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1
Liang, Hui, and Xiaobo Chen. "Viscous effects on the fundamental solution to ship waves." Journal of Fluid Mechanics 879 (October 1, 2019): 744–74. http://dx.doi.org/10.1017/jfm.2019.698.
Повний текст джерелаАнотація:
The fundamental solution to steady ship waves accounting for viscous effects (the viscous-ship-wave Green function) is investigated within the framework of the weakly damped free-surface flow theory. An explicit expression of the viscous-ship-wave Green function is firstly derived, and an accurate and efficient technique is described to evaluate the Green function via decomposing the free-surface term into the local-flow component and wave component. To delve into the physical features of the viscous-ship-wave Green function, the asymptotic approximations in the far field due to Kelvin, Havelock and Peters are presented for the flow-field point located inside, at and outside the Kelvin wedge. In addition, uniform approximations to the wave component based on the Chester–Friedman–Ursell (CFU) approximation and the Kelvin–Havelock–Peters (KHP) approximation are carried out. Both numerical evaluation and asymptotic approximations show that the singular behaviour is eliminated and the divergent waves associated with large wavenumbers leading to rapid oscillations are severely damped when viscous effects are accounted for. In addition, viscous effects also alter the apparent wake angle associated with the wave pattern created by a high-speed translating source, and the apparent wake angle is dependent on both $\mathscr{U}^{-1}$ and $\mathscr{U}^{-2}$, where $\mathscr{U}$ is the translating speed of the source.
2
Fang, Chung, and Cheng-Hsien Lee. "Unsteady Parallel Flows of an Elasto-Visco-Hypoplastic Fluid with Oscillating Boundary." Applied Rheology 18, no. 4 (August 1, 2008): 45001–1. http://dx.doi.org/10.1515/arh-2008-0014.
Повний текст джерелаАнотація:
Abstract In the present study, an evolution equation for the Cauchy stress tensor is proposed to take elastic, viscous and plastic characteristics of complex fluids simultaneously into account. In particular, hypoplasticity is incorporated to account for the plastic features. The stress model is applied to investigate time-dependent flows of an elasto-visco-plastic fluid driven by an oscillating boundary with/without an additional stationary boundary to study the cyclic responses and the model performance. Numerical simulations show that while different degrees of elastic and viscous effects can be captured by varying the model parameters, plastic deformation plays a significant role in the velocity distribution, and can be simulated appropriately by use of hypoplasticity. The stress model is capable of accounting for the combined elastic, viscous and plastic features of complex materials in transient motions, and applications may be found in geomorphic fluid motions like granular and debris flows, and flows involving polymers.
3
McMahon, Charles W., Joseph J. Kuehl, and Vitalii A. Sheremet. "A Viscous, Two-Layer Western Boundary Current Structure Function." Fluids 5, no. 2 (April 28, 2020): 63. http://dx.doi.org/10.3390/fluids5020063.
Повний текст джерелаАнотація:
The classic oceanographic problem of a 1.5-layer western boundary current evolving along a straight wall is considered. Here, building upon the previous work of Charney, Huang and Kamenkovich, we have derived, solved and validated a new numerical formulation for accounting for viscous effects in such systems. The numerical formulation is validated against rotating table experimental results.
4
Carlone, Pierpaolo, and Gaetano S. Palazzo. "Computational Modeling of the Pulling Force in a Conventional Pultrusion Process." Advanced Materials Research 772 (September 2013): 399–406. http://dx.doi.org/10.4028/www.scientific.net/amr.772.399.
Повний текст джерелаАнотація:
Pultrusion process is gaining increasing attention in several sectors, due to the high productivity and quality achievable. Recent researches highlighted the influence of the pulling force on the quality of pultruded products. In this paper a pulling force model, accounting for compacting, viscous, and frictional effects in a conventional pultrusion process has been implemented. The model is based on the combination of an impregnation, a thermochemical, and a frictional sub-models. Obtained outcomes evidenced, for the considered case,adominant role of the viscous drag.
5
Tafili, Merita, and Theodoros Triantafyllidis. "A simple hypoplastic model with loading surface accounting for viscous and fabric effects of clays." International Journal for Numerical and Analytical Methods in Geomechanics 44, no. 16 (August 11, 2020): 2189–215. http://dx.doi.org/10.1002/nag.3122.
Повний текст джерела
6
Yoshimoto, S., Y. Ito, and A. Takahashi. "Pumping Characteristics of a Herringbone-Grooved Journal Bearing Functioning as a Viscous Vacuum Pump." Journal of Tribology 122, no. 1 (June 23, 1999): 131–36. http://dx.doi.org/10.1115/1.555371.
Повний текст джерелаАнотація:
A laser scanner motor with low power and high speed has been developed. This scanner motor uses a herringbone-grooved journal bearing which functions as a viscous vacuum pump. The windage power loss of a polygon mirror is reduced, since the air inside the pump housing is pumped out by herringbone-grooved viscous vacuum action. In this paper, the theoretical pumping characteristic of this bearing is investigated, using the narrow-groove theory and accounting for first-order slip flow. The effects of various design parameters on the pumping characteristics are discussed. Optimum geometric design parameters were found to obtain the minimum inner chamber pressure of the housing. The theoretical predictions considering slip flow effects are in good agreement with experimental measurements. [S0742-4787(00)01801-4]
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Saxena, Nishank, and Gary Mavko. "Effects of fluid-shear resistance and squirt flow on velocity dispersion in rocks." GEOPHYSICS 80, no. 2 (March 1, 2015): D99—D110. http://dx.doi.org/10.1190/geo2014-0304.1.
