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How do the stators in axial compressors convert kinetic energy to pressure? Is this equivalent to a water hammer?

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Compressors are a combination of rotors and stators along a structure with reducing cross-section area. The rotors spin and push air down the compressor, but due to their spin there arises a circumferential velocity component to the air flow.

The stators don't revolve (hence the name) and they "straighten out" the flow, so as to direct the airflow to the next rotor set and achieve higher efficiencies without flow separation. But they still cause more compression because the cross section continues to get smaller and the shape of the blades reduces backwards motion by providing less resistance in one direction than in the other.

rotor-stator stages in compressor

Maybe this might help you visualise the flow better? It's from aviation.SE but I don't know the original source

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  • $\begingroup$ since ive asked this question i have learned the answer, so ill suggest a few edits: 1.Compression is due to crossection area increasing, not decreasing 2. the shape of the blades doesnt prevent backward motion, momentum does 3. the reducing crossection area of the compressor decreases the pressure inorder to maintain flow velocity between stages, but it's not reaponsible for compression $\endgroup$ – Francis L. Mar 12 at 17:23
  • $\begingroup$ @FrancisL. You're right that it's not just the shape that prevents the backward motion, but also the flow's momentum. Also maybe it wasn't clear in what I wrote, but I didn't mean the cross-section between the blades, but rather in the entire compressor (the shape is kind of like a cone). Smaller cross-section -> smaller volume -> more mass per volume = density. $\endgroup$ – Suryetto Mar 15 at 10:20
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    $\begingroup$ That's what i meant - smaller crossection leads to lower pressure and higher velocity. The purpose of the entire compressor crossection lowering is maintaing flow velocity between stages despite friction loses. The compression comes from accelarating the flow by the rotor and trading velocity for pressure om the stator due to it's increasing flow area N times $\endgroup$ – Francis L. Mar 15 at 10:28
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The stators will reduce the speed of stream of air but increase its pressure and density.

The flow's stagnation on the stators causes their kinetic energy to turn into pressure and help pack a lot more mass in the same space. Then the same air speed will carry a lot more air mass.

So the momentum mv, can be increased effectively increasing the thrust without the hassles of having to deal with supersonic stream and all the problems it would introduce.

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  • $\begingroup$ I know this perfectly well, as you can see in my post. I asked through what PROCESS the pressure increases. As in, how does it get from the state of high speed+lower pressure to low speed and higher pressure, what happens between point A and point B $\endgroup$ – Francis L. Jun 12 '20 at 9:57
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Stators convert kinetic energy to pressure energy by decelerating the flow. The shape of the blades and the passage between the blades is such that the flow's kinetic energy is transferred to pressure energy. If you're interested in the aerodynamics behind it, I'd begin by looking at how velocity triangles and isentropic compression processes work (http://www.seitzman.gatech.edu/classes/ae4803/compressor_angles.pdf). If you're interested in the compression process, look at the temperature vs. entropy diagrams in the attached document. This shows what happens to the fluid as its compressed through a compressor stage (i.e. from point A to B). There are tons of documents out there describing the thermodynamics and aerodynamics of turbomachines such as compressors.

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