Various types of turbine engines are used on aircraft today. Generally, air enters an inlet, is compressed, burnt, and the resulting exhaust gases are used to produce thrust either directly or to power propellers. In order for the combustor to work efficiently, it requires high- pressure air to mix with the fuel. The compressor provides the optimal air pressure for the combustion chamber. There are two main types of compressors: centrifugal flow and axial flow.
Centrifugal means that the object moves or tends to move away from the center. This force can be explained with an example of a tetherball— the ball is attached to a string and the string is attached to a pole. When the ball gets hit, it wants to move in a straight line, but it cannot due to the string. Centrifugal force is the energy of an object that is trying to move in a straight line when it cannot.
Centrifugal flow compressors pick up air through the inlet and accelerate it outwards through centrifugal action; the airflow is turned perpendicular to the axis of rotation. In these compressors, there is an impeller (rotor), a diffuser (stator), and a compressor manifold. Impellers accelerate air outward to the diffuser. They are either single or double entry. The diffuser delivers air to the manifold at a sufficient velocity and pressure. Manifolds divert the airflow from the diffuser to the combustion chamber.
Air in an axial flow compressor continue the direction of flow; the airflow travels parallel to the axis of rotation. It consists of two primary elements: a rotor and a stator. The rotor blades impel air towards the back and air like small airfoils. The air passes through a series of stages that further compress the air to the desired density. It produces high-velocity airflow. After the air goes through the rotor blades, it passes through the stator blades. They act as diffusers and convert high-velocity air into high pressure. The more blades, or stages, the higher the compressor ratio is.
Centrifugal flow compressors are lightweight, simple to manufacture, and have high-pressure rise per stage but they have a large frontal area and more than two stages are not practical. Axial flow compressors can handle high volumes of air, have a smaller frontal area, and have high ram efficiency but are more susceptible to foreign object damage, are expensive, and heavier than centrifugal flow compressors. Because of the different characteristics of both compressors, they are used on different engines. Smaller engines generally use centrifugal air compressors while most large engines used on transport and military aircraft use axial flow compressors.
