Local Fluid Flow Research Articles

On sharp-interface level-set method for heat and/or mass transfer induced Stefan problem

A detailed sharp interface level set method (SI-LSM) based CFD development methodology as well as its implementation and application to the various types of Stefan problem is not found and reported here. The methodology and code-validation are presented in-detail for heat and/or mass transfer induced Stefan flow, 2D Cartesian as well as axi-symmetric coordinate system and Dirichlet as well as jump boundary conditions at the interface. For the Dirichlet BC, a higher order extrapolation methodology is presented – for the computation of ghost fluid value across the interface. Whereas, for the jump BC, a generic finite volume method based discretized equation is proposed – consisting of additional source term and modification in diffusion coefficient for the control-volumes adjoining the interface. An excellent agreement between the present and published results are shown separately for Stefan flow problems induced by heat transfer (melting as well as solidification), mass transfer (isothermal evaporation) and heat as well as mass transfer (non-isothermal evaporation). Finally, a performance study is presented demonstrating a superior performance of the present sharp as compared to diffused interface level set method. The performance study is also presented for two different methods of computation of normal gradient across the interface, with regard to numerical oscillations in the results.The present work – involving localized fluid flow and heat as well as mass transfer in the two-phase domain – will be extremely useful to CFD developer on multi-phase flow.

Unsteady natural convection heat transfer from a pair of vertically aligned horizontal cylinders

This paper presents the results of a numerical study of unsteady natural convection heat transfer from a pair of isothermally heated horizontal cylinders in water. Particular attention is paid to the interaction between the two buoyant plumes and the relationship between unsteady fluid flow and heat transfer enhancement. When the cylinders are vertically aligned, the heat transfer effectiveness of the upper cylinder is affected by buoyancy-induced fluid flow induced by the lower cylinder. Moreover, strong oscillations appear in the local heat transfer rate and fluid flow field. A computational fluid dynamics model (CFD) is established and validated against experimental results for both averaged and local Nusselt number, for a range of Rayleigh numbers between 1.7×106 and 5.3×106 and a centre-to-centre cylinder spacing between 2 and 4 diameters. The validated CFD model is used to identify 3.5 diameters as the spacing which maximises the averaged Nusselt number on the upper cylinder among the values of Rayleigh number and spacing which were presently investigated. The transient CFD model is used to characterise the peak frequencies of the oscillating thermal plume, as well as analyse Fourier transforms and spectral coherence of the local Nusselt number and fluid velocity. This detailed numerical analysis has complemented previous experimental measurements, confirming some hypotheses on the mechanisms of heat transfer enhancement in this configuration.

Apatite fission-track evidence for regional exhumation in the subtropical Eocene, block faulting, and localized fluid flow in east-central Alaska

The origin and antiquity of the subdued topography of the Yukon–Tanana Upland (YTU), the physiographic province between the Denali and Tintina faults, are unresolved questions in the geologic history of interior Alaska and adjacent Yukon. We present apatite fission-track (AFT) results for 33 samples from the 2300 km2 western Fortymile district in the YTU in Alaska and propose an exhumation model that is consistent with preservation of volcanic rocks in valleys that requires base level stability of several drainages since latest Cretaceous–Paleocene time. AFT thermochronology indicates widespread cooling below ∼110 °C at ∼56–47 Ma (early Eocene) and ∼44–36 Ma (middle Eocene). Samples with ∼33–27, ∼19, and ∼10 Ma AFT ages, obtained near a major northeast-trending fault zone, apparently reflect hydrothermal fluid flow. Uplift and erosion following ∼107 Ma magmatism exposed plutonic rocks to different extents in various crustal blocks by latest Cretaceous time. We interpret the Eocene AFT ages to suggest that higher elevations were eroded during the Paleogene subtropical climate of the subarctic, while base level remained essentially stable. Tertiary basins outboard of the YTU contain sediment that may account for the required >2 km of removed overburden that was not carried to the sea by the ancestral Yukon River system. We consider a climate driven explanation for the Eocene AFT ages to be most consistent with geologic constraints in concert with block faulting related to translation on the Denali and Tintina faults resulting from oblique subduction along the southern margin of Alaska.

