扇贝仿生密封腔室内超临界二氧化碳泄漏流湍动能耗散机理研究

Turbulent Kinetic Energy Dissipation Mechanism of Supercritical Carbon Dioxide Leakage Flow in a Scallop Bionic Seal Cavity

摘要

为准确表征扇贝仿生密封腔室内超临界二氧化碳(sCO₂)泄漏流的复杂流动过程，揭示泄漏流湍动能耗散机理，提出了旋转机械强变物性真实气体流动高精度数值模拟方法。该数值模拟方法采用单体迎风格式实现数值通量分裂，通过高阶迎风方案实现数值通量三阶重构。所用欧拉全隐时间步进迭代方法支持多线程共享存储并行计算；采用了真实气体状态方程与亥姆霍兹自由能热物性查询表耦合迭代计算方法，可准确捕捉CO₂热物性非线性变化特征，计算偏差小于0.5%；通过分子示踪实验验证了数值模拟方法的准确性，并深入分析了扇贝仿生密封腔室内泄漏流涡旋空间分布及其对湍动能耗散率的影响机理。研究结果表明：sCO₂泄漏流进入密封腔室后发生膨胀，动能转化为压力势能，泄漏流当地马赫数降低至0.1以下，泄漏速率随之降低，泄漏流在高速转子剪切作用下产生涡旋并发生迁移、分裂和分离行为；泄漏流正则化螺旋度呈现正负值交替特征，表明密封腔室内存在多组顺、逆时针反向涡旋；每组反向涡旋有助于增强泄漏流湍动能耗散，无量纲湍动能耗散率大于1.95×10⁸，可有效改善密封封严性能；反向涡旋外缘交界点即为湍动能耗散率极值点，涡旋转向改变同样会增大泄漏流的湍动能耗散率。

Abstract

To accurately characterize the complex flow process of supercritical carbon dioxide (sCO₂) leakage flow in a scallop bionic seal cavity and to elucidate the mechanism of turbulent kinetic energy (TKE) dissipation, a high-order numerical simulation method for real gas flows with strongly variable physical properties in rotating machinery was proposed. In this method, the uni-particle upwind scheme was employed for numerical flux splitting, while third-order numerical flux reconstruction was achieved via the simple high-resolution upwind method. Euler’s fully implicit time-stepping iterative method was implemented, supporting open multi-processing (OpenMP) shared-memory parallel computing. A coupled iterative calculation method, integrating a real gas equation of state (EOS) with Helmholtz free energy-based thermophysical property lookup table, was adopted to accurately capture the nonlinear variations in CO₂ thermophysical properties, with calculation deviations below 0.5%. The accuracy of this numerical simulation method was validated through molecular tracing experiments. Furthermore, the spatial distribution of leakage flow vortices within the scallop bionic seal cavity and its impact on the TKE dissipation rate were analyzed in detail. The results indicate that as the sCO₂ leakage flow enters the seal cavity, expansion occurs, while the local Mach number remains below 0.1. Under the rapid shear of the rotor, the leakage flow generates vortices that exhibit migration, splitting, and separation behaviors. The normalized helicity of the leakage flow exhibits alternating positive and negative values, indicating the presence of multiple sets of counter-rotating (clockwise and counter-clockwise) vortices within the seal cavity. Each set of counter-rotating vortices increases the dimensionless TKE dissipation rate to over 1.95×10⁸, thereby effectively improving sealing performance. Moreover, the extrema of the TKE dissipation rate were identified at the outer boundaries of these counter-rotating vortices, where changes in vortex rotation direction also increase the TKE dissipation rate of the leakage flow.

关键词

超临界二氧化碳 / 扇贝仿生密封 / 泄漏流 / 湍动能耗散 / 涡旋空间分布

Key words

supercritical carbon dioxide / scallop bionic seal / leakage flow / turbulence kinetic energy dissipation / vortex distribution

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基金资助

国家自然科学基金资助项目(52506193)

中国博士后创新人才支持计划资助项目(BX20240283)

陕西省“三秦学者”创国家一流团队资助项目(2023STD03)