Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session Q25: Focus Session: Life Processes at Biologically Intermediate Reynolds NumbersBio Fluids: External Bio Fluids: Internal
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Chair: Laura Miller, University of North Carolina Room: 705 |
Tuesday, November 21, 2017 12:50PM - 1:03PM |
Q25.00001: Characterization of Hop-and-Sink Locomotion of Water Fleas A.N. Skipper, D.W. Murphy, D.R. Webster The freshwater crustacean \textit{Daphnia magna} is a widely studied zooplankton in relation to food webs, predator-prey interactions, and other biological/ecological considerations; however, their locomotion is poorly quantified and understood. These water fleas utilize a hop-and-sink mechanism that consists of making quick, impulsive jumps by beating their antennae to propel themselves forward (roughly 1 body length). The animals then sink for a period, during which they stretch out their antennae to increase drag and thereby reduce their sinking velocity. Time-resolved three-dimensional flow fields surrounding the animals were quantified with a unique infrared tomographic particle image velocimetry (tomo-PIV) system. Three-dimensional kinematics data were also extracted from the image sequences. In the current work, we compared body kinematics and flow disturbance among organisms of size in the range of 1.3 to 2.8 mm. The stroke cycle averaged 150 $+$/- 20 ms, with each stroke cycle split nearly evenly between power and recovery strokes. The kinematics data collapsed onto a self-similar curve when properly nondimensionalized, and a general trend was shown to exist between the nondimensionalized peak body speed and body length. The fluid flow induced by each antennae consisted of a viscous vortex ring that demonstrated a slow decay in the wake. The viscous dissipation showed no clear dependence on body size, whereas the volume of fluid exceeding 5 mm/s (the speed near the sinking speed of the animal) decayed more slowly with increasing body size. [Preview Abstract] |
Tuesday, November 21, 2017 1:03PM - 1:16PM |
Q25.00002: Heave and Flow: Understanding the role of resonance and shape evolution for heaving flexible panels Alexander Hoover, Ricardo Cortez, Eric Tytell, Lisa Fauci Many animals that swim or fly use their body to accelerate the fluid around them, transferring momentum from their bodies to the surrounding fluid. The emergent kinematics from this transfer are a result of the coupling between the fluid and the material properties of the body. Here we present a computational study of a 3-dimensional flexible panel that is heaved at its leading edge in an incompressible, viscous fluid. These high-fidelity numerical simulations enable us to examine the role of resonance, fluid forces, and panel deformations have on swimming performance. Varying both the passive material properties and the heaving frequency of the panel, we find peaks in trailing edge amplitude and forward swimming speed are determined by a dimensionless quantity, the effective flexibility. Modal decompositions of panel deflections reveal that the strength of each mode is related to the effective flexibility and peaks in the swimming speed and trailing edge amplitude correspond to peaks in the contributions of different modes. Panels of different material properties but with similar effective flexibilities have modal contributions that evolve similarly over the phase of the heaving cycle and agreement in dominant vortex structures generated by the panel. [Preview Abstract] |
Tuesday, November 21, 2017 1:16PM - 1:29PM |
Q25.00003: Hydrodynamic interactions in metachronal paddling: effects of varying stroke kinematics Milad Samaee, Vishwa Kasoju, Hong Kuan Lai, Arvind Santhanakrishnan Crustaceans such as shrimp and krill use a drag-based technique for propulsion, in which multiple pairs of limbs are paddled rhythmically from the tail to the head. Each limb is phase-shifted in time relative to its neighbor. Most studies of this type of metachronal swimming have focused on the jet formed in the animal's wake. However, synergistic hydrodynamic interactions between adjacent limbs in metachrony have received minimal attention. We used a dynamically scaled robotic model to experimentally investigate how variations in stroke kinematics impact inter-paddle hydrodynamic interactions and thrust generation. Physical models of limbs were fitted to the robot and paddled with two different motion profiles (MPs)---1) MP1: metachronal power stroke (PS) and metachronal recovery stroke (RS); and 2) MP2: metachronal PS and synchronous RS. Stroke frequency and amplitude were maintained constant across both MPs. Our results show that MP2 produced faster jets in the thrust-generating direction as compared to MP1. The necessity for a pause in MP2 after completion of PS by the paddles leading the motion, prior to executing the synchronous RS, aided in further downstream flow propagation. The effect of using asymmetric stroke kinematics on thrust generated will be discussed. [Preview Abstract] |
Tuesday, November 21, 2017 1:29PM - 1:42PM |
Q25.00004: Transitions in swimming behavior at intermediate Reynolds numbers of a reciprocal ``spherobot'' swimmer Shannon Jones, Amneet Bhalla, Boyce Griffith, Daphne Klotsa We used the immersed boundary method to study an internally-powered swimmer, affectionately called the ``spherobot'', composed of two unequal sized spheres that oscillated with respect to each other at intermediate Reynolds numbers (1-150). Because the spherobot has a reciprocal stroke, it does not swim in the Stokes regime; however, due to its asymmetrical geometry, it swims at intermediate Reynolds numbers. We observed that the spherobot remains stationary or swims depending on the Reynolds number. We were surprised to find that the direction of swimming also depends on the Reynolds number. We identified two Reynolds number regimes within the intermediate range: one where the spherobot moves in the direction of the large sphere and one where the spherobot swims in the direction of the small sphere. [Preview Abstract] |
