Showing papers on "Fluid dynamics published in 2017"
TL;DR: Although neural networks have been applied previously to complex fluid flows, the article featured here is the first to apply a true DNN architecture, specifically to Reynolds averaged Navier Stokes turbulence models, suggesting that DNNs may play a critically enabling role in the future of modelling complex flows.
Abstract: It was only a matter of time before deep neural networks (DNNs) – deep learning – made their mark in turbulence modelling, or more broadly, in the general area of high-dimensional, complex dynamical systems. In the last decade, DNNs have become a dominant data mining tool for big data applications. Although neural networks have been applied previously to complex fluid flows, the article featured here (Ling et al., J. Fluid Mech., vol. 807, 2016, pp. 155–166) is the first to apply a true DNN architecture, specifically to Reynolds averaged Navier Stokes turbulence models. As one often expects with modern DNNs, performance gains are achieved over competing state-of-the-art methods, suggesting that DNNs may play a critically enabling role in the future of modelling complex flows.
609 citations
TL;DR: The physics of droplet ejection under strong evaporative flow is described using simulations of the laser powder bed interactions to elucidate the experimental results and the relevance of vapor driven entrainment of metal micro-particles to similar fluid dynamic studies in other fields of science will be discussed.
Abstract: The results of detailed experiments and finite element modeling of metal micro-droplet motion associated with metal additive manufacturing (AM) processes are presented. Ultra high speed imaging of melt pool dynamics reveals that the dominant mechanism leading to micro-droplet ejection in a laser powder bed fusion AM is not from laser induced recoil pressure as is widely believed and found in laser welding processes, but rather from vapor driven entrainment of micro-particles by an ambient gas flow. The physics of droplet ejection under strong evaporative flow is described using simulations of the laser powder bed interactions to elucidate the experimental results. Hydrodynamic drag analysis is used to augment the single phase flow model and explain the entrainment phenomenon for 316 L stainless steel and Ti-6Al-4V powder layers. The relevance of vapor driven entrainment of metal micro-particles to similar fluid dynamic studies in other fields of science will be discussed.
333 citations
Posted Content•
TL;DR: The relativistic viscous fluid dynamics was formulated from first principles in an effective field theory framework, based entirely on the knowledge of symmetries and long-lived degrees of freedom.
Abstract: Ten years ago, relativistic viscous fluid dynamics was formulated from first principles in an effective field theory framework, based entirely on the knowledge of symmetries and long-lived degrees of freedom. In the same year, numerical simulations for the matter created in relativistic heavy-ion collision experiments became first available, providing constraints on the shear viscosity in QCD. The field has come a long way since then. We present the current status of the theory of non-equilibrium fluid dynamics in 2017, including the divergence of the fluid dynamic gradient expansion, resurgence, non-equilibrium attractor solutions, the inclusion of thermal fluctuations as well as their relation to microscopic theories. Furthermore, we review the theory basis for numerical fluid dynamics simulations of relativistic nuclear collisions, and comparison of modern simulations to experimental data for nucleus-nucleus, nucleus-proton and proton-proton collisions.
254 citations
TL;DR: In this paper, an integrated computational materials science approach for selective laser melting (SLM) at the mesoscale is presented a particle dropping model was developed to simulate the representative powder-bed particle distribution of a measured titanium alloy powder Thermal fluid flow and resulting microstructural evolution of a set of laser scanned single tracks with different powder layer thicknesses and scanning speeds were also studied using both computational and experimental approaches.
219 citations
TL;DR: In this article, the mixed convective flow of magneto-nanofluid bounded by a vertical stretchable surface considering Brownian motion and thermophoretic diffusion effects is analyzed.
169 citations
TL;DR: It is shown that the time-scales of interface movement and brine layer swelling leading to snap-off are several minutes, orders of magnitude slower than observed for Haines jumps in drainage, and the local capillary pressure increases rapidly aftersnap-off as the trapped phase finds a position that is a new local energy minimum.
Abstract: Understanding the pore-scale dynamics of two-phase fluid flow in permeable media is important in many processes such as water infiltration in soils, oil recovery, and geo-sequestration of CO2. The two most important processes that compete during the displacement of a non-wetting fluid by a wetting fluid are pore-filling or piston-like displacement and snap-off; this latter process can lead to trapping of the non-wetting phase. We present a three-dimensional dynamic visualization study using fast synchrotron X-ray micro-tomography to provide new insights into these processes by conducting a time-resolved pore-by-pore analysis of the local curvature and capillary pressure. We show that the time-scales of interface movement and brine layer swelling leading to snap-off are several minutes, orders of magnitude slower than observed for Haines jumps in drainage. The local capillary pressure increases rapidly after snap-off as the trapped phase finds a position that is a new local energy minimum. However, the pressure change is less dramatic than that observed during drainage. We also show that the brine-oil interface jumps from pore-to-pore during imbibition at an approximately constant local capillary pressure, with an event size of the order of an average pore size, again much smaller than the large bursts seen during drainage.
