# How Turbos Compresses Air

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Hi,

I wonder how turbos in cars can compress the air it gets. I've heard that the air compresses because the compressor wheel spins very fast. Why is the air compressed because of that?

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Hi,

I wonder how turbos in cars can compress the air it gets. I've heard that the air compresses because the compressor wheel spins very fast. Why is the air compressed because of that?

Hello,

You video is quite a good one - if you understand some basic facts so I will tailor my comments to the video.

But first try this experiment.

Take a book of heavy sheet of carboard or wood and see how fast you can wave it through the air.
You should have not trouble feeling the air resistance.
And the harder and faster you wave the greater that resistance.

It is this air resistance that is the key to the operation of both the turbine and the compressor.

Rotating turbines and compressors have two basic modes or types of operation.

Fluid (air) can enter or leave at right angles to the disk of  blades, along or parallel to the shaft.
This air is then directed outwards by the action of the blades against the air resistance.
As you found out in your experiment the greater the speed the greater the effect.
That is why the blades need to spin so fast.

This action turns the air flow through a right angle so it is now moving at right angles to the spinning shaft and parallel to the disk of blades.
The blades themselves are specially shaped to facilitate this.

The air then leaves or enters the casing at a hole in the outer edge into a pipe.

Note I said the air can enter or leave and then it leaves or enters.

You video shows this very well, can you identify which way the air is flowing in the turbine and the compressor parts?

Hint they are opposite directions.

This type of turbine or compressor is called a radial flow machine.

The other type is called an axial flow machine.
Here the air enters parallel to the shaft and does not change direction.

It remains flowing parallel to the shaft and so enters the machine at one end and exits at the other.

This type of compressor is used in jet engines.

Edited by studiot

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On 1/9/2019 at 4:23 AM, studiot said:

Hello,

You video is quite a good one - if you understand some basic facts so I will tailor my comments to the video.

But first try this experiment.

Take a book of heavy sheet of carboard or wood and see how fast you can wave it through the air.
You should have not trouble feeling the air resistance.
And the harder and faster you wave the greater that resistance.

It is this air resistance that is the key to the operation of both the turbine and the compressor.

Rotating turbines and compressors have two basic modes or types of operation.

Fluid (air) can enter or leave at right angles to the disk of  blades, along or parallel to the shaft.
This air is then directed outwards by the action of the blades against the air resistance.
As you found out in your experiment the greater the speed the greater the effect.
That is why the blades need to spin so fast.

This action turns the air flow through a right angle so it is now moving at right angles to the spinning shaft and parallel to the disk of blades.
The blades themselves are specially shaped to facilitate this.

The air then leaves or enters the casing at a hole in the outer edge into a pipe.

Note I said the air can enter or leave and then it leaves or enters.

You video shows this very well, can you identify which way the air is flowing in the turbine and the compressor parts?

Hint they are opposite directions.

This type of turbine or compressor is called a radial flow machine.

The other type is called an axial flow machine.
Here the air enters parallel to the shaft and does not change direction.

It remains flowing parallel to the shaft and so enters the machine at one end and exits at the other.

This type of compressor is used in jet engines.

I enjoyed the simple way you presented that! For me, it's a matter of air being a compressible fluid, and when compressed such that it experiences pressure greater than atmospheric pressure, it has the ability to move, to flow, attempting to relieve that pressure. Squeezing air to make it move is a much more forgiving process than doing so with a liquid, which is for most practical considerations, incompressible. However that fact may be, even metals can be compressed if subjected to extremely high stresses. If this copies, here is a chunk of metal being compressed under millions of pounds per square inch, the event copied by extremely high-speed X-Ray images:

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