If I check Export Animated Mesh for an Inflow in fluid dynamics, I lose the option of using local coordinates. Why? What can I do about it?
As far as I can tell this is a limitation, and I can't see a workaround.
Ideally you would be able to animate the inflow mesh shape, and at the same time use its motion to give the fluid a starting velocity like the local coordinates option does. This can work in principle but no one seems to have gotten around to implementing it.
I don't know how an animated mesh actually works, but my best guess (correct me if I'm wrong) is that it records each vertexes position individually over time, so the local coordinates don't actually get changed.
Since the local coordinates are then the same as the global coordinates, there is no point in having an option for local coordinates any more.
I'm not sure what you can really do about it, it depends on what exactly you are trying to do.
You may be able to cheat and use other objects to be the actual inflow, or bake some parent to keyframes (3D view>Object>Animation>Bake)