Journal articles: 'Particle-eddy interaction'

1

Agnihotri, Vivek, Ghader Ghorbaniasl, Sylvia Verbanck, and Chris Lacor. "An eddy interaction model for particle deposition." Journal of Aerosol Science 47 (May 2012): 39–47. http://dx.doi.org/10.1016/j.jaerosci.2011.12.003.

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Shen, Bin Xian, and Wei Qiang Liu. "Numerical Simulation of Turbulence-Chemical Interaction Models on Combustible Particle MILD Combustion." Advanced Materials Research 1070-1072 (December 2014): 1752–57. http://dx.doi.org/10.4028/www.scientific.net/amr.1070-1072.1752.

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Typical combustible particle coal has been analyzed by using turbulence-chemistry interaction models to realize which models are more accurate and reasonable on pulverized coal MILD combustion. Three turbulence-chemistry interaction models are examined: the Equilibrium Mixture Fraction/PDF (PDF), the Eddy Break Up (EBU), the Eddy Dissipation Concept (EDC). All of three models can give a suitable prediction of axial velocity on combustible particle coal MILD combustion because turbulence-chemistry interaction models have little influence on flow field and flow structure. The Eddy Dissipation Concept model (EDC), based on advanced turbulence-chemistry interaction with global and detailed kinetic mechanisms can produce satisfactory results on chemical and fluid dynamic behavior of combustible particle coal MILD combustion, especially on temperature and species concentrations.

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3

Jayanti, S., and S. Narayanan. "Computational Study of Particle-Eddy Interaction in Sedimentation Tanks." Journal of Environmental Engineering 130, no. 1 (January 2004): 37–49. http://dx.doi.org/10.1061/(asce)0733-9372(2004)130:1(37).

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4

Yu, Y., L. X. Zhou, C. G. Zheng, and Z. H. Liu. "Simulation of Swirling Gas-Particle Flows Using Different Time Scales for the Closure of Two-Phase Velocity Correlation in the Second-Order Moment Two-Phase Turbulence Model1." Journal of Fluids Engineering 125, no. 2 (March 1, 2003): 247–50. http://dx.doi.org/10.1115/1.1538630.

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Three different time scales—the gas turbulence integral time scale, the particle relaxation time, and the eddy interaction time—are used for closing the dissipation term in the transport equation of two-phase velocity correlation of the second-order moment two-phase turbulence model. The mass-weighted averaged second-order moment (MSM) model is used to simulate swirling turbulent gas-particle flows with a swirl number of 0.47. The prediction results are compared with the PDPA measurement results taking from references. Good agreement is obtained between the predicted and measured particle axial and tangential time-averaged velocities. There is some discrepancy between the predicted and measured particle axial and tangential fluctuation velocities. The results indicate that the time scale has an important effect. It is found that the predictions using the eddy interaction time scale give the right tendency—for example, the particle tangential fluctuation velocity is smaller than the gas tangential fluctuation velocity, as that given by the PDPA measurements.

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5

Graham, D. I. "An Improved Eddy Interaction Model for Numerical Simulation of Turbulent Particle Dispersion." Journal of Fluids Engineering 118, no. 4 (December 1, 1996): 819–23. http://dx.doi.org/10.1115/1.2835514.

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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.

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Jaszczur, Marek. "Large Eddy Simulations of particle-fluid interaction in a turbulent channel flow." Journal of Physics: Conference Series 318, no. 4 (December 22, 2011): 042052. http://dx.doi.org/10.1088/1742-6596/318/4/042052.

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Groll, R. "Statistical Eulerian Diffusion Approach of Four-Way-Coupled Multiphase Systems." Defect and Diffusion Forum 297-301 (April 2010): 832–37. http://dx.doi.org/10.4028/www.scientific.net/ddf.297-301.832.

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Volume-fraction weighted and Reynolds averaged momentum transport equations are solved in an Euler/Euler approach to simulate numerically the turbulent, dispersed two- phase °ow in a two-dimensional channel and a three-dimensional conic di®user °ow. Particular attention is given to the modelling of turbulent di®usion and particle wall interaction, assuming local equilibrium but introducing individual terms for particle/°uid drag interaction, particle collisions and trajectory crossings. These in°uences have been quanti¯ed in terms of partial viscosities, a restitution power and a turbulence structure parameter. Boussinesq approxima- tions have been used for each phase and their interaction, whose formulation was provided in the framework of the eddy-viscosity modelling concept.

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Yücesan, Sencer, Daniel Wildt, Philipp Gmeiner, Johannes Schobesberger, Christoph Hauer, Christine Sindelar, Helmut Habersack, and Michael Tritthart. "Interaction of Very Large Scale Motion of Coherent Structures with Sediment Particle Exposure." Water 13, no. 3 (January 20, 2021): 248. http://dx.doi.org/10.3390/w13030248.

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A systematic variation of the exposure level of a spherical particle in an array of multiple spheres in a high Reynolds number turbulent open-channel flow regime was investigated while using the Large Eddy Simulation method. Our numerical study analysed hydrodynamic conditions of a sediment particle based on three different channel configurations, from full exposure to zero exposure level. Premultiplied spectrum analysis revealed that the effect of very-large-scale motion of coherent structures on the lift force on a fully exposed particle resulted in a bi-modal distribution with a weak low wave number and a local maximum of a high wave number. Lower exposure levels were found to exhibit a uni-modal distribution.

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Etasse, Emmanuel, Charles Meneveau, and Thierry Poinsot. "Simple Stochastic Model for Particle Dispersion Including Inertia, Trajectory-Crossing, and Continuity Effects." Journal of Fluids Engineering 120, no. 1 (March 1, 1998): 186–92. http://dx.doi.org/10.1115/1.2819645.

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An eddy-lifetime, stochastic Lagrangian model for particle dispersion in weakly laden turbulent flows is proposed, in which the interaction time-scale between particles and turbulent eddies is parametrized so as to include several physical effects. It takes into account particle inertia, crossing-trajectory effect, the possible difference in lateral and longitudinal dispersion, and some Reynolds number effects. The parametrization is based on previous results, from a theoretical dispersion model in isotropic turbulence using the trajectory-velocity independence and Gaussian approximations, as well as from Large-Eddy-Simulation. Simple fits are introduced to efficiently capture the main results from these prior studies, allowing practical implementation within the context of k – ε engineering codes. Results from simulations using the proposed approach are compared with experimental data of dispersion in decaying isotropic turbulence.

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Paoli, Roberto, Xavier Vancassel, François Garnier, and Philippe Mirabel. "Large-eddy simulation of a turbulent jet and a vortex sheet interaction: particle formation and evolution in the near field of an aircraft wake." Meteorologische Zeitschrift 17, no. 2 (April 28, 2008): 131–44. http://dx.doi.org/10.1127/0941-2948/2008/0278.

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11

Watanabe, Yasunori, Yuta Mitobe, Yasuo Niida, and Ayumi Saruwatari. "APPLICATION OF LES-STOCHASTIC TWO-WAY MODEL TO TWO-PHASE BOUNDARY LAYER FLOWS." Coastal Engineering Proceedings 1, no. 32 (January 27, 2011): 5. http://dx.doi.org/10.9753/icce.v32.waves.5.

