open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi everybody,

My structure has been contacted in order to perform a hydraulic simulation requiered to be done with CFD tools. The project consists in assessing the influence of old concrete blocks that are situated just upstream of a spillway on the discharge capacity.

As far as I know, T3D seems to be an appropriate tool for such a case, with the assumption that the concrete blocks can be modelled as variations in bathymetry (refined mesh, ...).

An alternative would be to implement other "well-known" CFD software such as Fluent or similar. What are the main differences between such codes and the 3D numerical system solved by T3D for a simple "free surface flow" (no pressure flow, univocal water surface, ...).
Is there any significant differences in the way of solving the Z coordinates between these methods (vertical acceleration, ...) ?

Thank you very much in advance!

Best regards,
PL

Hello,

Well, I would say that if the geometry is compatible with Telemac-3D and if you can do the obstacles as a bottom variation or more conveniently as islands (to avoid steep uncovered slopes), it will be more accurate with "classical" CFD software. As a matter of fact VOF techniques have an accuracy in Z of the same order of magnitude than the mesh size on the vertical (their function F saying 0 or 1 for air or water is rather fuzzy within an element). Mass conservation is probably not ensured exactly. I know of two comparisons between finite elements and VOF done some years ago on a spillway, in one case VOF was slightly more accurate but in the other case VOF totally missed a hydraulic jump. To sum up the results may depend on the mesh refinement and the user's skill with one software or the other.

Regards,

JMH

Hi,

Thank you for your reply.
Just one thing: in your first sentence do you mean that T3D should be more or less accurate than VOF-software? (isn't a "than" missing before "with classical CFD software"?)
Otherwise the blocks are normally submerged entirely, so their modeling has to be done via bathymetry.

Finally, do you know if the two studies you mentionned are available somewhere on the internet?

Thank you in advance,
PL

Hello,

I meant that T3D can have a better description of free surface because it varies as a double precision and can ensure mass conservation at machine accuracy, whereas on VOF side their is a "quantum" which is the mesh size on the vertical (and probably no exact mass conservation since function F stating if there is air or water is advected by a non conservative advection equation and moreover has a specific treatment to keep it varying fastly from 0 to 1, if I understand well what is done in VOF method).

JMH