Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A15: Biofluids: Micro-PIV |
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Chair: Donald Webster, Georgia Institute of Technology Room: 28A |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A15.00001: Metachronal Propulsion, Hovering, and Signaling: High-Speed Tomographic PIV Measurements of Swimming Antarctic Krill J. Yen, D.W. Murphy, D.R. Webster Antarctic krill (\textit{Euphausia superba}) are pelagic crustaceans that must swim continuously to avoid sinking. Krill swim by beating their five pairs of swimming legs (known as pleopods) in a metachronal pattern. Although metachrony is a common propulsion technique among crustaceans, the hydrodynamics of multiple appendages paddling in series has not been well investigated. Furthermore, the hydrodynamic signal created by the metachronally stroking pleopods is thought to play a role in schooling propensity among krill conspecifics. We present time-resolved tomographic PIV measurements of the flow generated by free-swimming Antarctic krill. Detailed flow measurements around the pleopods of a hovering Antarctic krill reveal flow being drawn backwards with each pleopod stroke in this drag-based swimming technique. Vortices forming around each pleopod pair during the power stroke also were found and may create additional thrust. Measurements in the wake of the krill reveal a pulsed jet flow with mean and oscillatory components. This wake signature may form a communication channel with nearby conspecifics and is discussed in the context of sensory ecology. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A15.00002: Application of micro-PIV to the study of staphylococci bacteria bio-film dynamics Erica Sherman, Kenneth Bayles, Derek Moormeier, Timothy Wei Staphylococci bacteria are recognized as the most frequent cause of biofilm-associated infections. Although humans are regularly exposed to staphylococcus bacteria without consequence, a localized staph infection has the potential to enter the bloodstream and lead to serious infections such as endocarditis, pneumonia, or toxic shock syndrome. The mechanics of staphylococci biofilm formation and dispersion through the bloodstream are not well known. It has recently been observed that under certain flow conditions, bacteria grow in stable bio-films. Under other conditions, they organize in tower-like structures which break and are transported downstream by the flow. The fundamental questions addressed in this study are i) whether or not fluid mechanics plays a role in differentiating between film or tower formation and ii) whether or not the faulty towers are a bio-film propagation mechanism. This talk focuses on the application of micro-PIV to study this problem. Bacteria were cultured in a glass microchannel and subjected to a range of steady shear rates. Micro-PIV measurements were made to map the flow over and around different types of bio-film structures. Measurements and control volume analysis will be presented quantifying forces acting on these structures. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A15.00003: Roll and Yaw of Paramecium swimming in a viscous fluid Sunghwan Jung, Saikat Jana, Matt Giarra, Pavlos Vlachos Many free-swimming microorganisms like ciliates, flagellates, and invertebrates exhibit helical trajectories. In particular, the Paramecium spirally swims along its anterior direction by the beating of cilia. Due to the oblique beating stroke of cilia, the Paramecium rotates along its long axis as it swims forward. Simultaneously, this long axis turns toward the oral groove side. Combined roll and yaw motions of Paramecium result in swimming along a spiral course. Using Particle Image Velocimetry, we measure and quantify the flow field and fluid stress around Paramecium. We will discuss how the non-uniform stress distribution around the body induces this yaw motion. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A15.00004: Employing an Internal Wavemaker to Simulate Sensory Cues in the Plankton A.C. True, D.R. Webster, M.J. Weissburg, J. Yen Internal waves are a ubiquitous feature in many coastal marine ecosystems and as such are important features to consider in the spatiotemporal dynamics of thin planktonic layers. Oscillations of the pycnocline in stratified waters due to internal wave propagation generate fluxes of quantities, such as fluid momentum, thermal energy, and chemical concentration. These fields compose a set of hydrodynamic and thermochemical sensory cues that are fundamental to many planktonic life processes, including prey and predator detection, mate-tracking, habitat partitioning, nutrient and waste transport processes, and chemical communications. Thus, we expect that internal waves generate sensory cues in the water column, influence many fundamental biological processes, and broadly affect spatiotemporal productivity dynamics through unique biophysical coupling over a wide range of relevant scales. We constructed an internal wave generator facility to mimic characteristics that plankton observe \textit{in situ}. Simultaneous particle image velocimetry (PIV) and laser-induced fluorescence (LIF) are employed on internal waves generated in a two-layer stratification to quantify wave-induced scalar fluxes. Difficulties inherent in scaling down in situ conditions for laboratory-scale behavioral assays are discussed in the context of accurately matching spatiotemporal scales from a planktonic point of view. Finally, the results are interpreted in the context of zooplankton sensory ecology. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A15.00005: High Speed Tomographic PIV Measurements of Copepod Escape Jumps D.R. Webster, D.W. Murphy, J. Yen Copepods flee from predators via high-acceleration escape jumps that may reach speeds of up to 500 body lengths per second, i.e., relative speeds that are not reached by any other organism. We present time-resolved tomographic PIV measurements of the flow around an escaping calanoid copepod (\textit{Calanus finmarchicus}). Persistent body and wake vortices are created by the impulsive momentum transfer to the fluid surrounding the animal. It is shown that an impulsive stresslet model better describes the flow than an impulsive Stokeslet. Azimuthal asymmetry of the strength and position of the wake vortex is analyzed and attributed to the strong ventral flows created by the metachronally beating swimming legs and to yawing of the body. In addition, the energy required by a copepod escape jump is estimated by calculating the viscous energy dissipation rate using the spatial gradients of the measured three-dimensional velocity field. Finally, the three-dimensional flow measurements are compared to previous axisymmetric CFD simulations. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A15.00006: High-Speed Hopping: Time-Resolved Tomographic PIV Measurements of Water Flea Swimming D.W. Murphy, D.R. Webster, J. Yen Daphniids, also known as water fleas, are small, freshwater crustaceans that live in a low-to-intermediate Reynolds number regime. These plankters are equipped with a pair of branched, setae-bearing antennae that they beat to impulsively propel themselves, or ``hop,'' through the water. A typical hop carries the daphniid one body length forward and is followed by a period of sinking. We present time-resolved tomographic PIV measurements of swimming by \textit{Daphnia magna}. The body kinematics and flow physics of the daphniid hop are quantified. It is shown that the flow generated by each stroking antenna resembles an asymmetric viscous vortex ring. It is proposed that the flow produced by the daphniid hop can be modeled as a double Stokeslet consisting of two impulsively applied point forces separated by the animal width. The flow physics are discussed in the context of other species operating in the same Reynolds number range of 10 to 100: sea butterfly swimming and flight by the smallest flying insects. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A15.00007: Ontogenetic propulsive transitions from viscous to inertial flow regimes in the medusae \textit{Sarsia tubulosa} Kakani Katija, Houshuo Jiang, Sean Colin, John Costello Among marine organisms, the influences of flow regimes on swimming strategies are largely unknown. As an approach to examine this issue, we quantified how transitions from viscous to inertially dominated flow regimes, which commonly occur during the development of marine animals, relate to changes in swimming strategies. We used the hydromedusae \textit{Sarsia tubulosa} as a model organism for this investigation because its morphology and propulsive actuation mechanism are radially symmetric. This feature allows for determination of three-dimensional fluid quantities from two-dimensional flow measurement techniques. Digital particle image velocimetry was used to quantify the flow fields created by free-swimming hydromedusae and calculate the impulse generated by their swimming pulses at different life stages. Swimming strategies were evaluated by quantifying the relationship between impulse production and hydrodynamic swimming efficiency. Utilizing these metrics enable us to generalize our findings to the swimming strategies of other aquatic animals that swim in similar fluid regimes. [Preview Abstract] |
Sunday, November 18, 2012 9:31AM - 9:44AM |
A15.00008: 3D-PTV measurement of the phototactic movement of algae in shear flow Tatsuyuki Maeda, Takuji Ishikawa, Hironori Ueno, Keiko Numayama-Tsuruta, Yosuke Imai, Takami Yamaguchi Recently, swimming motion of algae cells is researched actively, because algae fuel is one of the hottest topic in engineering. It is known that algae swim toward the light for photosynthesis however, the effect of a background flow on the unidirectional swimming is unclear. In this study, we used {\it Volvox} as a model alga and placed them in a simple shear flow with or without light stimulus. The shear flow was generated by moving two flat sheets in the opposite direction tangentially. A red LED light (wave length 660 nm) was used as an observation light source, and a white LED light was used to stimulate cells for the phototaxis. The trajectories of individual cells were measured by a 3D-PTV system, consists of a pair of high-speed camera with macro lenses. The results were analyzed to understand the effect of the background shear flow on the phototaxis of cells. [Preview Abstract] |
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