Повний текст джерелаАнотація:
Laboratory measurements of rocks saturated with high-viscosity fluids (such as heavy-oil, bitumen, magma, kerogen, etc.) often exhibit considerable seismic velocity dispersion, which is usually underestimated by the Biot theory. Over the years, grain-scale dispersion mechanisms such as squirt (local-flow) and shear relaxation (nonzero shear stress in the pore fluid) have been more successful in explaining the measured dispersion. We developed a new method to quantify the combined high-frequency effects of squirt and shear dispersion on the effective moduli of rocks saturated with viscous fluids. Viscous fluid at high frequencies was idealized as an elastic solid of finite shear modulus, hydraulically locked in stiff and soft pores. This method entailed performing solid substitution in stiff pores of a dry rock frame, which itself was unrelaxed due to solid-filled soft pores. The unrelaxed frame stiffness solutions required information on the pressure dependency of the rock stiffness and porosity. This method did not have any adjustable parameters, and all required inputs can be directly measured. With various laboratory and numerical examples, we noted that accounting for combined effects of squirt and shear relaxation was necessary to explain laboratory-measured velocities of rocks saturated with fluids of high viscosity. Predictions of the new method were in good agreement with the laboratory data.
8
Li, Xu, Jun Li, Xiaoyi Zhang, Jianfeng Gao, and Chao Zhang. "Simplified analysis of cable-stayed bridges with longitudinal viscous dampers." Engineering, Construction and Architectural Management 27, no. 8 (July 30, 2020): 1993–2022. http://dx.doi.org/10.1108/ecam-07-2019-0400.
Повний текст джерелаАнотація:
PurposeViscous dampers are commonly used in large span cable-stayed bridges to mitigate seismic effects and have achieved great success.Design/methodology/approachHowever, the nonlinear analysis on damper parameters is usually computational intensive and nonobjective. To address these issues, this paper proposes a simplified method to determine the viscous damper parameters for double-tower cable-stayed bridges. An empirical formula of the equivalent damping ratio of viscous dampers is established through decoupling nonclassical damping structures and linearization of nonlinear viscous dampers. Shaking table tests are conducted to verify the feasibility of the proposed method. Moreover, this simplified method has been proved in long-span cable-stayed bridges.FindingsThe feasibility of this method is verified by the simplified model shaking table test. This simplified method for determining the parameters of viscous dampers is verified in cable-stayed bridges with different spans.Originality/valueThis simplified method has been validated in cable-stayed bridges with various spans.
9
Bico, J. "Cracks in bursting soap films." Journal of Fluid Mechanics 778 (July 30, 2015): 1–4. http://dx.doi.org/10.1017/jfm.2015.376.
Повний текст джерелаАнотація:
The rupture of soap films is traditionally described by a law accounting for a balance between momentum and surface tension forces, derived independently by Taylor and Culick in the 1960s. This law is highly relevant to the dynamics of thin liquid films of jets when viscous effects are negligible. However, the minute amounts of surfactant molecules present in soap films play a major role in interfacial rheology, and may result in complex behaviour. Petit et al. (J. Fluid Mech., vol. 774, 2015, R3) challenge standard thin film dynamics via intriguing experiments conducted with highly elastic surfactants. Unexpected structures reminiscent of faults are observed.
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Shankar, Usha, Neminath B. Naduvinamani, and Hussain Basha. "A generalized perspective of Fourier and Fick’s laws: Magnetized effects of Cattaneo-Christov models on transient nanofluid flow between two parallel plates with Brownian motion and thermophoresis." Nonlinear Engineering 9, no. 1 (April 23, 2020): 201–22. http://dx.doi.org/10.1515/nleng-2020-0009.
Повний текст джерелаАнотація:
AbstractPresent research article reports the magnetized impacts of Cattaneo-Christov double diffusion models on heat and mass transfer behaviour of viscous incompressible, time-dependent, two-dimensional Casson nanofluid flow through the channel with Joule heating and viscous dissipation effects numerically. The classical transport models such as Fourier and Fick’s laws of heat and mass diffusions are generalized in terms of Cattaneo-Christov double diffusion models by accounting the thermal and concentration relaxation times. The present physical problem is examined in the presence of Lorentz forces to investigate the effects of magnetic field on double diffusion process along with Joule heating. The non-Newtonian Casson nanofluid flow between two parallel plates gives the system of time-dependent, highly nonlinear, coupled partial differential equations and is solved by utilizing RK-SM and bvp4c schemes. Present results show that, the temperature and concentration distributions are fewer in case of Cattaneo-Christov heat and mass flux models when compared to the Fourier’s and Fick’s laws of heat and mass diffusions. The concentration field is a diminishing function of thermophoresis parameter and it is an increasing function of Brownian motion parameter. Finally, an excellent comparison between the present solutions and previously published results show the accuracy of the results and methods used to achieve the objective of the present work.
11
Petr, V., and M. Kolovratnik. "Modelling of the droplet size distribution in a low-pressure steam turbine." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 214, no. 2 (March 1, 2000): 145–52. http://dx.doi.org/10.1243/0957650001538245.
Повний текст джерелаАнотація:
Realization of numerous tests on the droplet size measurement with extinction probe, in a 200 MW low-pressure steam turbine, provides necessary experimental data for testing the theoretical models of the droplet nucleation process in steam turbines. The earlier computational model accounting for the unsteady and viscous effects given by Bakhtar and Heaton and by Guha and Young, where the steam particles follow randomly chosen different streamlines within the blade rows with prescribed polytropic efficiency distribution in the pitchwise direction, thus undergoing various nucleation conditions, has been extended in this paper to consider to some extent two-dimensional effects. Because several uncertainties still exist in the inversion methods, predicting the size distribution of droplets, this contribution is aimed at direct comparison of the computed and measured transmittance data I/I0.
12
Viola, Francesco, P. T. Brun, and François Gallaire. "Capillary hysteresis in sloshing dynamics: a weakly nonlinear analysis." Journal of Fluid Mechanics 837 (January 5, 2018): 788–818. http://dx.doi.org/10.1017/jfm.2017.860.