Oxygen isotope record of oceanic and high-pressure metasomatism: a P–T–time–fluid path for the Monviso eclogites (Italy)

Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. The Monviso ophiolitic sequence is composed of mafic, ultramafic and minor sediments that have been subducted to ~80 km depth. In this sequence, both localized fluid flow and channelized fluids along major shear zones have been documented. We investigate the timing and source of the fluids that affected the dominant mafic rocks using microscale U–Pb dating of zircon and oxygen isotope analysis of mineral zones (garnet, zircon and antigorite) in high-pressure rocks with variable degree of metasomatic modification. In mafic eclogites, Jurassic zircon cores are the only mineralogical relicts of the protolith gabbros and retain δ18O values of 4.5–6 ‰, typical of mantle melts. Garnet and metamorphic zircon that grew during prograde to peak metamorphism display low δ18O values between 0.2 and 3.8 ‰, which are likely inherited from high-temperature alteration of the protolith on the sea floor. This is corroborated by δ18O values of 3.0 and 3.6 ‰ in antigorite from surrounding serpentinites. In metasomatized eclogites within the lower shear zone, garnet rim formed at the metamorphic peak shows a shift to higher δ18O up to 6 ‰. The age of zircons in high-pressure veins and metasomatized eclogites constrains the timing of fluid flow at high pressure at around 45–46 Ma. Although the oxygen data do not contradict previous reports of interaction with serpentinite-derived fluids, the shift to isotopically heavier oxygen compositions requires contribution from sediment-derived fluids. The scarcity of metasediments in the Monviso sequence suggests that such fluids were concentrated and fluxed along the lower shear zone in a sufficient amount to modify the oxygen composition of the eclogitic minerals.

A wind tunnel study of flow structure adjustment on deformable sand beds containing a surface‐mounted obstacle

AbstractRoughness elements of varied scale and geometry commonly appear on the surfaces of sedimentary deposits in a wide range of planetary environments. They perturb the local fluid flow so that the entrainment, transport, and deposition of particles surrounding each element are fundamentally altered. Fluid dynamists have expended much effort in examining the flow structures surrounding idealized elements mounted on fixed, planar walls. However self‐regulation occurs in sedimentary systems as a result of the bed surface undergoing rapid topographic modification with sediment transport, until it reaches a stable form that enhances the net physical roughness. The present wind tunnel study examines how the flow pattern surrounding an isolated cylinder, a problem extensively studied in classical fluid mechanics, is altered through morphodynamic development of a deep well that envelopes the windward face and sidewalls of the roughness element. Spatial patterns in the fluid velocity, turbulence intensity, and Reynolds stress obtained from laser Doppler anemometer measurements suggest that the flow structures surrounding such a cylinder are fundamentally altered through self‐regulation of the bed topography as it reaches steady state. For example, flow stagnation and the turbulent dissipation of momentum are substantially increased at selected points surrounding the upwind face and sidewalls of the cylinder, respectively. Along the center line of the wake flow to the rear of the cylinder, several structures arising from flow separation are annihilated by strong upwelling of the airflow exhausted from the terminus of the well. Feedback plays a complex, time‐dependent role in this system.

Seismic attenuation due to heterogeneities of rock fabric and fluid distribution

AbstractThe study of the influence of rock fabric and porefluid distribution on the seismic wavefield is important for the prediction and detection of reservoir properties such as lithology and fluid saturation. Wave-induced local fluid flow (WILFF), which is affected by local heterogeneities of the pore structure and fluid saturation, is believed to be the main mechanism to explain the measured attenuation levels at different frequency bands. These two types of heterogeneity affect seismic waves as a combined WILFF process. In this work, we consider a double-porosity system, each part with a different compressibility and patchy saturation, and derive the wave equations from Hamilton's principle. A plane-wave analysis yields the properties of the classical P-wave and those of the four slow waves. The examples show that patchy fluid saturation dominates the peak frequency of the relaxation mechanism. The relation between seismic anelasticity (velocity dispersion and attenuation) and saturation depends on frequency and on the geometrical features of the two heterogeneities. The proposed theory constitutes the comprehensive description for wave propagation process through reservoirs rocks of shallow Earth and porous media in general, to estimate fluid content and distribution.

