flow simulation tells you if cavitation is happening and how large the region is
you can compare against other designs and see if it is larger or smaller and if the region changes
beyond that i am not aware of any further criteria
density plot is the easiest but there is also % vapor charts that can visualize the cavitation
the region of cavitation is that below the vapour pressure. When you turn on cavitation it is my understanding that the pressure calc is more reliable/accurate in the region below the vapour pressure. You pay a lot in compute time when you turn this on. Typically the goal is to avoid cavitation and hence you don't need to turn it on to see a good indication of where it is occurring. You turn it on when you want to examine the pressure in the cavitating region.
Is there any way to identify where the solid erosion is occurring due to cavitation?
more cavitation = more erosion
but again, flow simulation is based on the size and intensity of the cavitation, not absolutes that i think you are looking for
Once the pressure distribution plot is got, its easy to get it in the form of a data table. Therefore, its as simple as comparing pressure data (Px,y,z) with local vapour presure(Pv), that can be obtained, in a simple way and with a good approximation, from Atoine's equation.
The criteria is: Cavitation exists if P=<Pv.
If a non-dimensional form is prefered, then a Cavitation number can be defined from both pressures (P and Pv) and fluid velocity.
Ca=(P-Pv)/(1/2 dens V²): If Ca=<0, cavitation exists.