scholarly journals Contactless generation and trapping of hydrodynamic knots in sessile droplets by acoustic screw dislocations

2021 ◽  
Author(s):  
Shuren Song ◽  
Jia Zhou ◽  
Antoine Riaud ◽  
Antonino Marciano
Keyword(s):  
Screw Dislocation ◽  
Turbulent Flows ◽  
Particle Physics ◽  
Acoustic Streaming ◽  
Experimental Studies ◽  
Three Dimensional ◽  
External Boundary ◽  
Sessile Droplet ◽  
Three Dimensional Flow ◽  
Flow Evolution

Abstract Hydrodynamics knots are not only promising elementary structures to study mass and momentum transfer in turbulent flows, but also potent analogs for other topological problems arising in particle physics. However, experimental studies of knots are highly challenging due to the limited control over knot generation and difficult observation of the resulting fast-paced multiscale flow evolution. In this paper, we propose using acoustic streaming to tie hydrodynamic knots in fluids. The method is contactless, almost instantaneous and is relatively insensitive to viscosity. Importantly, it allows starting from quite arbitrary three dimensional flow structures without relying on external boundary conditions. We demonstrate our approach by using an acoustic screw dislocation to tie a knot in a sessile droplet. We observe an inversion of the knot chirality (measured by the hydrodynamic helicity) as the topological charge of the screw dislocation is increased. Combined with recent progress in acoustic field synthesis, this work opens a window to study more complex hydrodynamic knot topologies at a broader range of space and timescales.

PREDICTION OF UNSTEADY STATES IN LID-DRIVEN CAVITIES FILLED WITH AN INCOMPRESSIBLE VISCOUS FLUID

2012 ◽  
Vol 23 (04) ◽  
pp. 1250030 ◽  
Author(s):  
FAYÇAL HAMMAMI ◽  
NADER BEN-CHEIKH ◽  
ANTONIO CAMPO ◽  
BRAHIM BEN-BEYA ◽  
TAIEB LILI
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Three Dimensional ◽  
Staggered Grid ◽  
Three Dimensional Flow ◽  
Driven Cavity ◽  
Flow Evolution ◽  
2D And 3D ◽  
Benchmark Solutions ◽  
Good Agreement

In this work, a numerical study devoted to the two-dimensional and three-dimensional flow of a viscous, incompressible fluid inside a lid-driven cavity is undertaking. All transport equations are solved using the finite volume formulation on a staggered grid system and multi-grid acceleration. Quantitative aspects of two and three-dimensional flows in a lid-driven cavity for Reynolds number Re = 1000 show good agreement with benchmark results. An analysis of the flow evolution demonstrates that, with increments in Re beyond a certain critical value Rec, the steady flow becomes unstable and bifurcates into unsteady flow. It is observed that the transition from steadiness to unsteadiness follows the classical Hopf bifurcation. The time-dependent velocity distribution is studied in detail and the critical Reynolds number is localized for both 2D and 3D cases. Benchmark solutions for 2D and 3D lid-driven cavity flows are performed for Re = 1500 and 6000.

Numerical and Experimental Investigation of Secondary Flow in a High Speed Compressor Stator

1995 ◽  
Author(s):  
Y. Ohkita ◽  
H. Kodama ◽  
O. Nozaki ◽  
K. Kikuchi ◽  
A. Tamura
Keyword(s):  
Numerical Simulation ◽  
Experimental Investigation ◽  
Shear Flow ◽  
Secondary Flow ◽  
Total Pressure ◽  
High Speed ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Performance Recovery

A series of numerical and experimental studies have been conducted to understand the mechanism of loss generation in a high speed compressor stator with inlet radial shear flow over the span. In this study, numerical simulation is extensively used to investigate the complex three-dimensional flow in the cascades and to interpret the phenomena appeared in the high speed compressor tests. It has been shown that the inlet radial shear flow generated by upstream rotor had a significant influence on the stator secondary flow, and consequently on the total pressure loss. Redesign of the stator aiming at the reduction of loss by controlling secondary flow has been carried out and the resultant performance recovery was successfully demonstrated both numerically and experimentally.

scholarly journals MEASURING INFLUENCE OF DYNAMIC CHARACTERISTICS OF MIXERS ON STRUCTURAL AND MECHANICAL PROPERTIES OF MINCED FISH

2020 ◽  
Vol 0 (1) ◽  
pp. 138-144
Author(s):  
Viktor Vladimirovich Kogan
Keyword(s):  
Mechanical Properties ◽  
Dynamic Characteristics ◽  
Raw Materials ◽  
Structural Characteristics ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Angular Speed ◽  
Three Dimensional Flow ◽  
Minced Fish ◽  
The Relationship

The article presents the empirical results of estimating the dependence of viscoplastic properties of the minced ordinary fish raw materials from the kinematic and dynamic characteristics of mechanisms applied in the course of processing. When mixed in mechanical mixers, minced fish is subjected to shear and normal effects of rotating parts that create a complex three-dimensional flow. Optimization of the process of obtaining viscous-plastic culinary products depends on the dynamics of movement of the studied objects and the influence of working parts of various configurations. To establish the relationship between the duration of mixing, the angular speed of rotation of the working part of the horizontal mixer and general structural and mechanical properties of minced fish, there were carried out experimental studies using various types of mixer working parts: conveyer, screw and blade. The influence of the rotation speed of the mixer working part on the change in the rheological characteristics of the investigated raw materials has been confirmed. Specific energy costs should be emphasized as one of the main criteria for evaluating the performance of the supporting equipment. This parameter depends on redistribution of components during their mixing, changes in the structural and mechanical properties of minced fish and structural characteristics of the working parts. It has been stated that the lowest energy consumption and optimal mode for viscoplastic mixed mass can be achieved by using blades with an inclination angle to the axis of rotation = 20–30° and a humidity increase of mixed mass up to 0.7–0.8 kg/kg.

