Linear cascade experimental study of compressor performance degradation caused by fouling: Effects of fouling height and tip clearance

Tip fouling can progressively accumulate during compressor operation and significantly degrade aerodynamic performance through its interaction with tip-clearance flow structures. This study presents an experimental investigation of the effects of fouling height under different tip clearance conditions (1 mm, 1.5 mm, and 2 mm) in a compressor cascade. Fouling is emulated by applying strip-shaped sandpaper patches that introduce a controlled added thickness (0.4 mm) and a representative roughness level (R a ≈ 26.3 μ m, k _s ≈ 163 μ m), with two fouling heights defined relative to the blade tip. A smooth-surface counterpart with the same added thickness and planform is also tested to separate geometric build-up effects from roughness-induced penalties. Aerodynamic responses are quantified using pitchwise-averaged total pressure loss, exit-plane loss contours, normalized axial-velocity fields, and endwall oil-flow visualization. The results show that tip fouling causes pronounced loss redistribution in the near-tip/endwall region and increases the overall aerodynamic penalty, with stronger fouling sensitivity at smaller tip clearances. Relative to the baseline case, the mean loss increases by 6.99 % and 11.76 % at τ = 1.0 mm for the two fouling-height cases, compared with 4.72 % and 10.47 % at τ = 2.0 mm. Fouling is also associated with the appearance of a localized secondary high-loss core (SHLC) in the exit flow field, whose severity increases with fouling height. Endwall oil-flow patterns reveal an additional near-exit focal/recirculation-like feature at small and intermediate clearances, whereas this feature becomes less distinguishable at the largest clearance. Comparison between the smooth and rough fouling cases further indicates that geometric build-up and surface roughness play different roles: the former mainly affects the appearance and distribution of the localized SHLC-related loss structure, while the latter mainly intensifies local dissipation and influences the severe flow-deflection region associated with the SHLC.