Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session NH: Biofluids XIV |
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Chair: Martin Maxey, Brown University Room: Salt Palace Convention Center 250 B |
Tuesday, November 20, 2007 11:35AM - 11:48AM |
NH.00001: Biologically-Generated Turbulence by Two Krill Species Kimberly Catton, Donald Webster, Jeannette Yen Large schools of krill have been observed to generate turbulence at levels that contribute to both local and global mixing of the ocean. In these studies, estimates of krill-induced turbulence were determined with in situ acoustic profilers and calculated from krill swimming speeds; however, the turbulence level was not directly measured from krill-generated flow fields. In our study, we measured the flow fields around free swimming individual specimens of two species of krill, \textit{Euphausia pacifica} and \textit{Euphausia superba,} using an infrared Particle Image Velocimetry system. The krill-generated flow was characterized by a jet directed downward and to the rear with relatively large velocity magnitude in the core. Persistent vortices formed in the wake and eventually dissipated due to viscous effects. Regions of large energy dissipation rate were found near the body and in the wake of the krill at a maximum value of 1.5 W m$^{-3}$ for \textit{Euphausia superba} and 1.0 W m$^{-3 }$for \textit{Euphausia pacifica. }An estimate of biologically-generated turbulence will be calculated for each species of krill and compared to the field measurements of previous researchers. [Preview Abstract] |
Tuesday, November 20, 2007 11:48AM - 12:01PM |
NH.00002: On the hydrodynamics of planktonic microcrustacean locomotion: Numerical simulations and experiments Iman Borazjani, Fotis Sotiropoulos, Edwin Malkiel, Joeph Katz We develop a sharp-interface immersed boundary method for carrying out highly resolved simulations of the flow induced by a self-propelled copepod and integrate the simulations with high-resolution experiments to elucidate some aspects of the hydrodynamics of copepod swimming. A realistic copepod-like body is constructed, which includes most important parts of the animal's anatomy: the antennules, legs, and tail. The kinematics of the individual body appendages during an escape maneuver are prescribed based on data obtained using cinematic digital holography. The self-propelled motion of the copepod induced by the prescribed kinematics is simulated via a strongly-coupled fluid-structure interaction approach. The computed flowfields are compared with experimental results and analyzed to elucidate the structure and dynamics of the coherent wake vortices and quantify the specific contribution of each appendage on the production of propulsive thrust. [Preview Abstract] |
Tuesday, November 20, 2007 12:01PM - 12:14PM |
NH.00003: Hydrodynamics of contact of larvae of marine invertebrates with solids Gregory Zilman, Julia Novak, Yehuda Benayahu Attachment of larvae of marine invertebrates to solids is a fundamental phenomenon in marine ecology. The mechanism of initial contact of larvae with solids is a part of this phenomenon and a long-standing question of larval behavior. Marine larvae are transported to a solid along fluid streamlines, which do not cross the surface of the solid. However, neutrally buoyant and approximately spherical motile larvae do make contact with solids even in unidirectional laminar flows, for instance, in fully developed laminar tube flows, where neutrally buoyant spherical particles concentrate between the wall and the tube's axis. A new mathematical model explaining this controversy is proposed. The flow vorticity and larval locomotion are the key components of the hydrodynamic model. The motion of larvae is studied theoretically in a linear shear, the Couette, the Poiseuille and the Blasius boundary layer flows. Larvae trajectories and the contact probability are calculated. It is demonstrated that the contact probability depends on the flow enstrophy and larvae swimming velocities. The theoretical results compare favorably with available experimental data. [Preview Abstract] |
Tuesday, November 20, 2007 12:14PM - 12:27PM |
NH.00004: The Motion of an Artificial Micro-Swimmer Near a Rigid Surface Eric Keaveny, Martin Maxey The presence of a bounding surface can alter the swimming speed and direction of a nearby micro-organism. To understand the factors that contribute to such behavior, we conduct simulations of the recently realized artificial micro-swimmer (Dreyfus et. al., \emph{Nature}, \textbf{437}, 862-865 (2005)) in the proximity of a rigid boundary. To capture the dynamics of the magnetically driven flagellum-like tail composed of chemically linked paramagnetic beads, we treat the tail as a series of spheres tied together by inextensible, bendable links. These spheres interact magnetically through mutual dipole interactions, and hydrodynamic interactions are achieved by the force-coupling method. Depending on the applied field and the flexibility of the tail, a 20\% increase in the swimming speed can be achieved as the swimmer approaches contact with the surface. Additionally, in the case of spiral actuation, the swimmer exhibits a lateral drift (rolling motion). [Preview Abstract] |
