scholarly journals Choreographed swimming of copepod nauplii

2015 ◽  
Vol 12 (112) ◽  
pp. 20150776 ◽  
Author(s):  
Petra H. Lenz ◽  
Daisuke Takagi ◽  
Daniel K. Hartline
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Low Reynolds Number ◽  
Measurement Model ◽  
The Body ◽  
Morphological Data ◽  
Slender Body Theory ◽  
Viscous Forces ◽  
Video Images ◽  
Low Reynolds

Small metazoan paddlers, such as crustacean larvae (nauplii), are abundant, ecologically important and active swimmers, which depend on exploiting viscous forces for locomotion. The physics of micropaddling at low Reynolds number was investigated using a model of swimming based on slender-body theory for Stokes flow. Locomotion of nauplii of the copepod Bestiolina similis was quantified from high-speed video images to obtain precise measurements of appendage movements and the resulting displacement of the body. The kinematic and morphological data served as inputs to the model, which predicted the displacement in good agreement with observations. The results of interest did not depend sensitively on the parameters within the error of measurement. Model tests revealed that the commonly attributed mechanism of ‘feathering’ appendages during return strokes accounts for only part of the displacement. As important for effective paddling at low Reynolds number is the ability to generate a metachronal sequence of power strokes in combination with synchronous return strokes of appendages. The effect of feathering together with a synchronous return stroke is greater than the sum of each factor individually. The model serves as a foundation for future exploration of micropaddlers swimming at intermediate Reynolds number where both viscous and inertial forces are important.

scholarly journals Geometrically Similar Rectangular Passive Micromixers and the Scaling Validity on Mixing Efficiency and Pressure Drops

2019 ◽  
Vol 69 (1) ◽  
pp. 69-84
Author(s):  
Veldurthi Naresh ◽  
D. Bodas ◽  
Chandel Sunil ◽  
Bhave Tejashree
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Scale Factor ◽  
Mixing Efficiency ◽  
Scaling Effect ◽  
Pressure Drops ◽  
Viscous Forces ◽  
Linear Dimensions ◽  
Simulation Results ◽  
Low Reynolds

AbstractIn the present work, two geometrically similar passive geometries with dumbbell shape were designed to perturb the dominating viscous forces in the low Reynolds number (Re) flows of the fluids. The geometries were designated as PDM-I and PDM-II, in which all the linear dimensions were related by a constant scale factor of two. Mixing efficiencies and pressure drops of the species at various Reynolds number (Re) were calculated to estimate the scaling effect validations. Finally, the geometrically similar PDM geometries were fabricated in Polydimethylsiloxane (PDMS) polymer to evaluate the scaling effect on the mixing efficiencies of the dyes and validated with the simulation results of species mixing.

The physical-chemical environment of microbes

2018 ◽  
Author(s):  
David L. Kirchman
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Chemical Properties ◽  
Physical World ◽  
Chemical Environment ◽  
Viscous Forces ◽  
Physical Chemical ◽  
Terrestrial Habitats ◽  
Low Reynolds ◽  
Living Organisms

Many physical-chemical properties affecting microbes are familiar to ecologists examining large organisms in our visible world. This chapter starts by reviewing the basics of these properties, such as the importance of water for microbes in soils and temperature in all environments. Another important property, pH, has direct effects on organisms and indirect effects via how hydrogen ions determine the chemical form of key molecules and compounds in nature. Oxygen content is also critical, as it is essential to the survival of all but a few eukaryotes. Light is used as an energy source by phototrophs, but it can have deleterious effects on microbes. In addition to these familiar factors, the small size of microbes sets limits on their physical world. Microbes are said to live in a “low Reynolds number environment”. When the Reynolds number is smaller than about one, viscous forces dominate over inertial forces. For a macroscopic organism like us, moving in a low Reynolds number environment would seem like swimming in molasses. Microbes in both aquatic and terrestrial habitats live in a low Reynolds number world, one of many similarities between the two environments at the microbial scale. Most notably, even soil microbes live in an aqueous world, albeit a thin film of water on soil particles. But the soil environment is much more heterogeneous than water, with profound consequences for biogeochemical processes and interactions among microbes. The chapter ends with a discussion of how the physical-chemical environment of microbes in biofilms is quite different from that of free-living organisms.