Повний текст джерелаАнотація:
The sloshing of water waves in a vertical cylindrical tank is an archetypal damped oscillator in fluid mechanics. The wave frequency is traditionally derived in the potential flow limit (Lamb, Hydrodynamics, Cambridge University Press, 1932), and the damping rate results from the combined effects of the viscous dissipation at the wall, in the bulk and at the free surface (Case & Parkinson, J. Fluid Mech., vol. 2, 1957, pp. 172–184). Still, the classic theoretical prediction accounting for these effects significantly underestimates the damping rate when compared to careful laboratory experiments (Cocciaro et al., J. Fluid Mech., vol. 246, 1993, pp. 43–66). Specifically, theory provides a unique value for the damping rate, while experiments reveal that the damping increases as the sloshing amplitude decreases. Here, we investigate theoretically the effects of capillarity at the contact line on the decay time of capillary–gravity waves. To this end, we marry a model for the inviscid waves to a nonlinear empiric law for the contact line that incorporates contact angle hysteresis. The resulting system of equations is solved by means of a weakly nonlinear analysis using the method of multiple scales. Capillary effects have a dramatic influence on the calculated damping rate, especially when the sloshing amplitude gets small: this nonlinear interfacial term increases in the limit of zero wave amplitude. In contrast to viscous damping, where the wave motion decays exponentially, the contact angle hysteresis can act as Coulomb solid friction, thus yielding the arrest of the contact line in a finite time.
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Naik, Saurabh, Gabriel Malgaresi, Zhenjiang You, and Pavel Bedrikovetsky. "Well productivity enhancement by applying nanofluids for wettability alteration." APPEA Journal 58, no. 1 (2018): 121. http://dx.doi.org/10.1071/aj17149.
Повний текст джерелаАнотація:
Water blocking is a frequent cause for gas productivity decline in unconventional and conventional fields. It is a result of the capillary end effect near the wellbore vicinity. It creates significant formation damage and decreases gas well productivity. The alteration of the rock wettability by nanofluids is an effective way to reduce water blockage and enhance gas production. Presently, several types of surfactants and nanofluids are used in the industry for contact angle alteration. In this study, we developed an analytical model and analysed the sensitivity to several parameters. After the treatment, the porous medium in the well vicinity (or along the core) will have a stepwise constant contact angle profile. We derive analytical models for compressible steady-state two-phase linear and axi-symmetric flows, accounting for the piecewise-constant contact angle and contact-angle-dependent capillary pressure and relative permeability. The modelling reveals a complex interplay between the competing effects of compressibility, viscous and capillary forces, which influence the optimal contact angle for treatment. The optimal contact angle for treatment will depend on the initial wettability of the formation, the water cut and the capillary-viscous ratio.
14
Grigoropoulos, Gregory J., Christos Bakirtzoglou, George Papadakis, and Dimitrios Ntouras. "Mixed-Fidelity Design Optimization of Hull Form Using CFD and Potential Flow Solvers." Journal of Marine Science and Engineering 9, no. 11 (November 8, 2021): 1234. http://dx.doi.org/10.3390/jmse9111234.
Повний текст джерелаАнотація:
The present paper proposes a new mixed-fidelity method to optimize the shape of ships using genetic algorithms (GA) and potential flow codes to evaluate the hydrodynamics of variant hull forms, enhanced by a surrogate model based on an Artificial Neural Network (ANN) to account for viscous effects. The performance of the variant hull forms generated by the GA is evaluated for calm water resistance using potential flow methods which are quite fast when they run on modern computers. However, these methods do not take into account the viscous effects which are dominant in the stern region of the ship. Solvers of the Reynolds-Averaged Navier-Stokes Equations (RANS) should be used in this respect, which, however, are too time-consuming to be used for the evaluation of some hundreds of variants within the GA search. In this study, a RANS solver is used prior to the execution of the GA to train an ANN in modeling the effect of stern design geometrical parameters only. Potential flow results, accounting for the geometrical design parameters of the rest of the hull, are combined with the aforementioned trained meta-model for the final hull form evaluation. This work concentrates on the provision of a more reliable framework for the evaluation of hull form performance in calm water without a significant increase of the computing time.
15
Rashad, A. M., and A. Y. Bakier. "MHD Effects on Non-Darcy Forced Convection Boundary Layer Flow past a Permeable Wedge in a Porous Medium with Uniform Heat Flux." Nonlinear Analysis: Modelling and Control 14, no. 2 (April 25, 2009): 249–61. http://dx.doi.org/10.15388/na.2009.14.2.14523.
Повний текст джерелаАнотація:
The steady two-dimensional laminar forced flow and heat transfer of a viscous incompressible electrically conducting and heat-generating fluid past a permeable wedge embedded in non-Darcy high-porosity ambient medium with uniform surface heat flux has been studied. The governing equations are derived using the usual boundary layer and Bossinesq approximations and accounting for the applied magnetic filed, permeability of porous medium, variable porosity, inertia and heat generation effects. These equations and boundary conditions are non-dimenstionalized and transformed using non-similarity transformation. The resulting non-linear partial differential equations are then solved numerically subject to the transformed boundary conditions by a finite difference method. Comparisons with previously published works are performed and the results are found to be in excellent agreement. Numerical and graphical results for the velocity and temperature profiles as well as the skin friction and Nusselt number are presented and discussed for various parametric conditions.
16
Sangani, A. S., and R. Sureshkumar. "Linear acoustic properties of bubbly liquids near the natural frequency of the bubbles using numerical simulations." Journal of Fluid Mechanics 252 (July 1993): 239–64. http://dx.doi.org/10.1017/s002211209300374x.
Повний текст джерелаАнотація:
We consider the problem of determining linear acoustic properties of bubbly liquids near the natural frequency of the bubbles. Since the effective wavelength and attenuation length are of the same order of magnitude as the size of the bubbles, we devise a numerical scheme to determine these quantities by solving exactly the multiple scattering problem among many interacting bubbles. It is shown that the phase speed and attenuation are finite at natural frequency even in the absence of damping due to viscous, thermal, nonlinear, and liquid compressibility effects, thus validating a recent theory (Sangani 1991). The results from the numerical scheme are in good agreement with the theory but considerably higher than the experimental values for frequencies greater than the natural frequency. The discrepancy with experiments remains even after accounting for the effect of polydispersity, finite liquid compressibility, and non-adiabatic thermal changes.
