I am studying about stall and surge in rotodynamic compressors and want to understand which one is more prone to these phenomena.


Axial for sure. Its blades are wings subject to aerodynamic stall within the blade array.

Centrifugal compressors just throw air outward; they don't really "stall" if in-flow is restricted, but will surge due to the pressure drop and resulting load reduction on the compressor. Centrifugal compressor surge is what is happening when you block a vacuum cleaner and it goes vwwwwwweeeeeeeeeeeeeeeeeeeeee.

Axial compressors, being an array of little spinning wings, depend on a controlled angle of attack on the blades and are much more sensitive to flow disruptions. And once they do stall, the surge and flow disruptions throughout the engine are more severe (those whomp whomp sounds and flames coming out the front of the engine as reverse pressure waves are induced, that sort of thing).

So if you want efficiency and high compression ratios, you go with axial and live with the sensitivity, the high cost and complexity. If you want insensitivity to inflow disturbances and can live with a larger diameter engine and less efficiency, and want to make the engine cheaper, you go with centrifugal.

  • $\begingroup$ Blade stall can occur in centrifugal compressors, depending on the difference in whirl velocity. Not in a vacuum cleaner, no. $\endgroup$ – Koyovis Feb 7 '20 at 22:17
  • $\begingroup$ Well they call it stall as in flow disruption but I was trying to differentiate between that and stalling of the airfoil blades of axials being closer to a regular wing. I used the vacuum cleaner analogy because when air cycle machines get inflow restrictions (from letting the heat exchangers get dirty) they act like vacuum cleaners and surge and overspeed, and in the case of ACM spools they usually proceed to destroy themselves. $\endgroup$ – John K Feb 7 '20 at 23:19
  • $\begingroup$ Why is axial more prone to stall? If the pressure difference over at least part of the compressor increases above what it can produce, either will stall. The difference is in how much the pressure has to drop for them to recover, and how quickly they'll recover, but the condition to cause it is basically the same. $\endgroup$ – Jan Hudec Feb 8 '20 at 23:29
  • $\begingroup$ Well yes but the centrifugal can tolerate larger pressure disruptions before stall/surge sets in. On the 1st engines like the axial Jumo vs centrifugal Whittle, where the crude fuel metering system consisted of more or less a needle valve connected to the throttle with the pilot's eyes and brain the fuel control system, the Jumo had to be far more carefully managed, mostly because it was axial. $\endgroup$ – John K Feb 9 '20 at 0:12

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