Effects of Initial Perturbations in the Early Moments of an Explosive Dispersal of Particles

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Subramanian Annamalai ◽  
Bertrand Rollin ◽  
Frederick Ouellet ◽  
Christopher Neal ◽  
Thomas L. Jackson ◽  
...  
Keyword(s):  
Gas Phase ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
High Energy ◽  
Solid Particles ◽  
Dense Layer ◽  
Initial Particle ◽  
Particle Volume ◽  
Reactive Material ◽  
Explosive Dispersal

Recent experiments have shown that when a dense layer of solid particles surrounding a high-energy reactive material is explosively dispersed, the particles cluster locally leading to jetlike patterns. The formation of these coherent structures has yet to be fully understood and is believed to have its origin in the early moments of the explosive dispersal. This paper focuses on the early moments of an explosive dispersal of particles. In particular, the effect of initial perturbations on both the gas and particulate phase is investigated, considering heavy particles with a low initial particle volume fraction. Two-dimensional simulations are carried out, and results suggest that a distinctive heterogeneity in the form of a single wavelength perturbation in the rapidly expanding detonation products does not have a significant impact on the early evolution of neither the gas phase nor the cloud of particles. In contrast, the equivalent distinctive heterogeneity in the initial particle volume fraction distribution lingers for the duration of our simulations. Developing instabilities in the gas phase and at the inner- and outer-most front of the particle bed display a dominant wavelength equal to the wavelength of the initial perturbation in the particle volume fraction.

Early Time Evolution of Circumferential Perturbation of Initial Particle Volume Fraction in Explosive Cylindrical Multiphase Dispersion

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
M. Giselle Fernández-Godino ◽  
Frederick Ouellet ◽  
Raphael T. Haftka ◽  
S. Balachandar
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Early Time ◽  
High Energy ◽  
Initial Distribution ◽  
Solid Particles ◽  
Particle Migration ◽  
Two Dimensional ◽  
Initial Particle ◽  
Particle Volume

When an annular bed of solid particles that surrounds a cylindrical high-energy explosive core gets radially dispersed after detonation, the expanding front of particles undergoes instabilities. One of the possible causes of the instabilities is an inhomogeneous initial distribution of particles. This study explores this possibility by introducing two-dimensional perturbations to the initial distribution of particles within the annular bed and quantifying the growth of these perturbations over time using two-dimensional simulations. The initial perturbations are in the form of superposition of up to three sinusoidal azimuthal modal variations in the initial particle volume fraction (PVF, ratio of particle to cell volume). These are observed to impact the particle distribution at later times through a channeling instability whose effects are: (i) to decrease the velocity in regions of larger particle volume (PV) and (ii) to facilitate circumferential particle migration into the slow moving high PV sectors. These departures from axisymmetry are quantified by introducing two metrics. The effect of varying the number of azimuthal modes contained in the initial PVF perturbation, along with their amplitudes, wavelengths, and relative phases is investigated. The proposed metrics do not vary substantially with the relative phases; however, there is a strong variation in the metrics due to changes in the wavenumber. Unimodal perturbations were found to amplify both metrics the most.

Vortex Simulation for Behavior of Solid Particles Falling in Air

2011 ◽  
Author(s):  
Hisanori Yagami ◽  
Tomomi Uchiyama
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Air Flow ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Vortex Method ◽  
Solid Particles ◽  
Particle Volume ◽  
Two Phase ◽  
Spherical Region

The behavior of small solid particles falling in an unbounded air is simulated. The particles, initially arranged within a spherical region in a quiescent air, are made to fall, and their fall induces the air flow around them, resulting in the gas-particle two-phase flow. The particle diameter and density are 1 mm and 7.7 kg/m3 respectively. A three-dimensional vortex method proposed by one of the authors is applied. The simulation demonstrates that the particles are accelerated by the induced downward air flow just after the commencement of their fall. It also highlights that the particles are whirled up by a vortex ring produced around the downward air flow after the acceleration. The effect of the particle volume fraction at the commencement of the fall is also explored.

scholarly journals Parameters in Multiphase Flowing of Natural Gas NGH Slurry via Vertical Pipe

