270 results found
Britovsek G, Tomov A, Muller E, et al., 2018, Ethylene oligomerisation beyond Schulz-Flory distributions, 255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Matar O, Lee RY, Shaffee A, et al., 2018, Sand agglomeration in oil & gas reservoirs: Chemistry, experiments and simulations, 255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Che Z, Matar OK, 2018, Impact of droplets on immiscible liquid films, Soft Matter, Vol: 14, Pages: 1540-1551, ISSN: 1744-683X
The impact of droplets on liquid films is a ubiquitous phenomenon not only in nature but also in many industrial applications. Compared to the widely-studied impact of droplets on films of identical fluids, the impact of droplets on immiscible films has received far less attention. In the present work, we show using high-speed imaging that immiscibility has a profound effect on the impact dynamics. The impact of a water droplet on an oil film leads to the formation of a compound crown followed by a central jet, whereas that of an oil droplet on a water film results in rapid spreading on the film surface driven by a large, positive spreading factor. In the former scenario, the central jet occurs due to the severe stretching of the droplet during the formation of the crown and then the retraction of the droplet by capillarity, which leads to the collision of fluid at the impact point. A model for the elongation dynamics of the central jet is proposed based on energy conservation. The effects of key parameters controlling the impact process are analysed, including the droplet Ohnesorge and Weber numbers, the viscosity ratio, and the dimensionless film thickness. Different impact outcomes are discussed, such as bouncing, deposition, and oscillation of the impact droplet, the formation and collapse of the compound crown, and the formation and tip-pinching of the central jet. This study not only provides physical insights into the impact dynamics, but could also facilitate the control and optimisation of the droplet impact process in a number of applications as highlighted herein.
Seungwon S, Chergui J, Juric D, et al., 2018, A hybrid interface tracking – level set technique for multiphase flow with soluble surfactant, Journal of Computational Physics, Vol: 359, ISSN: 0021-9991
A formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu & Tryggvason (JCP 274 (2014) 737–757) is adapted to the context of the Level Contour Reconstruction Method, LCRM, (Shin et al. IJNMF 60 (2009) 753–778) which is a hybrid method that combines the advantages of the Front-tracking and Level Set methods. Particularly close attention is paid to the formulation and numerical implementation of the surface gradients of surfactant concentration and surface tension. Various benchmark tests are performed to demonstrate the accuracy of different elements of the algorithm. To verify surfactant mass conservation, values for surfactant diffusion along the interface are compared with the exact solution for the problem of uniform expansion of a sphere. The numerical implementation of the discontinuous boundary condition for the source term in the bulk concentration is compared with the approximate solution. Surface tension forces are tested for Marangoni drop translation. Our numerical results for drop deformation in simple shear are compared with experiments and results from previous simulations. All benchmarking tests compare well with existing data thus providing confidence that the adapted LCRM formulation for surfactant advection and diffusion is accurate and effective in three-dimensional multiphase flows with a structured mesh. We also demonstrate that this approach applies easily to massively parallel simulations.
Williams AGL, Sáenz PJ, Karapetsas G, et al., 2018, Evaporation of binary mixtures: Pools and droplets, Pages: 821-826, ISSN: 2377-424X
© 2018 International Heat Transfer Conference. All rights reserved. Evaporation of a binary mixture pool or droplet is a highly dynamic and complex process with flow driven by the presence of thermal and solutal Marangoni stresses. Experiments on ethanol/water drops have identified chaotic regimes on both the surface and interior of the droplet, while mixture composition has also been seen to govern drop wettability. Using both DNS and lubrication-type approaches, we present models for the evaporation of a binary mixture liquid pool and an axisymmetric binary droplet deposited on a heated substrate. For both cases we assume liquid surface tension is linearly dependent on both temperature and concentration while mixture properties such as viscosity also vary locally with concentration. In the case of the pool we consider a rectangular domain with a horizontal temperature gradient and use DNS to solve the governing equations. The Volume-of-Fluid method is used to account for the deformable liquid-gas interface. Systems with low Prandtl number (Pr < 1) are focused on and we examine the solutal effects arising from the introduction of the second component. For the drop we consider a thin profile with a moving contact line, taking also into account the commonly ignored effects of inertia which drives interfacial instability. We derive evolution equations and explore the dimensionless parameter space to examine the resultant effects on drop wetting and evaporation where we find qualitative agreement with experiments in both these areas.
