An Improved Eddy Interaction Model for Numerical Simulation of Turbulent Particle Dispersion

1996 ◽  
Vol 118 (4) ◽  
pp. 819-823 ◽  
Author(s):  
D. I. Graham
Keyword(s):  
Turbulent Flows ◽  
Interaction Model ◽  
Particle Dispersion ◽  
Solid Particles ◽  
Experimental Investigations ◽  
Time Step ◽  
Limiting Behavior ◽  
Stationary Turbulence ◽  
Low Concentrations ◽  
Turbulent Particle Dispersion

Three main effects have been observed in experimental investigations of the dispersion of low concentrations of solid particles in homogeneous turbulent flows, namely the crossing trajectories, inertia, and continuity effects. This paper discusses the development of a simple Lagrangian eddy interaction model to account for all three of these effects. By choosing the length, time, and velocity scales in the model so as to be consistent with the corresponding scales in homogeneous, isotropic, and stationary turbulence, the proper limiting behavior is ensured both for fluid particles and for heavy solid particles. Because only one time step is required per eddy, the computational efficiency of the model is ensured.

scholarly journals Particle dispersion processes in two-dimensional turbulence: a comparison with 2-D kinematic simulation.

2007 ◽  
Vol 14 (2) ◽  
pp. 139-151 ◽  
Author(s):  
R. Castilla ◽  
J. M. Redondo ◽  
P. J. Gámez-Montero ◽  
A. Babiano
Keyword(s):  
Turbulent Flows ◽  
Particle Dispersion ◽  
Space Time ◽  
Relative Dispersion ◽  
Kinematic Simulation ◽  
Space Time Structure ◽  
Coherent Vortices ◽  
The One ◽  
Turbulent Particle Dispersion ◽  
Kinematic Simulations

Abstract. We study numerically the comparison between Lagrangian experiments on turbulent particle dispersion in 2-D turbulent flows performed, on the one hand, on the basis of direct numerical simulations (DNS) and, on the other hand, using kinematic simulations (KS). Eulerian space-time structure of both DNS and KS dynamics are not comparable, mostly due to the absence of strong coherent vortices and advection processes in the KS fields. The comparison allows to refine past studies about the contribution of non-homogeneous space-time 2-D Eulerian structure on the turbulent absolute and relative particle dispersion processes. We particularly focus our discussion on the Richardson's regime for relative dispersion.

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.

scholarly journals In Vitro Synergistic Interactions of Isavuconazole and Echinocandins against Candida auris

Antibiotics ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 355
Author(s):  
Unai Caballero ◽  
Sarah Kim ◽  
Elena Eraso ◽  
Guillermo Quindós ◽  
Valvanera Vozmediano ◽  
...  
Keyword(s):  
Interaction Model ◽  
Antifungal Drugs ◽  
Health Concern ◽  
Candida Auris ◽  
Fungistatic Activity ◽  
Drug Concentrations ◽  
Low Concentrations ◽  
Wide Range ◽  
Time Kill

Candida auris is an emergent fungal pathogen that causes severe infectious outbreaks globally. The public health concern when dealing with this pathogen is mainly due to reduced susceptibility to current antifungal drugs. A valuable alternative to overcome this problem is to investigate the efficacy of combination therapy. The aim of this study was to determine the in vitro interactions of isavuconazole with echinocandins against C. auris. Interactions were determined using a checkerboard method, and absorbance data were analyzed with different approaches: the fractional inhibitory concentration index (FICI), Greco universal response surface approach, and Bliss interaction model. All models were in accordance and showed that combinations of isavuconazole with echinocandins resulted in an overall synergistic interaction. A wide range of concentrations within the therapeutic range were selected to perform time-kill curves. These confirmed that isavuconazole–echinocandin combinations were more effective than monotherapy regimens. Synergism and fungistatic activity were achieved with combinations that included isavuconazole in low concentrations (≥0.125 mg/L) and ≥1 mg/L of echinocandin. Time-kill curves revealed that once synergy was achieved, combinations of higher drug concentrations did not improve the antifungal activity. This work launches promising results regarding the combination of isavuconazole with echinocandins for the treatment of C. auris infections.