Tuesday, November 20, 2007 12:27PM - 12:40PM |
NH.00005: Attraction of swimming microorganisms by solid surfaces Eric Lauga, Allison Berke, Linda Turner, Howard Berg Swimming microorganisms such as spermatozoa or bacteria are usually observed to accumulate near surfaces. Here, we report on an experiment aiming at measuring the distribution of smooth-swimming E. coli when moving in a density-matched fluid and between two glass plates. The distribution for the bacteria concentration is found to peak near the glass plates, in agreement with a simple physical model based on the far-field hydrodynamics of swimming cells. [Preview Abstract] |
Tuesday, November 20, 2007 12:40PM - 12:53PM |
NH.00006: Optimal swimming at low Reynolds number Daniel Tam, A.E. Hosoi A vast majority of living organisms exist at micrometric scales. Many of them are able to propel themselves by beating flagella in a variety of different patterns. This study focuses on optimal flagellar swimming motions at low Reynolds number. We seek to optimize both the geometry of the swimmer and the kinematics of the flagellar beat pattern. A number of configurations are investigated including uniflagellate and biflagellate organisms. Results from our model are compared with existing data from biological microorganisms. [Preview Abstract] |
Tuesday, November 20, 2007 12:53PM - 1:06PM |
NH.00007: An algorithm for low to moderate Reynolds number swimming Oscar M. Curet, Neelesh A. Patankar, Malcolm A. MacIver A number of organisms in nature swim by active undulations or deformations of their bodies, fins or flagella. Swimming mechanisms employed by these organisms are inspiring basic science research as well as novel applications in bio-- and nano--technology. Here, we develop a numerical scheme capable of fully resolving the swimming motion of an organism as a result of its prescribed deformations. The numerical solution at a given time proceeds in two steps. In the first step we solve the Navier-Stokes equations in the entire fluid-organism domain. In the next step, the fluid velocity in the organism domain is corrected by a ``momentum redistribution'' scheme. This imposes the prescribed deforming velocity in the frame of reference of the organism. These steps are iterated until convergence. The resulting solution gives the swimming velocity of the organism and the surrounding flow field. A variety of body forms can be set up by this approach including 3D bodies with 2D fins or 1D flagella attached to it. It is suitable at low to moderate Reynolds (Re) numbers. Since it is an iterative implicit approach, it can be easily applied to `zero' Re swimmers. We will present some examples as well as validation of the numerical scheme. The approach is also applicable to problems like the self-organization of cellular organelles or designing swimming micro robots. [Preview Abstract] |
Tuesday, November 20, 2007 1:06PM - 1:19PM |
NH.00008: Slow and fast swimming with a reciprocal stroke Marcus Roper, Jon Wilkening, Howard Stone Millimeter-sized swimmers often employ different sets of limbs or locomotory gaits for fast and slow swimming. It is believed that these bifurcations in swimming behavior reflect fundamental constraints upon how propulsive force may be generated in the world of small Reynolds numbers inhabited by such swimmers. We explore these constraints using a rigid foil flapped in a time-reversible manner as a simulacrum of a propulsive limb. We show that, if shaped appropriately, the limb is always capable of generating useful thrust by imparting momentum to coherent masses of fluid, and continues to do so even if the rate of energy expenditure in flapping is allowed to become arbitrarily low. However, the most effective targets of this momentum transfer shift from steady coherent eddies to vortices shed from the fin edges as the foil is scaled up. [Preview Abstract] |
Tuesday, November 20, 2007 1:19PM - 1:32PM |
NH.00009: Cruise Speed Characteristics of a Self--Propelled Pulsed-Jet Underwater Vehicle Ali Moslemi, Justin Nichols, Paul Krueger Steady-jet propulsion has been widely used for air and marine vehicles. This system has a high propulsive efficiency for high vehicle velocities, but it ceases to be efficient as the vehicle velocity or Reynolds number (Re) decreases. One alternative for low Re propulsion is pulsed-jet propulsion similar to that utilized by squid and jellyfish. We have developed a self-propelled pulsed-jet underwater vehicle (``Robosquid'') to investigate the effectiveness of pulsed-jet propulsion as Re decreases. A piston-cylinder mechanism is used for generating pulsed flow. The system allows control of piston velocity program, pulsing frequency, and piston stroke-to-nozzle diameter ratio (L/D). In this preliminary study, the effects of L/D and time-averaged jet mass flow rate on the vehicle cruise speed are investigated. The results for cruise speed are presented for L/D = 3,5,{\ldots},15 at the same mass flow rate and increasing mass flow rate at the same L/D. The vehicle Re varied from 12000 to 14000 and results show that the mass flow rate is a dominant factor in vehicle cruise speed. [Preview Abstract] |
Tuesday, November 20, 2007 1:32PM - 1:45PM |
NH.00010: ABSTRACT WITHDRAWN |
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