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I have a few questions here-

  1. Why do you need an increase in static pressure, why not total pressure?

  2. The rotor vane increase total energy, is this energy converted into kinetic energy or total pressure or both? And then the stator vanes increase the static pressure.

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  • $\begingroup$ Migrate to Aviation SE ? $\endgroup$ Commented Nov 15, 2017 at 19:37
  • $\begingroup$ @StephemG I already did and those question were not answered. $\endgroup$
    – Itzyoboi
    Commented Nov 15, 2017 at 20:11
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    $\begingroup$ Why do you need an increase in static pressure for what? Also, the rotor vane increases total energy of what? $\endgroup$ Commented Nov 15, 2017 at 21:25
  • $\begingroup$ @probably_someone the static pressure of the fluid, beucase I asked on Avation stack exchange that and they said it make for good combustion conditions, why? $\endgroup$
    – Itzyoboi
    Commented Nov 15, 2017 at 23:16
  • $\begingroup$ @Itzyoboi that increases the oxygen concentration. At high altitudes the air is thinner, so pressurizing it ensures that you'll have enough oxygen to keep a flame lit. $\endgroup$ Commented Nov 16, 2017 at 10:17

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Total pressure is static plus dynamic pressure. A compressor will increase both (total and static pressure) together. Note that the flow speed in the different compressor stages is nearly constant and the flow is only decelerated for combustion after the last compressor stage in an area called diffusor.

The flow speed in the compressor is chosen such that you just avoid supersonic flow at the blade tips but maintain enough dynamic pressure so throughput is maximized and the whole engine can be built smaller. Supersonic compressor flow incurs higher losses and reduces efficiency.

Who says the stator vanes increase the pressure of the flow? They do not move, so they hardly can do work on the flow. All they do is to control swirl such that the direction of flow is optimised for the next stage. Note that compressor blades have very thin airfoils which work best at a distinct angle of attack. Higher variations in angle of attack would require a blunter nose shape and a thicker airfoil. This is similar to a slotted flap at the trailing edge of a wing. The stator vane is like the wing in that respect that it directs the flow in one direction, allowing a thin airfoil behind it.

The rotor vane then increases both total and static energy.

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  • $\begingroup$ ok how does the static pressure increase if you said the stator vanes only untwist the flow? One more question, the dynamic pressure gets it's pressure from the mechanical work being done on it by the rotor blades, correct? $\endgroup$
    – Itzyoboi
    Commented Nov 23, 2017 at 22:45
  • $\begingroup$ @Itzyoboi: Again, static vanes do not increase static pressure. This is all done by the rotor vanes. As you say, they do mechanical work on the air which results in a pressure increase. $\endgroup$ Commented Nov 24, 2017 at 0:03
  • $\begingroup$ Ok, But I thought static pressure was the pressure of something when it's stationary, but the rotor vanes are rotating so wouldn't it be increasesing the dynamic pressure? Thanks. $\endgroup$
    – Itzyoboi
    Commented Nov 24, 2017 at 0:36

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