17
DAHLKILD, A. A. "The motion of Brownian particles and sediment on an inclined plate." Journal of Fluid Mechanics 337 (April 25, 1997): 25–47. http://dx.doi.org/10.1017/s0022112096004703.
Повний текст джерелаАнотація:
The gravitational settling of a homogeneous suspension of Brownian particles on an inclined plate is considered. The hindered settling towards the wall and the viscous, buoyancy-driven bulk motion of the sediment are considered assuming steady conditions and accounting for the effects of Brownian diffusion, shear-induced diffusion and migration of particles due to a gradient in shear stress. Generally, the results show the development of a sediment boundary layer where the settling towards the wall is balanced by Brownian diffusion at the beginning of the plate and by shear-induced diffusion further downstream. Compared to previous results in the literature, the present theory allows steady-state solutions for extended values of the plate inclination and particle volume fraction above the sediment; upon reconsidering the case with non-Brownian particles, a new similarity solution, with a stable shock in particle density, is developed.
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Keyes, D. E., and F. H. Abernathy. "A model for the dynamics of polymers in laminar shear flows." Journal of Fluid Mechanics 185 (December 1987): 503–22. http://dx.doi.org/10.1017/s0022112087003288.
Повний текст джерелаАнотація:
A novel primitive model is proposed for the hydrodynamic behaviour of an isolated dissolved polymer molecule in a laminar shear flow. The model, in which inertial effects are neglected, allows for rotation and partial stretching of the molcule, but not for bending. Dilute solutions of flexible long-chain polymers have been experimentally observed to exhibit periodic velocity fluctuations distinct from turbulence over a broad frequency range when flowed in high-shear-rate water-table and pipe configurations. In these experiments, the frequency of the fluctuations does not increase with increasing shear rate; rather, it is lowest in the regions of the flow where the shear is the highest. A manifestation of viscous shear thickening has also been observed in these laminar flows. The proposed polymer representation appears capable of accounting for the salient features of these flows with adjustment of a single dimensionless parameter, a ratio of polymer-spring and solvent-viscosity forces.
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Sevilla, Alejandro. "The effect of viscous relaxation on the spatiotemporal stability of capillary jets." Journal of Fluid Mechanics 684 (September 2, 2011): 204–26. http://dx.doi.org/10.1017/jfm.2011.297.
Повний текст джерелаАнотація:
AbstractThe linear spatiotemporal stability properties of axisymmetric laminar capillary jets with fully developed initial velocity profiles are studied for large values of both the Reynolds number, $\mathit{Re}= Q/ (\lrm{\pi} a\nu )$, and the Froude number, $\mathit{Fr}= {Q}^{2} / ({\lrm{\pi} }^{2} g{a}^{5} )$, where $a$ is the injector radius, $Q$ the volume flow rate, $\nu $ the kinematic viscosity and $g$ the gravitational acceleration. The downstream development of the basic flow and its stability are addressed with an approximate formulation that takes advantage of the jet slenderness. The base flow is seen to depend on two parameters, namely a Stokes number, $G= \mathit{Re}/ \mathit{Fr}$, and a Weber number, $\mathit{We}= \rho {Q}^{2} / ({\lrm{\pi} }^{2} \sigma {a}^{3} )$, where $\sigma $ is the surface tension coefficient, while its linear stability depends also on the Reynolds number. When non-parallel terms are retained in the local stability problem, the analysis predicts a critical value of the Weber number, ${\mathit{We}}_{c} (G, \mathit{Re})$, below which a pocket of local absolute instability exists within the near field of the jet. The function ${\mathit{We}}_{c} (\mathit{Re})$ is computed for the buoyancy-free jet, showing marked differences with the results previously obtained with uniform velocity profiles. It is seen that, in accounting for gravity effects, it is more convenient to express the parametric dependence of the critical Weber number with use made of the Morton and Bond numbers, $\mathit{Mo}= {\nu }^{4} {\rho }^{3} g/ {\sigma }^{3} $ and $\mathit{Bo}= \rho g{a}^{2} / \sigma $, as replacements for $G$ and $\mathit{Re}$. This alternative formulation is advantageous to describe jets of a given liquid for a known value of $g$, in that the resulting Morton number becomes constant, thereby leaving $\mathit{Bo}$ as the only relevant parameter. The computed function ${\mathit{We}}_{c} (\mathit{Bo})$ for a water jet under Earth gravity is shown to be consistent with the experimental results of Clanet and Lasheras for the transition from jetting to dripping of water jets discharging into air from long injection needles, which cannot be properly described with a uniform velocity profile assumed at the jet exit.
20
Boyko, Evgeniy, Ran Eshel, Khaled Gommed, Amir D. Gat, and Moran Bercovici. "Elastohydrodynamics of a pre-stretched finite elastic sheet lubricated by a thin viscous film with application to microfluidic soft actuators." Journal of Fluid Mechanics 862 (January 14, 2019): 732–52. http://dx.doi.org/10.1017/jfm.2018.967.
Повний текст джерелаАнотація:
The interaction of a thin viscous film with an elastic sheet results in coupling of pressure and deformation, which can be utilized as an actuation mechanism for surface deformations in a wide range of applications, including microfluidics, optics and soft robotics. Implementation of such configurations inherently takes place over finite domains and often requires some pre-stretching of the sheet. Under the assumptions of strong pre-stretching and small deformations of the lubricated elastic sheet, we use the linearized Reynolds and Föppl–von Kármán equations to derive closed-form analytical solutions describing the deformation in a finite domain due to external forces, accounting for both bending and tension effects. We provide a closed-form solution for the case of a square-shaped actuation region and present the effect of pre-stretching on the dynamics of the deformation. We further present the dependence of the deformation magnitude and time scale on the spatial wavenumber, as well as the transition between stretching- and bending-dominant regimes. We also demonstrate the effect of spatial discretization of the forcing (representing practical actuation elements) on the achievable resolution of the deformation. Extending the problem to an axisymmetric domain, we investigate the effects arising from nonlinearity of the Reynolds and Föppl–von Kármán equations and present the deformation behaviour as it becomes comparable to the initial film thickness and dependent on the induced tension. These results set the theoretical foundation for implementation of microfluidic soft actuators based on elastohydrodynanmics.
