JET ENGINE

TURBOJET

The basic componets are still the compressor, combustor, and turbine.

The turbojet gets its propulsive power from reaction to the flow of hot gases. Air enters the inlet and ts pressure is increased by the compressor. Fuel is added in the combustor and the expansion created by heat forces the turbine wheel to rotate. The turbine in turn drives the compressor. The energy remaining downstream of the turbine in the tailpipe accelerates into the atmosphere and creates the reaction we refer to as thrust.

TURBOFAN

The turbofa, in effect, is a ducted, multi-blade propeller driven by a gas turbine engine. This fan procedures a pressure ratio on the order of 2:1 or two atmospheres of compression. Generrally, turbofan contain 20 to 40 fixed pitch blades. They were developed to provide a compromise between the best features of the turbejet type cruise speed capability and yet retains some of the short field takeoff capability of the  turboprop.

By comparison, the fan diameter of a turbofan engine is much less than that of the propeller on a turboprop engine, but it contains many more blades and moves the air with a greater velocity from its convergent exhaust nozzle.

Turbofan in civil aircraft are generally divided into three classifications: Low bypass, medium bypass and high bypass.

The low bypass classification indicates that the fan and the compressor sections are utilizing approximately the same mass airflow. They are described as having a bypass ratio of 1 to 1. The fan discharge air is ducted aling the entire length of the engine from what is called a full fan duct. The end of the duct is configured with a converging discharge nozzle to produce a velocity increase and reactive thrust.

In the fully ducted fan engine, the hot and cold streams mix before being discharged to the atmosphere. This results in a reduction in aerodynamic drag associated with short ducted turbofan.

Air passing over the core engine outer surface has much less skin friction if the air remains in the fan duct until it leaves the engine. With the full duct, there is gain implied when drag is reduced. This design also has a noise attenuating quality as hot gas become diluted by fan air in the common exhaust duct.

The turbofan core engine air is compreseed, ignited and discharger in the same manner as a turbojet engine. The thrust of each gas stream of the fully ducted engine, each delivering 8.000 to 10.000 pound of thrust, depending on the model.

Funny thing:
For subsonic speeds, the motor input is divergent and the output is convergent.
For supersonic speeds, the motor input is convergent and the output is divergent.
This is because both speed and pressure behave differently if the speed is higher or lower than mach