Hennessy M, Vitale A, Matar O, et al., 2017, Monomer diffusion into static and evolving polymer networks during frontal photopolymerisation, Soft Matter, Vol: 13, Pages: 9199-9210, ISSN: 1744-683X
Frontal photopolymerisation (FPP) is a directional solidification process that converts monomer-rich liquid into crosslinked polymer solid by light exposure and finds applications ranging from lithography to 3D printing. Inherent to this process is the creation of an evolving polymer network that is exposed to a monomer bath. A combined theoretical and experimental investigation is performed to determine the conditions under which monomer from this bath can diffuse into the propagating polymer network and cause it to swell. First, the growth and swelling processes are decoupled by immersing pre-made polymer networks into monomer baths held at various temperatures. The experimental measurements of the network thickness are found to be in good agreement with theoretical predictions obtained from a nonlinear poroelastic model. FPP propagation experiments are then carried out under conditions that lead to swelling. Unexpectedly, for a fixed exposure time, swelling is found to increase with incident light intensity. The experimental data is well described by a novel FPP model accounting for mass transport and the mechanical response of the polymer network, providing key insights into how monomer diffusion affects the conversion profile of the polymer solid and the stresses that are generated during its growth. The predictive capability of the model will enable the fabrication of gradient materials with tuned mechanical properties and controlled stress development.
Matar OK, Wilson SK, 2017, Preface to the special issue celebrating 50 years of the Journal of Engineering Mathematics, Journal of Engineering Mathematics, Vol: 107, Pages: 1-4, ISSN: 0022-0833
Poesio P, Damone A, Matar OK, 2017, A multiscale approach to interpret and predict the apparent slip velocity at liquid-liquid interfaces, 35th Italian-Union-of-Thermp-Fluid Dynamics (UIT) Heat Transfer Conference (UIT), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Adebayo IT, Matar OK, 2017, Droplet impact on flowing liquid films with inlet forcing: the splashing regime, Soft Matter, Vol: 13, Pages: 7473-7485, ISSN: 1744-683X
The impact process of droplets falling obliquely on thin flowing films is studied using a high-speed imaging system with a focus on splashing. Frequency-forcing of the flow rate at the inlet is applied in order to form solitary waves prior to droplet impact. The outcomes associated with impact on targeted regions of the waves are examined; these include the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effect of varying the film flow rate, droplet size, and speed on the splashing regime for each of these regions is elucidated. The results are further compared with those associated with uncontrolled flowing films, and with quiescent films. The present work has demonstrated, for the first time, the contribution made by the spatial structure of waves to the outcome of droplet impact on flowing films.
Conroy D, Matar OK, 2017, Dynamics and stability of three-dimensional ferrofluid films in a magnetic field, Journal of Engineering Mathematics, Vol: 107, Pages: 253-268, ISSN: 0022-0833
We consider the interfacial dynamics of a thin, ferrofluid film flowing down an inclined substrate, under the action of a magnetic field, bounded above by an inviscid gas. The fluid is assumed to be weakly conducting, and its dynamics are governed by a coupled system of the steady Maxwell, Navier–Stokes, and continuity equations. The magnetization of the film is a function of the magnetic field, and is prescribed by a Langevin function. We make use of a long-wave reduction in order to solve for the dynamics of the pressure, velocity, and magnetic fields inside the film. The potential in the gas phase is solved by means of Fourier Transforms. Imposition of appropriate interfacial conditions allows for the construction of an evolution equation for the interfacial shape, via use of the kinematic condition, and the magnetic field. We study the three-dimensional evolution of the film to spanwise perturbations by solving the nonlinear equations numerically. The constant-volume configuration is considered, which corresponds to a slender drop flowing down an incline. A parametric study is then performed to understand the effect of the magnetic field on the stability and structure of the interface.
