scholarly journals Flow Direction-Dependent Elastic Instability in a Symmetry-Breaking Microchannel

Micromachines ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1139
Author(s):  
Wu Zhang ◽  
Zihuang Wang ◽  
Meng Zhang ◽  
Jiahan Lin ◽  
Weiqian Chen ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Flow Direction ◽  
Weissenberg Number ◽  
Viscoelastic Flow ◽  
Elastic Instability ◽  
Directed Flow ◽  
Polyacrylamide Solution ◽  
Nozzle Structure

This paper reports flow direction-dependent elastic instability in a symmetry-breaking microchannel. The microchannel consisted of a square chamber and a nozzle structure. A viscoelastic polyacrylamide solution was used for the instability demonstration. The instability was realized as the viscoelastic flow became asymmetric and unsteady in the microchannel when the flow exceeded a critical Weissenberg number. The critical Weissenberg number was found to be different for the forward-directed flow and the backward-directed flow in the microchannel.

scholarly journals Upstream vortex and elastic wave in the viscoelastic flow around a confined cylinder

2019 ◽  
Vol 864 ◽  
Author(s):  
Boyang Qin ◽  
Paul F. Salipante ◽  
Steven D. Hudson ◽  
Paulo E. Arratia
Keyword(s):  
Elastic Wave ◽  
Wave Speed ◽  
Three Dimensional ◽  
Weissenberg Number ◽  
Viscoelastic Flow ◽  
Absolute Instability ◽  
Elastic Instability ◽  
Cylinder Wake ◽  
Cylinder Axis ◽  
Flow Past A Cylinder

Viscoelastic flow past a cylinder is a classic benchmark problem that is not completely understood. Using novel three-dimensional (3D) holographic particle velocimetry, we report three main discoveries of the elastic instability upstream of a single cylinder in viscoelastic channel flow. First, we observe that upstream vortices initiate at the corner between the cylinder and the wall, and grow with increasing flow rate. Second, beyond a critical Weissenberg number, the flow upstream becomes unsteady and switches between two bistable configurations, leading to symmetry breaking in the cylinder axis direction that is highly 3D in nature. Lastly, we find that the disturbance of the elastic instability propagates relatively far upstream via an elastic wave, and is weakly correlated with that in the cylinder wake. The wave speed and the extent of the instability increase with Weissenberg number, indicating an absolute instability in viscoelastic fluids.

scholarly journals Elastic-instability–enabled locomotion

2021 ◽  
Vol 118 (8) ◽  
pp. e2013801118
Author(s):  
Amit Nagarkar ◽  
Won-Kyu Lee ◽  
Daniel J. Preston ◽  
Markus P. Nemitz ◽  
Nan-Nan Deng ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Scaling Laws ◽  
Multiple Scales ◽  
Symmetric Cone ◽  
Simple Approach ◽  
Inertial Forces ◽  
Elastic Instability ◽  
Anisotropic Friction ◽  
Buckling Instability ◽  
Elastic Instabilities

Locomotion of an organism interacting with an environment is the consequence of a symmetry-breaking action in space-time. Here we show a minimal instantiation of this principle using a thin circular sheet, actuated symmetrically by a pneumatic source, using pressure to change shape nonlinearly via a spontaneous buckling instability. This leads to a polarized, bilaterally symmetric cone that can walk on land and swim in water. In either mode of locomotion, the emergence of shape asymmetry in the sheet leads to an asymmetric interaction with the environment that generates movement––via anisotropic friction on land, and via directed inertial forces in water. Scaling laws for the speed of the sheet of the actuator as a function of its size, shape, and the frequency of actuation are consistent with our observations. The presence of easily controllable reversible modes of buckling deformation further allows for a change in the direction of locomotion in open arenas and the ability to squeeze through confined environments––both of which we demonstrate using simple experiments. Our simple approach of harnessing elastic instabilities in soft structures to drive locomotion enables the design of novel shape-changing robots and other bioinspired machines at multiple scales.

