Mixer and Nozzle Process Description

Mixer

The hot air that is forced out of the combustor and through the turbine continues to exit the engine at the rearward. Before exiting however, this air must be mixed with the cooler bypass air that did not go through the compressor and combustor. These two airstreams are mixed in order to quiet the engine.

To understand how air can create noise, first consider the way water splashes and makes noise when a wave crashes. In the same way, when two different air streams traveling at extremely high speeds and at different temperatures collide with one another, noise is produced. In addition to the air streams colliding, the air also collides with the components of the engine and nacelle. Another example of air making noise is when wind hits a house. Even in a wind storm with small wind speeds, wind makes rushing and a grumbling noise against the outside walls of a house.

In order to mix the two air streams, the mixer directs the air escaping from the combustor and turbine blades outward towards the stream of bypass air. This is accomplished by stators, or channels that direct the air flow. There are stators in several other places in the engine, but their function is to stop the rotational momentum of the air and force it to fly straighter. After having turned the turbine blades, the air is given a spiraling motion which decreases its velocity. The stators correct this by channeling the air towards the nozzle so that it can be expelled as exhaust.

The mixer must withstand temperatures of more than 3000 degrees Fahrenheit. It is made of nickel alloys which are engineered to withstand heat. Without this heat resistance, the mixer would either melt or suffer distortions and permanent damage.

Although the mixer helps to reduce jet engine noise, it does not eliminate it entirely. The low grumbling sound of a jet is the result of the air mixing inside the engine and being expelled toward the rear of the aircraft. The air streams coming out of the rear of the engine also slap against the air outside the aircraft and even against parts of the aircraft itself.

Nozzle

The main function of the nozzle is to create thrust. As the hot gases are expelled out the nozzle, they exert a force on the plane and propel it forward. Gas turbine engines operate according to Newton's Third Law of Physics which states that for every action there is an opposite and equal reaction. When the engine expels the gases, the gases push back on the engine and therefore the aircraft. A simple example of how this works is blowing up a balloon and releasing it. The pressurized gas inside the balloon tries to escape to the normal atmospheric pressure surrounding the balloon. When the air