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Doubt with Downstream Pressure Boundary Condition

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Old   November 20, 2013, 15:45
Default Doubt with Downstream Pressure Boundary Condition
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Marcus Fernandes Araujo Filho
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Dear fellows,

Im trying to simulate a flow over a spillway and im 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 dont get a good result (the flow pattern is just wrong).

In order to solve the problem Ive tried some different downstream BC and was able to "solve" the problem by doing the following. Ive 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 Ive been able to run a sucessfull simulation. My question is if this boundary condition Im 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?

Ive 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,
Attached Images
File Type: jpg Geometry.jpg (77.8 KB, 11 views)
File Type: jpg Results.JPG (83.7 KB, 13 views)
File Type: jpg BC.JPG (67.6 KB, 13 views)
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boundary condition, spillway

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