汽水两相流介观模型及噪声特性研究

Steam-water two-phase flow is widely encountered in nature and industries, and it plays important roles for the efficiency and security of steam power systems. The mesoscale behaviors of steam-water flow, such as the bubble/droplet breakage and coalescence, usually results in significant vibration and noise, which would decrease the stealthiness of marines. The pressure pulsation, droplets entrainment and cavitation phenomenon may also cause erosions or even damage for the pipelines and valves in steam power systems, which raises security problems. The steam-water two-phase flow attracts intensive investigations for decades, and researchers gradually recognized that the mesoscale phenomena, including the evaluation of the vapor-water interface and the bubble/drop size distribution, are the bottleneck for steam-water two-phase investigations. In this project, the gas-liquid Energy-Minimization Multi-Scale (EMMS) approach would be introduced into the CFD-Population Balance Model (PBM) to construct a new mesoscale model for gas-liquid simulations: CFD-PBM-EMMS model, which takes the effects of energy multi-scale dissipation paths and the comprise of different dominant mechanisms on the interfacial forces and bubble/droplet breakage and coalescence kernels into considerations. Compared to the multi-fluid models in literatures, the CFD-PBM-EMMS model possesses the advantages in predicting the flow field and bubble/droplet size distribution of the steam-water flow in various flow regimes without empirical correlations or adjusting parameters. Then, the intrinsic relationships between the steam-water interface evaluation and the noise characteristics would be further explored, which aims to offer a new insight for predicting the spectrum characteristics of the steam-water flow noise. It is believed that this project will provide theoretical support for regulating the steam-water flow and reducing the noise of the steam power systems, which would further improve the power density, security and stealthiness of marines.

汽水两相流广泛存在于自然界与工业界，与蒸汽动力系统效率和安全性密切相关，其持续存在的汽泡/液滴破碎、聚并及溃灭等介观行为常诱发振动噪声，且压力脉动、高速液滴夹带及气蚀等还会对设备、管路及阀门造成损坏，影响舰船隐身性和安全性。相界面动态演化、汽泡/液滴尺寸分布等介观现象是汽水两相流研究的关键和瓶颈。本项目基于气液能量最小多尺度模型（EMMS），考虑能量多尺度耗散及不同控制机制协调对相间作用力及汽泡/液滴破碎聚并的影响，引入稳定性条件封闭动量方程和群体平衡方程（PBM），形成汽水两相流介观数值模拟方法：CFD-PBM-EMMS模型。该方法能摆脱曳力模型和群体平衡模型对经验参数的依赖，提高预测精度。随后进一步探索汽水两相流介观行为与噪声频谱特性的内在关联，基于介观数值模拟结果对噪声频谱特性进行预测，为动力系统两相流精确调控、振动噪声预测提供新思路，为提升舰船隐身性和安全性奠定理论基础。

本项目针对舰船动力系统汽水两相流机理复杂、预测难度大、热-流-声多场耦合等难点，从多相能质传递机理及汽水两相流介观现象出发，借鉴能量最小多尺度理论以及其在气固、气液、气液固等多相流中的成功应用经验，吸收群体平衡模型、界面浓度输运模型等介观模型理念，对汽液两相流体系进行能量和结构多尺度分析，针对气泡破碎聚并过程，以微尺度能耗趋于最小（Nsurf + Nturb → min）为封闭条件封闭多相流方程与气泡破碎聚并数密度函数方程，构建涉及气泡破碎聚并的汽液两相流介观模型。.本项目基于能量最小多尺度原理，构建了气液两相流介观模型，从宏观角度成功预测了气液两相流泡状流向弹状流的流型转变，在介观尺度，摆脱了群体平衡模型对经验影响因子的依赖，能在较宽工况范围成功预测气泡尺寸分布。在实验方面，搭建了蒸汽水下喷注可视化实验台架，并对不同过冷度、不同蒸汽流量等工况进行了流型分析以及噪声测量，分析了噪声频谱特性与气泡介观及宏观行为之间关联，揭示气泡破碎聚并与辐射噪声之间的耦合关联机理，为辐射噪声的抑制提供理论指导。.本项目共发表学术论文18篇，其中SCI论文2篇，EI论文9篇，国际会议论文8篇，国内会议论文2篇。申请国家发明专利10项。参加国际会议8人次，参加国内会议2人次。在人才培养方面，4人晋升为高级工程师，培养毕业硕士研究生2名。