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A particle / turbulence two-way coupling model, integrated with conventional stochastic and sub-grid stress models of three-dimensional Large Eddy Simulation (LES), has been applied to the particle-laden turbulent flow in a wave boundary layer developed over seabed with the aim to understand dynamic effects of the particle size and number density to the suspension process in shearing flow over the seabed. While the particle size affects local velocity fluctuations, the particle population significantly induces secondary large-scale flows varying over a scale of the wavelength, and intensifies the turbulent energy near the bed. The particle-induced turbulence may result in additional suspension from the bed, causing a recursive suspension process via the particle turbulence interaction in the boundary layer.

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12

YAMAMOTO, Y., M. POTTHOFF, T. TANAKA, T. KAJISHIMA, and Y. TSUJI. "Large-eddy simulation of turbulent gas–particle flow in a vertical channel: effect of considering inter-particle collisions." Journal of Fluid Mechanics 442 (August 24, 2001): 303–34. http://dx.doi.org/10.1017/s0022112001005092.

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The interaction between a turbulent gas flow and particle motion was investigated by numerical simulations of gas–particle turbulent downward flow in a vertical channel. In particular the effect of inter-particle collision on the two-phase flow field was investigated. The gas flow field was obtained by large-eddy simulation (LES). Particles were treated by a Lagrangian method, with inter-particle collisions calculated by a deterministic method. The spatial resolution for LES of gas–solid two-phase turbulent flow was examined and relations between grid resolution and Stokes number are presented. Profiles of particle mean velocity, particle wall-normal fluctuation velocity and number density are flattened as a result of inter-particle collisions and these results are in good agreement with experimental measurements. Calculated turbulence attenuation by particles agrees well with experimental measurements for small Stokes numbers, but not for large Stokes number particle. The shape and scale of particle concentrations calculated considering inter-particle collision are in good agreement with experimental observations.

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13

Huilier, Daniel G. F. "An Overview of the Lagrangian Dispersion Modeling of Heavy Particles in Homogeneous Isotropic Turbulence and Considerations on Related LES Simulations." Fluids 6, no. 4 (April 8, 2021): 145. http://dx.doi.org/10.3390/fluids6040145.

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Particle tracking is a competitive technique widely used in two-phase flows and best suited to simulate the dispersion of heavy particles in the atmosphere. Most Lagrangian models in the statistical approach to turbulence are based either on the eddy interaction model (EIM) and the Monte-Carlo method or on random walk models (RWMs) making use of Markov chains and a Langevin equation. In the present work, both discontinuous and continuous random walk techniques are used to model the dispersion of heavy spherical particles in homogeneous isotropic stationary turbulence (HIST). Their efficiency to predict particle long time dispersion, mean-square velocity and Lagrangian integral time scales are discussed. Computation results with zero and no-zero mean drift velocity are reported; they are intended to quantify the inertia, gravity, crossing-trajectory and continuity effects controlling the dispersion. The calculations concern dense monodisperse spheres in air, the particle Stokes number ranging from 0.007 to 4. Due to the weaknesses of such models, a more sophisticated matrix method will also be explored, able to simulate the true fluid turbulence experienced by the particle for long time dispersion studies. Computer evolution and performance since allowed to develop, instead of Reynold-Averaged Navier-Stokes (RANS)-based studies, large eddy simulation (LES) and direct numerical simulation (DNS) of turbulence coupled to Generalized Langevin Models. A short review on the progress of the Lagrangian simulations based on large eddy simulation (LES) will therefore be provided too, highlighting preferential concentration. The theoretical framework for the fluid time correlation functions along the heavy particle path is that suggested by Wang and Stock.

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14

Boudet, Jérôme, Nathalie Grosjean, and Marc C. Jacob. "Wake-Airfoil Interaction as Broadband Noise Source: A Large-Eddy Simulation Study." International Journal of Aeroacoustics 4, no. 1-2 (January 2005): 93–115. http://dx.doi.org/10.1260/1475472053730093.

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A large-eddy simulation is carried out on a rod-airfoil configuration and compared to an accompanying experiment as well as to a RANS computation. A NACA0012 airfoil (chord c = 0.1 m) is located one chord downstream of a circular rod (diameter d = c/10, Red = 48 000). The computed interaction of the resulting sub-critical vortex street with the airfoil is assessed using averaged quantities, aerodynamic spectra and proper orthogonal decomposition (POD) of the instantaneous flow fields. Snapshots of the flow field are compared to particle image velocimetry (PIV) data. The acoustic far field is predicted using the Ffowcs Williams & Hawkings acoustic analogy, and compared to the experimental far field spectra. The large-eddy simulation is shown to accurately represent the deterministic pattern of the vortex shedding that is described by POD modes 1 & 2 and the resulting tonal noise also compares favourably to measurements. Furthermore higher order POD modes that are found in the PIV data are well predicted by the computation. The broadband content of the aerodynamic and the acoustic fields is consequently well predicted over a large range of frequencies ([0 kHz; 10 kHz]).

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15

Yin, Zhaoqin, and Huijie Liu. "Numerical simulation of nanoparticles diffusion and coagulation in a twin-jet via a TEMOM method." International Journal of Numerical Methods for Heat & Fluid Flow 24, no. 6 (July 29, 2014): 1312–20. http://dx.doi.org/10.1108/hff-04-2013-0143.

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Purpose – The purpose of this paper is to study nanoparticles diffusion and coagulation processes in a twin-jet. Design/methodology/approach – Large eddy simulation (LES) and Taylor-series expansion moment method (TEMOM) are employed to deal with a nanoparticle-laden twin-jet flow. Findings – The numerical results show that the interaction of the two jets and turbulence eddy structures rolling-up, paring and shedding in flow sharply affects particles number concentration. Particle diameter grows quickly at the interfaces of jets. Coagulation shows more obvious effect at initial stage than that in the subsequent period. Then diffusion makes the particle diameter distribution much more uniform. Originality/value – In recent years a great number of attentions have been focussed on the issue of particulate dynamics processes including diffusion, coagulation and deposition, etc. However, up to now few works have been focus on the nanoparticles coagulation and dispersion in turbulent flows. The investigation on the diffusion and coagulation process of nanoparticles using TEMOM in a twin-jet flow has not been found.

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16

Graber, S. David. "Discussion of “Computational Study of Particle-Eddy Interaction in Sedimentation Tanks” by S. Jayanti and S. Narayanan." Journal of Environmental Engineering 131, no. 6 (June 2005): 994. http://dx.doi.org/10.1061/(asce)0733-9372(2005)131:6(994).

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17

Li, Tian, Li-Hao Zhao, Xiao-Ke Ku, Helge Andersson, and Terese Lovas. "Numerical investigation of particles turbulent dispersion in channel flow." Thermal Science 16, no. 5 (2012): 1510–14. http://dx.doi.org/10.2298/tsci1205510l.

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This paper investigates the performance of Reynolds-averaged Navier-Stokes model on dispersion of particles in wall turbulence. A direct numerical simulation of wall-bounded channel flow with particles suspensions was set as a benchmark. The standard k-? model coupled with two different eddy interaction models was used in Reynolds-averaged Navier-Stokes model and compared to the direct numerical simulation. Detailed comparisons between direct numerical simulation and Reynolds-averaged Navier-Stokes model on particle distribution evolving over time were carried out.

