A three stage compressor test incorporating casing inserts comprised of compound angled honeycomb cells demonstrated up to 10% higher stall margin than circumferential grooves casing treatment. This is attributed to effective tip flow energization resulting from the unsteady flow induced in and out of the cells as the blade tip sweeps by the cell openings. The rationale for selecting the cell inclination angles both relative to the normal and the tangential directions is discussed. The design intent of the cell orientation is to induce a high cell exit velocity as well as to impart a degree of flow alignment to the injected jets. A first order calculation of cell exit velocity variation based on the cell pressure/volume dynamics is indicative of unsteady blowing which is theorized to effectively mix the tip suction side flow and to enhance the tip flow streamwise momentum. This theory is partially substantiated by the presented compressor test results showing improved radial total pressure profiles, stage characteristics, and stall margin. Since a few unhealthy stages of a multi-stage compressor could make it stall prone, casing treatment of those weak stages could dramatically increase stall margin with negligible impact on overall adiabatic efficiency. In addition to the aerodynamic effectiveness, the mechanical suitability of this casing treatment to multistage compressors, based on its demonstrated abradability and packageability, is discussed.

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