166 citations
TL;DR: In this paper, the lattice Boltzmann (LB) method has attracted broad interest in the computational fluid dynamics and the numerical heat transfer communities, primarily due to its kinetic nature making it appropriate for modeling complex multiphase transport phenomena.
Abstract: Fuel cells and flow batteries are promising technologies to address climate change and air pollution problems. An understanding of the complex multiscale and multiphysics transport phenomena occurring in these electrochemical systems requires powerful numerical tools. Over the past decades, the lattice Boltzmann (LB) method has attracted broad interest in the computational fluid dynamics and the numerical heat transfer communities, primarily due to its kinetic nature making it appropriate for modeling complex multiphase transport phenomena. More importantly, the LB method fits well with parallel computing due to its locality feature, which is required for large-scale engineering applications. In this article, we review the LB method for gas–liquid two-phase flows, coupled fluid flow and mass transport in porous media, and particulate flows. Examples of applications are provided in fuel cells and flow batteries. Further developments of the LB method are also outlined.
153 citations
TL;DR: Forced convection of non-Newtonian nanofluid, aqueous solution of carboxymethyl cellulose (CMC)-Aluminum oxide through a microtube is studied numerically in this article.
Abstract: Forced convection of non-Newtonian nanofluid, aqueous solution of carboxymethyl cellulose (CMC)–Aluminum oxide through a microtube is studied numerically. The length and diameter of tube are L = 5 mm and D = 0.2 mm, respectively which means the length is long enough compared to the diameter. The effects of different values of nanoparticles volume fraction, slip coefficient and Reynolds number are investigated on the slip velocity and temperature jump boundary conditions. Moreover the suitable validations are presented to confirm the achieved results accuracy. The results are shown as the dimensionless velocity and temperature profiles; however the profiles of local and averaged Nusselt number are also provided. It is seen that more volume fraction and slip coefficient correspond to higher Nusselt number especially at larger amounts of Re.
148 citations
Book•
01 Nov 2017TL;DR: In this article, the authors present a review of single-phase flow concepts and their application in the context of two-phase flows. But their focus is on the application of these concepts in computer simulation and virtual prototyping.
Abstract: 1. Review of Single-Phase Flow 1.1 Basic Fluid Flow Concepts 1.2 Flow Field Descriptions 1.3 Conservation Laws 1.4 Turbulence 1.5 Solution Techniques 1.6 Homework Problem Assignments 2. Basic Concepts of Two-Phase Flow Theory 2.1 Flow Regime Classifications and Modeling Approaches 2.2 Dispersed Flow Definitions, Phase Properties and Phase Coupling 2.3 Mass, Momentum and Heat Transfer 2.4 Statistical Descriptions 2.5 Highlights of Industrial Dispersed Flows 2.6 Homework Problem Assignments 3. Derivations of Two-Phase Flow Modelling Equations 3.1 Averaging Techniques and Constitutive Equations 3.2 Mixture Models 3.3 Separated Flow Models 3.4 Problem Assignments 4. Analyses and Solutions of Basic Two-Phase Flow Problems 4.1 Numerical Solution Tools 4.2 Mixture Flow Applications 4.3 Particle Trajectory Dynamics 4.4 Two-Fluid Model Applications 4.5 Project Assignments 5. Selected Case Studies 5.1 Mathematical Modeling, Computer Simulation and Virtual Prototyping 5.2 Quasi-Homogeneous Equilibrium Flows (EULER) 5.3 Separated Flows 1: Fluid Particle Models (EULER_Lagrange) 5.4 Separated Flows 2: Two-Fluid Models (EULER-EULER) Appendicies
148 citations
TL;DR: The ability to simulate immiscible two-component flow imbibition and drainage is validated, with excellent results, by numerical simulations in a Berea sandstone, a frequently used benchmark case used in this field, using a complex geometry that originates from a 3D scan of a porous sandstone.
