scholarly journals Droplets in turbulence: a new perspective

2017 ◽  
Vol 816 ◽  
pp. 1-4 ◽  
Author(s):  
Martin R. Maxey
Keyword(s):  
Kinetic Energy ◽  
Surface Energy ◽  
Olive Oil ◽  
Immiscible Liquid ◽  
Direct Numerical Simulations ◽  
Carrier Fluid ◽  
Two Fluids ◽  
Interfacial Surface ◽  
New Perspective ◽  
Shape And Size

Stirring olive oil and vinegar to make salad dressing creates an emulsion of vinegar droplets in oil. More vigorous stirring gives smaller droplets, while if left to sit the droplets will begin to coalesce and the two fluids will separate. In this vein, Dodd & Ferrante (J. Fluid Mech., vol. 806, 2016, pp. 356–412) present a new analysis of how homogeneous turbulence in a carrier fluid interacts with a suspension of droplets of an immiscible liquid. Based on a set of direct numerical simulations, the authors provide new insights on how turbulence affects the motion of the droplets, their shape and size; then in turn how the droplets alter the flow including effects of interfacial surface energy on the kinetic energy of the flow.

Mathematical modeling of steady stratified flows

2003 ◽  
Vol 3 ◽  
pp. 195-207
Author(s):  
A.M. Ilyasov ◽  
V.N. Kireev ◽  
S.F. Urmancheev ◽  
I.Sh. Akhatov
Keyword(s):  
Stokes Equations ◽  
Approximate Model ◽  
Immiscible Liquid ◽  
Stratified Flows ◽  
Navier Stokes ◽  
Flat Channel ◽  
Navier Stokes Equations ◽  
Two Fluids ◽  
Flow Parameters ◽  
Direct Numerical Solution

The work is devoted to the analysis of the flow of immiscible liquid in a flat channel and the creation of calculation schemes for determining the flow parameters. A critical analysis of the well-known Two Fluids Model was carried out and a new scheme for the determination of wall and interfacial friction, called the hydraulic approximation in the theory of stratified flows, was proposed. Verification of the proposed approximate model was carried out on the basis of a direct numerical solution of the Navier–Stokes equations for each fluid by a finite-difference method with phase-boundary tracking by the VOF (Volume of Fluid) method. The graphical dependencies illustrating the change in the interfase boundaries of liquids and the averaged over the occupied area of the phase velocities along the flat channel are presented. The results of comparative calculations for two-fluid models are also given, according to the developed model in the hydraulic approximation and direct modeling. It is shown that the calculations in accordance with the hydraulic approximation are more consistent with the simulation results. Thus, the model of hydraulic approximation is the most preferred method for calculating stratified flows, especially in cases of variable volumetric content of liquids.

Particle Transport Coefficient (PTC) and Phase-Efficiency Diagram: A New Perspective to Evaluate Three-Phase Particle-Laden Flow

2020 ◽  
Author(s):  
Zhifeng Zhang ◽  
Antoine Jean-Claude Jacques Pruvot ◽  
Pablo Cisternas ◽  
James McAndrew
Keyword(s):  
Particle Transport ◽  
Transport Coefficient ◽  
Vertical Direction ◽  
Environmental Cost ◽  
Mathematical Form ◽  
Horizontal Pipe ◽  
Carrier Fluid ◽  
Transport Efficiency ◽  
Three Phase ◽  
New Perspective

Abstract Many technologies have been developed to improve the ability of fluids to transport particles. However, the evaluation of particle transport efficiency remains challenging, especially in complex flow such as three-phase flow. In the present research, theoretical and experimental work is conducted to develop a new perspective of evaluating particle transport technologies, particle transport coefficient (PTC) as the particle transport distance per unit volume of water consumption considering the transport efficiency and environmental cost. The mathematical form of the PTC for the steady-state transport case is derived, followed by three special transport cases: (a) PTC = 0 when particle settled or stuck, (b) PTC = infinity in the vertical direction, considering gravity or buoyant with carrier fluid stationary, while PTC = 0 in a horizontal pipe due to particle settlement; and (c) PTC = 2 for an infinitely small particle at the center of a fully-developed laminar flow in a pipe. Furthermore, the fluid property and surface property influence on PTC are experimentally demonstrated. We believe the proposed approach can promote the development of particle transport technologies.

Interphasial energy transfer and particle dissipation in particle-laden wall turbulence

2013 ◽  
Vol 715 ◽  
pp. 32-59 ◽  
Author(s):  
Lihao Zhao ◽  
Helge I. Andersson ◽  
Jurriaan J. J. Gillissen
Keyword(s):  
Energy Transfer ◽  
Kinetic Energy ◽  
Stokes Equations ◽  
Mechanical Energy ◽  
Wall Turbulence ◽  
Spherical Particles ◽  
Velocity Versus ◽  
Wall Region ◽  
Carrier Fluid ◽  
Stokes Force

