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
At the end, the air needs to be moving out faster than it was moving in. That’s how the engine pushes the jet forward.
There’s two streams of air in a modern jet engine. One going through the fan, and one going through the turbine. The air in the fan is super simple – it gets compressed a bit by the fan and this pressure pushes the air back/the plane forward. Most of the thrust of the engine comes from this air.
The turbine air is where the engine gets its energy. Running a giant fan at high speed costs a lot of energy. At the center of the fan, behind it, there is a series of turbines that compress the air more and more. Once fully compressed, the air reacts with fuel and expands, before going out another turbine at the back. This turbine at the back gets spun by the air and gets the energy to power the engine.
The reason this air is compressed is sort of simple. The fuel burning cannot compress the air at all, since the jet engine is really just a big tube. The pressure would just escape. What it does is cause the air to expand. This generates much more energy when the air is under pressure.
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