_wall" expression seen for the Nagano-Tagawa-model in the CFD-wiki: http://www.cfd-online.com/Wiki/Low-Re_k-epsilon_models . Hence: the epsilon_wall boundary conditions for the Launder-Sharma and the Chien models would be wrong, if the "epsilon_wall" expression is related to the "normal"-epsilon. BUT, if you read the Launder-Sharma original paper, they give a boundary condition for epsilon = 0... So, which one should I take? I am using OpenFOAM. And my question is: how can I calculate a boundary condition for epsilon, since I don't have an expression for "k" in order to apply sqrt on it and then differentiate in perpendicular direction of the wall? Or does OF use the modified expression for epsilon as "epsilon" in the 0-case folder? On the other side, according to Moukalled's text book (which focuses mainly on OF), the boundary condition for epsilon would be the one for the Chien low-Re model. And since this book focuses on OF, I could suppose that the given boundary conditions in this book are the ones to be applied in OF. Am I wrong? I would really appreciate your help. Best regards.

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June 30, 2016, 10:08		#2
thomas. Member thomas Join Date: Jul 2014 Posts: 50 Rep Power: 12	I answered the question myself. According to "http://www.tfd.chalmers.se/~hani/pdf_files/PiroozMoradnia.pdf" , OF solves the epsilon_modified equation. The 0/epsilon file should be actually be called "epsilon_mod" in order to avoid confusion. I would also then suppose that the epsilon-values at the wall in the CFD-wiki are the "epsilon_modified" values and NOT the actual epsilon values. If I am wrong, please correct me.