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18

Hellmuth, O. "Conceptual study on nucleation burst evolution in the convective boundary layer – Part II: Meteorological characterization." Atmospheric Chemistry and Physics Discussions 5, no. 6 (November 10, 2005): 11489–515. http://dx.doi.org/10.5194/acpd-5-11489-2005.

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Abstract. While in part I of the present paper a revised columnar high-order modelling approach to investigate gas-aerosol interactions in the convective boundary layer (CBL) was deduced, in the present part the model capability to predict the evolution of meteorological CBL parameters is demonstrated. Based on a model setup to simulate typical CBL conditions, predicted first-, second- and third-order moments were shown to agree very well with those obtained from in situ and remote sensing turbulence measurements such as aircraft, SODAR and LIDAR measurements as well as with those derived from ensemble-averaged large-eddy simulations and wind tunnel experiments. The results show that the model is able to predict the meteorological CBL parameters, required to verify or falsify, respectively, previous hypothesis on the interaction between CBL turbulence and new particle formation.

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19

Picot, J., R. Paoli, O. Thouron, and D. Cariolle. "Large-eddy simulation of contrail evolution in the vortex phase and its interaction with atmospheric turbulence." Atmospheric Chemistry and Physics 15, no. 13 (July 9, 2015): 7369–89. http://dx.doi.org/10.5194/acp-15-7369-2015.

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Abstract. In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES) coupled to a Lagrangian particle tracking method to treat the ice phase. In this paper, fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere and lower stratosphere. The initial flow field is composed of the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail descent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex breakup dominates over background turbulence until the end of the vortex regime and controls the mixing with ambient air. This results in mean microphysical characteristics such as ice mass and optical depth that are slightly affected by the intensity of atmospheric turbulence. However, the background humidity and temperature have a first-order effect on the survival of ice crystals and particle size distribution, which is in line with recent studies.

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20

Khandetskyi, V. S. "Determination of the conductivity of non-metallic powder materials by the eddy current method." Journal of Physics and Electronics 27, no. 1 (October 17, 2019): 63–70. http://dx.doi.org/10.15421/331911.

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A theoretical analysis of the interaction of the eddy current sensor field with powder particles makes it possible to calculate the particle conductivity using the measured value of the sensor added active resistance. Relative to its own reactance, the value of this resistance is proportional to powder density, frequency of the probing field, electrical conductivity of particles and square of their diameter. Particles of spherical shape and cylindrical shape, the height of which is equal to the diameter of the base, are considered. The analysis allows to explain the experimentally observed different character of the resistance frequency dependences for powder and corresponding solid material when measuring by the same sensor.

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21

Hellmuth, O. "Columnar modelling of nucleation burst evolution in the convective boundary layer – first results from a feasibility study Part II: Meteorological characterisation." Atmospheric Chemistry and Physics 6, no. 12 (September 21, 2006): 4215–30. http://dx.doi.org/10.5194/acp-6-4215-2006.

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Abstract. While in Paper I of four papers a revised columnar high-order modelling approach to investigate gas-aerosol-turbulence interactions in the convective boundary layer (CBL) was deduced, in the present Paper II the model capability to predict the evolution of meteorological CBL parameters is demonstrated. Based on a model setup to simulate typical CBL conditions, predicted first-, second- and third-order moments were shown to agree very well with those obtained from in situ and remote sensing turbulence measurements such as aircraft, SODAR and LIDAR measurements as well as with those derived from ensemble-averaged large eddy simulations and wind tunnel experiments. The results show, that the model is able to predict the meteorological CBL parameters, required to verify or falsify, respectively, previous hypothesis on the interaction between CBL turbulence and new particle formation.

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22

Bharadwaj, Nidheesh, and Christopher J. Rutland. "A LARGE-EDDY SIMULATION STUDY OF SUB-GRID TWO-PHASE INTERACTION IN PARTICLE-LADEN FLOWS AND DIESEL ENGINE SPRAYS." Atomization and Sprays 20, no. 8 (2010): 673–95. http://dx.doi.org/10.1615/atomizspr.v20.i8.20.

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23

Le Vu, Briac, Alexandre Stegner, and Thomas Arsouze. "Angular Momentum Eddy Detection and Tracking Algorithm (AMEDA) and Its Application to Coastal Eddy Formation." Journal of Atmospheric and Oceanic Technology 35, no. 4 (April 2018): 739–62. http://dx.doi.org/10.1175/jtech-d-17-0010.1.

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AbstractAutomated methods are important for the identification of mesoscale eddies in the large volume of oceanic data provided by altimetric measurements and numerical simulations. This paper presents an optimized algorithm for detecting and tracking eddies from two-dimensional velocity fields. This eddy identification uses a hybrid methodology based on physical parameters and geometrical properties of the velocity field, and it can be applied to various fields having different spatial resolutions without a specific fine-tuning of the parameters. The efficiency and the robustness of the angular momentum eddy detection and tracking algorithm (AMEDA) was tested with three different types of input data: the 1/8° Archiving, Validation, and Interpretation of Satellite Oceanographic Data (AVISO) geostrophic velocity fields available for the Mediterranean Sea; the output of the idealized Regional Ocean Modeling System numerical model; and the surface velocity field obtained from particle imagery on a rotating tank experiment. All these datasets describe the dynamical evolution of mesoscale eddies generated by the instability of a coastal current. The main advantages of AMEDA are as follows: the algorithm is robust to the grid resolution, it uses a minimal number of tunable parameters, the dynamical features of the detected eddies are quantified, and the tracking procedure identifies the merging and splitting events. The proposed method provides a complete dynamical evolution of the detected eddies during their lifetime. This allows for identifying precisely the formation areas of long-lived eddies, the region where eddy splitting or merging occurs frequently, and the interaction between eddies and oceanic currents.

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Haller, G., and A. C. Poje. "Eddy growth and mixing in mesoscale oceanographic flows." Nonlinear Processes in Geophysics 4, no. 4 (December 31, 1997): 223–35. http://dx.doi.org/10.5194/npg-4-223-1997.

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Abstract. We study the relation between changes in the Eulerian topology of a two dimensional flow and the mixing of fluid particles between qualitatively different regions of the flow. In general time dependent flows, streamlines and particle paths are unrelated. However, for many mesoscale oceanographic features such as detaching rings and meandering jets, the rate at which the Euierian structures evolve is considerably slower than typical advection speeds of Lagrangian tracers. In this note we show that for two-dimensional, adiabatic fluid flows there is a direct relationship between observable changes in the topology of the Eulerian field and the rate of transport of fluid particles. We show that a certain class of flows is amenable to adiabatic or near adiabatic analysis, and, as an example, we use our results to study the chaotic mixing in the Dutkiewicz and Paldor (1994) kinematic model of the interaction of a meandering barotropic jet with a strong eddy.

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Wu, Yun-Ta, Shih-Chun Hsiao, and Guan-Shiue Chen. "SOLITARY WAVE INTERACTION WITH A SUBMERGED PERMEABLE BREAKWATER: EXPERIMENT AND NUMERICAL MODELING." Coastal Engineering Proceedings 1, no. 33 (October 18, 2012): 30. http://dx.doi.org/10.9753/icce.v33.structures.30.

