scholarly journals Fluid Dynamics of Ballistic Strategies in Nematocyst Firing

Fluids ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 20 ◽  
Author(s):  
Christina Hamlet ◽  
Wanda Strychalski ◽  
Laura Miller
Keyword(s):  
Immersed Boundary Method ◽  
Short Distance ◽  
Reynolds Numbers ◽  
Two Dimensions ◽  
Immersed Boundary ◽  
Small Scale ◽  
Viscous Damping ◽  
Final Velocity ◽  
Inertial Regime ◽  
Surrounding Fluid

Nematocysts are stinging organelles used by members of the phylum Cnidaria (e.g., jellyfish, anemones, hydrozoans) for a variety of important functions including capturing prey and defense. Nematocysts are the fastest-known accelerating structures in the animal world. The small scale (microns) coupled with rapid acceleration (in excess of 5 million g) present significant challenges in imaging that prevent detailed descriptions of their kinematics. The immersed boundary method was used to numerically simulate the dynamics of a barb-like structure accelerating a short distance across Reynolds numbers ranging from 0.9–900 towards a passive elastic target in two dimensions. Results indicate that acceleration followed by coasting at lower Reynolds numbers is not sufficient for a nematocyst to reach its target. The nematocyst’s barb-like projectile requires high accelerations in order to transition to the inertial regime and overcome the viscous damping effects normally encountered at small cellular scales. The longer the barb is in the inertial regime, the higher the final velocity of the projectile when it touches its target. We find the size of the target prey does not dramatically affect the barb’s approach for large enough values of the Reynolds number, however longer barbs are able to accelerate a larger amount of surrounding fluid, which in turn allows the barb to remain in the inertial regime for a longer period of time. Since the final velocity is proportional to the force available for piercing the membrane of the prey, high accelerations that allow the system to persist in the inertial regime have implications for the nematocyst’s ability to puncture surfaces such as cellular membranes or even crustacean cuticle.

scholarly journals Analogue tuning of particle focusing in elasto-inertial flow

Meccanica ◽  
2021 ◽  
Author(s):  
I. Banerjee ◽  
M. E. Rosti ◽  
T. Kumar ◽  
L. Brandt ◽  
A. Russom
Keyword(s):  
Numerical Simulations ◽  
Cross Section ◽  
Immersed Boundary Method ◽  
Circular Cross Section ◽  
Finite Size ◽  
Reynolds Numbers ◽  
Immersed Boundary ◽  
Particle Focusing ◽  
Inertial Flow ◽  
Particle Behaviour

AbstractWe report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.

Modeling Insect Filiform Hair Motion Using the Penalty Immersed Boundary Method

2007 ◽  
Author(s):  
Toma´sˇ Gedeon ◽  
Jeff J. Heys ◽  
B. C. Knott ◽  
Jonas Mulder-Rosi
Keyword(s):  
Immersed Boundary Method ◽  
Immersed Boundary ◽  
Boundary Method ◽  
Wide Range ◽  
Fluid Environment ◽  
Induced Motion ◽  
Acheta Domestica ◽  
Model Equations ◽  
Surrounding Fluid ◽  
Filiform Hair

Many insects are able to sense their surrounding fluid environment through induced motion of their filiform hairs. The mechanism by which the insect can sense a wide range of input signals using the canopy of filiform hairs of different length and orientation is of great interest. Most of the previous filiform hair models have focused on a single, rigid hair in an idealized air field. We have developed [1] a model for a canopy of filiform hairs that are mechanically coupled to the surrounding air. The model equations are based on the penalty immersed boundary method. The key difference between the penalty immersed boundary method and the traditional immersed boundary method is the addition of forces to account for density differences between the immersed solid (the filiform hairs) and the surrounding fluid (air). In this work we validate the model by comparing the model predictions to experimental results on cricket Acheta domestica cercal system.

High Reynolds Number Airfoil Simulations Using the Immersed Boundary Method

2012 ◽  
Author(s):  
James P. Johnson ◽  
Gianluca Iaccarino ◽  
Kuo-Huey Chen ◽  
Bahram Khalighi
Keyword(s):  
Immersed Boundary Method ◽  
High Reynolds Number ◽  
Aerodynamic Force ◽  
Reynolds Numbers ◽  
Computational Approach ◽  
Immersed Boundary ◽  
Pressure Distributions ◽  
Boundary Method ◽  
High Reynolds ◽  
Naca 0012

The Immersed-Boundary Method is coupled to an incompressible-flow RANS solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0×105 and 1.8×106. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to show the need for locally refined grids to capture the thin boundary layers close to the airfoil leading edges. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The Immersed-Boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.