AbstractTransfer of mechanical energy between solid spherical particles and a Newtonian carrier fluid has been explored in two-way coupled direct numerical simulations of turbulent channel flow. The inertial particles have been treated as individual point particles in a Lagrangian framework and their feedback on the fluid phase has been incorporated in the Navier–Stokes equations. At sufficiently large particle response times the Reynolds shear stress and the turbulence intensities in the spanwise and wall-normal directions were attenuated whereas the velocity fluctuations were augmented in the streamwise direction. The physical mechanisms involved in the particle–fluid interactions were analysed in detail, and it was observed that the fluid transferred energy to the particles in the core region of the channel whereas the fluid received kinetic energy from the particles in the wall region. A local imbalance in the work performed by the particles on the fluid and the work exerted by the fluid on the particles was observed. This imbalance gave rise to a particle-induced energy dissipation which represents a loss of mechanical energy from the fluid–particle suspension. An independent examination of the work associated with the different directional components of the Stokes force revealed that the dominating energy transfer was associated with the streamwise component. Both the mean and fluctuating parts of the Stokes force promoted streamwise fluctuations in the near-wall region. The kinetic energy associated with the cross-sectional velocity components was damped due to work done by the particles, and the energy was dissipated rather than recovered as particle kinetic energy. Componentwise scatter plots of the instantaneous velocity versus the instantaneous slip-velocity provided further insight into the energy transfer mechanisms, and the observed modulations of the flow field could thereby be explained.

scholarly journals Partitioning Waves and Eddies in Stably Stratified Turbulence

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 420 ◽  
Author(s):  
Henri Lam ◽  
Alexandre Delache ◽  
Fabien S Godeferd
Keyword(s):  
Dispersion Relation ◽  
Kinetic Energy ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Direct Numerical Simulations ◽  
Energy Concentration ◽  
Kinetic Energy Density ◽  
Stratified Turbulence ◽  
The Waves

We consider the separation of motion related to internal gravity waves and eddy dynamics in stably stratified flows obtained by direct numerical simulations. The waves’ dispersion relation links their angle of propagation to the vertical θ , to their frequency ω , so that two methods are used for characterizing wave-related motion: (a) the concentration of kinetic energy density in the ( θ , ω ) map along the dispersion relation curve; and (b) a direct computation of two-point two-time velocity correlations via a four-dimensional Fourier transform, permitting to extract wave-related space-time coherence. The second method is more computationally demanding than the first. In canonical flows with linear kinematics produced by space-localized harmonic forcing, we observe the pattern of the waves in physical space and the corresponding concentration curve of energy in the ( θ , ω ) plane. We show from a simple laminar flow that the curve characterizing the presence of waves is distorted differently in the presence of a background convective mean velocity, either uniform or varying in space, and also when the forcing source is moving. By generalizing the observation from laminar flow to turbulent flow, this permits categorizing the energy concentration pattern of the waves in complex flows, thus enabling the identification of wave-related motion in a general turbulent flow with stable stratification. The advanced method (b) is finally used to compute the wave-eddy partition in the velocity–buoyancy fields of direct numerical simulations of stably stratified turbulence. In particular, we use this splitting in statistics as varied as horizontal and vertical kinetic energy, as well as two-point velocity and buoyancy spectra.

K–ϵ model for rotating homogeneous decaying turbulence

2016 ◽  
Vol 94 (11) ◽  
pp. 1200-1204 ◽  
Author(s):  
Hamed Marzougui
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Decay Rate ◽  
Rate Equation ◽  
Rotation Rate ◽  
Dissipation Rate ◽  
Direct Numerical Simulations ◽  
Uniform Rotation ◽  
Axis Of Rotation ◽  
Decaying Turbulence

In the present work, we propose a modification to the standard K–ϵ model for simulating homogeneous decaying turbulence subjected to uniform rotation. In this modification, the dissipation rate equation is formulated in terms of the rotation rate Ω, the integral length scales along the axis of rotation [Formula: see text], and its isotropic value [Formula: see text]. The comparison of our results with the corresponding direct numerical simulations proves that the new model reproduces in an excellent way the decay rate of the turbulent kinetic energy.

Parametric Analysis of Microdroplet Formation in Co-Axial Co-Flowing Immiscible Liquids in Microtubes

2011 ◽  
Author(s):  
In-Hwan Yang ◽  
Mohamed S. El-Genk
Keyword(s):  
Finite Element Method ◽  
Surface Tension ◽  
Parametric Analysis ◽  
Jump Condition ◽  
Reynolds Numbers ◽  
Immiscible Liquid ◽  
Liquid Droplets ◽  
Immiscible Liquids ◽  
Interfacial Surface ◽  
Disperse Liquid

This paper presents numerical results of disperse liquid droplets forming in the dripping regime at the tip of a microtube into another co-flowing immiscible liquid in a coaxial microtube of larger diameter. Investigated are the effects of the interfacial surface tension, velocities and viscosities of the liquids and the diameters of the coaxial microtubes on the forming dynamics and the size of the droplet. The 2-D, transient Navier-Stockes equations, in conjunction with the momentum jump condition across the interface between the co-flowing liquids are solved using a finite element method. The solution tracks the interface and the growth of the droplet and predicts droplet size and forming frequency. The droplet’s dimensionless radius (rd*) is correlated within ± 10% in terms of the continuous liquid capillary number (Cac) and ratios of Reynolds numbers (Red/Rec) and microtube radii (Rc/Rd) of the co-flowing liquids as: rd*=0.225R*0.466/(Cac0.5)(Red/Rec).0.05

scholarly journals Experimental investigation into inertial properties of Rayleigh–Taylor turbulence

