I read that the velocity of the air is increased at the nozzle guide vanes of a turbine before it actually hits the turbine blades, then compresses, and the process repeats. My question is, what’s the reasoning behind this? The way I’m thinking of it is like this:
Let’s compare compressed air to a sumo wrestler.
And then let’s compare just a normal guy.
If the sumo wrestler (compressed air) runs at you with a somewhat slow speed, he’ll apply a lot of force to you, but if a normal guy runs at you with a much faster speed, you’ll feel a lot of force too. I’m wondering where the logic is behind this, because can’t the same force be applied both as compressed air and sped up air if both mass and velocity contribute to momentum?
Thanks
In: 1
The way all planes generate thrust is by speeding up air.
A jet engine has a few important sections to make it generate it’s thrust. The first section is the inlet which is where the air enters the engine.
Next, is the section that controls how the air flows. This is to make the air flow smoothly so it doesn’t have random changes in air speed as well as make the air all flow in one direction. We do this so it doesn’t overload the compressor blades with extra stress from the changing air speeds.To do this we use guide vanes. This might be the section you refer to about the air speeding up before compression.
Next is the compression stage. This stage is used to pressurise the air for the combustion as this improves the efficiency of combustion. To compress the air we slow it down and constrict the area in which it can flow through.
After the compression stage we have the combustion stage which burns fuel to heat up the compressed air. Increasing the temperature of the air also increases the pressure of the air.
Finally we have the turbine section. This is where we convert the hot slow moving pressurised air into cool fast moving air. To do this, we pass air through blades with an expanding area for the air to pass through. This makes the air lose pressure (which for thermodynamic reasons also makes the air cooler). This decrease in pressure makes the air move faster, which generates the thrust the plane needs. To power the compression section, the turbine blades are connect by a strong metal rod to the compression section.
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