A mathematical model and computational framework for three-dimensional chondrocyte cell growth in a porous tissue scaffold placed inside a bi-directional flow perfusion bioreactor.

The in vitro chondrocyte cell culture for cartilage tissue regeneration in a perfusion bioreactor is a complex process. Mathematical modeling and computational simulation can provide important insights into the culture process, which would be helpful for selecting culture conditions to improve the quality of the developed tissue constructs. However, simulation of the cell culture process is a challenging task due to the complicated interaction between the cells and local fluid flow and nutrient transport inside the complex porous scaffolds. In this study, a mathematical model and computational framework has been developed to simulate the three-dimensional (3D) cell growth in a porous scaffold placed inside a bi-directional flow perfusion bioreactor. The model was developed by taking into account the two-way coupling between the cell growth and local flow field and associated glucose concentration, and then used to perform a resolved-scale simulation based on the lattice Boltzmann method (LBM). The simulation predicts the local shear stress, glucose concentration, and 3D cell growth inside the porous scaffold for a period of 30 days of cell culture. The predicted cell growth rate was in good overall agreement with the experimental results available in the literature. This study demonstrates that the bi-directional flow perfusion culture system can enhance the homogeneity of the cell growth inside the scaffold. The model and computational framework developed is capable of providing significant insight into the culture process, thus providing a powerful tool for the design and optimization of the cell culture process.

New indicators from bedding-parallel beef veins for the fault valve mechanism

Beef structures (bedding-parallel veins of fibrous calcite) are widespread within the Lower Triassic carbonate rocks in the Sichuan Basin of China, especially within clay-rich strata of low permeability. In the veins, fibrous calcite occurs in the outer zones, and coarse equant calcite in the inner zones. At least two generations of calcite crystallization took place during aqueous alteration, at the same time as deformation recorded by the calcite. The first-generation calcite fibers are at steep angles to the hydrocarbon-bearing host beds, and they grew vertically against the force of gravity at a time when the source rocks were maturing. Second-generation calcite occurs as coarse equant grains that sealed pores via localized fluid flow during horizontal tectonic compression, so that shear stresses acted at the fracture margins. Shearing of the host rock was accommodated in part by dissolution-precipitation creep (DPC), grain rotation, and grain slippage, recorded in crystallographic preferred orientations (CPOs) of the host calcite grains beside the crack walls. The beef veins formed during high pore-fluid overpressures along hydrofractures. We propose that the bedding-parallel veins with beef structures are evidence of a “crack-seal slip” fault valve process during hydrocarbon generation. The hydrocarbon-bearing calcite beef structure may be a good indicator of oil or gas migration, and of the flow direction of aqueous solutions.

Computational modelling of the scaffold-free chondrocyte regeneration: a two-way coupling between the cell growth and local fluid flow and nutrient concentration

The in vitro chondrocyte cell culture process in a perfusion bioreactor provides enhanced nutrient supply as well as the flow-induced shear stress that may have a positive influence on the cell growth. Mathematical and computational modelling of such a culture process, by solving the coupled flow, mass transfer and cell growth equations simultaneously, can provide important insight into the biomechanical environment of a bioreactor and the related cell growth process. To do this, a two-way coupling between the local flow field and cell growth is required. Notably, most of the computational and mathematical models to date have not taken into account the influence of the cell growth on the local flow field and nutrient concentration. The present research aimed at developing a mathematical model and performing a numerical simulation using the lattice Boltzmann method to predict the chondrocyte cell growth without a scaffold on a flat plate placed inside a perfusion bioreactor. The model considers the two-way coupling between the cell growth and local flow field, and the simulation has been performed for 174 culture days. To incorporate the cell growth into the model, a control-volume-based surface growth modelling approach has been adopted. The simulation results show the variation of local fluid velocity, shear stress and concentration distribution during the culture period due to the growth of the cell phase and also illustrate that the shear stress can increase the cell volume fraction to a certain extent.