Xie Z, Lu L, Stoesser T, et al., 2017, Numerical simulation of three-dimensional breaking waves and its interaction with a vertical circular cylinder, JOURNAL OF HYDRODYNAMICS, Vol: 29, Pages: 800-804, ISSN: 1001-6058
Wave breaking plays an important role in wave-structure interaction. A novel control volume finite element method with adaptive unstructured meshes is employed here to study 3-D breaking waves. The numerical framework consists of a “volume of fluid” type method for the interface capturing and adaptive unstructured meshes to improve computational efficiency. The numerical model is validated against experimental measurements of breaking wave over a sloping beach and is then used to study the breaking wave impact on a vertical circular cylinder on a slope. Detailed complex interfacial structures during wave impact, such as plunging jet formation and splash-up are captured in the simulation, demonstrating the capability of the present method.
Che Z, Matar OK, 2017, Impact of droplets on liquid films in the presence of surfactant, Langmuir, Vol: 33, Pages: 12140-12148, ISSN: 0743-7463
The impact of droplets on liquid films is ubiquitous in natural and industrial processes, and surfactants can significantly alter the impact process by changing the local surface tension. Here we study the impact of droplets on liquid films in the presence of surfactant using high-speed photography, and reveal the flow pattern by dye-tracing. The effects of the droplet size and speed, and the initial film thickness on the impact process are elucidated. The results show that the flow is significantly affected by adding surfactant to the droplet, the liquid film, or to both phases. In particular, the film dye patterns form concentric circles and flower-shaped structures at low and high droplet Weber numbers, respectively. We also show how surfactant-induced Marangoni stresses modify these flow patterns, and alter the characteristics of the phenomena associated with the impact process, such as the propagation of capillary waves, the evolution of the crown, and the formation of secondary droplets. During the impact of surfactant droplets on thin water films, the Marangoni stresses can be sufficiently strong so as to drive film dewetting.
Matar OK, Wilson SK, 2017, Preface to the inaugural "Perspectives" article entitled "The importance of being thin" by Stephen H. Davis, Journal of Engineering Mathematics, Vol: 105, Pages: 1-2, ISSN: 0022-0833
Adebayo I, Xie Z, Che Z, et al., 2017, Doubly-excited pulse waves on thin liquid films flowing down an inclined plane: An experimental and numerical study, Physical Review E, Vol: 96, ISSN: 1539-3755
The interaction patterns between doubly excited pulse waves on thin liquid films flowing down an inclined plane are studied both experimentally and numerically. The effect of varying the film flow rate, interpulse interval, and substrate inclination angle on the pulse interaction patterns is examined. Our results show that different interaction patterns exist for these binary pulses, which include solitary wave behavior, partial or complete pulse coalescence, and pulse noncoalescence. A regime map of these patterns is plotted for each inclination angle examined, parametrized by the film Reynolds number and interpulse interval. Finally, the individual effect of the system parameters mentioned above on the coalescence distance of binary pulses in the “complete pulse coalescence” mode is studied; the results are compared to numerical simulations of the two-dimensional Navier-Stokes equations yielding good agreement.
Nowak E, Xie Z, Kovalchuk NM, et al., 2017, Bulk advection and interfacial flows in the binary coalescence of surfactant-laden and surfactant-free drops, Soft Matter, Vol: 13, Pages: 4616-4628, ISSN: 1744-683X
This work focuses on the study of bulk flows accompanying the coalescence of two aqueous drops, one containing surfactant and the other surfactant-free, in silicone oils of various viscosities. It is observed that the surfactant-free drop intrudes into the surfactant-laden drop in the form of a penetrating jet whose speed increases and average radius decreases with increasing outer phase viscosity. Mixing patterns within the coalescing drops are due to the force imbalance caused by capillary pressure difference and surfactant-induced Marangoni stresses. The driving force for mixing associated with the difference in interfacial tension between the drops is considerably stronger than that related to the drop size. The long timescale mixing of the drops is driven by rapid interior convection, and the subsequent, slow, diffusive process. Three-dimensional numerical simulations show excellent qualitative and quantitative agreement with the experimental results. The implications of our results to formulation strategies of complex microstructures in practical applications are also discussed.