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Kamel, Mohammed H., Islam M. Eldesoky, Bilal M. Maher, and Ramzy M. Abumandour. "Slip Effects on Peristaltic Transport of a Particle-Fluid Suspension in a Planar Channel." Applied Bionics and Biomechanics 2015 (2015): 1–14. http://dx.doi.org/10.1155/2015/703574.
Повний текст джерелаАнотація:
Peristaltic pumping induced by a sinusoidal traveling wave in the walls of a two-dimensional channel filled with a viscous incompressible fluid mixed with rigid spherical particles is investigated theoretically taking the slip effect on the wall into account. A perturbation solution is obtained which satisfies the momentum equations for the case in which amplitude ratio (wave amplitude/channel half width) is small. The analysis has been carried out by duly accounting for the nonlinear convective acceleration terms and the slip condition for the fluid part on the wavy wall. The governing equations are developed up to the second order of the amplitude ratio. The zeroth-order terms yield the Poiseuille flow and the first-order terms give the Orr-Sommerfeld equation. The results show that the slip conditions have significant effect within certain range of concentration. The phenomenon of reflux (the mean flow reversal) is discussed under slip conditions. It is found that the critical reflux pressure is lower for the particle-fluid suspension than for the particle-free fluid and is affected by slip condition. A motivation of the present analysis has been the hope that such theory of two-phase flow process under slip condition is very useful in understanding the role of peristaltic muscular contraction in transporting biofluid behaving like a particle-fluid mixture. Also the theory is important to the engineering applications of pumping solid-fluid mixture by peristalsis.
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HEPPE, BURKHARD M. O. "Generalized Langevin equation for relative turbulent dispersion." Journal of Fluid Mechanics 357 (February 25, 1998): 167–98. http://dx.doi.org/10.1017/s0022112097008069.
Повний текст джерелаАнотація:
The relative velocity of two fluid particles in homogeneous and stationary turbulence is considered. Looking for reduced dynamics of turbulent dispersion, we apply the nonlinear Mori–Zwanzig projector method to the Navier–Stokes equations. The projector method decomposes the Lagrangian acceleration into a conditionally averaged part and a random force. The result is an exact generalized Langevin equation for the Lagrangian velocity differences accounting for the exact equation of the Eulerian probability density. From the generalized Langevin equation, we obtain a stochastic model of relative dispersion by stochastic estimation of conditional averages and by assuming the random force to be Gaussian white noise. This new approach to dispersion modelling generalizes and unifies stochastic models based on the well-mixed condition and the moments approximation. Furthermore, we incorporate viscous effects in a systematic way. At a moderate Reynolds number, the model agrees qualitatively with direct numerical simulations showing highly non-Gaussian separation and velocity statistics for particle pairs initially close together. At very large Reynolds numbers, the mean-square separation obeys a Richardson law with coefficient of the order of 0.1.
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Raatikainen, T., R. H. Moore, T. L. Lathem, and A. Nenes. "A coupled observation – modeling approach for studying activation kinetics from measurements of CCN activity." Atmospheric Chemistry and Physics Discussions 12, no. 1 (January 19, 2012): 1821–65. http://dx.doi.org/10.5194/acpd-12-1821-2012.
Повний текст джерелаАнотація:
Abstract. This paper presents an approach to study droplet activation kinetics from measurements of CCN activity by the Continuous Flow Streamwise Thermal Gradient CCN Chamber (CFSTGC) and a comprehensive model of the instrument and droplet growth. The model is evaluated against a series of experiments with ammonium sulfate calibration aerosol. Observed and model predicted droplet sizes are in excellent agreement for a water vapor uptake coefficient ~0.2, which is consistent with theoretical expectations. The model calculations can be considerably accelerated without significant loss of accuracy by assuming simplified instrument geometry and constant parabolic flow velocity profiles. With these assumptions, the model can be applied to large experimental data sets (to infer kinetic growth parameters) while fully accounting for water vapor depletion effects and changes in instrument operation parameters such as the column temperature, flow rates, sheath and sample flow relative humidities, and pressure. When the effects of instrument operation parameters, water vapor depletion and equilibrium dry particle properties on droplet size are accounted for, the remaining variations in droplet size are most likely due to non-equilibrium processes such as those caused by organic surface films, slow solute dissociation and glassy or highly viscous particle states. As an example of model application, data collected during a research flight in the ARCTAS 2008 campaign are analyzed. The model shows that water vapor depletion effects can explain changes in the observed average droplet size.
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Raatikainen, T., R. H. Moore, T. L. Lathem, and A. Nenes. "A coupled observation – modeling approach for studying activation kinetics from measurements of CCN activity." Atmospheric Chemistry and Physics 12, no. 9 (May 11, 2012): 4227–43. http://dx.doi.org/10.5194/acp-12-4227-2012.
Повний текст джерелаАнотація:
Abstract. This paper presents an approach to study droplet activation kinetics from measurements of CCN activity by the Continuous Flow Streamwise Thermal Gradient CCN Chamber (CFSTGC) and a comprehensive model of the instrument and droplet growth. The model, which can be downloaded from http://nenes.eas.gatech.edu/Experiments/CFSTGC.html , is evaluated against a series of experiments with ammonium sulfate calibration aerosol. Observed and modeled droplet sizes are in excellent agreement for a water vapor uptake coefficient ~0.2, which is consistent with theoretical expectations. The model calculations can be considerably accelerated without significant loss of accuracy by assuming simplified instrument geometry and constant parabolic flow velocity profiles. With these assumptions, the model can be applied to large experimental data sets to infer kinetic growth parameters while fully accounting for water vapor depletion effects and changes in instrument operation parameters such as the column temperature, flow rates, sheath and sample flow relative humidities, and pressure. When the effects of instrument operation parameters, water vapor depletion and equilibrium dry particle properties on droplet size are accounted for, the remaining variations in droplet size are most likely due to non-equilibrium processes such as those caused by organic surface films, slow solute dissociation and glassy or highly viscous particle states. As an example of model application, data collected during a research flight in the ARCTAS 2008 campaign are analyzed. The model shows that water vapor depletion effects can explain changes in the observed average droplet size.