Halogen Element and Stable Chlorine Isotope Fractionation Caused by Fluid–Rock Interaction (Bamble Sector, SE Norway)

Pervasive interaction between rock and fluid produces regional-scale alteration and/or metasomatism of rock units. The middle and upper crustal rocks from the Bamble sector (SE Norway) show a complex history of metamorphic and metasomatic events, accompanied by ore deposit formation, which provides an excellent context for investigation of regional-scale fluid‐rock interaction. Halogens are important agents of rock alteration and ore metal transportation in such hydrothermal regimes. Here we use F, Cl, Br and I concentrations and stable chlorine isotope ratios (d 37 Cl) to trace the metasomatic evolution of two gabbroic bodies and understand the interplay between localized and pervasive fluid flow in the upper crust. An alteration sequence was sampled from pristine gabbro to an amphibolitic shear zone, showing progressive amphibolitization and scapolitization caused by pervasive fluid ingress. Halogen concentrations and ratios suggest the evolution of a single fluid, causing enrichment of Cl, Br and I in samples nearest the shear zone. Owing to the differences in fluid‐mineral distribution coefficients, fluid‐mineral interaction resulted in either enrichment or depletion of halogens in the fluid as it reacted pervasively with the gabbro. Although scapolite formation leads to progressive desalination of the fluid near the shear zone, increasing Cl concentrations in amphibole near the gabbro reflect an increase in salinity towards the unaltered gabbro owing to desiccation of the fluid. The formation of alteration minerals mainly governs changes in the halogen chemistry of the fluid, showing that halogens do not behave fully conservatively during fluid‐rock interaction. Nevertheless, the evolving fluid has a feedback on the stability of alteration minerals such as scapolite and biotite, which form only close to the shear zone. The Br/Cl and I/Cl ratios of the most highly altered samples are 3 � 10 ‐3 and 25 � 10 ‐6 , respectively, and overlap with the range of ratios measured for marine pore fluids. Remobilization of evaporites would have produced distinctly lower halogen ratios and can be ruled out as a fluid source. The unaltered gabbro has d 37 Cl values near 0% and a similar value is inferred for the infiltrating fluid. Minimally altered samples, noted by the presence of <20 vol. % amphibole, have negative d 37 Cl values (average ¼ ‐0� 6 6 0� 1%). The d 37 Cl values increase (up to þ 1% nearest the shear zone) with increasing evidence of fluid‐rock interaction towards the shear zone. Mixing of different Cl reservoirs (i.e. gabbro and fluid) cannot explain the observed changes in the d 37 Cl values. Instead, isotopic fractionation owing to Rayleigh distillation with a fractionation factor of 1� 0010 can explain the observed negative d 37 Cl values of the alteration sequence by the evolution of a single fluid

Effect of local fluid flow on the propagation of elastic waves in a transversely isotropic double-porosity medium

This study considers the propagation of elastic waves in a fluid-saturated double-porosity solid. Constitutive relations are derived for the double porosity medium having the transverse isotropy with vertical axis of symmetry. The equations of motion are solved for the propagation of harmonic waves. Then, the amount of wave-induced fluid flow at any point is expressed in terms of normal strain components in the composite medium. For propagation in a plane, the equations of motion decouple into two independent systems. One of these represents the particle motion normal to the plane and identifies the SH-type motion for solid particles. The other system represents the in-plane motion of particles and governs the propagation of four coupled waves. Among these four waves, three are quasi-longitudinal (qP1, qP2, qP3) waves and one is a quasi-transverse (qSV) wave. A numerical example is solved to calculate the velocity and attenuation anisotropy of the five waves. Effect of local fluid flow is observed on the wave velocities as well as the polarization of the constituent particles in double porosity medium. Effects of wave-frequency, propagation direction, pore-fluid viscosity, permeability and radius of spherical inclusions are analysed on the velocities and attenuation.

Fluctuations and diffusion in sheared athermal suspensions of deformable particles

We analyze fluctuations of particle displacements and stresses in a sheared athermal suspension of elastic capsules (red blood cells). Upon variation of the volume fraction from the dilute up to the highly concentrated regime, our numerical simulations reveal different characteristic power-law regimes of the fluctuation variances and relaxation times. In the jammed phase and at high shear rates, anomalous scaling exponents are found that deviate from pure dimensional predictions. The observed behavior is rationalized via kinetic arguments and a dissipation balance model that takes into account the local fluid flows between the particles. Our findings support the view that the rheology of dense suspensions is essentially governed by the non-affine displacements.

