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Hello,

I'm trying to obtain a quasi-steady state with telemac2D. I impose a discharge at the upstream boundary and a constant water level at the downstream boundary. In the domain, there is a structure that causes some eddies that reach the downstream boundary. The model can cope with some, but at one point, the model will impose a very important entering flow at the downstream boundary, causing the model to be unstable. The model is started very slowly, and I do not have important waves in the model.

I've tried to change the relaxation factor without any success. I would like to found a solution that does not consist in changing the place of downstream boundary.

Any ideas?

Thanks!

Hello,

I am afraid that in your case with this geometry you do have a recirculation across the boundary, so the real solution would be a larger mesh. Otherwise you can try to add friction or a head loss. Given the fact that in your case re-entering velocities would have a negative component U maybe you could try to add a strong friction for points near the exit with negative U.

Having the correct diffusion coefficient must also be important, the larger the diffusion the shorter the recirculation, so starting with a large diffusion could be also a solution, maybe the first to try because simpler.

I do not really understand why you mention a relaxation factor in your case.

With best regards,

Jean-Michel Hervouet

Hello
i have the same problem, what should i do to solve it please ?
Regards

Hello,

The point is that you should not have velocities entering through a boundary where the velocity is free, otherwise your problem is not well posed. If no solution given in my previous post works, another possibility is to change the mesh so as to have an exit which is clearly an exit for all points of this exit.

With best regards,

Jean-Michel Hervouet