Wray AW, Matar OK, Papageorgiou DT, 2017, Accurate low-order modeling of electrified falling films at moderate Reynolds number, Physical Review Fluids, Vol: 2, ISSN: 2469-990X
The two- and three-dimensional spatio-temporal dynamics of a falling, electrified leakydielectric film are studied. The method of weighted residuals is used to derive high-ordermodels that account for both inertia as well as second-order electrostatic effects. Themodels are validated against both linear theory and direct numerical simulations of theNavier-Stokes equations. It is shown that a simplified model offers a rapid computationaloption at the cost of a minimal decrease in accuracy. This model is then used to perform aparametric study in three dimensions.
Ibarra R, Matar OK, Markides CN, 2017, Flow structures in low-inclination stratified oil-water pipe-flows using laser-based diagnostic techniques, International Conference on Multiphase Production, Publisher: BHR Group, Pages: 71-85
In this work, a novel two-line laser-based diagnostic measurement technique was developed and applied to obtain combined space- and time-resolved phase and velocity information in low-inclination upward (<+5°) stratified flows of oil (Exxsol D140) and water. The strength of this technique is in enabling direct measurements in the non-refractive-index-matched fluids of interest, as opposed to substitute (optically matched) fluids whose properties may be less representative of those in real field-applications. The experimental test-section consisted of a 32-mm internal diameter pipe with a total length of 8.5 m. Results reveal interesting interactions between the co-flowing liquid phases. The velocity gradients at the interface are enhanced at high pipe inclinations for upward flows as the oil and water velocities increase and decrease, respectively. This also has a direct effect on the velocity fluctuations (quantified through their rms) and on the interfacial instabilities, which in turn affect the local velocity distributions in both phases.
Theodorakis PE, Muller EA, Craster RV, et al., 2017, Physical insights into the blood-brain barrier translocation mechanisms, Physical Biology, Vol: 14, ISSN: 1478-3975
The number of individuals suffering from diseases of the central nervous system (CNS) is growing with an aging population. While candidate drugs for many of these diseases are available, most of these pharmaceutical agents cannot reach the brain rendering most of the drug therapies that target the CNS inefficient. The reason is the blood–brain barrier (BBB), a complex and dynamic interface that controls the influx and efflux of substances through a number of different translocation mechanisms. Here, we present these mechanisms providing, also, the necessary background related to the morphology and various characteristics of the BBB. Moreover, we discuss various numerical and simulation approaches used to study the BBB, and possible future directions based on multi-scale methods. We anticipate that this review will motivate multi-disciplinary research on the BBB aiming at the design of effective drug therapies.
Wray AW, Papageorgiou DT, Matar OK, 2017, Reduced models for thick liquid layers with inertia on highly curved substrates, SIAM Journal on Applied Mathematics, Vol: 77, Pages: 881-904, ISSN: 0036-1399
A method is presented for deriving reduced models for fluid flows over highly curved substrates with wider applicability and accuracy than existing models in the literature. This is done by reducing the Navier--Stokes equations to a novel system of boundary layer like equations in a general geometric setting. This is accomplished using a new, relaxed set of scalings that assert only that streamwise variations are “slow”. These equations are then solved using the method of weighted residuals, which is demonstrated to be applicable regardless of the geometry selected. A large number of results in the literature can be derived as special cases of our general formulation. A few of the more interesting cases are demonstrated. Finally, the formulation is applied to two thick annular flow systems as well as a conical system in both linear and nonlinear regimes, which traditionally has been considered inaccessible to such reduced models. Comparisons are made with direct numerical simulations of the Stokes equations. The results indicate that reduced models can now be used to model systems involving thick liquid layers.
Poesio P, Damone A, Matar OK, 2017, Slip at liquid-liquid interfaces, PHYSICAL REVIEW FLUIDS, Vol: 2, ISSN: 2469-990X
We address a problem of fundamental importance in the physics of interfaces, which is central to the description of multiphase fluid dynamics. This work is important to study interfaces in systems such as polymer melts and solutions, where velocity jumps have been observed and interpreted as a manifestation of slip. This is in violation of classical interfacial conditions that require continuity of velocity and has been remedied in the literature via use of ad hoc models, such as the so-called Navier slip condition. This paper suggests that it is possible to obviate completely the need for such an approach. Instead, we show that one simply requires knowledge of the density field and the molar fraction of the fluid components and the dependence of the viscosity on the density. This information can be obtained easily through molecular dynamics simulations.