2016 ◽  
Vol 2016 ◽  
pp. 1-7
Author(s):  
Dai Maolin ◽  
Wu Kaisong
Keyword(s):  
Pressure Drop ◽  
Natural Gas ◽  
Simulation Model ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Solid Particles ◽  
Small Scale ◽  
Vertical Pipe ◽  
Particle Volume ◽  
The Relationship

In recent years, the pipeline flowing of natural gas hydrate (hereinafter NGH) slurry has been a promising technique of multiphase flowing via pipe and that of crushed hydrate mixture slurry is also a key technique in solid fluidization mining method of nondiagenetic NGH reservoir below the seabed. In this paper, by using similarity rules, a small-scale simulation model was established to shorten the calculation time. The correctness of the simulation model has been verified through comparison with experiment. Thereby, the distribution of velocity and volume fraction of each phase in the vertical pipe was obtained, and the prototype of vertical pipe was analyzed. By study on the pipe resistance, the pressure drop of slurry, when flowing in vertical pipe, could be calculated asΔP=ρgh+0.23Cρv1.8. In the end, by adjusting volume fraction of particles in the mixture slurry, the relationship between the solid particles’ volume fraction and piezometric pressure drop was obtained. When the optimal flow velocity of the slurry is 2 m/s and the ratio of NGH volume fraction to that of sand is 4 : 1, the optimal particle volume fraction ranges from 20% to 40%.

Existence and uniqueness of normal shock waves in gas-particle mixtures

1969 ◽  
Vol 38 (3) ◽  
pp. 633-655 ◽  
Author(s):  
Barbara Schmitt-Von Schubert
Keyword(s):  
Shock Waves ◽  
Existence And Uniqueness ◽  
Constant Velocity ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Solid Particles ◽  
Equilibrium Flow ◽  
Particle Volume ◽  
Flow Parameters ◽  
Finite Particle

A mixture of a gas and small solid particles is considered which, far upstream, is in a constant equilibrium state, and moves with a constant velocity. The existence of shock waves is investigated in the four possible cases, namely for frozen flow, for two kinds of partly frozen flow, and for equilibrium flow. It is shown that, in all these cases, compressive shocks may exist, if the upstream velocity exceeds the velocity of sound appropriate to the type of flow. Rarefaction shocks are impossible in each case. Moreover, it is shown that the downstream values of the flow parameters are determined uniquely, and the direction of their change is given. Only rather general assumptions concerning the behaviour of the gas are needed. The paper takes into account the influence of the finite particle volume fraction unlike most previous papers on the topic.

Interaction of a Shock Wave With a Dense Corrugated Particle Curtain

2017 ◽  
Author(s):  
Bertrand Rollin ◽  
Marie Desenlis
Keyword(s):  
Shock Wave ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Initial Perturbation ◽  
Point Particle ◽  
Planar Geometry ◽  
Late Time ◽  
Initial Particle ◽  
Particle Volume ◽  
Initial Shape

A numerical experiment studying the gas-particle variant of the Richtmyer-Meshkov instability is presented. Using an Eulerian-Lagrangian approach, namely point particle simulations, we track trajectories of computational particles composing an initially corrugated particle curtain, after the curtain’s interaction with a shock wave. We solve the compressible multiphase Euler equations in a two-dimensional planar geometry and use state-of-the-art particle force models, including unsteady forces, for the gas-particle coupling. However, additional complexities associated with compaction of the curtain of particles to random close packing limit and beyond are avoided by limiting the simulations to relatively modest initial volume fraction of particles. At a fixed Mach number, we explore the effects of the initial perturbation amplitude, initial particle volume fraction and initial shape on the dispersal of the particle curtain. For this shock strength, our simulations suggests that the amplitude of the initial perturbation does not play a significant role in the late time particle dispersal, contrary to the volume fraction. Higher initial particle volume fraction tend to faster particles dispersal. Finally, higher frequency initial perturbations seem to be absorbed by lower frequency initial perturbations.

