Post processor - how to view only specific part water by 'age of fluid' etc
 

I'm looking at the water flows in a Pelton casing, however to get the water jet to initialize I let run for a number of timesteps before it interacts with the bucket, therefore this water is present in the casing when I visualize an isosuface etc.

I was wondering if there is a way to get rid of this water by only looking at the isosurface starting with water from 0.05 seconds say.

I've read that I could do an 'age of air' type calculation, however this is implemented in pre, I wonder if there is an alternative so I don't have to run the simulation again.

Kind regards,
Sean

Can't you just look at the simulation at a time step far enough from the start that the startup transient has gone?

But to answer your question: I cannot think of a rigorous way of doing this in post processing only. You could put streamlines on the inlet that only last a certain amount of time - but I can't see how to then convert this into the water region which is new and discard the old stuff.