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We study the interactions between a non-breaking solitary wave and a submerged permeable breakwater experimentally and numerically. The particle image velocimetry (PIV) technique was employed to measure instantaneous free surface displacements and velocity fields in the vicinity of the porous media. The porous media, consisted of uniform glass-made spheres, was mounted on the seafloor. Quantitative mean properties were obtained by ensemble averaging 30 repeated instantaneous measurements. In addition, two different numerical considerations are taken to simulate the experiments. One is to model an idealized volume-averaged porous media using a two-dimensional (2D) volume of fluid (VOF)-type model. This model is based on the Volume-Averaged Reynolds-Averaged Navier–Stokes (VARANS) equations coupled with the non-linear k-ε turbulence closure solver. The other is to model the real porous breakwater constructed by spheres using a three-dimensional (3D) VOF-type model. This model solves 3D incompressible Navier–Stokes equations with Large-eddy-simulation (LES) model. The comparisons were performed between measurements, 2D and 3D numerical results for the time histories of the free surface elevation, instantaneous free surface displacements and corresponding velocity properties around the permeable object. Fairly good agreements were obtained. The verified 3D numerical results were used to trace the trajectories of fluid particle around the porous media to help understand the possible sediment movements in suspended loads. Also, the 2D numerical model is used to estimate the energy reflection, transmission and dissipation using the energy integral method by varying the aspect ratio and the grain size of the permeable obstacle.

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Tavangar, Tooran, Hesam Tofighian, and Ali Tarokh. "Investigation of the Horizontal Motion of Particle-Laden Jets." Computation 8, no. 2 (April 8, 2020): 23. http://dx.doi.org/10.3390/computation8020023.

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Particle-laden jet flows can be observed in many industrial applications. In this investigation, the horizontal motion of particle laden jets is simulated using the Eulerian–Lagrangian framework. The two-way coupling is applied to the model to simulate the interaction between discrete and continuum phase. In order to track the continuum phase, a passive scalar equation is added to the solver. Eddy Life Time (ELT) is employed as a dispersion model. The influences of different non-dimensional parameters, such as Stokes number, Jet Reynolds number and mass loading ratio on the flow characteristics, are studied. The results of the simulations are verified with the available experimental data. It is revealed that more gravitational force is exerted on the jet as a result of the increase in mass loading, which deflects it more. Moreover, with an increase in the Reynolds number, the speed of the jet rises, and consequently, the gravitational force becomes less capable of deviating the jet. In addition, it is observed that by increasing the Stokes number, the particles leave the jet at higher speed, which causes a lower deviation of the jet.

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Gabreil, Eslam, Simon Tait, Andy Nichols, and Giulio Dolcetti. "3D SPH Simulation of Dynamic Water Surface and Its Interaction with Underlying Flow Structure for Turbulent Open Channel Flows Over Rough Beds." International Journal of Ocean and Coastal Engineering 01, no. 02 (June 2018): 1840003. http://dx.doi.org/10.1142/s2529807018400031.

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In this study, a fully 3D numerical model based on the Smoothed Particle Hydrodynamics (SPH) approach has been developed to simulate turbulent open channel flows over a fixed rough bed. The model focuses on the study of dynamic free surface behavior as well as its interaction with underlying flow structures near the rough bed. The model is improved from the open source code SPHysics ( http://www.sphysics.org ) by adding more advanced turbulence and rough bed treatment schemes. A modified sub-particle-scale (SPS) eddy viscosity model is proposed to reflect the turbulence transfer mechanisms and a modified drag force equation is included into the momentum equations to account for the existence of roughness elements on the bed as well as on the sidewalls. The computed results of various free surface patterns have been compared with the laboratory measurements of the fluctuating water surface elevations in the streamwise and spanwise directions of a rectangular open-channel flow under a range of flow conditions. The comparison has demonstrated that the proposed 3D SPH model can simulate well the complex free surface flows over a fixed rough bed.

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Cauteruccio, Arianna, Matteo Colli, and Luca Lanza. "On Neglecting Free-Stream Turbulence in Numerical Simulation of the Wind-Induced Bias of Snow Gauges." Water 13, no. 3 (January 31, 2021): 363. http://dx.doi.org/10.3390/w13030363.

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Numerical studies of the wind-induced bias of precipitation measurements assume that turbulence is generated by the interaction of the airflow with the gauge body, while steady and uniform free-stream conditions are imposed. However, wind is turbulent in nature due to the roughness of the site and the presence of obstacles, therefore precipitation gauges are immersed in a turbulent flow. Further to the turbulence generated by the flow-gauge interaction, we investigated the natural free-stream turbulence and its influence on precipitation measurement biases. Realistic turbulence intensity values at the gauge collector height were derived from 3D sonic anemometer measurements. Large Eddy Simulations of the turbulent flow around a chimney-shaped gauge were performed under uniform and turbulent free-stream conditions, using geometrical obstacles upstream of the gauge to provide the desired turbulence intensity. Catch ratios for dry snow particles were obtained using a Lagrangian particle tracking model, and the collection efficiency was calculated based on a suitable particle size distribution. The collection efficiency in turbulent conditions showed stronger undercatch at the investigated wind velocity and snowfall intensity below 10 mm h−1, demonstrating that adjustment curves based on the simplifying assumption of uniform free-stream conditions do not accurately portray the wind-induced bias of snow measurements.

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Bermejo-Moreno, Iván, Laura Campo, Johan Larsson, Julien Bodart, David Helmer, and John K. Eaton. "Confinement effects in shock wave/turbulent boundary layer interactions through wall-modelled large-eddy simulations." Journal of Fluid Mechanics 758 (October 3, 2014): 5–62. http://dx.doi.org/10.1017/jfm.2014.505.

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AbstractWe present wall-modelled large-eddy simulations (WLES) of oblique shock waves interacting with the turbulent boundary layers (TBLs) (nominal$\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\delta _{99}=5.4\ \mathrm{mm}$and${\mathit{Re}}_{\theta }\approx 1.4\times 10^4$) developed inside a duct with an almost-square cross-section ($45\ \mathrm{mm}\times 47.5\ \mathrm{mm}$) to investigate three-dimensional effects imposed by the lateral confinement of the flow. Three increasing strengths of the incident shock are considered, for a constant Mach number of the incoming air stream$M\approx 2$, by varying the height (1.1, 3 and 5 mm) of a compression wedge located at a constant streamwise location that spans the top wall of the duct at a 20° angle. Simulation results are first validated with particle image velocimetry (PIV) experimental data obtained at several vertical planes (one near the centre of the duct and three near one of the sidewalls) for the 1.1 and 3 mm-high wedge cases. The instantaneous and time-averaged structure of the flow for the stronger-interaction case (5 mm-high wedge), which shows mean flow reversal, is then investigated. Additional spanwise-periodic simulations are performed to elucidate the influence of the sidewalls, and it is found that the structure and location of the shock system, as well as the size of the separation bubble, are significantly modified by the lateral confinement. A Mach stem at the first reflected interaction is present in the simulation with sidewalls, whereas a regular shock intersection results for the spanwise-periodic case. Low-frequency unsteadiness is observed in all interactions, being stronger for the secondary shock reflections of the shock train developed inside the duct. The downstream evolution of secondary turbulent flows developed near the corners of the duct as they traverse the shock system is also studied.

