Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session L24: Minisymposium: Introduction to Topics in Fluid Dynamics |
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Chair: Margaret Byron, Pennslyvania State University; Alexander J. Smits, Princeton University Room: Georgia World Congress Center B312 |
Monday, November 19, 2018 4:05PM - 4:31PM |
L24.00001: Computation as a Tool of Fluid Dynamics Research Invited Speaker: Robert Moser Over the last several decades, computational fluid dynamics (CFD) has become an indispensable tool of fluid dynamics research. The reason is that the Navier-Stokes equations are a remarkably precise description of the behavior of many real fluids, so that their numerical solutions can be studied as a surrogate for real fluids. CFD studies have several unique advantages in fluid dynamics research. First, simulations provide access to three-dimensional velocity and scalar fields, allowing determination of quantities that are difficult or impossible to measure. Second, computer simulations allow detailed specification of the environment in which a flow is evolving (e.g. initial conditions, boundary conditions, forcing). Finally, CFD simulations can serve as non-physical experiments, allowing hypotheses regarding the causes of observed phenomena to be tested directly. In this talk we'll discuss the use of CFD in fundamental fluid dynamics research with several illustrative examples. We'll also discuss the limitations of CFD in fluid dynamics research, and potential future opportunities for its application. |
Monday, November 19, 2018 4:31PM - 4:57PM |
L24.00002: Biological Fluid Mechanics Invited Speaker: John O. Dabiri Biological fluid mechanics appears in an exciting and ever-growing range of applications, including locomotion, medicine, ecology, and bioinspired engineering. Despite the breadth of the field, research in biofluids is unified by common challenges in elucidating complex, unsteady flow-structure interactions. This talk will introduce approaches to the formulation and analysis of these problems, with particular emphasis on tradeoffs that are encountered in maintaining fidelity to the biology while achieving generalizable insights regarding the flow physics. Examples of both canonical and frontier topics in biofluid mechanics will be presented in this context. Opportunities for both new and seasoned researchers to make seminal contributions to theory, simulation, and measurements in biological fluid mechanics will be highlighted. |
Monday, November 19, 2018 4:57PM - 5:23PM |
L24.00003: An Introduction to Microfluidics Invited Speaker: Nadine Aubry In this talk, we will present an introduction to microfluidics which consists of small scale fluid dynamics when the typical length scale of the flow is 10-1000 microns. Such dimensions are similar to the thickness of a human hair (~100 microns) and larger than all the molecules present in the system so that the continuum assumption is still valid. Such devices are useful in a broad range of applications, including chemical synthesis, biosensing, drug discovery and, more generally, “lab-on-a-chip”. The goal is to design and fabricate devices capable of the precise manipulation and control of small fluid volumes as well as the nano/micrometer sized particles present in such volumes. Precision, low footprint, portability, low power requirement, automation and high throughput of microfluidic devices bring significant advantages and have enabled technological advances. Microfluidics typically involve laminar flows as Reynolds numbers are low; multiphase flows since particles and/or droplets are present; and multiphysics due to the easy manipulation of both liquids and particles using external (e.g., electric) fields. We will present some examples of microflows and microfluidic devices, which can be categorized essentially into two types, the channel flow and droplet flow types. In the former, reactions take place in microchannels while in the latter they occur in individual droplets. We will also discuss some of the challenges microfluidics present, including the difficulty to induce mixing at low Reynolds numbers although mixing is a necessary condition for efficient reactions to occur, such as those required for biochemical assays. We will show how both active and passive mixing techniques can be utilized for efficient mixers. Other opportunities and challenges related to the use of electric field in multiphase flows in small devices will be presented. |
Monday, November 19, 2018 5:23PM - 5:49PM |
L24.00004: Geophysical Fluid Dynamics Invited Speaker: Claudia Cenedese Geophysical Fluid Dynamics (GFD) is, in general, considered to be the branch of fluid dynamics concerned with naturally occurring flows such as lava flows, oceans, and planetary atmospheres, on Earth and other planets. In particular, the effects of stratification and Earth’s rotation need to be taken into account in the equations of motion when the interest is on the dynamics of the ocean and the atmosphere, which will be the focus of this talk. Classic examples of GFD flows are the Jet Stream and the weather system in general; the swirling vortices that fill the oceanic basins; and currents hugging the coastlines often being baroclinic unstable. A challenging aspect of GFD is the multiple scales associated with the flows of interest. For example, dense currents are an integral part of the large scale thermohaline circulation and their water properties are of global importance. Recent studies have highlighted how dense currents entrain ambient water while flowing over sills or through constrictions or during their descent over the continental slope. The turbulence and mixing occurring at very small scales affects the density of these dense currents and hence their water mass location in the open ocean water column. A correct parameterization of mixing processes in general circulation and climate models is then essential for a correct representation of the ocean circulation. Another example of multiple scales interactions is the influence of oceanic vortices on the large scale circulation. Recent work has focused on formulating robust parameterizations of eddies to represent the important dynamics of oceanic vortices in general circulation and climate models, which do not completely resolve all the dynamically relevant scales. A correct parameterization of subgrid processes in climate models requires an understanding of the underlying fluid dynamics and GFD will play a fundamental role in this societally relevant endeavor. |
Monday, November 19, 2018 5:49PM - 6:15PM |
L24.00005: Multiphase Flows Invited Speaker: Howard A Stone In this talk I will seek to describe the many ways that multiphase flows broaden the kinds of fluid dynamics problems that can be studied and some of the ways that these themes provide unexpected intersections with the other science and engineering departments, as well as many applications in industry. I will begin by reminding the audience of the (few) dimensionless parameters typical of a single-phase flow and the (many) dimensionless parameters common to studies of multiphase flows. Also, I will provide a few examples from the myriad possibilities of multiphase flows. Then, I will seek to identify possible future research themes ripe for investigations, especially those where the combination of experiments, modeling, and the increasingly powerful (often open source) computational tools offer opportunities for understanding, new ideas, and even discovery. |
Monday, November 19, 2018 6:15PM - 6:41PM |
L24.00006: Turbulence Invited Speaker: Beverley McKeon Richard Feynmann once described turbulence as “the most important unsolved problem of classical physics”, and indeed it is a flow phenomenon that impacts many aspects of our daily lives. This talk will address the general characteristics that define turbulence, what makes it an important unsolved problem (or, more generally, series of problems), and some of the features that make turbulent flows difficult to observe, simulate, understand and control. In contrast to laminar flows, turbulent ones are characterized by high mixing due to the existence of a self-sustaining fluctuating field, governed by the continuity, momentum and energy equations in the simplest cases, and consisting of a spatiotemporal range of energetic scales which grows rapidly with Reynolds number. Associated with this field are eddies or ``coherent structures’’, the precise definition of which can be hotly-debated, but which describe regions of high statistical (and often visual) correlation of at least one variable. We will review approaches to understanding the physics of turbulence: seminal flow visualizations going back to Da Vinci and Reynolds, elegant and key early dimensional scaling analyses, theoretical progress, experimental observations and diagnostic advances, the impact of numerical simulation, and inferences on the mechanisms which incur and sustain turbulence. Where possible the focus will be on the simplest manifestations of turbulence and geometric configurations, with a brief discussion of extensions to more complex flows of engineering interest, such as compressible, inhomogeneous and multi-phase flows. Some deeper discussion will be assigned to recent progress in wall-bounded turbulence. The talk will conclude with a brief outlook on the state-of-the art and some current challenges in the field. |
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