The supercritical CO_2 (SCO_2) compressor is the key component of the SCO_2 Brayton cycle. It is considered as one of the most promising power conversion systems, because the compressor could consume small compression work as operating condition near the critical point. In this paper, a researched SCO_2 compressor was designed to operate with slightly above the vapor-liquid critical point of CO_2. The flow characteristics were investigated by NUMECA FINE/Turbo, coupled with the thermophysical properties of CO_2 in REFPROP database. Particular attention was paid on the blade tip clearance flow characteristics. The formation and development mechanism of the blade tip low pressure regions and the parameters distributional difference were studied. Then, the effects of different blade tip clearance types on the low pressure regions of the blade leading edge tip and the aerodynamic performance of SCO_2 compressor stage were compared and discussed. The combined effects of the injecting action, the blade leading edge tip shedding vortex, and the flow acceleration can lead the fluid thermodynamic state to enter the low pressure and low temperature regions at the leading edge of both the main blade and splitter blade tip. Especially, the condensation maybe exist at sharp corner of the blade tip leading edge. However, the tip clearance leakage vortex can significantly inhibit and weaken the low pressure regions. With the increase of tip clearance, the distribution and development tendency of the static pressure and temperature on the main blade leading edge tip are similar, but there is a significant influence for the splitter blades tip. Furthermore, because the tip clearance increases, the SCO_2 compressor stage pressure ratio and isentropic efficiency have degraded in whole operating range, but the stable operation range is expanded. Therefore, the above comprehensive factors should be considered during the design process in order to select the suitable tip clearance shape.
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机译：超临界CO_2（SCO_2）压缩机是SCO_2布雷顿循环的关键组件。它被认为是最有前途的功率转换系统之一，因为在临界点附近的工作条件下，压缩机可能消耗少量的压缩功。本文设计了一种研究型SCO_2压缩机，使其工作在CO_2的气液临界点稍高的位置。流动特性通过NUMECA FINE / Turbo进行了研究，并结合了REFPROP数据库中CO_2的热物理性质。特别注意了叶尖间隙流动特性。研究了叶尖低压区的形成和发展机理以及参数分布差异。然后，比较并讨论了不同叶片尖端间隙类型对叶片前缘尖端的低压区域的影响以及SCO_2压缩机级的空气动力性能。注入作用，叶片前缘尖端脱落涡旋和流动加速的综合作用可导致流体热力学状态进入主叶片和分离叶片尖端的前缘处的低压和低温区域。特别地，冷凝水可能存在于叶片尖端前缘的尖角处。但是，尖端间隙泄漏涡流可以显着抑制和削弱低压区域。随着叶尖间隙的增加，主叶片前缘叶尖上静压和温度的分布和发展趋势相似，但对分流叶片叶尖产生重大影响。此外，由于叶尖间隙增加，所以在整个工作范围内SCO_2压缩机级压力比和等熵效率均下降，但稳定的工作范围得到了扩大。因此，在设计过程中应考虑上述综合因素，以选择合适的刀尖间隙形状。
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