how does an airplane compressor work?
Doesn’t the fans in the compressor stage just push the air towards the back of the engine and not compress the air?
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Yes, they push it backwards. But, the walls narrow in and the air has to get smaller to get through the narrow space. The blades, and the air behind it, give it no option but to go through the engine ducts.
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A compressor stage has two parts, a rotor and a stator. The rotor spins, the stator doesn’t. The spinning rotor pushes the air into the stator. The stator slows the air down and reduces the space available to the air, which is what actually compresses the air. This repeats over several stages to achieve a very high compression.
Oh shit. I took a class on jet engines in college….twenty years ago.
Let’s see what I can remember.
There are two types of compressors in jet engines. Axial flow (which is the one you’re thinking of) and radial or centrifugal compressors. The axial flow compressors do indeed push the air toward the back of the engine but right behind each row of compressor blades is a set of stator blades.
Jet engines have many rows of compressor stages. Typically 10-15. Each row is made up of a compressor stage and a stator stage. The stators look like compressor blades but they don’t move. They are fixed in position. They cause the air (that was sped up by the compressor) to slow down and it also redirects the air so that it meets the next compressor stage at the proper angle. Some jet engines have variable stator vanes that can be adjusted as the engine spools up or down to make sure the flow meets the following compressor stage at the correct angle. Same idea as a variable can timing in a car engine.
Also, as you move aft in the engine the area that the air is moving through gets smaller and smaller which further compresses the air.
In a lot of jet engines the last compressor stage will be a centrifugal compressor. This “flings” the air out from the centre of the engine which again compresses the air. Centrifugal compressors are better at compressing air, but they are big and bulky. Axial compressors aren’t as efficient but they can be made smaller which reduces the frontal area of the engine and therefore reduces drag.
If I remember correct a centrifugal stage will increase the air pressure by 4 or 5 times but axial compressors only compress the air by about 1.5 times. This is why most engines have multiple compressor stages following by one centrifugal stage.
All fans generate some pressure. If they didn’t, the air wouldn’t move. Fans can be optimized for static pressure or airflow. In the case of jet turbines, they are designed to operate in a middle ground, generating high pressure *and* high airflow at the cost of a huge amount of energy.
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