A numerical study on combined baffles quick-separation device

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ehsan Dehdarinejad ◽  
Morteza Bayareh ◽  
Mahmud Ashrafizaadeh
Keyword(s):  
Turbulent Flows ◽  
Separation Efficiency ◽  
Numerical Study ◽  
Turbulence Models ◽  
Complete Separation ◽  
Solid Particles ◽  
Flow Rates ◽  
Separation Device ◽  
Coupling Technique ◽  
Laminar And Turbulent Flows

Abstract The transfer of particles in laminar and turbulent flows has many applications in combustion systems, biological, environmental, nanotechnology. In the present study, a Combined Baffles Quick-Separation Device (CBQSD) is simulated numerically using the Eulerian-Lagrangian method and different turbulence models of RNG k-ε, k-ω, and RSM for 1–140 μm particles. A two-way coupling technique is employed to solve the particles’ flow. The effect of inlet flow velocity, the diameter of the splitter plane, and solid particles’ flow rate on the separation efficiency of the device is examined. The results demonstrate that the RSM turbulence model provides more appropriate results compared to RNG k-ε and k-ω models. Four thousand two hundred particles with the size distribution of 1–140 µm enter the device and 3820 particles are trapped and 380 particles leave the device. The efficiency for particles with a diameter greater than 28 µm is 100%. The complete separation of 22–28 μm particles occurs for flow rates of 10–23.5 g/s, respectively. The results reveal that the separation efficiency increases by increasing the inlet velocity, the device diameter, and the diameter of the particles.

scholarly journals Numerical analysis of pulverized biomass combustion

2021 ◽  
Vol 321 ◽  
pp. 01001
Author(s):  
Cansu Deniz Canal ◽  
Erhan Böke ◽  
Ali Cemal Benim
Keyword(s):  
Gas Phase ◽  
Radiative Heat ◽  
Particle Dispersion ◽  
Single Step ◽  
Biomass Combustion ◽  
Phase Conversion ◽  
Two Phase ◽  
Dissipation Model ◽  
Turbulent Particle Dispersion ◽  
Step Mechanism

Combustion of pulverized biomass in a laboratory swirl burner is computationally investigated. The two-phase flow is modelled by an Eulerian-Lagrangian approach. The particle size distribution and turbulent particle dispersion are considered. The radiative heat transfer is modelled by the P1 method. For modelling turbulence, different RANS modelling approaches are applied. The pyrolysis of the solid fuel is modelled by a single step mechanism. For the combustion of the volatiles a two-step reaction mechanism is applied. The gas-phase conversion rate is modelled by the Eddy Dissipation Model, combined with kinetics control. The results are compared with measurements.

A Modeling Study on Particle Dispersion in Wall-Bounded Turbulent Flows

2014 ◽  
Vol 6 (06) ◽  
pp. 764-782 ◽  
Author(s):  
Jian-Hung Lin ◽  
Keh-Chin Chang
Keyword(s):  
Turbulent Flows ◽  
Particle Dispersion ◽  
Hard Sphere Model ◽  
Wall Roughness ◽  
Mass Loading ◽  
Particle Collisions ◽  
Physical Mechanisms ◽  
Parametric Studies ◽  
Low Mass ◽  
Bounded Particle

AbstractThree physical mechanisms which may affect dispersion of particle’s motion in wall-bounded turbulent flows, including the effects of turbulence, wall roughness in particle-wall collisions, and inter-particle collisions, are numerically investigated in this study. Parametric studies with different wall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach. A low-Reynolds-numberk–εturbulence model is applied for the solution of the carrier-flow field, while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion. It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles. Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particle–laden flow. Since the investigated particles are associated with large Stokes numbers, i.e., larger thanO(1), in the test problem, the effects of turbulence on particle dispersion are much less considerable, as expected, in comparison with another two physical mechanisms investigated in the study.