COMPUTATIONAL SIMULATION OF FLUID FLOW OVER A TRIANGULAR STEP USING IMMERSED BOUNDARY METHOD

2013 ◽  
Vol 10 (04) ◽  
pp. 1350016 ◽  
Author(s):  
C. A. SALEEL ◽  
A. SHAIJA ◽  
S. JAYARAJ
Keyword(s):  
Fluid Flow ◽  
Immersed Boundary Method ◽  
Reynolds Numbers ◽  
Stream Line ◽  
Immersed Boundary ◽  
Complex Geometries ◽  
Backward Facing Step ◽  
Fractional Step Method ◽  
Boundary Method ◽  
Fluid Solid Interaction

Handling of complex geometries with fluid–solid interaction has been one of the exigent issues in computational fluid dynamics (CFD) because most engineering problems have complex geometries with fluid–solid interaction for the purpose. Two different approaches have been developed for the same hitherto: (i) The unstructured grid method and (ii) the immersed boundary method (IBM). This paper details the IBM for the numerical investigation of two-dimensional laminar flow over a backward facing step and various geometrically configured triangular steps in hydro-dynamically developing regions (entrance region) as well in the hydro-dynamically developed regions through a channel at different Reynolds numbers. The present numerical method is rooted in a finite volume approach on a staggered grid in concert with a fractional step method. Geometrical obstructions are treated as an immersed boundary (IB), both momentum forcing and mass source terms are applied on the obstruction to satisfy the no-slip boundary condition and also to satisfy the continuity for the mesh containing the immersed boundary. Initially, numerically obtained velocity profiles and stream line plots for fluid flow over backward facing step is depicted to show its excellent agreement with the published results in various literatures. There after profiles and plots in the channel with triangular steps are also being unveiled with in depth elucidation. Results are presented for different Reynolds numbers.

Vortex interaction between two tandem flexible propulsors with a paddling-based locomotion

2016 ◽  
Vol 793 ◽  
pp. 612-632 ◽  
Author(s):  
Sung Goon Park ◽  
Hyung Jin Sung
Keyword(s):  
Phase Difference ◽  
Immersed Boundary Method ◽  
Propulsion System ◽  
Immersed Boundary ◽  
Vortex Interaction ◽  
Flexible Bodies ◽  
Tandem Configuration ◽  
Boundary Method ◽  
The Cost ◽  
Surrounding Fluid

Schooling behaviours among self-propelled animals can benefit propulsion. Inspired by the schooling behaviours of swimming jellyfish, flexible bodies that self-propel through a paddling-based motion were modelled in a tandem configuration. This present study explored the hydrodynamic patterns generated by the interactions between two flexible bodies and the surrounding fluid in the framework of the penalty immersed boundary method. The hydrodynamic patterns produced in the wake revealed flow-mediated interactions between two tandem propulsors, including vortex–vortex and vortex–body interactions. Two tandem flexible propulsors paddling with identical amplitude and frequency produced stable configurations as a result of the flow-mediated interactions. Both the upstream and downstream propulsors benefited from the tandem configuration in terms of the locomotion velocity and the cost, compared with an isolated propulsion system. The interactions were examined as a function of the initial gap distance and the phase difference in the paddling frequency. The equilibrium gap distance between two propulsors remained constant, regardless of the initial gap distance, although it did depend on the phase difference in the paddling frequency.

Constructive and destructive interaction modes between two tandem flexible flags in viscous flow

2010 ◽  
Vol 661 ◽  
pp. 511-521 ◽  
Author(s):  
SOHAE KIM ◽  
WEI-XI HUANG ◽  
HYUNG JIN SUNG
Keyword(s):  
Numerical Simulation ◽  
Viscous Flow ◽  
Drag Force ◽  
Immersed Boundary Method ◽  
Reynolds Numbers ◽  
Immersed Boundary ◽  
Flexible Body ◽  
Boundary Method

Two tandem flexible flags in viscous flow were modelled by numerical simulation using an improved version of the immersed boundary method. The flexible flapping flag and the vortices produced by an upstream flag were found to interact via either a constructive or destructive mode. These interaction modes gave rise to significant differences in the drag force acting on the downstream flapping flag in viscous flow. The constructive mode increased the drag force, while the destructive mode decreased the drag force. Drag on the downstream flexible body was investigated as a function of the streamwise and spanwise gap distances, and the bending coefficient of the flexible flags at intermediate Reynolds numbers (200 ≤ Re ≤ 400).