Xie Z, Hewitt G, Pavlidis D, et al., 2017, Numerical study of three-dimensional droplet impact ona flowing liquid film in annular two-phase flow, Chemical Engineering Science, Vol: 166, Pages: 303-312, ISSN: 1873-4405
Annular flow with liquid entrainment occurs in a wide variety of two-phase flow system. A novel control volume finite element method with adaptive unstructured meshes is employed here to study three-dimensional droplet deposition process in annular two-phase flow. The numerical framework consists of a ‘volume of fluid’ type method for the interface capturing and a force-balanced continuum surface force model for the surface tension on adaptive unstructured meshes. The numerical framework is validated against experimental measurements of a droplet impact problem and is then used to study the droplet deposition onto a flowing liquid film at atmospheric and high pressure conditions. Detailed complex interfacial structures during droplet impact are captured during the simulation, which agree with the experimental observations, demonstrating the capability of the present method. It is found that the effect of the ambient pressure on the fluid properties and interfacial tension plays an important role in the droplet deposition process and the associated interfacial phenomena.
Saenz PJ, Wray AW, Che Z, et al., 2017, Dynamics and universal scaling law in geometrically-controlled sessile drop evaporation, NATURE COMMUNICATIONS, Vol: 8, ISSN: 2041-1723
The evaporation of a liquid drop on a solid substrate is a remarkably common phenomenon. Yet, the complexity of the underlying mechanisms has constrained previous studies to spherically symmetric configurations. Here we investigate well-defined, non-spherical evaporating drops of pure liquids and binary mixtures. We deduce a universal scaling law for the evaporation rate valid for any shape and demonstrate that more curved regions lead to preferential localized depositions in particle-laden drops. Furthermore, geometry induces well-defined flow structures within the drop that change according to the driving mechanism. In the case of binary mixtures, geometry dictates the spatial segregation of the more volatile component as it is depleted. Our results suggest that the drop geometry can be exploited to prescribe the particle deposition and evaporative dynamics of pure drops and the mixing characteristics of multicomponent drops, which may be of interest to a wide range of industrial and scientific applications.
Nania M, Foglia F, Matar OK, et al., 2017, Sub-100 nm wrinkling of polydimethylsiloxane by double frontal oxidation, Nanoscale, Vol: 9, Pages: 2030-2037, ISSN: 2040-3364
We demonstrate nanoscale wrinkling on polydimethylsiloxane (PDMS) at sub-100 nm length scales via a(double) frontal surface oxidation coupled with a mechanical compression. The kinetics of the glassy skinpropagation is resolved by neutron and X-ray reflectivity, and atomic force microscopy, combined withmechanical wrinkling experiments to evaluate the resulting pattern formation. In conventional PDMSsurface oxidation, the smallest wrinkling patterns attainable have an intrinsic lower wavelength limit dueto the coupling of skin formation and front propagation at fixed strain εprestrain, whose maximum is, inturn, set by material failure. However, combining two different oxidative processes, ultra-violet ozonolysisfollowed by air plasma exposure, we break this limit by fabricating trilayer laminates with excellent interfacialproperties and a sequence of moduli and layer thicknesses able to trivially reduce the surface topographyto sub-100 nm dimensions. This method provides a powerful, yet simple, non-lithographicapproach to extend surface patterning from visible to the deep UV range.
