The Interactions Between Vaporizing Liquid Droplets and a Turbulent Flow: Fully Resolved DNS and Experiment

提出的数值/实验研究的目的是加强对湍流中液滴蒸发和混合过程的理解。数值研究采用直接数值模拟（DNS）检查自由移动的蒸发液滴和各向同性湍流之间的双向相互作用。液滴将在3D空间和时间中完全解析，即不被视为点粒子，并且湍流运动的所有尺度都被解析到最小的相关长度和时间尺度。重点将放在蒸发液滴和周围湍流气体之间的质量，动量和能量的双向交换。该实验采用湍流产生主动网格和光学可达风洞部分来测量在各向同性湍流中自由飞行的单液滴（即单向耦合）的蒸发速率，其特性与DNS中的特性相同。变形光学成像和干涉条纹技术被用来提供一个大的轴向视野与高分辨率液滴大小的capability.Intellectual meriteththe建议DNS的研究将是第一个完全解决了大量的自由移动的蒸发液滴在湍流内部和外部的流动。建议DNS的详细结果，与液滴和湍流之间的双向耦合，可以用来开发和验证的大涡模拟（LES）的亚网格尺度的数学模型，以及雷诺平均模型。应该强调的是，从拟议研究中获得的详细DNS数据在任何已发表的实验或数值研究中都不可用（Birouk Gokalp，2006）。 本实验将研究湍流对各向同性湍流中单个液滴蒸发速率的影响。除了增强湍流和蒸发之间的相互作用的物理学的理解，测量将被用来验证我们的DNS方法，因为没有其他可比的实验数据存在自由飞行的液滴蒸发在各向同性湍流的湍流的Kolmogorov长度尺度小于初始液滴尺寸。因此，耦合的实验和计算将确定蒸发和湍流之间的关键相互作用。更广泛的影响所提出的研究结果将有显着的影响，能源的有效利用。 这种影响源于这样一个事实，即蒸发率是燃料液滴燃烧的主要控制机制，液体燃料是所有运输方式的最重要能源，并将在可预见的未来保持这种状态。了解湍流中蒸发和混合过程的物理细节是了解化学反应过程和最终控制/优化能量转换过程的必要前提。PI在研究领域以及研究与教学相结合方面取得了成就，包括向本科生和科学领域代表性不足的学生进行宣传。例如，三位女性博士。研究人员的毕业生现在是大学机械工程系（加州圣地亚哥大学，丹佛大学，加州。美国州立大学，洛杉矶）。此外，共同PI是加州少数民族参与联盟（CAMP）的区域主任，这是一项NSF资助的活动，旨在提高STEM领域代表性不足的学生的数量和成功。 通过CAMP，该项目可以为这些学生提供研究动机。本调查中的实验也将被用作COSMOS的演示，COSMOS是一个针对对co-PI参与的科学和工程感兴趣的有才华的高中生的夏季住宿计划。 我们的DNS数字化数据已传输到日本和巴西的大学以及欧洲科学基金会，供欧洲研究人员参考。G.M.教授选择了由这些数据制成的录像，显示了空间发展的湍流边界层中纵向涡结构的运动。Homsy（UCSB）将包括在多媒体流体力学II CD中，该CD为学生和专业人士提供了一个跨平台，交互式的视觉资源。 拟议研究的结果也将以同样方式传播

0933085ElghobashiThe objective of the proposed numerical/experimental study is to enhance the understanding of liquid droplet vaporization and mixing processes in a turbulent °ow. The numerical study employs direct numerical simulations (DNS) to examine the two way interactions between freely moving vaporizing droplets and isotropic turbulence. The droplets will be fully resolved in 3D space and time, i.e. not treated as point particles, and all the scales of the turbulent motion are resolved down to the smallest relevant length and time scales. The emphasis will be on the two way exchange of mass, momentum and energy between the vaporizing droplets and the surrounding turbulent gas. The experiment employs a turbulence generating active grid and optically accessible wind tunnel section to measure the evaporation rate of free flying single droplets (i.e. one way coupling) in isotropic turbulence with properties identical to those in the DNS. Anamorphic optics for imaging and an interferometric fringe technique are used to provide a large axial field of view with high resolution droplet-sizing capability.Intellectual meritThe proposed DNS study will be the first that fully resolves the flow inside and outside a large number of freely-moving vaporizing droplets in a turbulent flow. The detailed results of the proposed DNS, with two way coupling between the droplets and turbulence, can be used to develop and verify the mathematical models for the subgrid scales of large eddy simulations (LES) as well as Reynolds averaged models. It should be emphasized that the detailed DNS data which will be obtained from the proposed research are not available in any published experimental or numerical study (Birouk & Gokalp, 2006). The proposed experimental study will examine the exects of turbulence on the vaporization rate of a single droplet moving freely in isotropic turbulence. In addition to enhancing the understanding of the physics of interaction between turbulence and vaporization, the measurements will be used to validate our DNS methodology since no other comparable experimental data exist for free flying droplet evaporation in isotropic turbulence where the Kolmogorov length scale of turbulence is smaller than the initial droplet size. Hence, the coupled experiment and computations will determine the key interactions between evaporation and turbulence.Broader impactThe results of the proposed study will have a significant impact on the efficient utilization of energy. This impact stems from the fact that the vaporization rate is the main controlling mechanism of fuel droplet combustion and that liquid fuels are the most important source of energy for all modes of transportation and will remain as such for the foreseeable future. Understanding the physical details of the vaporization and mixing processes in a turbulent flow is an essential prerequisite to understanding the chemical reaction process and the eventual control/optimization of the energy conversion process. The PIs have a record of accomplishment in the field of study and in combining research and teaching, including outreach to undergraduate students and underrepresented students in the sciences. For example, three women Ph.D. graduates of the investigators are now University Mechanical Engineering faculty (Univ. of California San Diego, Univ. of Denver, Calif. State Univ., Los Angeles). In addition, the co-PI is Regional Director for the California Alliance for Minority Participation (CAMP), an NSF-funded activity to enhance the number and success of underrepresented students in STEM fields. Through CAMP, this project can provide research motivation for such students. The experiment in this investigation will also be used as a demonstration in COSMOS, a summer residential program for talented high school students interested in the sciences and engineering in which the co-PI participates. Our DNS digitized data have been transmitted to universities in Japan and Brazil as well as the European Science Foundation to be used as a reference for researchers in Europe. A video made of these data showing the motion of the longitudinal vortical structures in a spatially developing turbulent boundary layer has been selected by Prof. G.M. Homsy (UCSB) to include in the Multimedia Fluid Mechanics-II CD which provides a cross-platform, interactive, visual resource, for students and professional alike. The results of the proposed research will be disseminated similarly