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30

Nemitz, E., and M. A. Sutton. "Gas-particle interactions above a Dutch heathland: III. Modelling the influence of the NH3-HNO3-NH4NO3 equilibrium on size-segregated particle fluxes." Atmospheric Chemistry and Physics Discussions 4, no. 2 (March 15, 2004): 1567–621. http://dx.doi.org/10.5194/acpd-4-1567-2004.

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Abstract. Micrometeorological measurements of size-segregated particle number fluxes above Dutch heathlands and forests have repeatedly shown simultaneous apparent emission of particles with a diameter (Dp) < 0.18 µm and deposition of larger particles when measured with optical particle counters. In order to assess whether this observation may be explained by the equilibrium reaction of ammonia (NH3), nitric acid (HNO3) and ammonium (NH4+), a new numerical model is developed to predict the vertical concentration and flux profiles of the different species as modified by the interaction of equilibration and surface/atmosphere exchange processes. In addition to former studies, the new approach explicitly models the height-dependence of the NH4+ and total aerosol size-distribution. Using this model, it is demonstrated that both gas-to-particle conversion (gtpc) and aerosol evaporation can significantly alter the apparent surface exchange fluxes, and evoke the observed bi-directional particle fluxes under certain conditions. Thus, in general, the NH3-HNO3-NH4NO3 equilibrium needs to be considered when interpreting eddy-covariance particle fluxes. Applied to an extensive dataset of simultaneous flux measurements of particles and gases at Elspeet, NL, the model reproduces the diurnal pattern of the bi-directional exchange well. In agreement with the observation of fast NH4+ deposition, slow nitric acid deposition (both as measured by the aerodynamic gradient method) and small concentration products of NH3×HNO3 at this site, this study suggests that NH4+ evaporation at this site significantly alters surface exchange fluxes.

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31

Nemitz, E., and M. A. Sutton. "Gas-particle interactions above a Dutch heathland: III. Modelling the influence of the NH3-HNO3-NH4NO3 equilibrium on size-segregated particle fluxes." Atmospheric Chemistry and Physics 4, no. 4 (July 2, 2004): 1025–45. http://dx.doi.org/10.5194/acp-4-1025-2004.

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Abstract. Micrometeorological measurements of size-segregated particle number fluxes above Dutch heathlands and forests have repeatedly shown simultaneous apparent emission of particles with a diameter (Dp)<0.18 µm and deposition of larger particles when measured with optical particle counters. In order to assess whether this observation may be explained by the equilibrium reaction of ammonia (NH3), nitric acid (HNO3) and ammonium (NH4+), a new numerical model is developed to predict the vertical concentration and flux profiles of the different species as modified by the interaction of equilibration and surface/atmosphere exchange processes. In addition to former studies, the new approach explicitly models the height-dependence of the NH4+ and total aerosol size-distribution. Using this model, it is demonstrated that both gas-to-particle conversion (gtpc) and aerosol evaporation can significantly alter the apparent surface exchange fluxes, and evoke the observed bi-directional particle fluxes under certain conditions. Thus, in general, the NH3-HNO3-NH4NO3 equilibrium needs to be considered when interpreting eddy-covariance particle fluxes. Applied to an extensive dataset of simultaneous flux measurements of particles and gases at Elspeet, NL, the model reproduces the diurnal pattern of the bi-directional exchange well. In agreement with the observation of fast NH4+ deposition, slow nitric acid deposition (both as measured by the aerodynamic gradient method) and small concentration products of NH3×HNO3 at this site, this study suggests that NH4+ evaporation at this site significantly alters surface exchange fluxes.

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32

ZHOU, YONG, ANTHONY S. WEXLER, and LIAN-PING WANG. "Modelling turbulent collision of bidisperse inertial particles." Journal of Fluid Mechanics 433 (April 25, 2001): 77–104. http://dx.doi.org/10.1017/s0022112000003372.

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We study finite-inertia effects on the collision rate of bidisperse heavy particles in a turbulent gas, using direct numerical simulations and kinematic descriptions. As shown previously for a monodisperse system (Sundaram & Collins 1997; Wang, Wexler & Zhou 2000), a statistical mechanical description of the average collision kernel consists of two parts, namely a description of the relative velocity between two colliding particles (the turbulent transport effect) and of the non-uniform particle distribution due to dynamic interaction of particles with coherent vortex structures (the accumulation effect). We first show that this description remains valid and accurate for a bidisperse system involving two groups of particles of inertial response time τp1 and τp2, respectively. Numerical results for the turbulent transport effect and the accumulation effect have been obtained as a function of τp1 and τp2. Interestingly, the accumulation effect in a bidisperse system is bounded above by that of a monodisperse system. An explanation for this observation is given, in terms of the correlation between concentration fields of the two size groups. Simulations show that particles from two size groups were found in different regions of a vortex, thus reducing the net accumulation effect in a bidisperse system. The turbulent transport effect, on the other hand, is bounded below by the level in a monodisperse system, due to a differential inertia effect. The above observations imply that the size polydispersity enhances the turbulent transport effect but weakens the accumulation effect, relative to a monodisperse system.A simple eddy–particle interaction (EPI) model was developed and shown to give a reasonable prediction of the collision kernel, except for a small parametric region where both τp1 and τp2 are on the order of the ow Kolmogorov time τk and thus the accumulation effect must be included. A more accurate model incorporating both the turbulent transport effect and the accumulation effect has also been developed. The model would provide an upper bound on the collision rates for a non-dilute bidisperse system, since turbulence modulation and particle-particle interactions are not considered in this model.Finally, some consideration is given to the effect of nonlinear drag on the collision kernel. The results show that the drag nonlinearity can increase the collision kernel slightly (less than 10%) at large particle inertia.

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33

Wu, Hai Yyan, Meng Ding, and Yi Su. "The Study of Cavity Flow and Transpiration Cooling in Supersonic Combustion." Applied Mechanics and Materials 390 (August 2013): 370–74. http://dx.doi.org/10.4028/www.scientific.net/amm.390.370.

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To unravel the flow and heat transfer mechanism of the cavity in supersonic combustion, this paper studied the interaction of cavities and shear-layers by experiments and numerical simulation. The experiments of Nero-particle Plane Laser Scatter (NPLS) and Plane Laser-Induced Fluorescence (PLIF) were conducted to study the cavity shear-layer. In the same supersonic condition the flow was studied by the method of Large Eddy Simulation (LES). And we discussed the cavity shear-layer influence to supersonic flow and combustion, analyzed the evolvement of injection shear-layer, probed into the heat transfer of supersonic combustion, and studied the transpiration cooling of cavities. The results show: in supersonic combustion, the initial flame spreads to the upstream through the cavity shear layer, the highest wall temperature occur at the rear edge of cavity, and transpiration cooling can effectively protect the wall materials.

