Fluid Mechanics and Waves Seminar - Fall 2020

Justin Jaworski, Department of Mechanical Engineering and Mechanics, Lehigh University

Poroelastic Trailing-Edge Noise and the Silent Flight of Owls

Many owl species rely on specialized plumage to mitigate their aerodynamic noise and achieve functionally-silent flight while hunting. One such plumage feature, a tattered arrangement of flexible trailing-edge feathers, is idealized as a semi-infinite poroelastic plate to model the effects that edge compliance and flow seepage have on the noise production. The interaction of the poroelastic edge with a turbulent eddy is examined analytically with respect to how efficiently the edge scatters the eddy as aerodynamic noise. The scattering problem is solved using the Wiener-Hopf technique to identify how the noise scales with the flight velocity, where special attention is paid to the limiting cases of rigid-porous and elastic-impermeable plate conditions. Results from this analysis identify new parameter spaces where the porous and/or elastic properties of a trailing edge may be tailored to diminish or effectively eliminate the edge scattering effect and may contribute to the owl hush-kit.

David C. Venerus, Department of Chemical and Materials Engineering, NJIT

*Special Seminar: Wednesday, 2:00-300 PM

Tears of Wine: New Insights on an Old Phenomenon

Anyone who has enjoyed a glass of wine has undoubtedly noticed the regular pattern of liquid beads that fall along the inside of the glass commonly referred to as ‘tears of wine.’ This fascinating phenomenon is possible only if there is a flow against gravity in the liquid film that forms on the inside of the glass. In 1855, J. Thomson identified the driving force for the upwards flow necessary for the continuous formation of tears as a gradient in interfacial tension, which is known as a Marangoni stress. Here, we revisit the tears of wine phenomenon using a simple hydrodynamic model and experimental technique. Our results demonstrate that the Marangoni stress responsible for wine tears is the result of both composition and temperature gradients, which is strongly influenced by the thermodynamic behavior of ethanol-water mixtures. In addition, we present a novel theory for the description of interfacial transport phenomena.

Rayanne Luke, Department of Mathematical Sciences, University of Delaware

Parameter Identification for Tear Film Thinning and Breakup

Millions of Americans experience dry eye syndrome, a condition that decreases quality of vision and causes ocular discomfort. A phenomenon associated with dry eye syndrome is tear film breakup (TBU), or the formation of dry spots on the eye. The dynamics of the tear film can be studied using fluorescence imaging. Many parameters affecting tear film thickness and fluorescent intensity distributions within TBU are difficult to measure directly in vivo. We estimate breakup parameters by fitting computed results from thin film fluid PDE models to experimental fluorescent intensity data gathered from normal subjects’ tear films in vivo. Both evaporation and the Marangoni effect can cause breakup. The PDE models include these mechanisms in combination and separately.The parameters are determined by a nonlinear least squares minimization between computed and experimental fluorescent intensity, and they indicate the relative importance of each mechanism. Optimal values for computed breakup variables that cannot be measured in vivo fall near or within accepted experimental ranges for the general corneal region. Our results are a step towards characterizing the mechanisms that cause a wide range of breakup instances and help medical professionals to better understand tear film function and dry eye syndrome.

Xin Yong, Department of Mechanical Engineering, SUNY Binghamton

Colloids at Evaporating Fluid Interfaces: Transport and Assembly 

Colloidal particles at fluid-fluid interfaces exhibit rich transport and interfacial phenomena. This multi-component, multi-phase system not only allows researchers to explore a variety of fundamental questions in colloid and interface science, but also plays important roles in many practical applications. For example, the use of the fluid-fluid interface as a two-dimensional template facilitates the assembly of colloidal monolayers with diverse nano/microstructures, which opens a new avenue formanufacturing thin film materials. However, these structures suspended at the fluidic interface must be transferred into a dried form for practical applications. Evaporative deposition is the most widely used approach to obtain dry materials, but this process can be complicated by the well-known coffee-ring effect. The interplay of particle adsorption/desorption, capillary interaction, and surface hydrodynamics and heat transfer needs to be uncovered to establish the critical processing-structure relationship and allow better use of this interfacial system. This presentation will discuss recent advances in computational modeling and experimentation for understanding the dynamics of colloids on the surface of evaporating liquid masses and how colloidal interfacial assembly modulates deposition structures.

Charles Puelz, Baylor College of Medicine

Fluid-Structure Interaction Models for Describing the Physiology of Human Hearts

This talk will focus on the construction and numerical simulation of models for human hearts. Our goal is to apply these models to better understand intricate patterns and features within cardiovascular flows. These models describe blood and its interaction with cardiac tissue, including heart muscle, valves, and vessel walls. Our numerical approach uses a version of the immersed boundary method. Solid displacements and forces are approximated on a Lagrangian finite element mesh and blood pressures and velocities are approximated on a fixed Cartesian grid. This talk will cover the entire model construction pipeline, including segmentation of imaging data, parametrization, numerical methods, and preliminary results.

Angelo Tafuni, Department of Engineering Technology, NJIT

Gridless Simulation of Fluid Flow

This presentation will cover a brief introduction of particle methods and their role in CFD, followed by a focused section on Smoothed Particle Hydrodynamics (SPH) and its use in the solution of challenging engineering flows. SPH represents a powerful numerical method when simulating flow with large gradients and/or with one or more interfaces. I will introduce the DualSPHysics project (dual.sphysics.org), a massively parallel, open-source code that is developed by a consortium of five universities, including NJIT. I will also talk about projects that involve the use of SPH in my research lab, including new models for studying turbulence in a Lagrangian setting and multiphase flow.