open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi all,

The reference documentation for TELEMAC-2D v8p3r1 lists variables for graphic printout including TAU_S, OMEGA, and 1/R. I could not find anywhere in the User or Reference manuals where these variables were defined.

I thought TAU_S might be bed shear stress, so I activated it, but in my simulation, TAU_S has no units and reaches values of -160 to +160 – not sure what this could possibly correspond to

Does anyone know what TAU_S, OMEGA, and 1/R mean? Could they be defined in future iterations of TELEMAC-2D's documentation?

Thanks,
André Renault

Hello André,

Indeed, people who introduced these 3 variables did not write many things about them in the manuals.
These 3 variables are related to the "secondary currents" feature:
- TAU_S is streamwise shear stress and called SEC_TAU in the source code,
- 1/R is the reverse of local radius of curvature and is called SEC_R in the source code,
- OMEGA is the streamwise vorticity or the vorticity of the flow.

Currently, for more explanations, you can read the following paper:
henry.baw.de/handle/20.500.11970/104277?locale-attribute=en

If the explanations above are enough for you, I can do the job in the reference manual.

Hope this helps,

Chi-Tuan

Hello Chi-Tuan,

Thanks for these explanations. I took a glance at the paper, and I'm not sure that I follow everything, but it seems a useful reference for modelling secondary currents, as I am using secondary current parametrization in this project (quantifying bank shear stress).

I suspected TAU_S was shear stress, however I am surprised at the apparent discrepancy between TAU_S and the friction/shear velocity when I convert the latter to shear stress (using u*^2*rho). Am I missing a difference between these two?

In my simulation, TAU_S spans –160 to +160, while friction velocity -> shear stress spans 0 to 36 N/m². To me, a negative shear stress makes little sense, unless we're talking about orienting shear stress in the XY plane (even so, this seems suspicious to me), and the ±160 values make no physical sense compared to values derived from field measurements using an ADV (whereas 36 N/m² is close to measured values).

I think I don't need these variables anyway, so I will remove them from future output. Thanks again for providing some insight into what they are, hopefully it's not too much work to add them to the reference manual in due time!

Kind regards,
André Renault

Dear André,
Actually TAU_S represents the streamwise stress that results from the deviation of the velocity from the depth-averaged velocity. This is not the same value as the friction/shear stress value provided by Telemac-2d as it allows to show the “correction” done by the secondary currents parameterization. For further insight regarding the theoretical concepts behind the SC correction, I’d suggest taking a look at the article by Finnie, J., Donnell, B., Letter, J., & Bernard, R. S. (1999). Secondary flow correction for depth-averaged flow calculations. Journal of Engineering Mechanics, 125(7), 848-863.
I hope it helps,
Best wishes,
Pablo

Hello,

Thanks Pablo for the explanations.

FYI André, the 3 secondary currents variables are now more detailed in the TELEMAC-2D dictionary in the main so that next release will be better documented, thanks for having pointed it out.

Chi-Tuan