Abstract: This article presents a three-dimensional numerical framework for the simulation of fluid-fluid immiscible compounds in complex geometries, based on the multiple-relaxation-time lattice Boltzmann method to model the fluid dynamics and the color-gradient approach to model multicomponent flow interaction. New lattice weights for the lattices D3Q15, D3Q19, and D3Q27 that improve the Galilean invariance of the color-gradient model as well as for modeling the interfacial tension are derived and provided in the Appendix. The presented method proposes in particular an approach to model the interaction between the fluid compound and the solid, and to maintain a precise contact angle between the two-component interface and the wall. Contrarily to previous approaches proposed in the literature, this method yields accurate solutions even in complex geometries and does not suffer from numerical artifacts like nonphysical mass transfer along the solid wall, which is crucial for modeling imbibition-type problems. The article also proposes an approach to model inflow and outflow boundaries with the color-gradient method by generalizing the regularized boundary conditions. The numerical framework is first validated for three-dimensional (3D) stationary state (Jurin's law) and time-dependent (Washburn's law and capillary waves) problems. Then, the usefulness of the method for practical problems of pore-scale flow imbibition and drainage in porous media is demonstrated. Through the simulation of nonwetting displacement in two-dimensional random porous media networks, we show that the model properly reproduces three main invasion regimes (stable displacement, capillary fingering, and viscous fingering) as well as the saturating zone transition between these regimes. Finally, the ability to simulate immiscible two-component flow imbibition and drainage is validated, with excellent results, by numerical simulations in a Berea sandstone, a frequently used benchmark case used in this field, using a complex geometry that originates from a 3D scan of a porous sandstone. The methods presented in this article were implemented in the open-source PALABOS library, a general C++ matrix-based library well adapted for massive fluid flow parallel computation.
134 citations
TL;DR: In this article, scale-dependent spatial filtering on the Vlasov equation is used to extract information at prescribed scales and introduce several energy transfer functions, such as − (P · ∇ ) · u, which can trigger a channel of the energy conversion between fluid flow and random motions.
Abstract: Kinetic plasma turbulence cascade spans multiple scales ranging from macroscopic fluid flow to sub-electron scales. Mechanisms that dissipate large scale energy, terminate the inertial range cascade, and convert kinetic energy into heat are hotly debated. Here, we revisit these puzzles using fully kinetic simulation. By performing scale-dependent spatial filtering on the Vlasov equation, we extract information at prescribed scales and introduce several energy transfer functions. This approach allows highly inhomogeneous energy cascade to be quantified as it proceeds down to kinetic scales. The pressure work, − ( P · ∇ ) · u , can trigger a channel of the energy conversion between fluid flow and random motions, which contains a collision-free generalization of the viscous dissipation in collisional fluid. Both the energy transfer and the pressure work are strongly correlated with velocity gradients.
TL;DR: In this paper, an industrial-sized dual fluidized bed (DFB) system was simulated with the commercial code CPFD Barracuda and four drag models were tested, and it was found that the EMMS drag model fits best with an error of below 20%, whereas the other drag models produced much larger errors.
TL;DR: In this article, the authors presented a numerical study of the turbulent compressible fluid in a supersonic ejector and compared seven RANS turbulence closures with different near-wall modeling options to investigate the wall treatment effect on numerical results.
TL;DR: In this article, a fully coupled 3D hydro-mechanical model with real porous seepage is presented for simulating hydraulic fracturing, which can capture crack initiation and propagation, and the fluid pressure evolution during hydraulic fracturing.
TL;DR: In this article, the magnetohydrodynamics (MHD) flow of a third grade fluid over an exponentially stretching sheet is analyzed in the presence of first order chemical reaction. And convergent solutions of the resulting differential systems are presented in series forms.
TL;DR: A comprehensive literature review on the simulation techniques being developed in recent years for describing unique flow behaviors in shale and tight gas reservoirs is provided in this paper, where the advances in modeling gas flow and transport mechanisms during the primary and enhanced gas recovery processes are reviewed in detail.
TL;DR: In this article, a fully coupled, hydro-mechanical (HM) formulation for finite-discrete element method computer code is presented, where fluid flow is assumed to occur through the same triangular mesh used for the mechanical calculations.
TL;DR: In this paper, numerical analysis of natural convective heat transfer and fluid flow inside a porous wavy cavity filled with a nanofluid has been carried out, where a heat source of constant temperature is located on the right vertical wall.
TL;DR: The results show that helicity can remain constant even in a viscous fluid and provide an improved basis for understanding and manipulating helicity in real flows.
Abstract: Helicity, a topological measure of the intertwining of vortices in a fluid flow, is a conserved quantity in inviscid fluids but can be dissipated by viscosity in real flows. Despite its relevance across a range of flows, helicity in real fluids remains poorly understood because the entire quantity is challenging to measure. We measured the total helicity of thin-core vortex tubes in water. For helical vortices that are stretched or compressed by a second vortex, we found conservation of total helicity. For an isolated helical vortex, we observed evolution toward and maintenance of a constant helicity state after the dissipation of twist helicity by viscosity. Our results show that helicity can remain constant even in a viscous fluid and provide an improved basis for understanding and manipulating helicity in real flows.
TL;DR: In this article, a 3D computational fluid dynamics (CFD) simulation of endothermic steam methane reforming in a random packed bed of 807 spherical catalyst particles at a tube-to-particle diameter ratio of N = 5.96 with constant wall heat flux is presented.