Uppal AS, Matar OK, Craster RV, 2017, Dynamics of spreading thixotropic droplets, Journal of Non-Newtonian Fluid Mechanics, Vol: 240, Pages: 1-14, ISSN: 1873-2631
The e ect of thixotropy on the two-dimensional spreading of a sessiledrop is modelled using lubrication theory. Thixotropy is incorporated by theinclusion of a structure parameter, , measuring structure build-up governedby an evolution equation linked to the droplet micromechanics. A number ofmodels are derived for coupled to the interface dynamics; these range frommodels that account for the cross-stream dependence of to simpler ones inwhich this dependence is prescribed through appropriate closures. Numericalsolution of the governing equations show that thixotropy has a profound e ecton the spreading characteristics; the long-time spreading dynamics, however,are shown to be independent of the initial structural state of the droplet. Wealso compare the predictions of the various models and determine the rangeof system parameters over which the simple models provide su ciently goodapproximations of the full, two-dimensional spreading dynamics.
Nikolaou A, Booth P, Gordon F, et al., 2017, Multi-physics modeling of light-limited microalgae growth in raceway ponds, IFAC Proceedings Volumes (IFAC-PapersOnline), Vol: 49, Pages: 324-329, ISSN: 1474-6670
This paper presents a multi-physics modeling methodology for the quantitative prediction of microalgae productivity in raceway ponds by combining a semi-mechanistic model of microalgae growth describing photoregulation, photoinhibition and photoacclimation, with models of imperfect mixing based on Lagrangian particle-tracking and heterogeneous light distribution. The photosynthetic processes of photoproduction, photoregulation and photoinhibition are represented by a model of chlorophyll fluorescence developed by Nikolaou et al. (2015), which is extended to encompass photoacclimation. The flow is simulated with the commercial CFD package ANSYS, whereas light attenuation is described by the Beer-Lambert law as a first approximation. Full-scale simulation results are presented on extended time horizons. Comparisons are made in terms of areal productivities under both imperfect and idealized (CSTR) mixing conditions, and for various extraction rates and water depths.
Smith ER, Müller EA, Craster RV, et al., 2016, A Langevin model for fluctuating contact angle behaviour parametrised using molecular dynamics, Soft Matter, Vol: 12, Pages: 9604-9615, ISSN: 1744-6848
Molecular dynamics simulations are employed to develop a theoretical model to predict the fluid-solid contact angle as a function of wall-sliding speed incorporating thermal fluctuations. A liquid bridge between counter-sliding walls is studied, with liquid-vapour interface-tracking, to explore the impact of wall-sliding speed on contact angle. The behaviour of the macroscopic contact angle varies linearly over a range of capillary numbers beyond which the liquid bridge pinches off, a behaviour supported by experimental results. Nonetheless, the liquid bridge provides an ideal test case to study molecular scale thermal fluctuations, which are shown to be well described by Gaussian distributions. A Langevin model for contact angle is parametrised to incorporate the mean, fluctuation and auto-correlations over a range of sliding speeds and temperatures. The resulting equations can be used as a proxy for the fully-detailed molecular dynamics simulation allowing them to be integrated within a continuum-scale solver.
Hennessy MG, Ferretti GL, Cabral JT, et al., 2016, A minimal model for solvent evaporation and absorption in thin films, Journal of Colloid and Interface Science, Vol: 488, Pages: 61-71, ISSN: 0021-9797
We present a minimal model of solvent evaporation and absorption in thin films consisting of a volatile solvent and non-volatile solutes. An asymptotic analysis yields expressions that facilitate the extraction of physically significant model parameters from experimental data, namely the mass transfer coefficient and composition-dependent diffusivity. The model can be used to predict the dynamics of drying and film formation, as well as sorption/desorption, over a wide range of experimental conditions. A state diagram is used to understand the experimental conditions that lead to the formation of a solute-rich layer, or “skin”, at the evaporating surface during drying. In the case of solvent absorption, the model captures the existence of a saturation front that propagates from the film surface towards the substrate. The theoretical results are found to be in excellent agreement with data produced from dynamic vapour sorption experiments of ternary mixtures comprising an aluminium salt, glycerol, and water. Moreover, the model should be generally applicable to a variety of practical contexts, from paints and coatings, to personal care, packaging, and electronics.