The Mechanism of Size-Based Particle Separation by Dielectrophoresis in the Viscoelastic Flows

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Teng Zhou ◽  
Yongbo Deng ◽  
Hongwei Zhao ◽  
Xianman Zhang ◽  
Liuyong Shi ◽  
...  
Keyword(s):  
Electric Field ◽  
Newtonian Fluid ◽  
Finite Size ◽  
Particle Separation ◽  
Weissenberg Number ◽  
Viscoelastic Flow ◽  
Viscoelastic Flows ◽  
Arbitrary Lagrangian Eulerian ◽  
Particle Movement ◽  
Physical Insight

Viscoelastic solution is encountered extensively in microfluidics. In this work, the particle movement of the viscoelastic flow in the contraction–expansion channel is demonstrated. The fluid is described by the Oldroyd-B model, and the particle is driven by dielectrophoretic (DEP) forces induced by the applied electric field. A time-dependent multiphysics numerical model with the thin electric double layer (EDL) assumption was developed, in which the Oldroyd-B viscoelastic fluid flow field, the electric field, and the movement of finite-size particles are solved simultaneously by an arbitrary Lagrangian–Eulerian (ALE) numerical method. By the numerically validated ALE method, the trajectories of particle with different sizes were obtained for the fluid with the Weissenberg number (Wi) of 1 and 0, which can be regarded as the Newtonian fluid. The trajectory in the Oldroyd-B flow with Wi = 1 is compared with that in the Newtonian fluid. Also, trajectories for different particles with different particle sizes moving in the flow with Wi = 1 are compared, which proves that the contraction–expansion channel can also be used for particle separation in the viscoelastic flow. The above results for this work provide the physical insight into the particle movement in the flow of viscous and elastic features.

Experimental Investigation of Fluid-Elastic Vibration of Square Array Tube Bundle in Two Phase Flow

2019 ◽  
Author(s):  
Ryoichi Kawakami ◽  
Seinosuke Azuma ◽  
Toshifumi Nariai ◽  
Kazuo Hirota ◽  
Hideyuki Morita ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Tube Bundle ◽  
Flow Direction ◽  
Phase Flow ◽  
Elastic Instability ◽  
Steam Generators ◽  
Two Phase ◽  
Critical Flow Velocity ◽  
Tube Bundles ◽  
Square Array

Abstract The in-plane (in-flow) fluid-elastic instability (in-plane FEI) of triangular tube arrays caused tube-to-tube wear indications as observed in the U-bend regions of tube bundles of the San Onofre Unit-3 steam generators[1]. Several researches revealed that the in-plane FEI is likely to occur in a tightly packed triangular tube array under high velocity and low friction conditions, while it is not likely to occur in a square array tube bundle. In order to confirm the potential of steam-wise fluid-elastic instability of square arrays, the critical flow velocity in two-phase flow, (sulfur hexafluoride-ethanol) which simulates steam-water flow, was investigated. Two types of test rigs were prepared to confirm the effect of the tube diameter and tube pitch ratio on the critical velocity. In both rigs, vibration amplitudes were measured in both in-flow and out-of-flow directions in various flow conditions. In any case, in-flow fluid elastic instability was not detected. Based on the results of the tests, it is concluded that the flow interaction force is small for concern to occur the fluid-elastic instability in the in-flow direction of the square tube bundles of steam generators.

Effect of chain scission on flow characteristics of wormlike micellar solutions past a confined microfluidic cylinder: a numerical analysis

Soft Matter ◽  
2020 ◽  
Vol 16 (22) ◽  
pp. 5261-5272 ◽  
Author(s):  
Mohd Bilal Khan ◽  
C. Sasmal
Keyword(s):  
Numerical Analysis ◽  
Elastic Wave ◽  
Micellar Solution ◽  
Flow Characteristics ◽  
Chain Scission ◽  
Critical Value ◽  
Weissenberg Number ◽  
Elastic Instability ◽  
Micellar Solutions ◽  
Wave Phenomena

Elastic instability and elastic wave phenomena can be seen for the flow of a wormlike micellar solution past a confined microfluidic cylinder once the Weissenberg number exceeds a critical value.

scholarly journals A mechanism for oscillatory instability in viscoelastic cross-slot flow