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34

Wu, Wen, Giovanni Soligo, Cristian Marchioli, Alfredo Soldati, and Ugo Piomelli. "Particle resuspension by a periodically forced impinging jet." Journal of Fluid Mechanics 820 (May 5, 2017): 284–311. http://dx.doi.org/10.1017/jfm.2017.210.

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When hovering over sandy terrain, the rotor of helicopters generates a downward jet that induces resuspension of dust and debris. We investigate the mechanisms that govern particle resuspension in such flow using an Eulerian–Lagrangian approach based on large-eddy simulation of turbulence. The wake generated by the helicopter is modelled as a vertical impinging jet, to which a sequence of periodically forced azimuthal vortices is superposed. The resulting flow field provides a unique range of flow scales with which the particles can interact. Downstream of the impingement region, layers of negative azimuthal vorticity (secondary vortices) form on the upwash side of the primary azimuthal (large-scale) vortices. These layers then detach from the surface together with the near-wall (small-scale) vortices populating the wall-jet region. We show how the dynamics of sediments is governed by its interaction with these structures. After initial lift off from the impingement surface, particles accumulate in regions where near-wall vortices roll around the impinging azimuthal vortex, forming rib-like structures that either propel particles away from the azimuthal vortex or entrap them in the shear layer between the azimuthal and secondary vortices. We demonstrate that these trapped particles are more likely to reach the outer flow region and generate a persistent cloud of airborne particles. We also show that, in a time-averaged sense, particle resuspension and deposition fluxes balance each other near the impingement surface.

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35

Li, Zhiqiang, Yuan Wang, and Yang Zhang. "A numerical study of particle motion and two-phase interaction in aeolian sand transport using a coupled large eddy simulation - discrete element method." Sedimentology 61, no. 2 (June 28, 2013): 319–32. http://dx.doi.org/10.1111/sed.12057.

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36

Fan, J. R., K. Luo, X. Y. Zhang, and K. C. Cen. "Large Eddy Simulation of the Anti-Erosion Characteristics of the Ribbed-Bend in Gas-Solid Flows." Journal of Engineering for Gas Turbines and Power 126, no. 3 (July 1, 2004): 672–79. http://dx.doi.org/10.1115/1.1760523.

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In order to find out the ribs with the best anti-erosion efficiency, the erosion effects in three 90° duct bend gas-solid flows with different ribs are investigated and compared with that in the bare bend. Three different kinds of ribs are studied, which have square cross section, isosceles right-angled triangle shape cross section and isosceles triangle shape cross section, respectively. The arrangement and the geometry dimensions of the ribs are the same. The gas phase flow field is solved by the large eddy simulation technique considering the interaction between the gas and the particles, whereas the particles are tracked by Lagrangian method. The results exhibit that the erosion rates of all the ribbed bends are greatly reduced due to the adding of the ribs compared with that of the bare bend. Among the three different kinds of ribs, the isosceles right-angled triangle ribs have the highest anti-erosion ability. The reason is that the particle impact velocity on the walls in the isosceles right-angled triangle ribbed bends is decreased to the utmost and the corresponding particle impact angle is altered adequately due to the special shape of the ribs. In addition, the rib erosion rate, the sidewall erosion rate and the bend wall erosion rate are calculated separately. It is found that the rib erosion rate is half of the wall erosion rate, and the sidewall erosion rate is so low that it can be omitted compared with the bend wall erosion rate.

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37

Chang, Jianlong, Xudong Shao, Xiao Hu, and Shuangbiao Zhang. "Flow Characteristics of a Low Reynolds Number Jet in Crossflow with an Obstacle Block." Open Fuels & Energy Science Journal 9, no. 1 (September 21, 2016): 37–46. http://dx.doi.org/10.2174/1876973x01609010037.

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The jet in crossflow at very low Reynolds number (Re=100) with and without block is performed by means of large eddy simulation for the jet-to-crossflow velocity ratios (r) ranging from 1 to 3, and the corresponding flow characteristics are compared. The results show that the time-averaged particle trajectories of the jet are slightly changed if a block is presented, and the mixed vortices are weakened. The existence of the block also can accelerate the formation of stable counter-rotating vortex pair. At lower velocity ratio (r=1), the block has little effect on the jet in crossflow with a symmetrically positive and negative kidney shaped vortices. As the velocity ratio increases, the effect of block not only can generate an asymmetry of positive and negative kidney shaped vortices, but also it can reinforce the interaction between the positive and negative vortices in the jet in crossflow. The effect of block on the temperature field is also analyzed in detail.

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38

Daniele, S., J. Mantzaras, P. Jansohn, A. Denisov, and K. Boulouchos. "Flame front/turbulence interaction for syngas fuels in the thin reaction zones regime: turbulent and stretched laminar flame speeds at elevated pressures and temperatures." Journal of Fluid Mechanics 724 (April 29, 2013): 36–68. http://dx.doi.org/10.1017/jfm.2013.141.

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AbstractExperiments were performed in dump-stabilized axisymmetric flames to assess turbulent flame speeds (${S}_{T} $) and mean flamelets speeds (stretched laminar flame speeds, ${S}_{L, k} $). Fuels with significantly different thermodiffusive properties have been investigated, ranging from pure methane to syngas (${\mathrm{H} }_{2} \text{{\ndash}} \mathrm{CO} $ blends) and pure hydrogen, while the pressure was varied from 0.1 to 1.25 MPa. Flame front corrugation was measured with planar laser-induced fluorescence (PLIF) of the OH radical, while turbulence quantities were determined with particle image velocimetry (PIV). Two different analyses based on mass balance were performed on the acquired flame images. The first method assessed absolute values of turbulent flame speeds and the second method, by means of an improved fractal methodology, provided normalized turbulent flame speeds (${S}_{T} / {S}_{L, k} $). Deduced average Markstein numbers exhibited a strong dependence on pressure and hydrogen content of the reactive mixture. It was shown that preferential-diffusive-thermal (PDT) effects acted primarily on enhancing the stretched laminar flame speeds rather than on increasing the flame front corrugations. Interaction between flame front and turbulent eddies measured by the fractal dimension was shown to correlate with the eddy temporal activity.

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39

Stirrat, Sarah, Mohammed Z. Afsar, and Edmondo Minisci. "Assessment of Optimization Methods for Aeroacoustic Prediction of Trailing-Edge Interaction Noise in Axisymmetric Jets." Mathematics 9, no. 9 (April 28, 2021): 998. http://dx.doi.org/10.3390/math9090998.

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Our concern in this paper is in the fine-tuning of the arbitrary parameters within the upstream turbulence structure for the acoustic spectrum of a rapid-distortion theory (RDT)-based model of trailing-edge noise. RDT models are based on an appropriate asymptotic limit of the Linearized Euler Equations and apply when the interaction time of the turbulence with the surface edge discontinuity is small compared to the eddy turnover time. When an arbitrary transversely sheared jet mean flow convects a finite region of nonhomogeneous turbulence, the acoustic spectrum of the pressure field scattered by the trailing-edge depends on (among other things) the upstream turbulence via the Fourier transform of the correlation function, R22 (where subscript 2 refers to a co-ordinate surface normal to the plate). We show that the length and time scale parameters that govern the spatial and temporal de-correlation of R22 can be found using formal optimization methods to avoid any uncertainty in their selection by hand-tuning. We assess various optimization methods that are broadly categorized into an ‘evolutionary’ and ‘non-evolutionary’ paradigm. That is, we optimize the acoustic spectrum using the Multi-Start algorithm, Particle Swarm Optimization and the Multi-Population Adaptive Inflationary Differential Evolution Algorithm. The optimization is based upon different objective functions for the acoustic spectrum and/or turbulence structure. We show that this approach, while resulting in the total modest increase in computation time (on average 2 h), gives excellent prediction over most frequencies (within 2–4 dB) where the trailing-edge noise associated amplification in sound exists.

