Experimental investigation of blade-tip leakage flow control in a low-speed axial compressor using natural aspiration through casing wall slot

Mitigating rotor blade tip leakage flow in axial compressors is crucial for improving aerodynamic performance and extending the stable operating range. This study experimentally evaluates natural aspiration through a circumferential casing slot upstream of an isolated rotor blade row, with the configuration informed by previous numerical studies. The treatment passively admits ambient air without an external compressed-air supply. Experiments at 1600 rpm compared plain and treated casings using performance measurements, casing-wall static pressures, and single-wire hot-wire anemometry. Fourier-based spectral analysis was used to examine the measured flow unsteadiness. The performance curves indicated an approximately 1.2% increase in the pressure-rise coefficient. The reported operating points extended to an inlet-flow coefficient of 0.28 for the treated casing and 0.32 for the plain casing. Wall-pressure distributions and velocity spectra provided complementary information on the near-tip flow response, without independently establishing vortex weakening or a specific stall-inception mechanism. The admitted mass flow and overall efficiency were not quantified, limiting conclusions about rotor-throughflow-based stability improvement and efficiency. The results provide an experimental basis for evaluating passive air admission as a compressor casing treatment.