when studying the compressor map and the turbine map of a gas turbine, I noticed that the flow capacity of the compressor increases with speed increase (RPM) and the flow capacity of the turbine decreases with speed increase (when the rotor is getting chocked and not the NGV).

i) What causes the flow capacity of the axial compressor to increase as the speed increases?

ii) What causes the flow capacity of the axial turbine to decrease as the speed increases?


1 Answer 1


Inertia - fluid fails to move into the space vacated by the blade sufficiently quickly.

  • $\begingroup$ How does that explain the 'increase' of capacity in case of axial compressor (with increase in speed)? $\endgroup$
    Oct 30, 2023 at 12:34
  • 1
    $\begingroup$ @GRANZER When the blade is still sufficiently slow and its speed increased then more fluid gets accelerated... Once the limit has been exceeded then the output falls. Check out cavitation. $\endgroup$
    – Solar Mike
    Oct 30, 2023 at 13:37

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