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Chamkha, Ali J. "On Two-Dimensional Laminar Hydromagnetic Fluid-Particle Flow Over a Surface in the Presence of a Gravity Field." Journal of Fluids Engineering 123, no. 1 (November 27, 2000): 43–49. http://dx.doi.org/10.1115/1.1343460.
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A continuum two-phase fluid-particle model accounting for particle-phase stresses and a body force due to the presence of a magnetic field is developed and applied to the problem of two-dimensional laminar hydromagnetic flow of a particulate suspension over a horizontal surface in the presence of a gravity field. Analytical solutions for the velocity distributions and the skin-friction coefficients of both phases are reported. Two cases of wall hydrodynamic (velocity) conditions corresponding to stationary and oscillatory velocity distributions are considered. Numerical evaluations of the analytical solutions are performed and the results are reported graphically to elucidate special features of the solutions. The effects of the particle-phase stresses and the magnetic field are illustrated through representative results for the horizontal velocity profiles, fluid-phase displacement thickness, and the complete skin-friction coefficient for various combinations of the physical parameters. It is found that the presence of the magnetic field increases the fluid-phase skin-friction coefficient for various particulate volume fraction levels while the presence of the particle-phase viscous stresses reduces it for various particle-to-fluid density ratios.
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Thorsteinsson, Throstur, and Edwin D. Waddington. "Folding in strongly anisotropic layers near ice-sheet centers." Annals of Glaciology 35 (2002): 480–86. http://dx.doi.org/10.3189/172756402781816708.
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AbstractConditions for passive folding near ice-sheet centers are derived treating the ice as an anisotropic viscous medium. Vertical uniaxial compression at a dome, or pure shear stress near a ridge divide, both tend to stretch and flatten folds, while horizontal simple shear deformation tends to overturn folds. Overturned folding is likely in a given vicinity in a steady-state flow field, if the initial slope of a layer disturbance exceeds the ratio of compressive/extensive deformation to shear deformation. Analytical equations for particle tracks in steady state allow us to model the evolution of layers with initial slope disturbances (``wrinkles’’). the effects of anisotropy are explored using an analytical solution for the strain rate as a function of a vertically symmetric c-axis orientation distribution, called a cone fabric. Stronger anisotropy (small cone angle) makes the material softer in horizontal shear, and facilitates folding, i.e. elements with smaller slopes can be overturned for the same stress. the relation between anisotropy and folding is complicated by the fact that, for a range of cone angles, the material is also softer in compression, which opposes folding. Simulating a layer with spatially variable tilt of cone symmetry axes, and accounting for fabric development, demonstrates that variations in the fabric cause localized flow variations that could create the initial perturbations.
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Battista, F., J. P. Mollicone, P. Gualtieri, R. Messina, and C. M. Casciola. "Exact regularised point particle (ERPP) method for particle-laden wall-bounded flows in the two-way coupling regime." Journal of Fluid Mechanics 878 (September 10, 2019): 420–44. http://dx.doi.org/10.1017/jfm.2019.622.
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The exact regularised point particle (ERPP) method is extended to treat the inter-phase momentum coupling between particles and fluid in the presence of walls by accounting for vorticity generation due to particles close to solid boundaries. The ERPP method overcomes the limitations of other methods by allowing the simulation of an extensive parameter space (Stokes number, mass loading, particle-to-fluid density ratio and Reynolds number) and of particle spatial distributions that are uneven (few particles per computational cell). The enhanced ERPP method is explained in detail and validated by considering the global impulse balance. In conditions when particles are located close to the wall, a common scenario in wall-bounded turbulent flows, the main contribution to the total impulse arises from the particle-induced vorticity at the solid boundary. The method is applied to direct numerical simulations of particle-laden turbulent pipe flow in the two-way coupling regime to address turbulence modulation. The effects of the mass loading, the Stokes number and the particle-to-fluid density ratio are investigated. The drag is either unaltered or increased by the particles with respect to the uncoupled case. No drag reduction is found in the parameter space considered. The momentum stress budget, which includes an extra stress contribution by the particles, provides the rationale behind the drag behaviour. The extra stress produces a momentum flux towards the wall that strongly modifies the viscous stress, the culprit of drag at solid boundaries.
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Yang, Peiran, Zhao Jing, Bingrong Sun, Lixin Wu, Bo Qiu, Ping Chang, and Sanjiv Ramachandran. "On the Upper-Ocean Vertical Eddy Heat Transport in the Kuroshio Extension. Part I: Variability and Dynamics." Journal of Physical Oceanography 51, no. 1 (January 2021): 229–46. http://dx.doi.org/10.1175/jpo-d-20-0068.1.
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AbstractOceanic eddies play a crucial role in transporting heat from the subsurface to surface ocean. However, dynamics responsible for the vertical eddy heat transport QT have not been systematically understood, especially in the mixed layer of western boundary current extensions characterized by the coincidence of strong eddy activities and air–sea interactions. In this paper, the winter (December–March) QT in the Kuroshio Extension is simulated using a 1-km regional ocean model. An omega equation based on the geostrophic momentum approximation and generalized to include the viscous and diabatic effects is derived and used to decompose the contribution of QT from different dynamics. The simulated QT exhibits a pronounced positive peak around the center of the mixed layer (~60 m). The value of QT there exhibits multi-time-scale variations with irregularly occurring extreme events superimposed on a slowly varying seasonal cycle. The proposed omega equation shows good skills in reproducing QT, capturing its spatial and temporal variations. Geostrophic deformation and vertical mixing of momentum are found to be the two major processes generating QT in the mixed layer with the former and the latter accounting for its seasonal variation and extreme events, respectively. The mixed layer instability and the net effect of frontogenesis/frontolysis contribute comparably to the geostrophic deformation induced QT. The contribution of QT from vertical mixing of momentum can be understood on the basis of turbulent thermal wind balance.
