A systematic numerical study has been carried out to investigate the effects of casing treatment slots geometry and location on the stall margin and peak efficiency of an isolated mixed-flow rotor at high subsonic flow conditions. Based on the literature review for axial rotor, a semi-circular axial skewed slot casing treatment placed in the leading edge region was chosen as the starting configuration as it has the best potential of producing stall margin improvement with low peak efficiency loss. A computational parametric study was performed from this baseline casing treatment geometry to identify the most important geometrical design parameters and to arrive at a design with noticeable stall margin improvement and no loss in peak efficiency. The results show that the design parameters with the largest impact on stall margin improvement and peak efficiency are: open area ratio, slot skew angle, slot axial length and slot axial position. The slots depth and slot shape seem to have only limited influence on performance. While not yet optimized, a slot casing treatment design with significant stall margin improvement and no loss in peak efficiency was obtained. To the authors' knowledge, this work is the most extensive slot casing treatments parametric study so far in term of number of design parameters considered.
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