[anna1]

Hi!
I´m new to Star CCM+ and I´m struggeling with setting up a Translational Reference Frame. My case is a rising bubble in an endless tank and to reduce computational effort i would like to just simulate a small part of the tank. The Frame should move with the same velocity as the bubble rises, so that the bubble is kept in the middle of the Frame/Part. I tried a "Rotational and Translational Reference Frame" but it does not work as expected (or I did something wrong). Maybe someone has a better idea how to solve the problem?
Many Thanks in advance!

[me3840]

If your bubble is stationary with respect to the tank, you do not need to model the tank's physical motion. From a relative sense, moving the fluid over the bubble is good enough, no?

[anna1]

Thanks for your reply!
Its not really stationary, it starts rising and after a certain time it has a constant velocity. And I don´t want the tank to move physically, I´m looking for a solution that the Frame shows only a small part of the tank and that this frame rises with the bubble. Don´t know if its relevant but I´m using VOF method.
Also I´m unsure with the boundary conditions. The tank should be kind of endless around the bubble and the frame should be slightly larger than the bubble. So the Fluid auround the bubble has to move out of the frame and come in as the flow would be without the frame. I tried Pressure Outlet at all Boundaries with the "extrapolated" Backflow specification but I think it´s not the right condition.
Again many thanks in advance!

[me3840]

Is the bubble moving through a changing hydrostatic pressure field?