During which conditions is a compressor stall most likely to occur?

During which conditions is a compressor stall most likely to occur?

• A. During high power settings, low speed, high angle of attack
• B. During low-power, high-speed, high angle of attack
• C. During high power, high speed, low angle of attack
• D. During low power, low speed

Answer: (C)

Compressor stall is a flow instability that happens when the compressor can’t move the air the engine demands, causing the airflow through the blades to separate and the pressure rise to collapse momentarily. This instability is most likely when the engine is asked to deliver a large amount of air while spinning at high speed, because both conditions push the compressor toward its surge limit—the point where, despite high energy in the rotor, the downstream flow can’t be sustained and a surge travels backward or oscillates through the stage. With a high power setting and high speed, the compressor must handle a large mass flow and a high pressure ratio, which brings it closest to its stability boundary. If the inlet flow remains relatively clean and axial (low angle of attack), external distortions are minimized, so the dominant risk factor is the compressor’s own demand exceeding what it can sustain at that operating point, making stall more likely. If the angle of attack were high, inlet distortions could also provoke stall, but the situation described emphasizes the high demand and high-speed condition with a relatively undistorted inlet, where stall risk peaks. Low power or low speed move the operating point away from the surge boundary, reducing the likelihood of stall.

Compressor stall is a flow instability that happens when the compressor can’t move the air the engine demands, causing the airflow through the blades to separate and the pressure rise to collapse momentarily. This instability is most likely when the engine is asked to deliver a large amount of air while spinning at high speed, because both conditions push the compressor toward its surge limit—the point where, despite high energy in the rotor, the downstream flow can’t be sustained and a surge travels backward or oscillates through the stage.

With a high power setting and high speed, the compressor must handle a large mass flow and a high pressure ratio, which brings it closest to its stability boundary. If the inlet flow remains relatively clean and axial (low angle of attack), external distortions are minimized, so the dominant risk factor is the compressor’s own demand exceeding what it can sustain at that operating point, making stall more likely. If the angle of attack were high, inlet distortions could also provoke stall, but the situation described emphasizes the high demand and high-speed condition with a relatively undistorted inlet, where stall risk peaks. Low power or low speed move the operating point away from the surge boundary, reducing the likelihood of stall.