Collaborative Research: Experimental and numerical study on the Reynolds number dependence of surfaces in von Karman turbulent swirling flows

表面的生长被认为是将具有不同热物理性质的流体占据的区域分开的无限薄的界面，是一个具有内在和实际意义的过程，在自然界、科学和技术设备中有着广泛的应用。由于不同流体的混合和相互作用与分隔它们的界面面积成比例，因此表面生长和破坏速度的定量表征至关重要。目前还没有一个全面的理论来描述湍流中的这些过程，而湍流是最常见的流动。该项目的最终目标是形成一种系统的理论，根据流体的运动状态来描述湍流中表面的动力学。关于表面动力学的全面理论将加强湍流的一般理论，包括在化学和能量转换系统中发现的具有混合和化学反应的流动。此外，我们的项目将提高对自然界中观察到的物理过程的理解，例如云的形成，其中界面的演变是速率限制过程。因此，尽管这项工作本质上是基础性的，但它有可能对科学和技术产生广泛的影响。该项目将支持两名研究生的教育，还将包括重要的外展教育活动，重点是通过调查流体混合的性质，让4-7年级的学生参与科学发现。该项目的总体目标是量化湍流中表面的演变与雷诺数的关系。我们将直接数值模拟和测量相结合，在一种新型的von Karman湍流旋流装置中，在高雷诺数下，对旋叶轮之间具有充分发展的湍流的剪切驱动闭合流动进行了描述。在这种典型的实验室流动中，表面的演变被定量地跟踪，而描述流动形态的参数被明智地改变，以探索参数空间中不同的条件，其中不同的影响被认为对表面的演变起作用。该项目将通过集中于两个推进来实现这一广泛的目标：(I)证明或反驳湍流中大表面的面积和增长率与雷诺数的关系；(Ii)通过对湍流中表面的输运方程中的项的详细分析，确定衡量湍流中表面演变的参数。整个装置的直接数值模拟包括所有几何复杂性，而实验则以一种新颖的方式按需生成表面，并采用最先进的速度场体积测量和湍流的3D表示。这一新颖而独特的研究计划是史无前例的，因为它包括了湍流表面研究中所考虑的最广泛的范围和最高的雷诺数。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The growth of surfaces, thought of as infinitely thin interfaces that separate regions occupied by fluids with dissimilar thermo-physical properties, is a process of intrinsic and practical interest with wide ranging applications in nature, science, and technical devices. As dissimilar fluids mix and interact proportionally to the area of the interface that separates them, the quantitative characterization of the rates of growth and destruction of surfaces is of critical importance. A comprehensive theory that describes these processes in turbulent flows, which are the most common flows encountered, is unavailable at present. The end goal of the project is to formulate a systematic theory that describes the dynamics of surfaces in turbulent flows depending on the state of the motion of the fluid. A comprehensive theory on the dynamics of surfaces will augment the general theory of turbulent flows, including flows with mixing and chemical reaction, which are found in chemical and energy conversion systems. In addition, our project will improve the understanding of physical processes observed in nature, such as cloud formation, where the evolution of interfaces is the rate limiting process. Thus, although the work is fundamental in nature, it has the potential for broad impacts in science and technology. The project will support the education of two graduate students, and it will also include significant outreach educational activities, which will focus on engaging grades 4-7 students in scientific discovery by investigating the properties of fluid mixing.The overarching goal of the project is to quantify the dependence of the evolution of surfaces in turbulent flows on the Reynolds number. We combine direct numerical simulations and measurements in a novel von Karman turbulent swirling flow setup featuring a shear-driven closed flow between counter-rotating impellers with fully developed turbulence at high Reynolds numbers. The evolution of surfaces in this canonical laboratory flow is tracked quantitatively, while the parameters that describe the flow configuration are varied judiciously to probe a broad range of conditions in the parameter space where different effects are believed to play a role on the evolution of surfaces. The project will fill this broad goal by focusing on two thrusts: (i) Prove or disprove the Reynolds number dependence of the area and growth rates of large surfaces in turbulent flows; (ii) Identify the parameters that scale the evolution of surfaces in turbulent flow through a detailed analysis of the terms in the transport equation for surfaces in turbulence. The direct numerical simulations of the entire device include all geometrical complexities, while experiments feature a novel manner of generating surfaces on demand and state-of the art volumetric measurements of the velocity field and 3D representation of the turbulent. This novel and unique research program is unprecedented as it includes both the broadest range and highest Reynolds numbers ever considered in the study of surfaces in turbulent flows.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.