Approximate Analytical Model for Oil Film Force of Finite Length Squeeze Film Damper Under Low Reynolds Number

2013 ◽  
Author(s):  
Yongliang Wang ◽  
Yu Gao ◽  
Jingjun Zhong ◽  
Ling Yang ◽  
Huawei Lu
Keyword(s):  
Reynolds Number ◽  
Analytical Model ◽  
Finite Length ◽  
High Speed ◽  
Low Reynolds Number ◽  
Separation Of Variables ◽  
Squeeze Film ◽  
Force Model ◽  
Oil Film ◽  
Low Reynolds

Squeeze film dampers (SFDs) are widely used in aero-engines and other high speed rotating machines as damping elements, owing to their remarkable damping effect. The oil-film force model of SFDs is the key to investigate the dynamic characteristics of the rotor-bearing systems involving SFDs. In this paper, the analytical solution of the oil film pressure of a finite length SFD is obtained by employing the separation of variables method to solve the Reynolds equation (at low Reynolds number) based upon the dynamic π boundary condition. The analytical expression of the oil film force is then derived by applying the integral method. The oil film force from the analytical model is compared with the results from other well-known methods, i.e. the long bearing approximation, the short bearing approximation and the finite difference method. The results clearly show that within a wider length-diameter ratio range, the newly proposed model can accurately predict the oil film characteristics of the SFDs at low Reynolds numbers.

Active control of high-speed and high-Reynolds-number jets using plasma actuators

2007 ◽  
Vol 578 ◽  
pp. 305-330 ◽  
Author(s):  
M. SAMIMY ◽  
J.-H. KIM ◽  
J. KASTNER ◽  
I. ADAMOVICH ◽  
Y. UTKIN
Keyword(s):  
Reynolds Number ◽  
Nozzle Exit ◽  
High Speed ◽  
Low Reynolds Number ◽  
Plasma Actuators ◽  
Mixing Enhancement ◽  
Azimuthal Mode ◽  
Potential Core ◽  
Low Speed ◽  
Low Reynolds

Localized arc filament plasma actuators are used to control an axisymmetric Mach 1.3 ideally expanded jet of 2.54 cm exit diameter and a Reynolds number based on the nozzle exit diameter of about 1.1×106. Measurements of growth and decay of perturbations seeded in the flow by the actuators, laser-based planar flow visualizations, and particle imaging velocimetry measurements are used to evaluate the effects of control. Eight actuators distributed azimuthally inside the nozzle, approximately 1 mm upstream of the nozzle exit, are used to force various azimuthal modes over a large frequency range (StDF of 0.13 to 1.3). The jet responded to the forcing over the entire range of frequencies, but the response was optimum (in terms of the development of large coherent structures and mixing enhancement) around the jet preferred Strouhal number of 0.33 (f = 5 kHz), in good agreement with the results in the literature for low-speed and low-Reynolds-number jets. The jet (with a thin boundary layer, D/θ ∼ 250) also responded to forcing with various azimuthal modes (m = 0 to 3 and m = ±1, ±2, ±4), again in agreement with instability analysis and experimental results in the literature for low-speed and low-Reynolds-number jets. Forcing the jet with the azimuthal mode m = ±1 at the jet preferred-mode frequency provided the maximum mixing enhancement, with a significant reduction in the jet potential core length and a significant increase in the jet centreline velocity decay rate beyond the end of the potential core.

The wakes of cylindrical bluff bodies at low Reynolds number

1978 ◽  
Vol 288 (1354) ◽  
pp. 351-382 ◽  
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
The Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Near Wake ◽  
Cross Sectional ◽  
Molecular Diffusivity ◽  
Splitter Plates ◽  
Low Reynolds

Experiments on the near wake of a cylinder will be discribed in an attempt to present a coherent picture of the events encountered as the Reynolds number increases from small values up to values of a few thousand. Much work on this subject has already been done, but there are gaps in our description of these flows as well as more fundamental deficiencies in our understanding of them. The subject has been reviewed several times and most recently by Berger & Wille (1972) whose paper covers much of the ground that will be discussed again here. The present work may be regarded as built upon this latest review. I remember with gratitude many helpful discussions with the late Rudolph Wille who contributed so much to this subject. The investigation has concentrated on circular cylinders, but the wakes of bluff cylinders of different cross sectional shapes have also been observed. Bluff cylinders in general are considered in §§4 and 5, together with the effect of splitter plates on circular cylinders in §9. The experiments concern, almost exclusively, flow visualization of the wakes by means of dye washed from the bodies. The patterns of dye observed are, therefore, filament line representations of the flow leaving the separation lines on the body. It must be stressed that the dye does not make visible the vorticity bearing fluid because at low Reynolds number, vorticity diffuses considerably more rapidly than does dye. The ratio of the molecular diffusivity of momentum to that of mass of dye is of the order of 100.

scholarly journals Control of Uniflagellar Soft Robots at Low Reynolds Number Using Buckling Instability

