Collaborative Research: Fuel Droplet Disruption under Locally Supersonic Conditions

该奖项由2009年《美国复苏和再投资法案》(Public Law 111-5).0853817/0853396Hermanson/TryggvasonThis Public Law 111-5).0853817/0853396Hermanson/TryggvasonThis)资助，初步实验和计算研究计划将研究超音速流动中液滴破裂和汽化的物理机制。这些机制包括气动力引起的液滴变形，与液滴加速有关的惯性不稳定，以及由于液滴表面的高速流动而产生的剪切不稳定。另一种不稳定可能是由于测试段中的低静压而导致液滴流体过热而导致的快速蒸发。通过改变流动和热边界条件，包括相对于液滴和液体组成的马赫数，将系统地研究这些机制的作用。将探索是否存在最佳参数组合，如液滴大小、蒸汽压和可压缩自由流条件，以实现最快的液滴破裂和汽化。这项研究的原创性和潜在的变革性方面源于局部超音速条件和潜在的液体过热的结合，该研究探索了一种实际重要的液滴破裂制度，迄今尚未深入或系统地进行研究。华盛顿大学(UW)的小型超音速风洞将向超音速气流中注入液滴。液滴按需发生器将产生足够小的单分散液滴，使液滴不会太快地破裂，但足够大，使液滴将“滞后”超音速气流，创造相对于液滴的可压缩条件。不同的试验段几何形状将产生相对于周围流动具有亚音速和超音速马赫数的液滴。诊断技术将包括平面激光诱导荧光(PLIF)、火花纹影/阴影成像、双脉冲激光测速和直接摄影。这些技术将提供关于液滴变形/破裂、排出的蒸汽的扩散、液滴加速、液滴附近的可压缩流场以及界面不稳定性特征的详细知识。伍斯特理工学院(WPI)的计算模型将采用有限体积/前沿跟踪方法，能够模拟可压缩流动条件下液滴的变形和爆炸蒸发。模拟将与实验协同进行，使用实验获得的流动信息来指导数值模拟的开发和实施。反过来，数值模拟将有助于指导实验的进行，并通过提供实验不易获得的关键信息来帮助解释实验结果，例如液滴附近的压力变化和汽化速度。这一研究课题在一些涉及高速流动中液体喷射的实际重要问题上有应用，包括超音速燃烧冲压发动机、脉冲爆震发动机、再入物体冷却和高速流动中的表面侵蚀。这种应用受到液滴破裂的性质和所要研究的液体燃料液滴的蒸发机理的严重影响。这项研究也将直接影响教育。平面激光诱导荧光和脉冲激光液滴/粒子速度测量技术通过威斯康星大学现有的实验方法课程引入本科生课程。同样，数值工作将产生的例子将被用作WPI的课堂范例。本科生也将直接参与开展这项研究。研究生将积极参与该计划的本科生部分，在教师的监督下，担任研究本科生部分的“助学金监督员”。最后，联合私人投资督学将从代表性不足的团体中招聘合格和有兴趣的成员，在华盛顿大学和伍斯特理工学院进行研究。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0853817/0853396Hermanson/TryggvasonThis preliminary experimental and computational research program will study the physical mechanisms of disruption and vaporization of liquid droplets in supersonic flow. These mechanisms include the deformation of the droplet due to aerodynamic forces, the inertial instability associated with droplet acceleration, and shear instability due to the high-speed flow across the droplet surface. An additional instability can result from the rapid evaporation that can result from the droplet fluid becoming superheated due to the low static pressure in the test section. The action of these mechanisms will be systematically studied by varying both the flow and thermal boundary conditions, including the Mach number relative to the droplet and the liquid composition. The possible existence of optimum combinations of parameters, such as droplet size, vapor pressure, and compressible free-stream conditions for the most rapid droplet disruption and vaporization will be explored. The original and potentially transformative aspects of this research stem from the combination of locally supersonic conditions with potential liquid superheating, which explores a practically important regime of droplet disruption that has not been examined in depth or in a systematic fashion to date. Droplets will be injected into supersonic flow using small-scale supersonic wind tunnels at the University of Washington (UW). A droplet-on-demand generator will produce monodisperse droplets sufficiently small that the droplets will not disrupt too quickly, but sufficiently large so that the droplets will "lag" the supersonic airflow to create compressible conditions relative to the droplet. Different test section geometries will produce droplets with both subsonic and supersonic Mach numbers relative to the surrounding flow. Diagnostic techniques will include planar laser-induced fluorescence (PLIF), spark schlieren/shadowgraph imaging, double-pulsed laser velocity measurement, and direct photography. These techniques will provide detailed knowledge of the droplet deformation/disruption, the dispersion of the expelled vapor, the droplet acceleration, the compressible flow field near the droplet, and the features of the interfacial instabilities. The computational modeling at Worcester Polytechnic Institute (WPI) will employ a finite volume/front-tracking method capable of simulating droplet deformation and explosive evaporation under compressible flow conditions. The simulations will be conducted synergistically with the experiments, using flow information from the experiments to guide the development and implementation of the numerical modeling. In turn, the numerical simulations will serve both to guide the conduct of the experiments as well as to help interpret the experimental results by providing key information not readily accessible by the experiments, such as the pressure variation in the vicinity of the droplets and the rate of vaporization. This research topic has applications to a number of practically important problems involving the injection of liquids in high-speed flows, including supersonic combustion ramjets (scramjets), pulsed detonation engines, re-entry body cooling, and surface erosion in high-speed flows. Such applications are impacted critically by the nature of droplet disruption and vaporization mechanisms of the liquid fuel droplets to be studied. This research will also directly impact education. The planar laser induced fluorescence and pulsed-laser droplet/particle velocity measurement techniques introduced into the undergraduate curriculum through existing experimental methods courses at the UW. Similarly, the numerical work will lead to examples that will be utilized as classroom examples at WPI. Undergraduate students will also participate directly in carrying out the research. The graduate students will actively participate in the undergraduate component of the program by serving, under faculty supervision, in the role of "grant monitor" for the undergraduate component of the research. Lastly, the co-PIs will recruit qualified and interested members of under-represented groups to conduct research at the University of Washington and at Worcester Polytechnic Institute.