TL;DR: In this paper, the authors evaluated the heat transfer and flow rate characteristics of the nanofluid that converges into the square ducts with different aspect ratios, and established a baseline modeling for the fluid flow over a rectangular chamber that is designed in the form of a square duct of ratio 1:1.
Abstract: The study evaluates the nanofluid using finite element analysis with base fluid (water) and seeding particles (Aluminum oxide). This is placed over a convergence channel consisting of varying aspect ratio that are evaluated quantitatively to enhance the heat transfer properties of the nanofluid.We have considered frictional loss characteristics that increases the flow of the fluid with Reynolds numbers varying from 100-2000 is compared.A baseline modeling is established using the methodology analysis for the fluid flow over a rectangular chamber that is designed in the form of a square duct of ratio 1:1. The analysis is carried out over the heat transfer and flow rate characteristics of the nanofluid that converges into the square ducts with different aspect ratio, is analyzed.The concentration of the nano fluid is maintained at the constant rate, which is used for studying the flow rate influence over different aspect ratios. The thermal and flow characteristics is analyzed in such situation and validated against other literatures to check the efficiency in the converging rectangular oxygen free copper channel.The simulation results shows an increase in temperature on the duct out and drop in temperature on the inlet walls of the tube.The pressure changes and shear stress along the walls of the chamber is not much noticed and it is constant throughout the entire chamber.
TL;DR: In this paper, the authors investigated the dual effect of viscosity on gas holdup and flow regime transition as well as bubble size distributions in a large-diameter and large-scale bubble column.
TL;DR: In this article, the Laplace transform method was used to solve the convection flow of differential type fluid with non-integer order Caputo-fractional derivatives, and the non-dimensional temperature, concentration, and velocity fields were solved by using Laplace Transform method.
TL;DR: In this paper, a non-Darcy model is introduced and the corresponding correlation parameters are derived by fitting the available experimental data, which is used to estimate the well performance of a vertical well and a multi-fractured horizontal well.
TL;DR: In this article, the authors analyzed the influence of shear processes on nonlinear flow behavior through 3D rough-walled rock fractures and found that the relationship between the volumetric flow rate and hydraulic gradient can be well fit using Forchheimer's law.
TL;DR: In this paper, the effect of applying homogeneous magnetic field in Hartman numbers of 0, 30 and 60 on the natural and forced heat transfer parameters of nanofluid has been analyzed and compared.
TL;DR: In this paper, the effect of dimensions of a new design of ribs on heat transfer parameters and laminar flow of the nanofluid Water-TiO 2 has been investigated.
Abstract: In this study, the effect of dimensions of a new design of ribs on heat transfer parameters and laminar flow of the nanofluid Water-TiO 2 has been investigated. The inventive design of the ribs has been simulated in the form of semi-attached and offset mid-truncated ribs in a 3D microchannel with triangular cross-section. The offset mid-truncated ribs design also exercises less prevention-where the ribs are located for the fluid flow. The semi-attached and offset mid-truncated ribs have been located inside the channel to improve heat transfer and the effects of the dimensions and the number of the ribs have been studied. In this study, the base fluid is Water while the effect of volume fraction of the nanoparticle (TiO 2 ) on heat transfer and physical properties of the fluid is investigated. The results indicate that the ribs affect the physics of the fluid whose effect greatly depends on the Reynolds number of the flow.
TL;DR: In this article, an improved surface tension model is proposed to take into account the influence of sulfur content and temperature at the surface of a melt pool, and the results show that the sulfur redistribution leads to transitional Marangoni flow.
TL;DR: In this article, heat transfer in MHD stagnation point flow of cross fluid over a stretched surface is studied, which is a kind of generalized Newtonian liquid whose viscosity relies on shear rate Fluid is electrically conducting in the presence of an applied magnetics fluids System of ordinary differential equations is obtained by appropriate transformation.
Abstract: The present investigation studies heat transfer in MHD stagnation point flow of Cross fluid over a stretched surface A Cross fluid is a kind of generalized Newtonian liquid whose viscosity relies on shear rate Fluid is electrically conducting in the presence of an applied magnetics fluids System of ordinary differential equations is obtained by appropriate transformation The flow equations are solved with the help of Runga-Kutta-Fehlberg method Convergent series solutions are computed for the resulting nonlinear differential system Impact of different parameters on the velocity and temperature profiles is studied It is observed that velocity distribution decreases for larger values of Weissenberg number However temperature decays for rising values of Prandtl number Further computation for surface drag force and heat transfer rate are presented and discussed through numerical data
TL;DR: In this paper, a numerical analysis of laminar natural convection with entropy generation in a partially heated open triangular cavity filled with a Cu-water nanofluid has been carried out.