Tuesday, November 21, 2017 1:42PM - 1:55PM |
Q25.00005: Copepod behavior response to Burgers' vortex treatments mimicking turbulent eddies D. Elmi, D.R. Webster, D.M. Fields Copepods detect hydrodynamic cues in the water by their mechanosensory setae. We expect that copepods sense the flow structure of turbulent eddies in order to evoke behavioral responses that lead to population-scale distribution patterns. In this study, the copepods' response to the Burgers' vortex is examined. The Burgers' vortex is a steady-state solution of three-dimensional Navier-Stokes equations that allows us to mimic turbulent vortices at the appropriate scale and eliminate the stochastic nature of turbulence. We generate vortices in the laboratory oriented in the horizontal and vertical directions each with four intensity levels. The objective of including vortex orientation as a parameter in the study is to quantify directional responses that lead to vertical population distribution patterns. The four intensity levels correspond to target vortex characteristics of eddies corresponding to the typical dissipative vortices in isotropic turbulence with mean turbulent dissipation rates in the range of 0.002 to 0.25 cm$^{\mathrm{2}}$/s$^{\mathrm{3}}$. These vortices mimic the characteristics of eddies that copepods most likely encounter in coastal zones. We hypothesize that the response of copepods to hydrodynamic features depends on their sensory architecture and relative orientation with respect to gravity. Tomo-PIV is used to quantify the vortex circulation and axial strain rate for each vortex treatment. Three-dimensional trajectories of the copepod species \textit{Calanus finmarchicus} are analyzed to examine their swimming kinematics in and around the vortex to quantify the hydrodynamic cues that trigger their behavior. [Preview Abstract] |
Tuesday, November 21, 2017 1:55PM - 2:08PM |
Q25.00006: Pulsing soft corals generate sustained upward jets and regions of strong mixing between their tentacles. Laura Miller, Julia Samson, Shilpa Khatri Xeniid soft corals increase the local flows around each individual polyp as well as the whole colony through the collective pulsing behaviour of their polyps. This pulsing behaviour is thought to increase mass transfer of nutrients and gas exchange between the organism and its environment. We present a description of the flow fields around pulsing polyps and qualitatively compare actual flow data to both 2D and 3D immersed boundary simulations of polyps. We analyze the flows generated using Lagrangian coherent structure (LCS) and circulation analysis. LCS analysis describes the effective boundaries between mixing regions; particles found in one LCS might be restricted to a certain region of the flow field and never trade places with particles from another structure. Our results show that oppositely spinning vortices are generated during each contraction and expansion of the tentacles. Strong sustained mixing occurs within the polyp during the expansion phase. In addition, a continuous upward jet is sustained during the entire pulsing cycle. [Preview Abstract] |
Tuesday, November 21, 2017 2:08PM - 2:21PM |
Q25.00007: Parachuting with bristled wings Vishwa Kasoju, Arvind Santhanakrishnan, Michael Senter, Kristen Armel, Laura Miller Free takeoff flight recordings of thrips (body length \textless 1 mm) show that they can intermittently cease flapping and instead float passively downwards by spreading their bristled wings. Such drag-based parachuting can lower the speed of falling and aid in long distance dispersal by minimizing energetic demands needed for active flapping flight. However, the role of bristled wings in parachuting remains unclear. In this study, we examine if using bristled wings lowers drag forces in parachuting as compared to solid (non-bristled) wings. Wing angles and settling velocities were obtained from free takeoff flight videos. A solid wing model and bristled wing model with bristle spacing to diameter ratio of 5 performing translational motion were comparatively examined using a dynamically scaled robotic model. We measured force generated under varying wing angle from 45-75 degrees across a Reynolds number (Re) range of 1 to 15. Drag experienced by the wings decreased in both wing models when varying Re from 1 to 15. Leakiness of flow through bristles, visualized using spanwise PIV, and implications for force generation will be presented. Numerical simulations will be used to investigate the stability of free fall using bristled wings. [Preview Abstract] |
Tuesday, November 21, 2017 2:21PM - 2:34PM |
Q25.00008: Rheosensing by impulsive cells at intermediate Reynolds numbers Arnold Mathijssen, Saad Bhamla, Manu Prakash For aquatic organisms, mechanical signals are often carried by the surrounding liquid, through viscous and inertial forces. Here we consider a unicellular yet millimetric ciliate, {\it Spirostomum ambiguum}, as a model organism to study hydrodynamic sensing. This protist typically swims at moderate Reynolds numbers, Re $<$ 0.5, but upon stimulation it surges to Re $>$ 100 during impulsive contractions where its elongated body recoils within milliseconds. First, using high-speed PIV and an electrophysiology setup, we deliver controlled voltage pulses to induce these rapid contractions and visualise the vortex flows generated thereby. By comparing these measurements with CFD simulations the range of these hydrodynamic ``signals'' is characterized. Second, we probe the mechano-sensing of the organism with externally applied flows and find a critical shear rate necessary to trigger a contraction. The combination of high Re flow generation and rheosensing could facilitate intercellular communication over large distances. Please also see our other talk ``Collective hydrodynamic communication through ultra-fast contractions''. [Preview Abstract] |
