Strange behavior with open channel inlet BC
Hi everyone,
I'm encountering a problem when modelling an open channel case.
For inlet and outlet BCs i used open channel inlet and open channel outlet.
At the inlet BC happens something strange: at some spots below the water surface alpha.water drops to 0. Visually it looks like air is blown into the domain below the water surface, resulting in inplausible velocity (since the same volume flow rate with an smaller area with alpha.water =1 is introduced into the domain).
First i thought maybe its related to the mesh resolution, but i tried sevaral grid sizes and its alwas the same. Anybody else encountered this problem and is there a simple fix? Is it a software bug or an application error?
Best regards
Dear Al Kik,
It doesn't seem to be a software bug; rather, there appears to be an issue with the calculation. Since the alpha value at the inlet is not fixed in the open channel inlet boundary condition, a problem likely arose during the calculation, resulting in areas where alpha is 0 below the water surface. The cause of the problem could be attributed to various factors, such as the boundary conditions, time step size, or numerical scheme.
It’s hard to say for sure without knowing the exact nature of the problem, but I suspect it might be related to using an open channel outlet as the outlet boundary condition.
An open channel outlet requires a specified outlet velocity, but in some cases, it’s difficult to determine the exact average outlet velocity. In such cases, using an outflow condition at the outlet might be the correct approach.
Best regards
I’m attaching an example case with open channel inlet boundary conditions in case it’s helpful. It’s a tutorial from OpenFOAM.
Uploaded files: