open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

We are trying to modify k-epsilon model for our simulation. But we find out that in the subroutine SOUKEP.f the parameter OPTKEPS=2, which implies that it automatically applies the “OPTKEPS=2 : LINEAR PRODUCTION + YAP + RNG”, instead of “OPTKEPS=1 : STANDARD MODEL (BEWARE: NO WIND)”. Why is the option 2 set as the default? Thanks!

Best regards,
Qilong

Hello,

We have hardcoded option 2 because it is more stable, and we have included the effect of wind by introducing the wind stress directly into the production term, which is not standard. You may choose the other option and try what you want. Anyway I personnally think that the k-epsilon model is not well adapted to our applications where we generally have large mesh sizes of several meters, which gives small unphysical gradients of velocities, leading to underestimating the turbulence. This is not like internal flows, where people have much smaller mesh sizes.

With best regards,

Jean-Michel Hervouet

Hello,

Thanks Jean-Michel.

Is it possible to have a literature reference List about the k-epsilon model option 2 (LINEAR PRODUCTION + YAP + RNG)? We are trying to understand the background of this special version of k-epsilon model and there is not much details in the manual or in the code.

The other question is that there are two keywords for the turbulence model:
HORIZONTAL TURBULENCE MODEL and VERTICAL TURBULENCE MODEL. When the k-epsilon model is chosen for the VERTICAL TURBULENCE MODEL, the HORIZONTAL TURBULENCE MODEL will automatically set to k-epsilon model. How does k-epsilon model work for both horizontal and vertical? Is there any literature about this?

Thanks!

Best regards,
Qilong

Hello again,

Here is a reference kindly provided by my colleague Pablo Tassi:

Applied Turbulence Modelling in Marine Waters by Hans Burchard

books.google.fr/books?id=e6MEnPOhv7cC&redir_esc=y

With best regards,

Jean-Michel Hervouet

Thanks for the reference!

Best regards,
Qilong

Hello,

Here are other references given by Dominique Laurence :

Development of turbulence models for shear flows by a double expansion technique. V Yakhot, SA Orszag, S Thangam, TB Gatski… - Physics of Fluids A: Fluid …, 1992

Impinging jet studies for turbulence model assessment—II. An examination of the performance of four turbulence models
TJ Craft, LJW Graham… - … Journal of Heat and Mass Transfer, 1993 - Elsevier

Regards,

JMH

Thank you very much!

Best regards,
Qilong

Hi,Qilong

I'm currently frustrated by the turbulent modeling techniques in TELEMAC-3D with k-epsilon. Since that if choosing k-epsilon for the VERTICAL TURBULENCE MODEL, the HORIZONTAL TURBULENCE MODEL will automatically be set to k-epsilon too. This is quite different from other coastal ocean models using Smagorinski model(horizontal) instead because horizontal eddy viscosity/diffusivity is usually much larger that in the vertical and thus my modeling result was questioned by others.
I'm sure that my model result is ok with k-epsilon for both vertical and horizontal, but just do not have any literature to support this
So, could please be kind to recommend one or two papers(coastal ocean, estuary)?
Thanks for your help.

Regards.
Robinson

P.S.

I could not find any information about this from those references suggested by Mr Hervouet...

Hello,

I would say that the background literature should be given by those using two different turbulence models, which e.g. is against the basic assumptions of turbulence isotropy in the k-epsilon model. The large diffusion coefficients on the horizontal have more to see with the problem of aspect ratio and stability of advection schemes than to real turbulence. Anyway I think we'll think of releasing this (actually we just force k-epsilon on horizontal when it is asked on vertical, and we could remove this).

With best regards,

Jean-Michel Hervouet