Hydrodynamics of flexible fins propelled in tandem, diagonal, triangular and diamond configurations

2018 ◽  
Vol 840 ◽  
pp. 154-189 ◽  
Author(s):  
Sung Goon Park ◽  
Hyung Jin Sung
Keyword(s):  
Immersed Boundary Method ◽  
Leading Edge ◽  
Input Power ◽  
Immersed Boundary ◽  
Diamond Formation ◽  
Propulsive Efficiency ◽  
Fish Schools ◽  
Fluid Environment ◽  
Dimensional Simulation ◽  
Surrounding Fluid

A fish may gain hydrodynamic benefits from being a member of a school. Inspired by fish schools, a two-dimensional simulation was performed for flexible fins propelled in tandem, diagonal, triangular and diamond configurations. The flow-mediated interactions between the flexible fins were analysed by using an immersed boundary method. A transverse heaving motion was prescribed on the leading edge of each fin, and other posterior parts passively adapted to the surrounding fluid as a result of the fluid–flexible-body interaction. The flexible fins were allowed to actively adjust their relative positions in the horizontal direction. The four basic stable configurations are spontaneously formed and self-sustained purely by the vortex–vortex and vortex–body interactions. The hydrodynamic benefits depend greatly on the local positions of the members. For the same heaving motion prescribed on the leading edge, the input power of the following fin in the stable tandem and diagonal configurations is lower by 14 % and 6 %, respectively, than that of the leading fin. The following fin in the diagonal formation can keep pace with the leading fin even for reduced heaving amplitudes because of the help of the leader via their shared fluid environment, where its required input power is reduced by 21 %. The heaving amplitudes of the trailing fins are reduced to optimize the propulsive efficiency, and the average efficiencies in the triangular and diamond configurations increase by up to 14 % and 19 %, respectively, over that of the isolated swimmer. The propulsive efficiencies are enhanced by 22 % for the fins in the second row and by 36 % for the fin in the third row by decreasing the heaving amplitude in the diamond formation.

Particle impaction on a cylinder in a crossflow as function of Stokes and Reynolds numbers

2010 ◽  
Vol 661 ◽  
pp. 239-261 ◽  
Author(s):  
NILS ERLAND L. HAUGEN ◽  
STEINAR KRAGSET
Keyword(s):  
Reynolds Number ◽  
Immersed Boundary Method ◽  
Reynolds Numbers ◽  
Stokes Number ◽  
High Order ◽  
Immersed Boundary ◽  
Back Side ◽  
Front Side ◽  
Viscous Boundary Layer ◽  
Boundary Method

A high-order direct numerical simulation code (The Pencil Code) has been used together with the immersed boundary method on a Cartesian grid to simulate particle impaction on a cylinder in a crossflow. The direct numerical scheme concerns only the fluid flow, into which the particles are subsequently coupled through a one-way drag-coefficient law. The immersed boundary method is extended to work with high-order discretization, and the particle impaction efficiency has been measured for Stokes numbers ranging from 0.001 to 40 for a range of different Reynolds numbers. Three modes of impaction on the front side of the cylinder are identified, where, for the large-Stokes-number mode (St > 0.3), an alternative to the traditional Stokes number is presented that provides better scaling. The intermediate impaction mode has a very steep decrease in impaction efficiency as the Stokes number is decreased, and this is identified as the range of Stokes numbers where the viscous boundary layer starts to take effect. The third mode of front-side impaction is for the very small particles with St < 0.1 exactly following the flow but impacting on the cylinder due to their finite radii. There will not be any capture on the front side of the cylinder for impact angles larger than ~56° for this mode. Finally, it is found that the particle impaction on the back side of the cylinder is strongly dependent on the flow Reynolds number, where large Reynolds numbers lead to larger impaction efficiencies. The upper limiting Stokes number of back-side impaction is around 0.13, apparently irrespective of the Reynolds number.

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