1997 ◽  
Vol 15 (1) ◽  
pp. 25-31 ◽  
Author(s):  
Yu.A. Kucherenko ◽  
S.I. Balabin ◽  
R. Cherret ◽  
J.F. Haas
Keyword(s):  
Experimental Investigation ◽  
Kinetic Energy ◽  
Turbulent Mixing ◽  
Average Density ◽  
Taylor Instability ◽  
X Ray ◽  
Two Fluids ◽  
Time Space ◽  
Rayleigh Taylor Instability ◽  
Region Size

An experimental investigation into inertial properties of the developed Rayleigh–Taylor instability with the different initial values of the kinetic energy of turbulence has been performed. The experiments were performed by using two fluids having different densities with density ration n = 3. Fluids were placed in an ampoule. At the unstable stage of motion, the ampoule was moving under an acceleration. At a certain instant of time the acceleration was removed and the ampoule moved under the force of inertia. By means of pulsed X-ray photography, the mixing region size and the time-space distributionof the average density of matter in the turbulent mixing region have been determined at different instants of time. The time-space distributions are compared with those obtained by semiempirical theories of mixing.

Stress Field Near a Nanosized Spheroidal Cavity under Bi-Axial Tension Perpendicular to the Revolution Axis

2008 ◽  
Vol 33-37 ◽  
pp. 1005-1010
Author(s):  
Zhi Ying Ou ◽  
Gang Feng Wang ◽  
Tie Jun Wang
Keyword(s):  
Surface Energy ◽  
Stress Field ◽  
Elasticity Theory ◽  
Surface Elasticity ◽  
Elastic Field ◽  
Classical Elasticity ◽  
Axial Tension ◽  
Spheroidal Cavity ◽  
Shape And Size ◽  
The Revolution

The elastic field around a nanosized spheroidal cavity is derived on the basis of surface elasticity theory. The effects of surface energy, shape and size of the cavity are discussed. It is seen that the stress field near the nanosized cavity depends on the shape and the size of the cavity as well as the properties of the surface. These new characteristics are different from those predicted by the classical elasticity and may illuminate some new mechanisms at nanoscale.

Turbulent/non-turbulent interfaces in wakes in stably stratified fluids

2016 ◽  
Vol 797 ◽  
Author(s):  
Tomoaki Watanabe ◽  
James J. Riley ◽  
Stephen M. de Bruyn Kops ◽  
Peter J. Diamessis ◽  
Qi Zhou
Keyword(s):  
Reynolds Number ◽  
Energy Dissipation ◽  
Kinetic Energy ◽  
Internal Wave ◽  
Stable Stratification ◽  
Direct Numerical Simulations ◽  
Wave Radiation ◽  
Kolmogorov Scale ◽  
Conditional Averaging ◽  
Quantities Of Interest

We report on a study, employing direct numerical simulations, of the turbulent/non-turbulent interface of a wake in a stably stratified fluid. It is found that thresholds for both enstrophy and potential enstrophy are needed to identify the interface. Using conditional averaging relative to the location of the interface, various quantities of interest are examined. The thickness of the interface is found to scale with the Kolmogorov scale. From an examination of the Ozmidov and Kolmogorov length scales as well as the buoyancy Reynolds number, it is found that the buoyancy Reynolds number decreases and becomes of order 1 near the interface, indicating the suppression of the turbulence there by the stable stratification. Finally the overall rate of loss of energy due to internal wave radiation is found to be comparable to the overall rate of loss due to turbulent kinetic energy dissipation.

The Physical Essence of Mono-dispersed Nanometer Particle Surface Energy by Boundary bond Interaction

2013 ◽  
Vol 1505 ◽  
Author(s):  
Lihong Su ◽  
Xiaowei Yin ◽  
Caixia Wan ◽  
Shengru Qiao
Keyword(s):  
Surface Energy ◽  
Standing Wave ◽  
Critical Size ◽  
Particle Surface ◽  
Traditional Theory ◽  
Cutting Surface ◽  
Interfacial Surface ◽  
Nanometer Material ◽  
Nanometer Powder ◽  
Nanometer Particle

ABSTRACTThe surface energy quantifies the disruption of intermolecular bond that occurs when a surface is created. The paper discusses critical size dc of mono-dispersed nanometer particle by analyzing the change of interfacial surface energy. The traditional theory neglects that the mono-dispersed nanometer particle has quantum standing wave in its internal structure with a size below critical dc. During the preparation of mono-dispersed nanometer powder, the large surface energy is formed ont only by cutting surface bond but also by forming quantum standing wave that opposites to interfacial edge unsaturated bond on the nanometer partcile surface atom. The preparation process of nanometer material needs more energy than the size surpass dc material. The new theory can explain why the melting point of nanometer powder decreases and other phenomina of nanometer material.

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