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Mojtaba Forghani ◽  
Weicheng Huang ◽  
M. Khalid Jawed
Keyword(s):  
Reynolds Number ◽  
Angular Velocity ◽  
Dimensional Space ◽  
Low Reynolds Number ◽  
Three Dimensional ◽  
Slender Body Theory ◽  
Fluid Medium ◽  
Buckling Instability ◽  
Low Reynolds ◽  
Three Dimensional Space

Abstract In this paper, we analyze the inverse dynamics and control of a bacteria-inspired uniflagellar robot in a fluid medium at low Reynolds number. Inspired by the mechanism behind the locomotion of flagellated bacteria, we consider a robot comprising a flagellum—a flexible helical filament—connected to a spherical head. The flagellum rotates about the head at a controlled angular velocity and generates a propulsive force that moves the robot forward. When the angular velocity exceeds a threshold value, the hydrodynamic force exerted by the fluid can cause the soft flagellum to buckle, characterized by a dramatic change in its shape. In this computational study, a fluid–structure interaction model that combines Discrete Elastic Rods algorithm with Lighthill's Slender Body Theory is employed to simulate the locomotion and deformation of the robot. We demonstrate that the robot can follow a prescribed path in three-dimensional space by exploiting buckling of the flagellum. The control scheme involves only a single (binary) scalar input—the angular velocity of the flagellum. By triggering the buckling instability at the right moment, the robot can follow the path in three-dimensional space. We also show that the complexity of the dynamics of the helical filament can be captured using a deep neural network, from which we identify the input–output functional relationship between the control input and the trajectory of the robot. Furthermore, our study underscores the potential role of buckling in the locomotion of natural bacteria.

Measurements of Low Reynolds Number Flow in Rotating Channels

2007 ◽  
Author(s):  
Alberto Di Sante ◽  
Rene´ Van den Braembussche
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
High Speed ◽  
Low Reynolds Number ◽  
Continuous Light ◽  
Suction Side ◽  
Pressure Side ◽  
Low Reynolds ◽  
The Impact ◽  
Rotating Channel

The impact of Coriolis forces on low Reynolds number decelerating flows is studied by means of time resolved Particle Image Velocimetry in a 6° diverging channel. Measurements are made with a high speed camera and a continuous light source rotating at the same speed as the rotating channel. This allows a direct and accurate recording of the time varying relative velocity. The Reynolds number can be varied from 3 000 to 30 000 in combination with a change of rotation number between 0.0 and 0.33. These values are characteristic for the flow in the blade passage of centrifugal impellers used in micro gasturbines. Increasing rotation stabilizes the flow on the suction side. The peak turbulence intensity shifts away from the wall with a small increase of its amplitude. The turbulence intensity on the pressure side increases its peak value and concentrates closer to the wall when increasing rotation. Instantaneous flow field analyses indicate that elongated vortical structures characterize the boundary layer in the stationary case and on the pressure side of the rotating channel. Isotropic vortices develop relatively distant from the wall on the suction side. Their position and size are tracked in time by means of a wavelet analysis.

scholarly journals An assessment of the laminar kinetic energy concept for the prediction of high-lift, low-Reynolds number cascade flows

2011 ◽  
Vol 225 (7) ◽  
pp. 995-1003 ◽  
Author(s):  
R Pacciani ◽  
M Marconcini ◽  
A Arnone ◽  
F Bertini
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
High Speed ◽  
Low Reynolds Number ◽  
Flow Region ◽  
Freestream Turbulence ◽  
High Lift ◽  
Numerical Predictions ◽  
Wide Range ◽  
Low Reynolds

The laminar kinetic energy (LKE) concept has been applied to the prediction of low-Reynolds number flows, characterized by separation-induced transition, in high-lift airfoil cascades for aeronautical low-pressure turbine applications. The LKE transport equation has been coupled with the low-Reynolds number formulation of the Wilcox's k − ω turbulence model. The proposed methodology has been assessed against two high-lift cascade configurations, characterized by different loading distributions and suction-side diffusion rates, and tested over a wide range of Reynolds numbers. The aft-loaded T106C cascade is studied in both high- and low-speed conditions for several expansion ratios and inlet freestream turbulence values. The front-loaded T108 cascade is analysed in high-speed, low-freestream turbulence conditions. Numerical predictions with steady inflow conditions are compared to measurements carried out by the von Kármán Institute and the University of Cambridge. Results obtained with the proposed model show its ability to predict the evolution of the separated flow region, including bubble-bursting phenomenon and the formation of open separations, in high-lift, low-Reynolds number cascade flows.

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