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Shiraiwa, Manabu, and Ulrich Pöschl. "Mass accommodation and gas–particle partitioning in secondary organic aerosols: dependence on diffusivity, volatility, particle-phase reactions, and penetration depth." Atmospheric Chemistry and Physics 21, no. 3 (February 4, 2021): 1565–80. http://dx.doi.org/10.5194/acp-21-1565-2021.
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Abstract. Mass accommodation is an essential process for gas–particle partitioning of organic compounds in secondary organic aerosols (SOA). The mass accommodation coefficient is commonly described as the probability of a gas molecule colliding with the surface to enter the particle phase. It is often applied, however, without specifying if and how deep a molecule has to penetrate beneath the surface to be regarded as being incorporated into the condensed phase (adsorption vs. absorption). While this aspect is usually not critical for liquid particles with rapid surface–bulk exchange, it can be important for viscous semi-solid or glassy solid particles to distinguish and resolve the kinetics of accommodation at the surface, transfer across the gas–particle interface, and further transport into the particle bulk. For this purpose, we introduce a novel parameter: an effective mass accommodation coefficient αeff that depends on penetration depth and is a function of surface accommodation coefficient, volatility, bulk diffusivity, and particle-phase reaction rate coefficient. Application of αeff in the traditional Fuchs–Sutugin approximation of mass-transport kinetics at the gas–particle interface yields SOA partitioning results that are consistent with a detailed kinetic multilayer model (kinetic multilayer model of gas–particle interactions in aerosols and clouds, KM-GAP; Shiraiwa et al., 2012) and two-film model solutions (Model for Simulating Aerosol Interactions and Chemistry, MOSAIC; Zaveri et al., 2014) but deviate substantially from earlier modeling approaches not considering the influence of penetration depth and related parameters. For highly viscous or semi-solid particles, we show that the effective mass accommodation coefficient remains similar to the surface accommodation coefficient in the case of low-volatility compounds, whereas it can decrease by several orders of magnitude in the case of semi-volatile compounds. Such effects can explain apparent inconsistencies between earlier studies deriving mass accommodation coefficients from experimental data or from molecular dynamics simulations. Our findings challenge the approach of traditional SOA models using the Fuchs–Sutugin approximation of mass transfer kinetics with a fixed mass accommodation coefficient, regardless of particle phase state and penetration depth. The effective mass accommodation coefficient introduced in this study provides an efficient new way of accounting for the influence of volatility, diffusivity, and particle-phase reactions on SOA partitioning in process models as well as in regional and global air quality models. While kinetic limitations may not be critical for partitioning into liquid SOA particles in the planetary boundary layer (PBL), the effects are likely important for amorphous semi-solid or glassy SOA in the free and upper troposphere (FT–UT) as well as in the PBL at low relative humidity and low temperature.
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Kempski, Philipp, Eliot Quataert, Jonathan Squire, and Matthew W. Kunz. "Shearing-box simulations of MRI-driven turbulence in weakly collisional accretion discs." Monthly Notices of the Royal Astronomical Society 486, no. 3 (May 3, 2019): 4013–29. http://dx.doi.org/10.1093/mnras/stz1111.
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ABSTRACT We present a systematic shearing-box investigation of magnetorotational instability (MRI)-driven turbulence in a weakly collisional plasma by including the effects of an anisotropic pressure stress, i.e. anisotropic (Braginskii) viscosity. We constrain the pressure anisotropy (Δp) to lie within the stability bounds that would be otherwise imposed by kinetic microinstabilities. We explore a broad region of parameter space by considering different Reynolds numbers and magnetic-field configurations, including net vertical flux, net toroidal-vertical flux, and zero net flux. Remarkably, we find that the level of turbulence and angular-momentum transport are not greatly affected by large anisotropic viscosities: the Maxwell and Reynolds stresses do not differ much from the MHD result. Angular-momentum transport in Braginskii MHD still depends strongly on isotropic dissipation, e.g. the isotropic magnetic Prandtl number, even when the anisotropic viscosity is orders of magnitude larger than the isotropic diffusivities. Braginskii viscosity nevertheless changes the flow structure, rearranging the turbulence to largely counter the parallel rate of strain from the background shear. We also show that the volume-averaged pressure anisotropy and anisotropic viscous transport decrease with increasing isotropic Reynolds number (Re); e.g. in simulations with net vertical field, the ratio of anisotropic to Maxwell stress (αA/αM) decreases from ∼0.5 to ∼0.1 as we move from Re ∼ 103 to Re ∼ 104, while 〈4$\pi$Δp/B2〉 → 0. Anisotropic transport may thus become negligible at high Re. Anisotropic viscosity nevertheless becomes the dominant source of heating at large Re, accounting for ${\gtrsim } 50 {{\ \rm per\ cent}}$ of the plasma heating. We conclude by briefly discussing the implications of our results for radiatively inefficient accretion flows on to black holes.
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Fujimoto, Hitoshi, and Natsuo Hatta. "Deformation and Rebounding Processes of a Water Droplet Impinging on a Flat Surface Above Leidenfrost Temperature." Journal of Fluids Engineering 118, no. 1 (March 1, 1996): 142–49. http://dx.doi.org/10.1115/1.2817492.
