液滴是自然界中的一类典型和普遍存在的物质形态。液滴的平衡、迁移和运 动、以及液滴之间的相互作用等一直都是流体力学的研究热点。利用温度梯度产 生的表面张力可以驱动液滴热毛细迁移，对液滴迁移规律的探索，实现液滴的主 动驱动控制，不仅有重要的学术意义，同时具有巨大的工业价值。

        依托空间站流体物理实验柜，突破数字全息干涉测温与粒子图像测速同步测 量的关键技术，开展了两相和三相液滴热毛细迁移地面实验研究，实现了对均匀 温度梯度场中液滴热毛细迁移过程的温度场和速度场同时测量。

       讨论分析了均匀温度梯度场中液滴迁移的尾迹和边界层机理。通过对液滴迁 移速度场的测量，首次发现了液滴后部出现速度场为零的区域、四个涡胞结构、 以及双液滴迁移偏离轴线等新现象，并通过数值模拟进行了验证。从力学的角度 对物理现象进行了分析和讨论，分析了多物理场耦合关联以及影响因素，发现无 论是单液滴还是双液滴迁移，母液中液滴后部均出现速度零区、四个涡胞结构； 同相双液滴热毛细迁移时，后继大液滴迁移速度受到前导小液滴对温度场扰动的 影响，会比孤立迁移时小；三相双液滴迁移过程中，当后继小粘性小直径液滴追 赶并超越前导大粘性大直径液滴后，液滴中心连线发生了逆时针转动。分析了 Ma 数对液滴迁移距离和液滴迁移速度的影响，与前人的研究结果一致，并补充 了 Ma 数增加时液滴迁移速度的变化规律。

       在深入了解均匀温度梯度中温度场与速度场的耦合作用后，更进一步地研究 了局部温度梯度场对液滴的作用机理，提出了利用激光在液滴周围建立局部温度 梯度完成驱动且较精准控制液滴热毛细迁移方向的方法。通过数值模拟激光驱动 控制液滴过程的流场结构，验证了该方法的可行性；确定了在固定实验工况下能 够在液滴附近产生局部温度梯度的激光，搭建了自动识别和跟踪液滴的实验平台， 实现了局部温度梯度驱动并控制液滴热毛细迁移；并利用数字全息干涉系统实时 测量了激光驱动控制液滴过程的温度场分布。当激光直径不同时，会影响母液中 温度分布情况，造成高温区与低温区分布位置相反，从而影响温度梯度方向，使 得液滴在水平方向上朝向激光入射点或背离激光入射点运动，证明了激光的确控 制液滴迁移的方向。

       依托“空间三相多液滴迁移行为研究”实验项目研制了空间实验载荷“三相 液滴载荷”，开展了从母液中排出液滴或气泡的关键技术攻关，并在微重力环境 中完成了该关键技术验证及前期气泡热迁移实验。

        Droplet is a typical and universal class of material forms in nature. The equilibrium, migration and motion of droplets, as well as the interactions between droplets have always been the research hotspots of fluid mechanics. The surface tension generated by the temperature gradient can drive the thermocapillary migration of droplets. The exploration of the migration law of droplets and the realization of the active drive control of droplets not only have important academic significance, but also have great industrial value.

        Relying on the fluid physics experimental cabinet of the space station, breakthroughs were made in the key technology of synchronized measurement of digital holographic interferometry and particle image velocimetry, and the ground experimental study of two-phase and three-phase droplet thermocapillary migration was carried out, which realizes the simultaneous measurement of the temperature and velocity fields of the droplet thermocapillary migration process in a uniform temperature gradient.

        The wake and boundary layer mechanisms of droplet migration in a uniform temperature gradient field are discussed and analyzed. New phenomena such as a region of zero velocity field at the back of droplets, four vortex cell structures, and double-droplet migration off-axis are found for the first time by measuring the velocity field of droplet migration and verified by numerical simulation. The physical phenomena are analyzed and discussed from the mechanical point of view, and the multi-physical field coupling correlation as well as the influencing factors are analyzed, and it is found that whether it is a single droplet or a double droplets migration, the back of the droplet in the mother liquor appears to have a zero velocity region and four vortex cells structure; in the case of the same-phase double-droplet thermocapillary migration, the migration velocity of the succeeding large droplet is affected by the temperature field perturbations by the leading small droplet, and it will be smaller than that in the case of the isolated migration. During the three-phase two-droplet migration process, the droplet center line undergoes a counterclockwise rotation when the succeeding small-viscous small-diameter droplet catches up with and overtakes the leading large-viscous large-diameter droplet. The effects of Ma number on droplet migration distance and droplet migration velocity are analyzed, which are consistent with the results of the previous studies, and the change rule of droplet migration velocity when Ma number increases is added.

        After deeply studying of the coupling between the temperature field and velocity field in the uniform temperature gradient, the mechanism of the local strong interfacial tension gradient on the droplets is further investigated, and the method of using the laser to establish the local temperature gradient around the droplets to complete the drive and control the direction of the droplets' thermocapillary migration with greater precision is proposed. The feasibility of the method is verified by numerically simulating the flow field structure of the laser-driven controlled droplet process; the laser capable of generating a localized temperature gradient near the droplet under fixed experimental conditions is identified, and an experimental platform for automatic identification and tracking of the droplet is constructed to realize the localized temperature gradient-driven and controlled thermocapillary migration of the droplet; and a digital holographic interferometric system is used to measure the real-time temperature field distribution. The temperature distribution in the mother liquor is affected when the laser diameters are different, which resulting in the high-temperature and low-temperature zones being distributed in opposite positions. Different temperature zone distribution affects the direction of the temperature gradient and drive the droplets move horizontally towards or away from the laser, which proving that the laser does control the direction of droplet migration.

        Relying on the experimental project "Research on the Migration Behavior of Three-Phase Multi-Droplet in Space", a space experimental load "Three-Phase Droplet Load" was developed, and the key technology of exhausting droplets or bubbles from mother liquids was tackled, and the validation of the key technology and the preliminary bubble thermal migration experiments were completed in microgravity environment.