CO2两相引射器流动特性动态模型化研究

Dynamic simulation is the effective mean to reseach dynamic performance of two-phase ejector and ejector system. The existing one-dimensional lumped parameter model does not reflect the dynamic changes of the working condition parameter inside the ejector with the space-time states. And this model can not express adequately on typical process and phenomenon inside ejector such as the choking, phase delay, the shock wave and boundary layer interference as well. This project analysis the complex flow mechanism inside transcrical CO2 two-phase ejector using the computational fluid dynamics simulation and visualization experiments. The main physical factors are induced that affect the transfer process between primary flow and suction flow. One-dimensional spatial distribution framework assumption that primary flow and suction flow merge together at the end of ejector mixing section is put forward. Furthermore, one dimensional distribution parameters dynamic model reflecting the space-time states of the internal flow basing on this framework is built. This project can improve the ejector turbulence model, explore reasonable measures to realize internal flow visualization of the ejector, illustrate the effect strength and sensitivity of the different typical phenomenon and control parameters on the ejector performance. In the end, the evaluation method of the ejector internal performance on the basis of the turbulent mixing degree is obtained. This project contributes to deep understanding the fluid mechanics of the ejector, guides the design of the ejector, lays a foundation for the optimization control and the thermal strengthening of the ejector system, as well as has certain academic significance and engineering value.

动态模拟是研究两相引射器和引射系统动态特性的必要手段，目前其所使用的一维集总参数模型并不反映引射器内剧烈随时空动态变化的工况参数，对壅塞、相变延迟、激波、边界层干扰等典型特征的表达也不充分。本项目通过计算流体力学模拟和可视化实验，分析跨临界CO2两相引射器内部复杂流动机理，归纳影响主动流、引射流混合传递的主要物理作用，提出在引射器混合段后端才合二为一的一维空间分布架构设想，构建此架构下反映内流时空状态的一维分布参数动态模型。研究能够完善引射器湍流模型，探索引射器内部流动可视化的合理方法，阐明不同典型现象和控制参数对引射器性能上的作用强度与敏感度，获得基于湍流混合程度的引射器内在性能评价方法，进一步揭示引射器的动态规律与响应特性。项目有助于引射器流体力学结构核心机理的认知，指导引射器的设计，为引射系统优化控制与系统热力强化奠定基础理论，研究具有重要的学术研究意义和工程应用价值。

跨临界CO2两相引射器内部的相变、激波、湍流混合等复杂流动现象对引射器性能和引射膨胀制冷系统性能有着重要影响，本项目利用理论分析、数值模拟和实验研究相结合的方法揭示了CO2两相引射器内部的流动机理和性能提升方法。项目构建了跨临界CO2两相引射器主动喷嘴一维分布参数模型，提出了非平衡汽化过程和非平衡冷凝过程中均匀弛逾模型弛豫时间的新计算公式和适用常数范围，比较了均匀平衡模型、均匀弛逾模型和延迟平衡模型的准确性。耦合摩擦模型和激波模型，探讨了不同喷嘴渐扩角时影响主动流膨胀的主要机制和激波传递特性。构建了单相引射器喷嘴的动态一维分布参数模型，研究了背压扰动下喷嘴内压力的动态响应特性。. 开发了基于压焓的跨临界CO2引射器可压缩CFD模型，比较分析了可调引射器和固定结构引射器主动流、引射流之间的相互作用面以及㶲传递和损失分布规律，对引射器关键结构开展了敏感性分析，获得了结构参数对引射器性能的协同作用规律，进一步构建了基于压力和温度的可压缩非平衡相变CFD模型，研究了相变过程中的气相和液相之间的传质和传热规律，量化了蒸发和空化传质速率。. 搭建了跨临界CO2引射器可视化实验平台，利用直接拍摄法获得了引射器内部流场结构特征和轴向压力分布，研究了操作条件和结构参数对主动流相变的影响规律，基于可视化图片对主动喷嘴内的成核过程进行了分析，获得了操作条件和结构参数变化时主动流膨胀状态的转变规律，探讨了主动流膨胀程度和膨胀轮廓对引射器性能的影响。