Civil Aircraft Exhaust Nozzles
Civil aircraft nozzles are conical in shape, on which the TR is integrated. Small turbofan aircraft may not need a TR but regional jet (RJ) aircraft and larger use a TR. Inclusion of a TR may slightly elongate the nozzle, but this is not discussed in this book.
In general, the nozzle exit area is sized as a perfectly expanded nozzle (pe = pTO) at LRC condition; at higher engine ratings, it is pe > pTO. The exit nozzle of a long- duct turbofan does not run choked at cruise ratings. At takeoff ratings, the back pressure is high at a lower altitude; therefore, a long-duct turbofan does not need to run choked (i. e., the low-pressure secondary flow mixes in the exhaust duct). An exhaust nozzle runs in a favorable pressure gradient; therefore, its shaping results
in a relatively simpler establishment of geometrical dimensions. However, it is not simple engineering at elevated temperatures and for suppressing noise levels.
The nozzle exit plane is at the end of the engine. Its length from the turbine exit plane is 0.8 to 1.5 times the fan-face diameter. The nozzle-exit-area diameter is roughly half to three fourths of the intake-throat diameter in this study.