Turbulent mixing between a shock-accelerated vortex ring and its surroundings

当冲击波传播通过由不同气体占据的区域时，它在波边界处产生气体运动，这导致以比在没有冲击波的情况下发生的速率高得多的速率混合。这种现象可能发生在设计用于以比常规喷气式运输机所用的速度高得多的极高速度运行的一类喷气式发动机中。对这类流动的研究通常非常具有挑战性，因为流动特性（如速度、局部气体成分和温度）在空间和时间上以非常复杂的方式变化。本研究项目将研究这种类型的流的简单版本。研究人员将研究涡环对脉冲加速度的反应。根据涡环流场的性质，这种初始条件应包含一个比喷气发动机更连贯、更有组织、更可预测和更可测量的涡量场。结果将形成一个高度精炼的积木数据库，可用于开发这些流的更复杂版本的预测能力。研究生和本科生将大量参与这项研究，通过校园内现有的不同项目招募代表性不足的少数民族成员。该项目还将提供教育和接触最先进的技术和一些最新的科学和工程挑战。本文采用平面激光诱导荧光（PLIF）和粒子图像测速（PIV）技术研究了平面激波与涡环相互作用引起的湍流混合。该项目的目标是测量一些最相关的流动特性，包括两种气体的浓度及其在气体混合区域内各处的速度。将以两种不同的方式实现这一目标：1）测量将在离散的时刻进行，具有非常高的空间分辨率，以及2）测量将以较小的空间分辨率进行，但是使用成像系统，该成像系统将允许以高达20的速率收集整个浓度场，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

When a shock wave propagates through a region occupied by different gases, it generates gas motions at the wave boundary that lead to mixing at much higher rates than would have occurred in the absence of the shock wave. Phenomena of this kind can occur in a category of jet engines designed to operate at extremely high speeds that are much higher than those used in conventional jet transport. The study of these kinds of flows is generally very challenging because flow properties such as velocity, local gas composition, and temperature vary in space and time in very complicated ways. This research project will study a simple version of this type of flow. The researchers will study the response of a vortex ring to impulsive acceleration. By the nature of the vortex ring flow field, this initial condition should contain a much more coherent, well organized, predictable and measurable vorticity field than that of the jet engine. The results will form a highly refined building block database which could be used to develop a predictive capability for the more complicated version of these flows. Graduate and undergraduate students will be heavily involved in the research, with members of underrepresented minorities recruited through different programs already existing on campus. This project also will provide education in and exposure to state-of-the-art technologies and some of the most current challenges in science and engineering. The turbulent mixing induced by the interaction of a planar shock wave with a vortex ring consisting of a gas different than its surroundings will be investigated using planar laser induced fluorescence (PLIF) and particle image velocimetry (PIV). The goal of the project is to measure some of the most relevant flow properties, including the concentrations of the two gas species and their velocities everywhere within the region where the gases mix. This objective will be pursued in two different ways: 1) measurements will be made at discrete instants in time, with very high spatial resolution, and 2) measurements will be carried out with lesser spatial resolution but using an imaging system that will allow to collect entire concentration fields at a rate of up to 20,000 fields per second.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.