The effect of nozzle outlet diameter of a single-spool, mixed-flow turbofan engine on its performance

Thrust and specific fuel consumption are two essential parameters in a gas turbine engine. The fundamental design of various engine components is required to enhance thrust and provide optimum specific fuel consumption. This paper studies the effects of the nozzle exit area on the operating lines of fan, compressor, and turbine in a single-spool, mixed-flow, and low bypass ratio turbofan engine. The zero-dimensional modeling of the engine is examined in GasTurb, and the nozzle area is changed in 6 cases by ±5, ±10, and ±15 percent relative to design point. The inlet temperature of turbine rotor and the spool speed of the engine are limited to their maximum amount. The results show that any change in the nozzle exit area will reduce the net thrust of the engine. On the other hand, with the reduction of the nozzle area, the operating line of the fan and compressor becomes closer to the surge line, reducing the surge margin, while with the increase of the nozzle area, the surge margin of the fan and compressor increases. Also, the changes in specific fuel consumption are inversely proportional to the changes in the nozzle outlet area.