Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session S30: Biofluids: Respiration and Tear Films |
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Chair: Lydia Bourouiba, Massachusetts Institute of Technology Room: Ballroom IV |
Tuesday, November 22, 2011 3:05PM - 3:18PM |
S30.00001: Experiments on the fluid dynamics of the human cough Gary Settles Human coughing is studied non-intrusively by high-speed schlieren videography, revealing a turbulent jet lasting up to 1 sec with a total expelled air volume of about 2 L. Velocimetry of eddy motion reveals a jet centerline airspeed of at least 8 m/sec. With Re roughly 18,000 the cough jet is inertia-driven and buoyancy is negligible. It shows typical round-turbulent-jet behavior, including a conical spreading angle of 24 deg, despite irregular initial conditions. The cough jet is projected several m into the surrounding air before it mixes out. It is well known that a cough can transmit infectious agents, and we are advised to cover our mouths in an apparent attempt to thwart the jet formation. Present experiments have shown that wearing a surgical mask or respirator designed to prevent the inhalation of infectious agents also interferes with the cough-jet formation, redirecting it into the person's rising thermal plume. (Tang et al., J. Royal. Soc. Interface 6, S727, 2009.) [Preview Abstract] |
Tuesday, November 22, 2011 3:18PM - 3:31PM |
S30.00002: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2011 3:31PM - 3:44PM |
S30.00003: Surface shear viscosity of a lung surfactant: Newtonian to non-Newtonian transition Amir Sadoughi, Amir Hirsa, Juan Lopez DPPC molecule is the most prevalent constituent of lung surfactant, and understanding its behavior as a monolayer may lead to better simulations of respiration. At low surface pressures (i.e. large surface tensions, corresponding to area per molecule of about 50 angstrom squared, or greater), DPPC behaves as a purely viscous film with surface shear viscosity that is Reynolds number independent. Transition to a non-Newtonian regime occurs at large surface pressures. At the small scales associated with the liquid lining of the alveoli, the relative effects of surface viscosities can be comparable to that of surface tension. Here, we examine the interfacial hydrodynamics by isolating the effects of the surface shear viscosity. DPPC monolayer is spread from a concentrated solution at the air/water interface in a deep channel viscometer, consisting of an annular region between two stationary cylinders and a rotating floor. The interfacial velocity is measured non-invasively (without any seeding particles) using Brewster angle microscopy with short laser pulses. The departure from Newtonian behavior is quantified by comparisons to numerical simulations of Navier-Stokes with a Boussinesq--Scriven surface model and various surface shear viscosities. [Preview Abstract] |
Tuesday, November 22, 2011 3:44PM - 3:57PM |
S30.00004: The influence of surfactant on the propagation of a semi-infinite bubble through a liquid- filled compliant channel David Halpern, Donald Gaver Pulmonary airway closure may occur as a result of fluid accumulation and surfactant insufficiency. This results in ``compliant collapse'' with the airway walls buckled and held in apposition by a liquid plug that blocks the passage of air. Airway reopening is vital to the recovery of adequate ventilation, but has been associated with ventilator- induced injury because of the exposure of airway epithelial cells to large pressure gradients. Surfactant replacement is helpful in modulating this harmful stimulus, but is limited in its effectiveness due to slow surfactant adsorption. We investigate the effect of surfactant on reopening by considering the steady two-dimensional motion of a semi-infinite bubble propagating through a liquid-filled compliant channel doped with soluble surfactant. Many parameters affect reopening, but we primarily investigate the capillary number $Ca$ (the ratio of viscous to surface tension forces), the reopening (bubble) pressure $p_b$, the adsorption depth parameter $\lambda$ (a bulk concentration parameter) and the bulk Peclet number $Pe_b$ (the ratio of bulk convection to diffusion). The behavior of this system, and the impact of the flow field on surfactant transport and the applied stresses on the wall will be discussed. [Preview Abstract] |
Tuesday, November 22, 2011 3:57PM - 4:10PM |
S30.00005: Tear film dynamics with evaporation and osmolarity Javed Siddique, Richard Braun We consider a model problem for the evaporation and breakup up of tear film. The model includes the effects of surface tension, Marangoni stresses, insoluble surfactant transport, evaporation, osmolarity transport, osmosis and wetting of corneal surface. Evaporation is made dependent on surface concentration in order to mimic the lipid layer of the tear film when there is a single fluid layer in the model. In many cases for a single layer, the Marangoni effect seems to eliminate a localized area of increased evaporation due to reduced surfactant concentration. In this model the osmolarity in the tear film increases because of average evaporation rate rather than by a locally increased evaporation rate. If time permits, the effect of having a second fluid layer, representing the lipid layer, will be explored as well. [Preview Abstract] |
Tuesday, November 22, 2011 4:10PM - 4:23PM |
S30.00006: Modeling the evaporation of a pre-lens tear film on a contact lens Daniel Anderson, Kevin Talbott, Amber Xu, Padmanabhan Seshaiyer We develop a model for evaporation of a post-blink pre-lens tear film in the presence of a porous contact lens. The tear film is modeled as a Newtonian fluid and the flow in the contact lens is assumed to obey Darcy's law. The evaporation model treats the contact lens as a wetting surface. Evaporative mass flux thins the pre-lens film down to a nonzero steady thickness at which point evaporation continues by drawing fluid up through the contact lens. Both one and two-dimensional models are explored. The post-lens film (between the contact lens and the corneal surface) is not included explicitly in the model but is assumed to act as a reservoir that supplies fluid drawn up through the contact lens. [Preview Abstract] |
Tuesday, November 22, 2011 4:23PM - 4:36PM |
S30.00007: A Two-Dimensional Model for Tear Flow through a Permeable Contact Lens Matthew Gerhart, Daniel Anderson This is an investigation into the flow of an incompressible fluid in a thin pre-lens, contact lens, and post-lens system. The pre-lens and post-lens layers are coupled through the middle layer being a thin permeable contact lens. Included in this system are the effects of evaporation of the pre-lens film and the settling of the contact lens over time. This analysis is done through the nondimensionalization of the governing equations which include the Navier-Stokes' equations for the pre- and post-lens tear film and Darcy's equations for the contact lens layer along with heat equations for temperature. Lubrication theory is then applied to the resulting system leaving a reduced coupled system of equations whose properties we explore. [Preview Abstract] |
Tuesday, November 22, 2011 4:36PM - 4:49PM |
S30.00008: Tear Film Dynamics and Cooling of the Anterior Eye Longfei Li, Richard Braun A model for cooling of the human tear film is formulated by incorporating the heat transfer from the interior of the eye. A single PDE that governs the thickness of the film is derived from lubrication theory; the nonlinear partial differential equation is to be solved along the edge of a model rectangular domain for the anterior eye that includes the cornea (thin and thick substrate cases are treated separately). Optimal parameters to reproduce observed temperature decreases are found. [Preview Abstract] |
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