Tuesday, November 21, 2017 2:34PM - 2:47PM |
Q25.00009: Collective hydrodynamic communication through ultra-fast contractions Saad Bhamla, Arnold Mathijssen, Manu Prakash The biophysical relationships between physiological sensors and actuators were fundamental to the development of early life forms, as responding to external stimuli promptly is key to survival. We study an unusual protist {\it Spirostomum ambiguum}, a single-celled organism that can grow up to 4mm in size, visible to the naked eye, as a model system for impulsive systems. Coiling its cytoskeleton, this ciliate can contract its long body within milliseconds, one of the fastest accelerations known in cell biology. We demonstrate that these rapid contractions generate long-ranged vortex flows that can trigger other cells to contract, repeatedly, which collectively leads to an ultra-fast hydrodynamic signal transduction across a colony that moves hundreds of times faster than the swimming speed. By combining high-speed PIV experiments and analytical modelling we determine the critical rheosensitivity required to sustain these signal waves. Whereas the biological motive is not fully understood, contractions are known to release toxins from membrane-bound extrusomes, thus we hypothesize that synchronised discharges could facilitate the repulsion of large-scale predators cooperatively. Please also see our other talk ``Rheosensing by impulsive cells at intermediate Reynolds numbers''. [Preview Abstract] |
Tuesday, November 21, 2017 2:47PM - 3:00PM |
Q25.00010: Exploring the effects of scaling on a simple model of peristalsis Lindsay Waldrop Functional systems that must operate at or through intermediate Reynolds numbers are often complex and not well understood. Peristaltic pumping by valveless, tubular hearts -- widespread among animal groups and scales -- is one such system, having many parameters that control functional performance (fluid driven through circulatory systems) in a fluid regime that is dominated by neither viscosity nor inertia. To better understand the relative performance of valveless, tubular hearts, we use uncertainty quantification on a simple model of peristalsis driving fluid in a racetrack to perform sensitivity analyses on three parameters known to influence fluid flow: compression ratio (how much the tube compresses during a contraction), Womersley number ($Wo$; similar to $Re$ for pulsatile flow), and compression frequency. We find that compression ratio dominates volume flow rates through the circulatory system, while $Wo$ and compression frequency have little or no effect on flow performance. These results point to peristaltic pumping by valveless, tubular hearts as being an effective and robust mechanism to drive fluid flow across scales. [Preview Abstract] |
Tuesday, November 21, 2017 3:00PM - 3:13PM |
Q25.00011: Biomimetic model systems of rigid hair beds: Part I - Theory Kaitlyn Hood, Mani S.S. Jammalamadaka, Anette Hosoi Crustaceans - such as lobsters, crabs, and stomapods - have hairy appendages that they use to recognize and track odorants in the surrounding fluid. An array of rigid hairs impedes flow at different rates depending on the spacing between hairs and the Reynolds number, Re. At larger Reynolds numbers (Re \textgreater 1), fluid travels through the hairs rather than around them, a phenomenon called leakiness. Crustaceans flick their appendages at different speeds in order to manipulate the leakiness between the hairs, allowing the hairs to either detect odors in a sample of fluid or collect a new sample. A single hair can be represented as a slender body attached at one end to a wall. Using both slender body theory and numerical methods, we observe that there is a region of flow around the hair that speeds up relative to the unobstructed flow. As the Reynolds number increases, this fast flow region moves closer to the hair. Using this model, we predict that an array of hairs can be engineered to have a desired leakiness profile. [Preview Abstract] |
Tuesday, November 21, 2017 3:13PM - 3:26PM |
Q25.00012: Biomimetic model systems of rigid hair beds: Part II -- Experiment Mani S.S Jammalamadaka, Kaitlyn Hood, Anette Hosoi Crustaceans -- such as lobsters, crabs and stomapods -- have hairy appendages that they use to recognize and track odorants in the surrounding fluid. An array of rigid hairs impedes flow at different rates depending on the spacing between hairs and the Reynolds number, Re. At larger Reynolds number (Re\textgreater 1), fluid travels through the hairs rather than around them, a phenomenon called leakiness. Crustaceans flick their appendages at different speeds in order to manipulate the leakiness between the hairs, allowing the hairs to either detect the odors in a sample of fluid or collect a new sample. Theoretical and numerical studies predict that there is a fast flow region near the hairs that moves closer to the hairs as Re increases. Here, we test this theory experimentally. We 3D printed rigid hairs with an aspect ratio of 30:1 in rectangular arrays with different hair packing fractions. We custom built an experimental setup which establishes poiseuille flow at intermediate Re, Re$\le $200. We track the flow dynamics through the hair beds using tracer particles and Particle Imaging Velocimetry. We will then compare the modelling predictions with the experimental outcomes. [Preview Abstract] |
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