闪蒸界面传播现象（又称为表面沸腾、闪蒸波等）是闪蒸现象的一种特殊表现形式，指的是过热液体内部的核化过程被抑制时，发生在气液界面临近区域内的液体剧烈气化，且气液界面向液体内部移动的现象。这种现象常见于液体向低压环境主动排放或被动泄露中，往往主导着相应流动的特征以及温度、压力的分布，是预测闪蒸排液过程特征、评估液体排放效率和安全性时需重点关注的基础物理现象。

已有的闪蒸界面传播研究主要针对的是过热度较高或管径较大的情形，且理论发展并不完善，难以满足航天器常用小管道常温排液过程分析的需求。因此，本文开展了小管径直管内低过热度条件下的闪蒸界面传播现象研究，主要内容和成果如下：

首先，根据研究目标和要求搭建了闪蒸实验平台，优化了闪蒸界面传播实验流程，发展了数据提取和处理方法。系统研究了不凝气体对闪蒸起始及其传播现象的影响，提出了严格的组合式减压除气流程，并采用在气液界面下方人工预置核化点的方法激发闪蒸，有效避免了不凝气体含量差异引起的闪蒸界面传播特征的显著差别；基于数字图像处理技术，提出了闪蒸界面位置自动识别方法，准确追踪闪蒸界面的瞬态传播过程，获得关于闪蒸界面传播现象的客观数据，为相关规律分析提供坚实基础。

其次，实验研究了不同管径直管道内闪蒸界面传播机制，建立了闪蒸界面传播现象分区准则和表观速度预测模型。实验观测了不同初始液温、管径、重力方向等参数条件下的闪蒸界面形态以及其自我维持过程，分析了闪蒸界面传播的内在机制，提出了闪蒸界面传播可否持续的分区准则；分析了闪蒸界面传播的间歇性特征，归纳提出了闪蒸界面传播表观速度的经验预测模型。

最后，提出了描述复杂闪蒸界面的多尺度数值模型，深入分析了直管内闪蒸界面传播现象的基本特征和内在规律。针对闪蒸界面的多尺度特征，提出将闪蒸界面分解为“宏观波动+局部粗糙”的组合模型，其中，宏观波动特性对应的界面面密度采用基于平直界面等概率随机分布假设计算，局部粗糙特性对应的界面面密度修正则采用基于流体动力学稳定性的气相韦伯数模型计算；此外，管径对闪蒸界面传播的影响通过核化单元的量子化假设进行估算。基于混合模型和分区表征的界面面密度模型，对气液强烈掺混的闪蒸界面传播现象进行了数值模拟，模拟结果和实验观测符合甚好，验证了本文新建闪蒸界面模型的正确性，同时确定了模型参数的取值。进一步的模拟分析揭示了闪蒸界面传播现象中的压力、温度分布特征，以及初始温度、出口压力、管径、出口孔径等因素对闪蒸界面传播现象的影响规律。

The flashing front propagation (also known as surface boiling, flashing wave, etc.) is a special kind of flash evaporation phenomenon. It refers to the phenomenon that flashing mainly occurs in the vicinity of the gas-liquid interface, and the interface moves towards the interior of the liquid, while the nucleation process inside the superheated liquid is suppressed. This phenomenon is common when liquid is discharged or leaked into low pressure environments, and it usually dominates the flow characteristics and the distribution of temperature and pressure. Therefore, flashing front propagation phenomenon is a key fundamental physical phenomenon when predicting flashing discharging process or evaluating the flashing discharging efficiency and safety.

The previous studies on flashing front propagation phenomenon mainly focuses on situations with high superheat or large tube diameter. The theoretical development is far from perfection and is insufficient to support the analysis and prediction of the liquid discharge process of spacecraft, which is usually with room temperature and small tube diameter. Therefore, we conduct research on the flashing front propagation phenomenon, and focus on the laws of phenomenon under small tube diameter and low superheat conditions. The main contents and achievements are as follows:

First, based on the experimental objectives and requirements, a flashing experiment platform is established, the experimental process is improved, and methods for data reduction are developed. Specifically, we study the influence of noncondensable gas on flashing inception and its propagation, propose a rigorous combined method for degassing during depressurization, and trigger flashing by an artificially preplaced nucleation site, thus avoiding the phenomenon difference brought by inconsistent noncondensable gas content. Based on digital image processing technique, we propose a method for flashing front position recognition, which makes it possible to track the transient characteristics of flashing front propagation and get the objective data of flashing front propagation, thus providing a good foundation for the analysis of the phenomenon.

Next, experimentally study the flashing front propagation mechanism in various tube diameter, establish the pattern maps of flashing front propagation, and propose a model for predicting the superficial velocity. Specifically, we observe the morphological characteristics and the self-sustaining process of flashing front under various conditions of initial liquid temperature, tube diameter and gravity orientation, analyzed the mechanism of flashing front propagation, and propose a criterion for predicting whether the propagation could sustain itself. We analyze the intermittent characteristics of flashing front propagation and summarize an empirical model for predicting the superficial velocity.

Finally, a multi-scale numerical model is proposed to describe the complex interface of flashing front, and the basic characteristics and inherent laws of flashing front propagation in straight tubes are deeply analyzed. According to the multi-scale characteristics of the flashing front, a combined model of "macro fluctuation + local roughness" is proposed, in which the interfacial area concentration corresponding to the macro fluctuation characteristics is calculated based on the assumption of equal probability random distribution of the flat interface, and the interfacial area concentration correction corresponding to the local roughness characteristics is calculated using the gas phase Weber number model based on hydrodynamic stability. In addition, the influence of tube diameter on flashing front propagation is estimated by the quantization assumption of nucleation unit. Based on the mixture model and the interfacial area concentration model that characterized with zoning, the numerical simulation of the flashing front propagation phenomenon with strong gas-liquid mixing is carried out. The simulation results are in good agreement with the experimental observations, verifies the correctness of the new flashing front model in this paper, and determines the value of the model parameters. Further simulation analysis reveals the pressure and temperature distribution characteristics in the flashing front propagation phenomenon, as well as the influence of initial temperature, outlet pressure, tube diameter, outlet diameter and other factors on the flashing front propagation phenomenon.