Bulb Turbine Head: Inlet, Outlet & Head Explained

[Dirk123]

Hi All,

My question is about bulb turbines and head.
Bulb turbines are used for tidal energy.
I guess the inlet and the outlet of the turbine (or the pipe where the turbine is mounted) are both under water.
Is head the difference in height between the water surface at the inlet and the water surface at the outlet?

And what if a bulb turbine is used in a way that the outlet is not under water?
Is the head the difference between the surface and the center of the turbine?
Or between the surface and the top of the turbine?
Or is this situation not possible and must a bulb turbine always be completely under water?