On the influence of non-uniform roughness distribution in a compressor rotor row

Fouling refers to the process of particle deposition on surfaces, leading to increased blade thickness and surface roughness in turbomachines. These effects contribute to operational wear on the compressor and engine. This investigation examines the impact of fouled rotor blades in a 1.5-stage low-speed compressor using artificially roughened blades. Four setups were considered: one reference case with a fully smooth rotor, one fully rough setup, and two setups with 50% smooth and 50% rough blades arranged in different circumferential distributions. Integral measurements of efficiency and pressure rise were conducted, along with detailed wake measurements using a 5-hole probe and a transient 1-hole probe. The roughness parameters for the artificial roughness were derived from surface measurements of a worn CFM-56 engine. The results indicate that an alternating distribution of smooth and rough blades is beneficial for high mass flows. A uniform distribution of rough blades results in more evenly distributed circumferential blockage and a more consistent inflow condition for the downstream stator. Near the stall limit, a non-uniform distribution featuring two rough quadrants demonstrates better pressure rise and efficiency. However, the operating range of both non-uniform and fully rough setups is reduced compared to a fully smooth rotor.