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An unsteady computational parametric study of the axial slot casing treatments (ASCTs) is performed in a tip-critical transonic rotor. Other than previous practices of considering the compressor overall performance as the design target directly, this paper takes the recirculation flow inside the slot cavity as the bridge to link the overall performance with geometric parameters of ASCT. The recirculation flow has a compound effect on the rotor tip flow field, leading to a significant influence on compressor stability and efficiency. Thus, a design strategy is proposed to improve the ASCT effectiveness based on recirculation flow control. Firstly, the study of the relationship between the recirculation flow and the ASCT effectiveness is carried out on a single rotor row with a standard semi-circular ASCT. The recirculation is quantitatively described by crucial recirculation parameters, the injection flow rate, the injection axial momentum, and the injection angle. The influence of these parameters on stall margin and efficiency is clarified through analyzing the tip region axial momentum and flow losses at design and near stall point. Then, the geometry of ASCT is characterized by three key parameters: the axial position, the open area ratio, and the skew angle. According to the parametric study, the variations of recirculation parameters with the slot geometric parameters can be quantitatively analyzed. Consequently, the influence mechanisms of geometric parameters on ASCT effectiveness are elucidated from the perspective of recirculation flow. Based on the above understanding, the effectiveness of ASCT can be improved by changing the geometric parameters to redesign the recirculation parameters. Finally, a new semi-circular ASCT configuration is improved by this strategy. The numerical results show that compared with the standard configuration, the new ASCT configuration increases the stall margin from 7.38% to 15.81% with almost the same peak efficiency. |
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