scholarly journals Analysis of Induced Vibrations in Fully-Developed Turbulent Pipe Flow Using a Coupled LES and FEA Approach

2010 ◽  
Author(s):  
Thomas Shurtz ◽  
Daniel Maynes ◽  
Jonathan Blotter
Keyword(s):  
Structural Model ◽  
Fluid Model ◽  
Surface Displacement ◽  
Turbulent Pipe Flow ◽  
Experimental Investigations ◽  
Time Step ◽  
Pipe Surface ◽  
Wall Displacement ◽  
Fully Developed Turbulent Flow ◽  
Pipe Vibration

This paper presents an approach using numerical simulations that have been used to characterize pipe vibration resulting from fully developed turbulent flow in a straight pipe. The vibration levels as indicated by; pipe surface displacement, velocity, and acceleration are characterized in terms of the influences of geometric and material properties of the pipe, and the effects of varying flow velocity, fluid density and viscosity have considered Reynold’s numbers ranging from 9.1×104 – 1.14×106. A large eddy simulation fluid model was coupled with a finite element structural model to simulate the fluid structure interaction using both one-way and two-way coupled techniques. The one-way technique passes the spatially and temporally varying wall pressure from a completed flow solution with fixed wall boundaries to the structural model. The structural model is then solved for wall displacements. The two-way technique involves the additional passing of wall displacement back to the fluid model which is then resolved given the new boundary location. The structural and fluid models are thus continually updated until convergence is reached at each time step. The results indicate a strong nearly quadratic dependence of pipe wall displacement on fluid average velocity. This relationship has also been verified in experimental investigations of pipe vibration. The results also indicate the pipe vibration has a power law type dependence on several variables. Dependencies on investigated variables are non-dimensionalized and assembled to develop a functional relationship that characterizes turbulence induced pipe vibration.

Solids Distribution in Sediment-Laden Open-Channel Flow: Experiment and Prediction

2020 ◽  
Author(s):  
Václav Matoušek ◽  
Jan Krupička ◽  
Tomáš Picek ◽  
Štěpán Zrostlik
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Transport Model ◽  
Plane Surface ◽  
Open Channel Flow ◽  
Solid Particles ◽  
Experimental Results ◽  
Transport Layer ◽  
Experimental Investigations ◽  
Solids Concentration

Abstract Solid-liquid flow is studied in an open channel with a mobile bed at the condition of intense transport of solids. It is flow of high-concentrated mixture of coarse sediment and water over a plane surface of the bed eroded due to high bed shear. In the flow, solid particles are non-uniformly distributed across the flow depth. The flow develops a transport layer, adjacent to the the top of the bed, in which transported particles interact with each other. Results are presented of experimental investigations of the sediment-laden open-channel flow in a recirculating titling flume. The experiments included measurements (using ultrasonic techniques) of the distribution of solids velocity across the transport layer. The related distribution of solids concentration was deduced from the measured distribution of velocity and from other measured flow quantities. Since recently, a direct measurement of the solids distribution across the transport layer has been added to the experiments using a measuring technique svideo camera and a laser sheet. This work discusses results of combined measurements of the distributions of solids concentration and velocity in steady uniform turbulent flow for two lightweight solids fractions and various flow conditions (a broad range of the bed Shields parameter, discharge of solids, discharge of mixture, and the longitudinal slope of the bed). Furthermore, the camera-based measuring method and the deducing method for a determination of solids distribution are discussed and their results compared to show a good agreement in a majority of the test runs. The experimental results are compared with predictions of a recently developed bed-load transport model. Among other outputs, the model predicts the position of the top of the transport layer and the local velocity of sediment particles at this position. The presented model predictions agree well with experimental results based on the measured distibutions.

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