SPLASH, VORTICES AND TURBULENT SHEARS IN PARTIAL DAM-BREAK FLOWS -- SPLASH MODEL OF WAVE-BREAKING AND OVERTOPPING --

Three-dimensional evolution of local fluid flows and surface shapes under partial collapse of a water column is characterized during computational experiments using three-dimensional large eddy simulation in this paper. The free-surface behaviors highly depend on the collapse level and ambient water layer depth via mechanical interactions between the surface and vortices. It has been found major three modes of the splashing responses of the free-surfaces and vortex structures; (i) forward projection of secondary jets, which organizes a typical rib-like vortex structure stretched underneath the jets, (ii) backward jet projection with an inverse form of the rib structure, and (iii) blob-like waves induced by an array of the horizontal roller vortices. These findings provide new perspectives to understand wave breaking behaviors as well as practical assessments for the fluid responses in the splashing area for sea wall overflow and overtopping.

Mechanisms of particle clustering in Gaussian and non-Gaussian synthetic turbulence.

We use synthetic turbulence simulations to study how inertial particles cluster in a turbulent flow, for a wide range of Stokes numbers. Two different types of synthetic turbulence are used: one Gaussian, where the time evolution of the velocity field is a simple phase shift, and one non-Gaussian, where convection is used to evolve the velocity field in time. In both flow types we observe significant particle clustering over a wide range of scales and Stokes numbers. The clustering found at low Stokes numbers can be attributed to the vortex centrifuge effect, where heavy particles are expelled from regions dominated by vorticity. This mechanism is much more effective in the non-Gaussian turbulence, because local flow structures are convected with the particles. The preferential sampling of regions with low vorticity is almost negligible in the Gaussian turbulence. At higher Stokes numbers, caustics are formed in a very similar manner in both Gaussian and non-Gaussian synthetic turbulence. In non-Gaussian turbulence, heavy particles cluster in regions of low fluid kinetic energy, while the opposite is true in Gaussian turbulence. Our results show that synthetic simulations cannot correctly predict how the particle clustering correlates with local fluid flow properties, without including convection.

Microfluidic control of axonal guidance.

The precision of axonal pathfinding and the accurate formation of functional neural circuitry are crucial for an organism during development as well as during adult central and peripheral nerve regeneration. While chemical cues are believed to be primarily responsible for axonal pathfinding, we hypothesize that forces due to localized fluid flow may directly affect neuronal guidance during early organ development. Here, we report direct evidence of fluid flow influencing axonal migration, producing turning angles of up to 90°. Microfluidic flow simulations indicate that an axon may experience significant bending force due to cross-flow, which may contribute to the observed axonal turning. This method of flow-based guidance was successfully used to fasciculate one advancing axon onto another, showcasing the potential of this technique to be used for the formation of in vitro neuronal circuits.

Effect of Local Fluid Flow on Rayleigh Waves in a Double Porosity Solid

Abstract This study considers the propagation of attenuated waves in a double porosity solid half‐space permeated by two different pore regimes. Pores in both the regimes are saturated with the same viscous fluid. The compressional effect of the Rayleigh wave transforms into different fluid‐pressure fields in two pore regimes. The resulting pressure gradient in porous aggregate induces a local flow of fluid through the connected pores. In return, this local wave‐induced fluid flow affects the propagation and polarization of Rayleigh waves in a double porosity solid half‐space. The pores exposed at the surface control the fluid discharge and characterize the boundary of the porous solid to be pervious or impervious. For either boundary, the propagation and attenuation of Rayleigh waves are represented by a complex irrational dispersion equation, which is solved numerically after rationalizing into an algebraic equation. Complex solution of this dispersion equation is resolved to define the phase velocity and attenuation coefficient for the propagation of Rayleigh waves as an inhomogeneous wave in dissipative double porosity solid. A numerical example is solved to illustrate the propagation, attenuation, and polarization of the Rayleigh wave. Numerical results suggest the existence of an additional (second) Rayleigh wave in the double porosity solid saturated with low‐viscosity pore fluid.

