Clive,
What am I missing please?
On the nozzle efficiency chart:
If pj goes up, say, ps/pj goes down. Also if pj goes up the primary jet will expand some more and the 2ndary annulus area would decrease.
But 2ndary annulus area decreasing arrow is pointing up. I'd have expected down.
I'm thinking of what's happening at a particular nozzle plane. Perhaps the "2ndary annulus area decreasing" arrow means in the direction of flow?