|Quoting dakota123 (Reply 2):|
Another common way for surge to develop is if one or more sets of variable-incidence stator vanes are off-schedule, such that the volume of air fed to its associated compressor stage from the preceding stage is too great and an aerodynamic stall results
It's more the case that variable stator vanes being off schedule will mean the angle of incidence at the next compressor stage is not optimal, which may lead to a stall.
The problem with an axial compressor is that the air is effectively being driven up hill, against the pressure gradient. It doesn't take much disturbance to cause a partial or complete breakdown of flow. Too much airflow at too low rpm will cause surge. Inlet guide vanes and VSVs help to guide the air to more optimal angles. Surge bleeds can be opened to take air out of the compressor, reducing airflow and increasing the surge margin and the fuel control unit will have an acceleration limiting function to keep rpm and airflow relationship away from the surge boundary.
The glass isn't half empty, or half full, it's twice as big as it needs to be.