A comprehensive modeling study of in-cylinder fluid flows in a high-swirl, light-duty optical diesel engine

The effectiveness of computational fluid dynamics modeling as a tool for researching fuel-lean, low temperature engine combustion strategies relies on its capability to capture the local fluid flow properties that affect spray dynamics, mixture preparation and ignition kinetics. In this study, a comprehensive model of an optically accessible, single-cylinder light-duty diesel engine was developed for engine combustion research. The computational model includes the realistic combustion chamber and ducts geometries. Variable orientation throttles in the intake ducts were modeled to reproduce variable swirl generation. Full induction stroke calculations were run over a portfolio of intake swirl conditions, and validated against extensive measurements featuring global intake swirl ratios, in-cylinder particle image velocimetry (PIV)-measured velocity fields and swirl centers. The results showed good agreement with the experiments, and the model was used to understand the effects of different swirl generation strategies on the in-cylinder flow field. The implications of using simplified sector mesh geometries on the predictiveness of in-cylinder flow and turbulence quantities are described.

Anomalous orientations of a rigid carbon nanotube in a sheared fluid.

The nanoparticle orientation in fluid systems can be correlated with the rotational diffusion and is widely used to tune the physical properties of functional materials. In the current work, the controllability of the orientation of a single rigid carbon nanotube in a fluid is investigated by imposing a linear shear flow. Molecular dynamics simulations reveal three forms of anomalous behavior: (i) “Aligned orientation” when the nanotube oscillates around a particular direction which is close to the flow direction at a small angle of about 10° in the velocity-gradient plane; (ii) “Interrupted orientation” when the oscillation is interrupted by a 360° rotation now and then; (iii) “Random orientation” when 360° rotations dominate with the rotational direction coinciding with the local fluid flow direction. The orientation order is a function of the Peclet number (Pe). The results show that the correlation between Pe and the orientation order from the two-dimensional model does not apply to the three-dimensional cases, perhaps due to some anomalous behavior and cross-section effects. This work provides clear pictures of the nanoparticle movement that can be used to guide particle manipulation techniques.

A combined fluid–structure interaction and multi–field scalar transport model for simulating mass transport in biomechanics

SUMMARYMass transport processes are known to play an important role in many fields of biomechanics such as respiratory, cardiovascular, and biofilm mechanics. In this paper, we present a novel computational model considering the effect of local solid deformation and fluid flow on mass transport. As the transport processes are assumed to influence neither structure deformation nor fluid flow, a sequential one‐way coupling of a fluid–structure interaction (FSI) and a multi‐field scalar transport model is realized. In each time step, first the non‐linear monolithic FSI problem is solved to determine current local deformations and velocities. Using this information, the mass transport equations can then be formulated on the deformed fluid and solid domains. At the interface, concentrations are related depending on the interfacial permeability. First numerical examples demonstrate that the proposed approach is suitable for simulating convective and diffusive scalar transport on coupled, deformable fluid and solid domains. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Interrelation between external oscillatory muscle coupling amplitude and in vivo intramedullary pressure related bone adaptation

Interstitial bone fluid flow (IBFF) is suggested as a communication medium that bridges external physical signals and internal cellular activities in the bone, which thus regulates bone remodeling. Intramedullary pressure (ImP) is one main regulatory factor of IBFF and bone adaptation related mechanotransduction. Our group has recently observed that dynamic hydraulic stimulation (DHS), as an external oscillatory muscle coupling, was able to induce local ImP with minimal bone strain as well as to mitigate disuse bone loss. The current study aimed to evaluate the dose dependent relationship between DHS's amplitude, i.e., 15 and 30mmHg, and in vivo ImP induction, as well as this correlation on bone's phenotypic change. Simultaneous measurements of ImP and DHS cuff pressures were obtained from rats under DHS with various magnitudes and a constant frequency of 2Hz. ImP inductions and cuff pressures upon DHS loading showed a positively proportional response over the amplitude sweep. The relationship between ImP and DHS cuff pressure was evaluated and shown to be proportional, in which ImP was raised with increases of DHS cuff pressure amplitudes (R2=0.98). A 4-week in vivo experiment using a rat hindlimb suspension model demonstrated that the mitigation effect of DHS on disuse trabecular bone was highly dose dependent and related to DHS's amplitude, where a higher ImP led to a higher bone volume. This study suggested that sufficient physiological DHS is needed to generate ImP. Oscillatory DHS, potentially induces local fluid flow, has shown dose dependence in attenuation of disuse osteopenia.