高速细微喷雾碰壁后油膜流动与破碎的动态机理研究

Spray impingement is the phenomenon during which spray droplets hit solid surfaces and physical process such as stick, rebound, secondary breakup, etc., takes place and forms fuel film on the wall. Reducing the mass of combustor wall film can effectively reduce harmful combustion emission. While most existing literature only covers phenomenological investigations of spray impingements. There are also experimental studies of low-speed, single large droplet impingement for fundamental impingement mechanism analysis. However, analysis of high-speed, micron droplets analogous to those in practical fuel sprays for transition criteria investigation and fuel film dynamic movement is rare. This project proposes to utilize a high-speed co-flow single droplet generator for impingement experiments to approximate high-speed projecting micron droplets in practical sprays. With various high-speed, microscopic, quantitative laser diagnostic techniques, this project will precisely measure the physical characteristics of droplets before and after impingement, and quantitatively determine the deformation transition criteria of impinging droplets. Meanwhile, this project will measure the surface wave motion of the impingement fuel film, and analyze the mechanisms of such motions and corresponding secondary film disintegration induced by high-speed co-flow. Based on a great amount of experimental data and dynamic mechanism research, this project will establish numerical models to approximate high-speed micron spray droplet impingement, and utilize a Eulerian approach to solve the governing equations of the fuel film movement and predict the dynamic features of the fuel film.

喷雾碰壁现象是喷雾液滴碰撞固体表面后发生粘附、反弹、二次破碎等一系列物理过程，并在壁面形成油膜的现象。减少燃油喷雾在燃烧器壁面的油膜附着量可有效降低燃烧有害排放物生成。已有喷雾碰壁研究主要集中在基于喷雾碰壁宏观形态观察的现象学研究，也有基于低速大液滴碰壁实验分析碰壁现象机理的基础性研究。但是针对实际燃油喷雾的高速细小液滴碰壁现象的临界准则数分析和油膜运动状态的机理研究比较缺乏。本课题拟采用高速协流单液滴发生器模拟实际喷雾中存在的高速穿行微米级油滴进行碰壁实验，建立多种高速显微定量激光光学诊断方法对液滴碰壁前后的形态变化各特征物理量进行精准测量，并量化分析导致各种形态变化的特征准则数。同时，观察在高速气流影响下碰壁油膜波动现象，解析油膜表面波动过程和油膜边缘二次破碎的机理。基于大量实验数据和动态机理解明、创建实际高速细微喷雾碰壁油膜的数值模型，应用欧拉法求解油膜流动，并预测油膜动力学形态。

喷雾碰壁现象是喷雾液滴碰撞固体表面后发生粘附、反弹、二次破碎等一系列物理过程，并在壁面形成油膜的现象。减少燃油喷雾在燃烧器壁面的油膜附着量是有效降低燃烧有害排放物生成的可行思路。本课题针对现有研究中，实际燃油喷雾的高速细小液滴碰壁现象的临界准则数分析和油膜运动状态的机理研究比较缺乏的痛点，采用高速协流单液滴发生器模拟实际喷雾中存在的高速穿行微米级油滴进行碰壁实验，建立多种高速显微定量激光光学诊断方法对液滴碰壁前后的形态变化各特征物理量进行精准测量，并量化分析导致各种形态变化的特征准则数，根据实验结果扩充了碰壁二次粒子运动模态物理模型，完善了壁面附着油膜质量预测模型。同时，观察在高速气流影响下碰壁油膜波动现象，解析油膜表面波动过程和油膜边缘二次破碎的机理，从传热传质角度提出了冷启动等典型工况下降低油膜附着质量的可行控制策略。基于大量实验数据和动态机理解明、创建实际高速细微喷雾碰壁油膜的数值模型，应用欧拉法求解油膜流动，并预测油膜动力学形态，弥补了传统单体系无法适配离散喷雾-连续油膜转化的关键缺失，通过耦合二次粒子滑移、液膜波浪破碎等物理过程，进一步降低了数值模拟结果与实际实验结果之间的偏差。本研究结果对于燃烧动力系统缸内油膜附着预测及其控制策略设计具有重要意义，同时研究成果也能够迁移至微表面清洁、电池板冷却换热等其他场景，具有工程实际意义。