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40

Kähler, Christian J., Sven Scharnowski, and Christian Cierpka. "Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions." Journal of Fluid Mechanics 796 (April 29, 2016): 257–84. http://dx.doi.org/10.1017/jfm.2016.250.

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The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

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41

Pedersen, Nicholas, Poul S. Larsen, and Christian B. Jacobsen. "Flow in a Centrifugal Pump Impeller at Design and Off-Design Conditions—Part I: Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) Measurements." Journal of Fluids Engineering 125, no. 1 (January 1, 2003): 61–72. http://dx.doi.org/10.1115/1.1524585.

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Detailed optical measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller of industrial design have been performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). Results include instantaneous and ensemble averaged PIV velocity vector maps as well as bin-resolved LDV data acquired in the midplane between hub and shroud of the impeller. The flow is surveyed at both design load and at severe off-design conditions. At design load, Q=Qd, the mean field of relative velocity is predominantly vane congruent, showing well-behaved flow with no separation. At quarter-load, Q=0.25Qd, a previously unreported “two-channel” phenomenon consisting of alternate stalled and unstalled passages was observed, with distinct flow congruence between every second of the six passages. A large recirculation cell blocked the inlet to the stalled passage while a strong relative eddy dominated the remaining parts of the passage. The stall phenomenon was steady, nonrotating and not initiated via the interaction with stationary components. The study demonstrates that the PIV technique is efficient in providing reliable and detailed velocity data over a full impeller passage, also in the close vicinity of walls due to the use of fluorescent seeding. A quantitative comparison of blade-to-blade distributions of mean fields obtained by PIV and LDV showed a satisfactory agreement.

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42

Durango-Cogollo, Marvin, Jose Garcia-Bravo, Brittany Newell, and Andres Gonzalez-Mancera. "CFD Modeling of Hydrocyclones—A Study of Efficiency of Hydrodynamic Reservoirs." Fluids 5, no. 3 (July 21, 2020): 118. http://dx.doi.org/10.3390/fluids5030118.

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The dynamics of hydrocyclones is complex, because it is a multiphase flow problem that involves interaction between a discrete phase and multiple continuum phases. The performance of hydrocyclones is evaluated by using Computational Fluid Dynamics (CFD), and it is characterized by the pressure drop, split water ratio, and particle collection efficiency. In this paper, a computational model to improve and evaluate hydrocyclone performance is proposed. Four known computational turbulence models (renormalization group (RNG) k- ε , Reynolds stress model (RSM), and large-eddy simulation (LES)) are implemented, and the accuracy of each for predicting the hydrocyclone behavior is assessed. Four hydrocyclone configurations were analyzed using the RSM model. By analyzing the streamlines resulting from those simulations, it was found that the formation of some vortices and saddle points affect the separation efficiency. Furthermore, the effects of inlet width, cone length, and vortex finder diameter were found to be significant. The cut-size diameter was decreased by 33% compared to the Hsieh experimental hydrocyclone. An increase in the pressure drop leads to high values of cut-size and classification sharpness. If the pressure drop increases to twice its original value, the cut-size and the sharpness of classification are reduced to less than 63% and 55% of their initial values, respectively.

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43

Giglio, Federico, Stefania Romano, Sonia Albertazzi, Francesca Chiarini, Mariangela Ravaioli, Marco Ligi, and Lucilla Capotondi. "Sediment Dynamics of the Neretva Channel (Croatia Coast) Inferred by Chemical and Physical Proxies." Applied Sciences 10, no. 3 (January 23, 2020): 807. http://dx.doi.org/10.3390/app10030807.

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We examined the transport of sediments and their surficial pathways from the mouth of Neretva River, through the Neretva Channel, toward the Adriatic Sea. This research was based on twelve box-cores and five grab samples collected within the Neretva Channel. Sediment dynamics were evaluated using several proxies, such as organic matter, radiochemical isotopes and select metal concentrations and physical parameters. The data analysis showed that the influence of the river on particle distribution along the Neretva Channel decreases northward, with an estimated sediment accumulation rate ranging from 1.9 to 8.5 mm/yr. The lowest accumulation rate was found in the sector not influenced by river inflow, whereas the preferential sediment accumulation area is in the center of the basin. We speculate that dispersion and accumulation of sediments are both driven by an eddy in the waters of the Neretva Channel triggered/or intensified seasonally by the interaction of karstic springs, river input and Adriatic Sea waters. Our results indicate that the anthropogenic factor does not affect the concentration of metals within the channel and that the river particles dynamics determine the Pb areal distribution, while Cr and Ni have a possible source located to the northwest of the river-mouth.

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44

Bushuk, Mitchell, David M. Holland, Timothy P. Stanton, Alon Stern, and Callum Gray. "Ice scallops: a laboratory investigation of the ice–water interface." Journal of Fluid Mechanics 873 (June 28, 2019): 942–76. http://dx.doi.org/10.1017/jfm.2019.398.

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Ice scallops are a small-scale (5–20 cm) quasi-periodic ripple pattern that occurs at the ice–water interface. Previous work has suggested that scallops form due to a self-reinforcing interaction between an evolving ice-surface geometry, an adjacent turbulent flow field and the resulting differential melt rates that occur along the interface. In this study, we perform a series of laboratory experiments in a refrigerated flume to quantitatively investigate the mechanisms of scallop formation and evolution in high resolution. Using particle image velocimetry, we probe an evolving ice–water boundary layer at sub-millimetre scales and 15 Hz frequency. Our data reveal three distinct regimes of ice–water interface evolution: a transition from flat to scalloped ice; an equilibrium scallop geometry; and an adjusting scallop interface. We find that scalloped-ice geometry produces a clear modification to the ice–water boundary layer, characterized by a time-mean recirculating eddy feature that forms in the scallop trough. Our primary finding is that scallops form due to a self-reinforcing feedback between the ice-interface geometry and shear production of turbulent kinetic energy in the flow interior. The length of this shear production zone is therefore hypothesized to set the scallop wavelength.

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45

Tachie, M. F., and K. K. Adane. "PIV Study of Shallow Open Channel Flow Over d- and k-Type Transverse Ribs." Journal of Fluids Engineering 129, no. 8 (March 13, 2007): 1058–72. http://dx.doi.org/10.1115/1.2746910.

