Unsteady swimming of small organisms

2012 ◽  
Vol 702 ◽  
pp. 286-297 ◽  
Author(s):  
S. Wang ◽  
A. M. Ardekani
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Fundamental Equation ◽  
Added Mass ◽  
Natural Environments ◽  
Mean Velocity ◽  
Unsteady Forces ◽  
Uniform Background ◽  
Low Reynolds

AbstractSmall planktonic organisms ubiquitously display unsteady or impulsive motion to attack a prey or escape a predator in natural environments. Despite this, the role of unsteady forces such as history and added mass forces on the low-Reynolds-number propulsion of small organisms, e.g. Paramecium, is poorly understood. In this paper, we derive the fundamental equation of motion for an organism swimming by means of the surface distortion in a non-uniform background flow field at a low-Reynolds-number regime. We show that the history and added mass forces are important as the product of Reynolds number and Strouhal number increases above unity. Our results for an unsteady squirmer show that unsteady inertial effects can lead to a non-zero mean velocity for the cases with zero streaming parameters, which have zero mean velocity in the absence of inertia.

Steric scattering of rod-like swimmers in low Reynolds number environments

Soft Matter ◽  
2021 ◽  
Author(s):  
Kentaro Hoeger ◽  
Tristan Ursell
Keyword(s):  
Reynolds Number ◽  
Cell Size ◽  
Low Reynolds Number ◽  
Surface Curvature ◽  
Natural Environments ◽  
Solid Objects ◽  
Low Reynolds

While navigating natural environments, interactions with cell-size solid objects alter paths of swimming microbes. We characterized such ‘scattering’ from synthetic objects of controlled surface curvature. A sterics-only model agrees well with the data.

Shear Layer Development, Separation, and Stability Over a Low-Reynolds Number Airfoil

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Paul Ziadé ◽  
Mark A. Feero ◽  
Philippe Lavoie ◽  
Pierre E. Sullivan
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Base Flow ◽  
Mean Velocity ◽  
Laminar Separation ◽  
Low Reynolds ◽  
Layer Development

The shear layer development for a NACA 0025 airfoil at a low Reynolds number was investigated experimentally and numerically using large eddy simulation (LES). Two angles of attack (AOAs) were considered: 5 deg and 12 deg. Experiments and numerics confirm that two flow regimes are present. The first regime, present for an angle-of-attack of 5 deg, exhibits boundary layer reattachment with formation of a laminar separation bubble. The second regime consists of boundary layer separation without reattachment. Linear stability analysis (LSA) of mean velocity profiles is shown to provide adequate agreement between measured and computed growth rates. The stability equations exhibit significant sensitivity to variations in the base flow. This highlights that caution must be applied when experimental or computational uncertainties are present, particularly when performing comparisons. LSA suggests that the first regime is characterized by high frequency instabilities with low spatial growth, whereas the second regime experiences low frequency instabilities with more rapid growth. Spectral analysis confirms the dominance of a central frequency in the laminar separation region of the shear layer, and the importance of nonlinear interactions with harmonics in the transition process.

Vertical Migration of the Small Organisms in a Stratified Fluid

2012 ◽  
Author(s):  
Amin Doostmohammadi ◽  
Arezoo M. Ardekani
Keyword(s):  
Reynolds Number ◽  
Vertical Migration ◽  
Low Reynolds Number ◽  
Nonlinear Effects ◽  
Stratified Fluid ◽  
Salinity Gradients ◽  
Density Interfaces ◽  
Low Reynolds ◽  
Made In

Significant progress has been made in analyzing low-Reynolds number locomotion in homogeneous fluids. Even though density interfaces due to temperature or salinity gradients (pycnoclines), ubiquitously occur in oceans and lakes, the effects of stratification on the hydrodynamics of swimming of small organisms, their interaction with each other and their migration are very poorly understood. In this article, we implement a direct numerical simulation of the migration of swimmers at pycnoclines and illustrate the role of the diffusivity of the stratified agent on the swimming of small organisms. We demonstrate that for an archetypal swimmer model, squirmer, the migration at density stratified fluid can be largely influenced by buoyancy effects. We also show that the effects of density stratification are increased as the diffusivitty of the stratified agent is reduced. The results demonstrate that the stratification suppresses the vertical migration and consequently affects the life of low Reynolds number swimmers across pycnoclines. Our recent computational results reveal the full nonlinear effects of stratification on the locomotion of small organisms.

Particle Image Velocimetry Study of Rough-Wall Turbulent Flows in Favorable Pressure Gradient

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
G. F. K. Tay ◽  
D. C. S. Kuhn ◽  
M. F. Tachie
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Particle Image ◽  
Low Reynolds Number ◽  
Plane Channel ◽  
Mean Velocity ◽  
Image Velocimetry ◽  
Favorable Pressure Gradient ◽  
Low Reynolds

This paper reports an experimental investigation of the effects of wall roughness and favorable pressure gradient on low Reynolds number turbulent flow in a two-dimensional asymmetric converging channel. Flow convergence was produced by means of ramps (of angles 2 deg and 3 deg) installed on the bottom wall of a plane channel. The experiments were conducted over a smooth surface and over transitionally rough and fully rough surfaces produced from sand grains and gravel of nominal mean diameters 1.55 mm and 4.22 mm, respectively. The dimensionless acceleration parameter was varied from 0.38×10−6 to 3.93×10−6 while the Reynolds number based on the boundary layer momentum thickness was varied from 290 to 2250. The velocity measurements were made using a particle image velocimetry technique. From these measurements, the distributions of the mean velocity and Reynolds stresses were obtained to document the salient features of transitionally and fully rough low Reynolds number turbulent boundary layers subjected to favorable pressure gradient.

Low Reynolds Number Effect on Open Channel Flow Over a Rib

2014 ◽  
Author(s):  
Ebenezer E. Essel ◽  
Kathryn Atamanchuk ◽  
Samuel d’Auteuil ◽  
Mark F. Tachie
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Open Channel ◽  
Low Reynolds Number ◽  
Open Channel Flow ◽  
Recirculation Region ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Low Reynolds

An experimental study was conducted to investigate low Reynolds number effects on open channel flow over a transverse square rib. Particle image velocimetry technique was used to perform detailed velocity measurement in the upstream and recirculation region of a square rib of height, h = 12 mm. The Reynolds number based on the freestream velocity and rib height, Reh = 1510, 2650 and 3950 and the ratio of the boundary layer thickness to step height, δ/h = 2.5 ± 0.2. The results showed that the reattachment length of Reh = 2650 and 3950 increased by 5.7% compared with corresponding value of Reh = 1510. The mean velocities were independent of Reynolds number in the recirculation region but at the reattachment point, Reh = 3650 reduced the streamwise mean velocity and enhanced the wall-normal mean velocity in the region adjacent to the wall. The turbulent kinetic energy beyond the center of the recirculation region increased with increasing Reynolds number.

scholarly journals Role of symmetry in driven propulsion at low Reynolds number

2018 ◽  
Vol 98 (6) ◽  
Author(s):  
Johannes Sachs ◽  
Konstantin I. Morozov ◽  
Oded Kenneth ◽  
Tian Qiu ◽  
Nico Segreto ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Low Reynolds
Sign in / Sign up

Export Citation Format

Share Document