The isentropic exponent in the near-critical region can sharply change with operation condition transitions of a closed Brayton cycle, thus having significant impacts on the compressor aerodynamic performance and the internal flow of the compressor embedded into the cycle. This paper investigates the isentropic exponent effects of the supercritical carbon dioxide (CO₂) using theoretical analyses and three-dimensional computational fluid dynamic (CFD) simulations. The theoretical analysis reveals that the increasing isentropic exponent mitigates the impeller work coefficient and the impeller outlet Mach number but raises the suction side Mach number of the impeller blade and blade loading at the leading edge. The CFD results provide validations for the theoretical results. Based on the findings, a suggestion is offered to guide the physical experiment design of a centrifugal compressor with supercritical CO₂ as its working fluid.

中文翻译：

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等熵指数对超临界CO2离心压缩机内部流动的影响的理论分析

近临界区域的等熵指数会随着闭合布雷顿循环的工况转变而急剧变化，从而对压缩机气动性能和嵌入循环的压缩机内部流动产生重大影响。本文研究了超临界二氧化碳（CO ₂) 使用理论分析和三维计算流体动力学 (CFD) 模拟。理论分析表明，增大的等熵指数降低了叶轮功系数和叶轮出口马赫数，但提高了叶轮叶片的吸力侧马赫数和前缘叶片载荷。CFD 结果为理论结果提供了验证。根据研究结果，提出了指导以超临界CO ₂为工作流体的离心压缩机物理实验设计的建议。