Numerical and Experimental Investigation of Secondary Flow in a High-Speed Compressor Stator

1997 ◽  
Vol 119 (2) ◽  
pp. 169-175
Author(s):  
Y. Ohkita ◽  
H. Kodama ◽  
O. Nozaki ◽  
K. Kikuchi ◽  
A. Tamura
Keyword(s):  
Numerical Simulation ◽  
Experimental Investigation ◽  
Shear Flow ◽  
Secondary Flow ◽  
Total Pressure ◽  
High Speed ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Performance Recovery

A series of numerical and experimental studies have been conducted to understand the mechanism of loss generation in a high-speed compressor stator with inlet radial shear flow over the span. In this study, numerical simulation is extensively used to investigate the complex three-dimensional flow in the cascades and to interpret the phenomena that appeared in the high-speed compressor tests. It has been shown that the inlet radial shear flow generated by the upstream rotor had a significant influence on the stator secondary flow, and consequently on the total pressure loss. Redesign of the stator aiming at the reduction of loss by controlling secondary flow has been carried out and the resultant performance recovery was successfully demonstrated both numerically and experimentally.

PSL—An Economical Approach to the Numerical Analysis of Near-Wall, Elliptic Flow

1984 ◽  
Vol 106 (2) ◽  
pp. 241-242 ◽  
Author(s):  
H. Iacovides ◽  
B. E. Launder
Keyword(s):  
Numerical Analysis ◽  
Numerical Computation ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Elliptic Flow ◽  
Computational Time ◽  
Three Dimensional Flow ◽  
Fine Grid ◽  
Dimensional Flow ◽  
Grid Analysis

The paper points out that, in the numerical computation of elliptic or three-dimensional turbulent flows, the neglect of pressure-variations across the very thin viscosity affected region near the wall allows a fine-grid analysis of this sublayer without prohibitive penalties in core or computational time. The scheme has been successfully applied to the three-dimensional flow around a U-bend.

scholarly journals Span effect on the turbulence nature of flow past a circular cylinder

2019 ◽  
Vol 878 ◽  
pp. 306-323 ◽  
Author(s):  
Bernat Font Garcia ◽  
Gabriel D. Weymouth ◽  
Vinh-Tan Nguyen ◽  
Owen R. Tutty
Keyword(s):  
Circular Cylinder ◽  
Turbulent Flows ◽  
Large Scale ◽  
Three Dimensional ◽  
Small Scale ◽  
Flow Past ◽  
Energy Cascades ◽  
Flow Evolution ◽  
Scale Structures ◽  
Small Scale Structures

Turbulent flow evolution and energy cascades are significantly different in two-dimensional (2-D) and three-dimensional (3-D) flows. Studies have investigated these differences in obstacle-free turbulent flows, but solid boundaries have an important impact on the cross-over from 3-D to 2-D turbulence dynamics. In this work, we investigate the span effect on the turbulence nature of flow past a circular cylinder at $Re=10\,000$. It is found that even for highly anisotropic geometries, 3-D small-scale structures detach from the walls. Additionally, the natural large-scale rotation of the Kármán vortices rapidly two-dimensionalise those structures if the span is 50 % of the diameter or less. We show this is linked to the span being shorter than the Mode B instability wavelength. The conflicting 3-D small-scale structures and 2-D Kármán vortices result in 2-D and 3-D turbulence dynamics which can coexist at certain locations of the wake depending on the domain geometric anisotropy.

Experimental studies of a distorted turbulent spot in a three-dimensional flow

1996 ◽  
Vol 329 ◽  
pp. 1-24 ◽  
Author(s):  
M. Jahanmiri ◽  
A. Prabhu ◽  
R. Narasimha
Keyword(s):  
Experimental Studies ◽  
Three Dimensional ◽  
Turbulent Spot ◽  
Three Dimensional Flow ◽  
Streamline Curvature ◽  
Trailing Edges ◽  
Series Of Experiments ◽  
Tollmien Schlichting ◽  
Wing Tips ◽  
Made In

We report here on the results of a series of experiments carried out on a turbulent spot in a distorted duct to study the effects of a divergence with straight streamlines preceded by a short stretch of transverse streamline curvature, both in the absence of any pressure gradient. It is found that the distortion produces substantial asymmetry in the spot: the angles at which the spot cuts across the local streamlines are altered dramatically (in contradiction of a hypothesis commonly made in transition zone modelling), and the Tollmien–Schlichting waves that accompany the wing tips of the spot are much stronger on the outside of the bend than on the inside. However there is no strong effect on the internal structure of the spot and the eddies therein, or on such propagation characteristics as overall spread rate and the celerities of the leading and trailing edges. Both lateral streamline curvature and non-homogeneity of the laminar boundary layer into which the spot propagates are shown to be strong factors responsible for the observed asymmetry. It is concluded that these factors produce chiefly a geometric distortion of the coherent structure in the spot, but do not otherwise affect its dynamics in any significant way.

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