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 G17: Biofluids: Microswimmers Experiments I |
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Chair: Sung Kwon Cho, University of Pittsburgh Room: 28C |
Monday, November 19, 2012 8:00AM - 8:13AM |
G17.00001: Experiments and models of low Reynolds number flows generated by a precessing rod over a plane James Martindale, Roberto Camassa, Richard M. McLaughlin, Leandra Vicci, Longhua Zhao Slender body asymptotics and experiments are developed to emulate dynamics biological interest such as primary cilia in developing embryos. Experiments are performed using high viscosity silicon oil with magnetically actuated precessing rod in a table-top setup. Stereoscopic Lagrangian tracking show quantified long-time agreement with an appropriately imaged slender body theory to enforce the no-slip boundary condition of the floor. In contrast, breaking symmetry by a bent rod creates additional flow components which destroy quantitative short time agreement with the theory while maintaining its qualitative features including the creation of large scale Lagrangian tori. Higher order asymptotic corrections are implemented and compared in an attempt to restore quantitative predictability. Direct comparison with 3D stereoscopic PIV measurements will be presented. [Preview Abstract] |
Monday, November 19, 2012 8:13AM - 8:26AM |
G17.00002: Microscale underwater propulsion by oscillating air bubble columns Jian Feng, Sung Kwon Cho We will present microscale underwater propulsion using oscillating air bubble columns. A cylindrical air bubble column is formed in a microchannel immersed in water (one end is open and directly exposed to water and the other is closed). Under an external acoustic field, the cylindrical air bubble column axially oscillates and generates a net flow near the open end of the microchannel. This net flow can generate a propelling force depending on many parameters such as oscillating frequency and amplitude. In this presentation, we will report and discuss detailed fabrication, testing and experimental results of this micvroscale propulsion. [Preview Abstract] |
Monday, November 19, 2012 8:26AM - 8:39AM |
G17.00003: Performance of three different artificial swimmers in Newtonian and complex fluids F. Godinez, R. Zenit, E. Lauga We present an experimental investigation of three simple swimming devices at low Reynolds number. Each swimmer is composed of a magnetic head attached to a propulsive tail. The robots are driven by an external magnetic field and three different kinds of tails are used: (i) a flexible filament periodically oscillated (the flexible oar mechanism); (ii) a rigid helical filament rotated by the external field (the corkscrew mechanism); (iii) a flexible filament that, when rotated by the field, acquires a conical helical shape (a hybrid case). Each swimmer is tested in two different fluids with the same shear viscosity, a Newtonian and a Boger fluid. Surprisingly, even though the tests were conducted with the same fluid, the results for the viscoelastic fluid are contrastingly different. The device based on flexible oar mechanism swims faster in the Boger fluid than in the Newtonian one; on the contrary, the hybrid device swims at lower speeds in the Boger fluid than in the Newtonian one. And unexpectedly, the device based on the corkscrew mechanism practically swims at the same velocity in both fluids. These results, suggest that the swimming performance of a biomimetic device strongly depends on the details of the swimming actuation. We can conclude that a general viscoelastic effect [Preview Abstract] |
Monday, November 19, 2012 8:39AM - 8:52AM |
G17.00004: Swimming of \emph{Chlamydomonas reinhardtii} in weakly elastic fluids Jing Yang, Jerry Gollub, Paulo Arratia The swimming behavior of the algae \emph{Chlamydomonas reinhardtii} in weakly elastic fluids is investigated in experiments using microscopy and tracking methods. The effects of fluid viscosity and elasticity on the swimming speed, flagellar shape, beating frequency, and efficiency are examined. Here, the fluid viscosity is varied using water and sucrose solutions, while fluid elasticity is introduced by adding flexible polymer CMC (carboxymethyl cellulose) to the buffer solution. Swimming experiments are performed in a thin-film apparatus equipped with a microscope and high-speed camera. We find that even small amounts of fluid elasticity can have a significant effect on the swimming kinematics and dynamics of \emph{Chlamydomonas} because of the relatively high beating frequency of its flagella (50-60 Hz). For example, the \emph{Chlamydomonas} swimming speed is hindered by fluid elasticity compared to Newtonian fluids. In addition, the algae swimming speed decreases as the fluid elasticity is increased. [Preview Abstract] |
Monday, November 19, 2012 8:52AM - 9:05AM |
G17.00005: Tracing the run-flip motion of an individual bacterium Bin Liu, Michael Morse, Jay Tang, Thomas Powers, Kenneth S. Breuer We have developed a digital 3D tracking microscope in which the microscope stage follows the motion of an individual motile microorganism so that the target remains focused at the center of the view-field. The tracking mechanism is achieved by a high-speed feedback control through real-time image analysis and the trace of the microorganism is recorded with submicron accuracy. We apply this tracking microscope to a study of the motion of an individual Caulobacter crescentus, a bacterium that moves up to 100 microns (or 50 body lengths) per second and reverses its direction of motion occasionally by switching the rotation direction of its single helical flagellum. By tracking the motion of a single cell over many seconds, we show how a flip event occurs with submicron resolution and how the speed of a single cell varies over time and with the rotational rate of the flagellum. We also present statistics for the run-reverse dynamics of an ensemble of cells. [Preview Abstract] |