Development and Validation of Two-Way Fluid-Particle Coupling in Turbulent Flows for a CFD Code

2013 ◽  
Author(s):  
Jianjun Xiao ◽  
Anatoly Svishchev ◽  
Thomas Jordan
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Gas Flow ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Continuous Phase ◽  
Particle Dispersion ◽  
Solid Particles ◽  
Particle Volume ◽  
Discrete Phase

A Lagrangian approach was used in CFD code GASFLOW to describe particle dispersion in turbulent flows. One-way coupling between fluid and particle is often used due to its simplicity of implementation. However, in case of higher particle volume fraction or mass loading in the continuous phase, one-way coupling is not sufficient to simulate the interaction between fluid and particles. For instance, the liquid droplets released by a spray nozzle in the nuclear power plant will lead to a strong gas entrainment, and consequently impact the gas flow field. When the volume fraction of the discrete phase is not negligible compared to the continuous phase, the interaction between the continuous fluid and dispersed phase becomes significant. Two-way momentum coupling between fluid and solid particles was developed in CFD code GASFLOW. The dynamics of the discrete particles was solved by an implicit algorithm to ensure the numerical stability. The contribution of all particles to a fluid cell was treated as the source term to the continuous phase which was solved with Arbitrary-Lagrangian-Eulerian (ALE) methodology. In order to verify and validate the code, the calculation results were then compared to theoretical results, predictions of other CFD codes and experimental data. Predictions compared favorably with the experimental data. It indicates that the effect of two-way coupling is significant when the volume fraction of discrete phase is not negligible. Two-way coupling of mass, energy and turbulence will be implemented in the future development of the GASFLOW code.

Numerical study of heat transfer and Hall current impact on peristaltic propulsion of particle-fluid suspension with compliant wall properties

2019 ◽  
Vol 33 (35) ◽  
pp. 1950439 ◽  
Author(s):  
M. M. Bhatti ◽  
Rahmat Ellahi ◽  
A. Zeeshan ◽  
M. Marin ◽  
N. Ijaz
Keyword(s):  
Heat Transfer ◽  
Volume Fraction ◽  
Hall Current ◽  
Numerical Study ◽  
Nonlinear Differential Equations ◽  
Particle Volume Fraction ◽  
Mathematical Formulation ◽  
Solid Particles ◽  
Particle Volume ◽  
The Impact

In this paper, the effects of heat transfer and Hall current on the sinusoidal motion of solid particles through a planar channel has been discussed. The walls of the channel are considered as compliant under the effects of magnetohydrodynamics. The mathematical formulation has been performed using energy equation, momentum equation, and Ohm’s law. The modeled equations are further modified by taking the assumption of a zero Reynolds number and long wavelength. Numerical shooting technique has been employed to solve the nonlinear differential equations. The impact of all the emerging parameters such as wall rigidity, wall tension, mass characterization, Hall parameter, Hartmann number, Weissenberg number, particle volume fraction, Prandtl number, and Eckert number, respectively. Particularly, we discussed their effects on velocity and temperature profile.

Experimental Investigation of Freezing Behavior of Melt/Solid Particles Mixture on to Metal Structure

2010 ◽  
Author(s):  
Md. Abdul Malek Soner ◽  
Shunichi Seo ◽  
Yu Hasegawa ◽  
Yusuke Himuro ◽  
Koji Morita ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Thermal Conditions ◽  
Metal Structure ◽  
Video Camera ◽  
Solid Particles ◽  
Particle Volume ◽  
Penetration Length ◽  
Solid Mixture ◽  
Penetration Behavior

The freezing and penetration of molten core fuel and structural materials penetrating into flow channels are important thermal-hydraulics phenomena to safety assessment of postulated core disruptive accidents in liquid metal reactors. The main objective of this study is to investigate fundamental characteristics of freezing and penetration behavior involved in melt and solid mixture flowing on-to structure material. In our study, solid copper particles mixed with molten wood’s metal (melting point 78.8°C) was used as a simulant melt, while stainless steel and brass were used as freezing structures. A series of fundamental experiments was performed to study the effects of solid particles on the freezing and penetration behavior under the various thermal conditions of molten metal and varying solid particle volume fraction and structure metal. The melt flow and distribution were observed using a digital video camera. The melt penetration length on the structure and proportion of adhered frozen metal on to structure surfaces were measured in the present series of experiments. The results indicate that penetration length becomes shorter with increasing solid particles volume fraction in melt. The present results will be utilized to build a relevant database for verification of fast reactor safety analysis codes.

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