Define compressor surge and describe a common cause.

• A. Dynamic instability where airflow through the compressor collapses; caused by high inlet pressure reducing stability margins.
• B. A stable operating condition with maximum efficiency.
• C. A dynamic instability where airflow through the compressor collapses; caused by excessive fuel flow, throttle movement, or low inlet pressure reducing stability margins.
• D. A mechanical failure in the turbine.

Answer: (C)

Compressor surge is a dynamic instability in which the flow through the compressor collapses, often causing flow reversal and large pressure pulsations in the system. A common reason this happens is when conditions undermine the compressor’s stability margin—such as rapid throttle changes, excessive fuel flow, or low inlet pressure, all of which reduce the ability of the compressor to sustain the required mass flow for the given pressure rise. This is not a stable, efficient operating state, nor a mechanical turbine failure; it’s an aerodynamic instability that can cycle and cause severe fluctuations.