Monday, November 19, 2012 9:05AM - 9:18AM |
G17.00006: Characterization of gyrotactic swimmers using digital holographic microscopy Michael Barry, William M. Durham, Anwar Chengala, Jian Sheng, Roman Stocker Observations from the ocean reveal that motility can exert a strong influence on the spatial distribution of phytoplankton at multiple scales, from thin layers and harmful algal blooms to Kolmogorov-scale accumulations in turbulence. Aside from a few model organisms, however, little is known about the fundamental motility characteristics of marine phytoplankton species, in particular their stability and the noise in their swimming orientation. In the absence of fluid flow, a phytoplankter's swimming direction is governed by the competition between an intrinsic stabilizing torque and stochastic fluctuations resulting from noise in the flagellar beat. These two processes can be parameterized by a gyrotactic reorientation time scale and an effective rotational diffusivity, respectively. Here we obtain measurements of these two parameters by using digital holographic microscopy to capture three-dimensional trajectories of phytoplankton. Novel inverse techniques are applied to individual tracks, which are analyzed for noise in the swimming direction and the rate of reorientation to the vertical. This approach can easily be extended to other species, promising to improve our understanding of how the interaction of motility and flow affects the distribution of phytoplankton communities. [Preview Abstract] |
Monday, November 19, 2012 9:18AM - 9:31AM |
G17.00007: ABSTRACT MOVED TO E17.00006 |
Monday, November 19, 2012 9:31AM - 9:44AM |
G17.00008: Experimental Study on the Euglena gracilis for Micro-Transportation using a Phototatic Control Jihoon Kim, Vu Dat Nguyen, Doyoung Byun Recently, there has been growing interests in micro or nano-scale biological organisms for the micro-robotics to develop actively controlled micro or nano-level machines. The Euglena gracilis is a genus of unicellular protists, whose body size ranges from 30 to 70 $\mu $m. The Euglena gracilis contains an eyespot, a primitive organelle that filters sunlight into the light-detecting, photo-sensitive structures. It actively swims at the base of the flagellum. In this study, we investigated the controllability of Euglena gracilis for transporting a structure attaching itself. When a LED light is detected, the Euglena gracilis accordingly adjust its position to enhance photosynthesis. Using the phototactic control, we achieved the efficient transportation of a micro-structure. [Preview Abstract] |
Monday, November 19, 2012 9:44AM - 9:57AM |
G17.00009: The effect of shear thinning viscosity on the performance of low Reynolds number swimmers R. Zenit, F. Godinez, C. Belleville, E. Lauga In addidion to viscoelastic effects, biological fluids can also show shear-thinning viscosity as part of their non Newtonian behavior. To assess the effect of a varying viscosity with shear rate on the performance of swimming, we conducted experiments using two types of magnetically driven swimmers. We consider oscillating flexible tail and rotating rigid coil devices to test this effect. We prepared carbopol-based inelastic shear-thinning fluids with different values of the thinning coefficient, $n$, and an equivalent Newtonian liquid for comparisons. The motion was filmed and the swimming velocity was measured via digital image processing. We found that the swimming efficiency changes in an important manner if the fluid does not have constant viscosity. We will present and discuss our preliminary results. To our knowledge, this effect has not been addressed in the specialized literature to date. [Preview Abstract] |
Monday, November 19, 2012 9:57AM - 10:10AM |
G17.00010: Flow visualization study on the near-surface motility of a flagellar propeller Dongwook Yim, Jaehyeong Cho, Songwan Jin, Jung Yul Yoo Understanding of the near-surface motility of microorganisms is important in many bioengineering applications including the initial formation of biofilms and energy-efficient propulsion system which is the most important part of microrobots. In particular, a new type of propeller that is optimized for low Reynolds numbers is required to propel a small object in a medium where the flow is dominated by viscous force rather than inertial force. A propeller in the shape of a bacterial flagellum seems an appropriate choice for this purpose. Thus, in this study, we carried out a flow visualization study on the velocity field near the solid surface, induced by a spring-like propeller inspired by the \textit{E. coli} flagellum, by using a macroscopic model and applying stereoscopic particle image velocimetry. Silicone oil, which has a kinematic viscosity 100,000 times that of water, was used as the working fluid to generate the low Reynolds number condition for the macroscopic model. Thrust, torque, and velocity were measured as functions of pitch and rotational speed, and the efficiency of the propeller was calculated from the measured results. [Preview Abstract] |
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