open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello Telemac community,

I have a question related to Telemac2D validation case #17, which is a hydraulic simulation of a river confluence. I believe that my question also applies to any other validation case.

I'm wondering if a flume experiment with exactly the same setup as in validation case #17 was ever completed on this planet. In particular, the main channel is 0.8m wide and the tributary is 0.5m wide. The tributary connects to the main channel at an angle of 55 degrees and the longitudinal slope is 0.1%. Flow discharges at inlets are 70 and 35 litres per second and downstream water depth is 18.22cm. I'm aware that flume experiments have been run in confluences with various dimensions, flow discharges and junction angles, but I'm not aware of any experiment that would have been conducted with the same characteristics as in validation #17. If you know the existence of such a flume experiment, please let me know.

This brings me to my more general second question, which is related to all validation cases. Are validation cases in Telemac relying on physical experiments in which measurements were taken? Or are these cases simply useful to test new version of the software (in other words to ensure that the software remain functional after a modification of the code)? For instance, the documentation on validation case #17 refers to the work by Gurram et al. 1997. However, the experiment described is related to a channel with slightly different characteristics (narrower channel). Thus, perhaps, in that case, the verification of the ability of Telemac-2D to correctly simulate flow field in a confluence is qualitative, according to the general knowledge of confluences in real rivers?

Any answer, or part of answer, will be helpful.

Regards,

Yannick

Hello,

This test case stems from a general study on head losses and I think it was based on a handbook of hydraulics like Idelcik. The head losses of bridge piers were also tested at that time after a handbook published in the U.S. by Bradley (a series of curves covering all sorts of situations, numbers, skewness and shapes of piers). The agreement was always within 10%, except when we had to extrapolate from the curves.

Our test case are of different sorts, you can refer to the validation documents, some are comparisons with exact solutions, measurements, others are simply examples, or they just test specific options to check new versions. For example the test case called gouttedo for Telemac-2D checks that a circular initial shape of the free surface gives a circular wave (the contrary would show some polarization and a somewhat square shape for example, which happens e.g. with ADI techniques in finite differences), if you do the same test with Telemac-3D in non-hydrostatic mode you will see that the "real" solution is largely different.

With best regards,

Jean-Michel Hervouet