Question 87Gas Turbine - Assistant Engineer

The correct answer is C) Efficiency at various speeds. Variable stator vanes in an axial gas turbine compressor allow the compressor to maintain high efficiency over a wide range of operating speeds. By adjusting the angle of the stator vanes, the airflow through the compressor can be optimized for different rotational speeds, preventing stall and surge at low speeds and maintaining high pressure ratios at high speeds. This flexibility in airflow management is what gives variable stator vanes the capability to improve compressor efficiency across the operating envelope. The other answer choices are incorrect because: A) Increasing pressure ratios is a general capability of axial compressors, not specifically related to variable stator vanes. B) Increased primary air flow is not a direct capability of variable stator vanes. D) Ability to operate at constant speeds is not a primary advantage of variable stator vanes.