In the convergent nozzle component type, isentropic expansion is calculated to ambient pressure, or up to sonic speed when the nozzle is choked. A velocity coefficient CV can be specified to represent losses via a reduction of the average jet velocity that is used to calculate the flow rate and thrust.
The throat area is not specified, but calculated in the Design point calculation, from the flow and pressure ratio resulting from up-stream calculated design point data.
For a convergent nozzle, the exit station (usually 9 for a hot exhaust) is defined to coincide with the throat station (usually 8 for a hot exhaust). Therefore all gas properties of station 8 and 9 will be equal.
A throat discharge coefficient CD (usually 'CD8') represents the relation between geometric and effective throat flow cross areas:
A_geom = CD * A_eff
The effective area is lower than geometric area due to boundary layer effects on the flow (reduced velocity due to friction).
In the design point A_eff is always directly determined by the upstream gas path calculation and A_geom derived using a user specified CD or directly user specified. Off-design either A_eff or A_geom can be user controlled depending on selected Exhaust nozzle options.
Convergent exhaust nozzle
