What’s NCVA at the end of the F135 engine? And what does it do?
NCVA: Nozzle cooling valve actuator.
It allows a cooling flow to enter the nozzle. From Wikipedia:
In this configuration most of the bypass flow is ducted to the wing nozzles, known as roll posts. Some is used for cooling the rear exhaust nozzle, known as the 3-bearing swivel duct nozzle (3BSD). At the same time an auxiliary inlet is opened on top of the aircraft to provide additional air to the engine with low distortion during the hover.