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
Whether the rotor uses velocity or pressure to drive it depends on the type of turbine: impulse or reaction respectively.
The overall aim is to extract energy from the working fluid. It arrives with non-zero pressure and velocity, and ideally leaves at zero pressure and velocity (relative to some baseline). Where these conversions occur within the many stages of the turbine (for gas and steam turbines) depends on the design constraints. A reaction turbine can be more efficient, but maintains higher pressure through the stages, and needs more of them, so is heavier overall. An impulse turbine trades pressure for velocity earlier and so can have a lighter body.
So in answer to your question, yes you can use either velocity or pressure to push your rotor at a given stage in the turbine, and there are various factors that go into that decision.
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