2009 ◽  
Vol 622 ◽  
pp. 145-165 ◽  
Author(s):  
LI XI ◽  
MICHAEL D. GRAHAM
Keyword(s):  
Reynolds Number ◽  
Stagnation Point ◽  
Low Reynolds Number ◽  
Polymer Processing ◽  
Weissenberg Number ◽  
Polymer Chains ◽  
Oscillatory Instability ◽  
Viscoelastic Flow ◽  
Two Dimensional ◽  
Viscoelastic Liquids

Interior stagnation-point flows of viscoelastic liquids arise in a wide variety of applications including extensional viscometry, polymer processing and microfluidics. Experimentally, these flows have long been known to exhibit instabilities, but the mechanisms underlying them have not previously been elucidated. We computationally demonstrate the existence of a supercritical oscillatory instability of low-Reynolds-number viscoelastic flow in a two-dimensional cross-slot geometry. The fluctuations are closely associated with the ‘birefringent strand’ of highly stretched polymer chains associated with the outflow from the stagnation point at high Weissenberg number. Additionally, we describe the mechanism of instability, which arises from the coupling of flow with extensional stresses and their steep gradients in the stagnation-point region.

K-1210 Numerical Techniques Improving Convergence Behavior of Viscoelastic Flow Analysis at High Weissenberg Number

2001 ◽  
Vol II.01.1 (0) ◽  
pp. 83-84
Author(s):  
Ikuhisa GOTO ◽  
Tomomi HAYAKAWA ◽  
Hikaru WAKI ◽  
Shuichi IWATA ◽  
Hideki MORI ◽  
...  
Keyword(s):  
Flow Analysis ◽  
Weissenberg Number ◽  
Viscoelastic Flow ◽  
Numerical Techniques ◽  
Convergence Behavior

scholarly journals Flow-induced vibrations of a rotating cylinder

2014 ◽  
Vol 740 ◽  
pp. 342-380 ◽  
Author(s):  
Rémi Bourguet ◽  
David Lo Jacono
Keyword(s):  
Symmetry Breaking ◽  
Flow Direction ◽  
Cross Flow ◽  
Maximum Amplitude ◽  
Rotating Cylinder ◽  
Free Vibrations ◽  
Cylinder Surface ◽  
Single Vortex ◽  
Flow Induced Vibrations ◽  
The Impact

AbstractThe flow-induced vibrations of a circular cylinder, free to oscillate in the cross-flow direction and subjected to a forced rotation about its axis, are analysed by means of two- and three-dimensional numerical simulations. The impact of the symmetry breaking caused by the forced rotation on the vortex-induced vibration (VIV) mechanisms is investigated for a Reynolds number equal to $100$, based on the cylinder diameter and inflow velocity. The cylinder is found to oscillate freely up to a rotation rate (ratio between the cylinder surface and inflow velocities) close to $4$. Under forced rotation, the vibration amplitude exhibits a bell-shaped evolution as a function of the reduced velocity (inverse of the oscillator natural frequency) and reaches $1.9$ diameters, i.e. three times the maximum amplitude in the non-rotating case. The free vibrations of the rotating cylinder occur under a condition of wake–body synchronization similar to the lock-in condition driving non-rotating cylinder VIV. The largest vibration amplitudes are associated with a novel asymmetric wake pattern composed of a triplet of vortices and a single vortex shed per cycle, the ${\rm T} + {\rm S}$ pattern. In the low-frequency vibration regime, the flow exhibits another new topology, the U pattern, characterized by a transverse undulation of the spanwise vorticity layers without vortex detachment; consequently, free oscillations of the rotating cylinder may also develop in the absence of vortex shedding. The symmetry breaking due to the rotation is shown to directly impact the selection of the higher harmonics appearing in the fluid force spectra. The rotation also influences the mechanism of phasing between the force and the structural response.

Viscoelastic flow in an obstructed microchannel at high Weissenberg number

2016 ◽  
Vol 20 (7) ◽  
Author(s):  
Kevin P. Nolan ◽  
Akshat Agarwal ◽  
Shenghui Lei ◽  
Robin Shields
Keyword(s):  
Weissenberg Number ◽  
Viscoelastic Flow
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