[Marcus.filho]

Dear fellows,

I´m trying to simulate a flow over a spillway and i´m having trouble performing the simulation. As a downstream boundary condition I first tried to use a PRESSURE boundary with defined elevation in order to simulate my downstream rating curve. With this BC the model is unstable and I don´t get a good result (the flow pattern is just wrong).

In order to solve the problem I´ve tried some different downstream BC and was able to "solve" the problem by doing the following. I´ve used a PRESSURE boundary condition with defined fluid elevation, fluid fraction equal to one, checked the "stagnation pressure" option and defining the pressure value as atmospheric (see attachment). By doing so I´ve been able to run a sucessfull simulation. My question is if this boundary condition I´m using represents reality the way it should be, is it physically accurate? I need the water surface elevation downstream of my model to be constant, am I able to do so with this setup of boundary condition? Whta else should I do?

I´ve attached three pictures, one of the geometry of the model, one with the results of the simulation and one with the BC screen. If furthur information is needed I would be glad to provide.

Thank you in advance,
Marcus