What happens to the compressor when there is an accumulation of contaminants?

• A. It increases blade wear without affecting performance
• B. It causes the compressor to stall at low speeds
• C. It reduces overall airflow through the compressor
• D. It reduces aerodynamic efficiency of the blades, thereby reducing engine performance

Answer: (D)

Contaminants on compressor blades disrupt the smooth, aerodynamic flow the blades are designed to handle. The deposits and surface roughness increase skin-friction drag and promote boundary-layer disturbance, which can lead to earlier flow separation on the blade surfaces. This lowers the blade’s ability to generate the required pressure rise for a given mass flow, i.e., it reduces aerodynamic efficiency. With less efficient compression, engine performance drops, as you get less overall pressure rise and more losses through the stage. While wear and other issues can accompany contamination, the primary and most direct impact is the reduction in aerodynamic efficiency, which explains why this option is the best description.