Morgan RG, Ibarra R, Zadrazil I, et al., 2016, On the role of buoyancy-driven instabilities in horizontal liquid–liquid flow, International Journal of Multiphase Flow, Vol: 89, Pages: 123-135, ISSN: 0301-9322
Horizontal flows of two initially stratified immiscible liquids with matched refractive indices, namely an aliphatic hydrocarbon oil (Exxsol D80) and an aqueous-glycerol solution, are investigated by combining two laser-based optical-diagnostic measurement techniques. Specifically, high-speed Planar Laser-Induced Fluorescence (PLIF) is used to provide spatiotemporally resolved phase information, while high-speed Particle Image and Tracking Velocimetry (PIV/PVT) are used to provide information on the velocity field in both phases. The two techniques are applied simultaneously in a vertical plane through the centreline of the investigated pipe flow, illuminated by a single laser-sheet in a time-resolved manner (at a frequency of 1–2 kHz depending on the flow condition). Optical distortions due to the curvature of the (transparent) circular tube test-section are corrected with the use of a graticule (target). The test section where the optical-diagnostic methods are applied is located 244 pipe-diameters downstream of the inlet section, in order to ensure a significant development length. The experimental campaign is explicitly designed to study the long-length development of immiscible liquid–liquid flows by introducing the heavier (aqueous) phase at the top of the channel and above the lighter (oil) phase that is introduced at the bottom, which corresponds to an unstably-stratified “inverted” inlet orientation in the opposite orientation to that in which the phases would naturally separate. The main focus is to evaluate the role of the subsequent interfacial instabilities on the resulting long-length flow patterns and characteristics, also by direct comparison to an existing liquid–liquid flow dataset generated in previous work, downstream of a “normal” inlet orientation in which the oil phase was introduced over the aqueous phase in a conventional stably-stratified inlet orientation. To the best knowledge of the authors this
Xie Z, Pavlidis D, Salinas P, et al., 2016, A balanced-force control volume finite element method for interfacial flows with surface tension using adaptive anisotropic unstructured meshes, Computers & Fluids, Vol: 138, Pages: 38-50, ISSN: 0045-7930
A balanced-force control volume finite element method is presented for three-dimensional interfacial flows with surface tension on adaptive anisotropic unstructured meshes. A new balanced-force algorithm for the continuum surface tension model on unstructured meshes is proposed within an interface capturing framework based on the volume of fluid method, which ensures that the surface tension force and the resulting pressure gradient are exactly balanced. Two approaches are developed for accurate curvature approximation based on the volume fraction on unstructured meshes. The numerical framework also features an anisotropic adaptive mesh algorithm, which can modify unstructured meshes to better represent the underlying physics of interfacial problems and reduce computational effort without sacrificing accuracy. The numerical framework is validated with several benchmark problems for interface advection, surface tension test for equilibrium droplet, and dynamic fluid flow problems (fluid films, bubbles and droplets) in two and three dimensions.
Ibarra R, Morgan R, Zadrazil I, et al., 2016, Investigation of oil-water flow in horizontal pipes using simultaneous two-line planar laser-induced fluorescence and particle velocimetry, HEFAT, 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
The flow of oil and water in pipes represents a challenging configuration in multiphase flows due to complex hydrodynamics which are still not fully understood. This can be observed in the large number of flow regimes encountered, which extend from smooth stratified flows to complex dispersions such as droplets of oil-in-water and water-in-oil. These flow configurations are the result of the inherent properties of the liquid phases, e.g., their densities and viscosities, interfacial tension and contact angle, as well as of flow conditions and related phenomena, such as turbulence, which have a direct effect on the interface instabilities giving rise to flow regime transitions. In this paper, experimental data are reported that were acquired at low water cuts and low mixture velocities using an aliphatic oil (Exxsol D140) and water as the test fluids in an 8.5 m long and 32 mm internal diameter horizontal pipe. A copper-vapour laser, emitting two narrow-band laser beams, and two high-speed cameras were used to obtain quantitative simultaneous information of the flow (specifically, spatiotemporally resolved fluid-phase and velocity information in both phases) based on simultaneous two-line Planar Laser-Induced Fluorescence (PLIF) and Particle Image and Tracking Velocimetry (PIV/PTV). To the best knowledge of the authors this is the first such instance of the application of this combined technique to these flows. It is found that the rms of the fluctuating velocity show peaks in high shear regions, i.e. at the pipe wall and interface.
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