A The nozzle design is very important becuase it determines the turbine entry temperature (and hence the work done by the turbine) as well as the mass flow of the engine and the exit velocity and pressure (all four of which determine thrust).

A A nozzle is often a pipe or tube of varying cross sectional area, and it can be used to direct or modify the flow of a fluid (liquid or gas). Nozzles are frequently used to control the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that emerges from them.