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A particle image velocimetry was used to study shallow open channel turbulent flow over d-type and k-type transverse ribs of square, circular, and semi-circular cross sections. The ratio of boundary layer thickness to depth of flow varied from 50% to 90%. The mean velocities and turbulent quantities were evaluated at the top plane of the ribs to characterize interaction between the cavities and overlying boundary layer. It was found that the overlying boundary layer interacts more strongly with k-type cavities than observed for d-type cavities. The profiles of the mean velocities and turbulent statistics were then spatially averaged over a pitch, and these profiles were used to study the effects of rib type and cross section on the flow field. The mean velocity gradients were found to be non-negligible across the boundary layer, and the implications of this observation for momentum transport, eddy viscosity, and mixing length distributions are discussed. The results show that the skin friction coefficient, Reynolds stresses and mixing length distributions are independent of rib cross section for d-type. For the k-type ribs, significant variations in skin friction coefficient values, mean flow, and turbulence fields are observed between square ribs and circular/semi-circular ribs.

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46

Giridhar, R. "Computational Study of Operating Parameters on Performance of Compound Hydrocyclone." International Journal for Research in Applied Science and Engineering Technology 9, no. VII (July 30, 2021): 2517–24. http://dx.doi.org/10.22214/ijraset.2021.36878.

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The dynamics of hydro cyclones is complex, because it is a multiphase flow problem that involves interaction between a discrete phase and multiple continuum phases. The performance of hydro cyclones is evaluated by using Computational Fluid Dynamics (CFD), and it is characterized by the pressure drop, split water ratio, and particle collection efficiency. In this paper, a computational model to improve and evaluate hydro cyclone performance is proposed. Computational turbulence models (renormalization group (RNG) k-ε, Reynolds’s stress model (RSM), and large-eddy simulation (LES)) are implemented, and the accuracy of each for predicting the hydro cyclone behavior is assessed. Four hydro cyclone configurations were analyzed using the RSM model. By analyzing the streamlines resulting from those simulations, it was found that the formation of some vortices and saddle points affect the separation efficiency. Furthermore, the effects of inlet width, cone length, and vortex finder diameter were found to be significant. The cut-size diameter was decreased compared to the Hsieh experimental hydro cyclone. An increase in the pressure drops leads to high values of cut-size and classification sharpness. If the pressure drop increases to twice its original value, the cut-size and the sharpness of classification are reduced to their initial values, respectively.

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47

Čajová Kantová, Nikola, Sławomir Sładek, Jozef Jandačka, Alexander Čaja, and Radovan Nosek. "Simulation of Biomass Combustion with Modified Flue Gas Tract." Applied Sciences 11, no. 3 (January 30, 2021): 1278. http://dx.doi.org/10.3390/app11031278.

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The combustion of biomass is accompanied by the formation of particulate matter, the presence of which in the atmosphere harms human health. It is important to show the issues of reducing these pollutants and their impact on human health. This article focuses on the process of biomass combustion. The used model consists of two parts: the combustion chamber and the flue gas tract. The article shows four types of modification of the flue gas tract designed to reduce the amount of particulate matter in the atmosphere. Baffles are located in the flue gas tract, which is designed to capture the particulate matter. The final model is simulated by turbulent–viscosity models, k-ε realizable model, and then k-ω shear stress transport model. The interaction between turbulence and chemical reactions is expressed by using the Eddy Dissipation Concept model. The results then show different profiles of temperature, velocity, and particle distribution. Based on the evaluated data from two different calculations, it can be concluded that the baffles have a significant effect on the reduction of particulate matter in the atmosphere. The used baffles are able to capture mainly particles with a diameter greater than 100 µm. A significant number of particles with a diameter lower than 100 µm flows from the flue gas tract to the surrounding environment.

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48

Wu, Shijie, Matteo Rubinato, and Qinqin Gui. "SPH Simulation of Interior and Exterior Flow Field Characteristics of Porous Media." Water 12, no. 3 (March 24, 2020): 918. http://dx.doi.org/10.3390/w12030918.

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At the present time, one of the most relevant challenges in marine and ocean engineering and practice is the development of a mathematical modeling that can accurately replicate the interaction of water waves with porous coastal structures. Over the last 60 years, multiple techniques and solutions have been identified, from linearized solutions based on wave theories and constant friction coefficients to very sophisticated Eulerian or Lagrangian solvers of the Navier-Stokes (NS) equations. In order to explore the flow field interior and exterior of the porous media under different working conditions, the Smooth Particle Hydrodynamics (SPH) numerical simulation method was used to simulate the flow distribution inside and outside a porous media applied to interact with the wave propagation. The flow behavior is described avoiding Euler’s description of the interface problem between the Euler mesh and the material selected. Considering the velocity boundary conditions and the cyclical circulation boundary conditions at the junction of the porous media and the water flow, the SPH numerical simulation is used to analyze the flow field characteristics, as well as the longitudinal and vertical velocity distribution of the back vortex flow field and the law of eddy current motion. This study provides innovative insights on the mathematical modelling of the interaction between porous structures and flow propagation. Furthermore, there is a good agreement (within 10%) between the numerical results and the experimental ones collected for scenarios with porosity of 0.349 and 0.475, demonstrating that SPH can simulate the flow patterns of the porous media, the flow through the inner and outer areas of the porous media, and the flow field of the back vortex region. Results obtained and the new mathematical approach used can help to effectively simulate with high-precision the changes along the water depth, for a better design of marine and ocean engineering solutions adopted to protect coastal areas.

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49

Burton, Tristan M., and John K. Eaton. "High-resolution simulations of particle–eddy interactions." Powder Technology 125, no. 2-3 (June 2002): 104–10. http://dx.doi.org/10.1016/s0032-5910(01)00496-x.

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50

Pérez-Landa, G., P. Ciais, G. Gangoiti, J. L. Palau, A. Carrara, B. Gioli, F. Miglietta, M. Schumacher, M. M. Millán, and M. J. Sanz. "Mesoscale circulations over complex terrain in the Valencia coastal region, Spain – Part 2: Modeling CO2 transport using idealized surface fluxes." Atmospheric Chemistry and Physics 7, no. 7 (April 16, 2007): 1851–68. http://dx.doi.org/10.5194/acp-7-1851-2007.

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Abstract. Vertical profiles of CO2 concentration were collected during an intensive summer campaign in a coastal complex-terrain region within the frame of the European Project RECAB (Regional Assessment and Modelling of the Carbon Balance in Europe). The region presents marked diurnal mesoscale circulation patterns. These circulations result in a specific coupling between atmospherically transported CO2 and its surface fluxes. To understand the effects of this interaction on the spatial variability of the observed CO2 concentrations, we applied a high-resolution transport simulation to an idealized model of land biotic fluxes. The regional Net Ecosystem Exchange fluxes were extrapolated for different land-use classes by using a set of eddy-covariance measurements. The atmospheric transport model is a Lagrangian particle dispersion model, driven by a simulation of the RAMS mesoscale model. Our simulations were able to successfully reproduce some of the processes controlling the mesoscale transport of CO2. A semi-quantitative comparison between simulations and data allowed us to characterize how the coupling between mesoscale transport and surface fluxes produced CO2 spatial gradients in the domain. Temporal averages in the simulated CO2 field show a covariance between flux and transport consisting of: 1) horizontally, a CO2 deficit over land, mirrored by a CO2 excess over the sea and 2) vertically, the prevalence of a mean CO2 depletion between 500 and 2000 m, and a permanent build-up of CO2 in the lower levels.

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Journal articles on the topic 'Particle-eddy interaction'

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