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This paper treats numerical analyses of the deformation and rebounding processes of a water droplet impinging on a flat solid surface above the Leidenfrost temperature with a speed in the order of a few [m/s], as well as the flow field inside the droplet. These calculations were performed using the MAC-type solution method to solve a finite differencing approximation of the axisymmetric Navier-Stokes equations governing incompressible fluid flows. Also, the whole dynamic process of a droplet from the moment of collision with a hot surface including the rebound from it was recorded by using a video camera equipped with a macro lens. First, the water film formed by the droplet impinging on the surface spreads radially in a fairly thin discoid-like shape until it reaches a maximum. Next, the water film begins to recoil backwards towards the center and the recoiling process continues to occur owing to the surface tension effect at the periphery. Subsequently, the center part of the liquid drop begins to elongate upwards and the liquid near the top of the drop pulls up the lower part of the remaining liquid. Finally, a vortical ring structure appearing at the bottom of the elongated droplet induces the rotative motion in such a way as to form the rising flow and the droplet rebounds from the surface as a bowling pin-shaped mass. The numerical model to predict the deformation and rebounding processes was built up by accounting for the presence of viscous and surface tension effects. The numerical results obtained by the model were compared with the experimental data and discussed from a practical point of view.
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Solazzi, Santiago G., Simón Lissa, J. Germán Rubino, and Klaus Holliger. "Squirt flow in partially saturated cracks: a simple analytical model." Geophysical Journal International 227, no. 1 (June 28, 2021): 680–92. http://dx.doi.org/10.1093/gji/ggab249.
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SUMMARY Obtaining the seismic response of rocks containing cracks whose scales are much smaller than the prevailing wavelengths is a classic and important problem in rock physics. Seminal analytical models yield the seismic signatures of cracked rocks saturated with a single fluid phase. However, in a wide variety of practically relevant scenarios, cracks may be partially saturated with multiple immiscible fluids of contrasting compressibilities, such as gas and water. When a passing seismic wave deforms the medium, fluid pressure gradients arise within such partially saturated cracks, which, in turn, tend to relax through a process commonly known as squirt flow. The corresponding viscous dissipation may greatly affect the seismic amplitudes and velocities, as well as the anisotropic behaviour of the medium. To date, extensions of classical analytical models to include squirt flow occurring within isolated partially saturated cracks remain limited either in the saturation or in the frequency range. In this work, we present a simple analytical model to compute the seismic response of rocks containing partially saturated aligned cracks accounting for squirt flow effects. First, we solve the linearized Navier–Stokes equations within a partially saturated penny-shaped crack subjected to an oscillatory strain. Then, we obtain a closed analytical expression for a complex-valued frequency-dependent effective fluid bulk modulus which accounts for the stiffness variations of each crack due to squirt flow. Using classic effective medium models, together with such an effective saturating fluid, we retrieve the effective compliance matrix of the probed partially saturated cracked rock. The proposed analytical solution is validated by comparison with corresponding 3-D numerical simulations and existing analytical models.
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Jamiolahmady, Mahmoud, Ali Danesh, D. H. Tehrani, and Mehran Sohrabi. "Variations of Gas/Condensate Relative Permeability With Production Rate at Near-Wellbore Conditions: A General Correlation." SPE Reservoir Evaluation & Engineering 9, no. 06 (December 1, 2006): 688–97. http://dx.doi.org/10.2118/83960-pa.
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Summary It has been demonstrated, first by this laboratory and subsequently by other researchers, that the gas and condensate relative permeability can increase significantly by increasing rate, contrary to the common understanding. There are now a number of correlations in the literature and commercial reservoir simulators accounting for the positive effect of coupling and the negative effect of inertia at near-wellbore conditions. The available functional forms estimate the two effects separately and include a number of parameters, which should be determined with measurements at high-velocity conditions. Measurements of gas/condensate relative permeability at simulated near-wellbore conditions are very demanding and expensive. Recent experimental findings in this laboratory indicate that measured gas/condensate relative permeability values on cores with different characteristics become more similar if expressed in terms of fractional flow instead of the commonly used saturation. This would lower the number of rock curves required in reservoir studies. Hence, we have used a large data bank of gas/condensate relative permeability measurements to develop a general correlation accounting for the combined effect of coupling and inertia as a function of fractional flow. The parameters of the new correlation are either universal, applicable to all types of rocks, or can be determined from commonly measured petrophysical data. The developed correlation has been evaluated by comparing its prediction with the gas/condensate relative permeability values measured at near-wellbore conditions on reservoir rocks not used in its development. The results are quite satisfactory, confirming that the correlation can provide reliable information on variations of relative permeability at near-wellbore conditions with no requirement for expensive measurements. Introduction The process of condensation around the wellbore in a gas/condensate reservoir, when the pressure falls below the dewpoint, creates a region in which both gas and condensate phases flow. The flow behavior in this region is controlled by the viscous, capillary, and inertial forces. This, along with the presence of condensate in all the pores, dictates a flow mechanism that is different from that of gas/oil and gas/condensate in the bulk of the reservoir (Danesh et al. 1989). Accurate determination of gas/condensate relative permeability (kr) values, which is very important in well-deliverability estimates, is a major challenge and requires an approach different from that for conventional gas/oil systems. It has been widely accepted that relative permeability (kr) values at low values of interfacial tension (IFT) are strong functions of IFT as well as fluid saturation (Bardon and Longeron 1980; Asar and Handy 1988; Haniff and Ali 1990; Munkerud 1995). Danesh et al. (1994) were first to report the improvement of the relative permeability of condensing systems owing to an increase in velocity as well as that caused by a reduction in IFT. This flow behavior, referred to as the positive coupling effect, was subsequently confirmed experimentally by other investigators (Henderson et al. 1995, 1996; Ali et al. 1997; Blom et al. 1997). Jamiolahmady et al. (2000) were first to study the positive coupling effect mechanistically capturing the competition of viscous and capillary forces at the pore level, where there is simultaneous flow of the two phases with intermittent opening and closure of the gas passage by condensate. Jamiolahmady et al. (2003) developed a steady-dynamic network model capturing this flow behavior and predicted some kr values, which were quantitatively comparable with the experimentally measured values.
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Dawes, W. N. "Turbomachinery computational fluid dynamics: asymptotes and paradigm shifts." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 365, no. 1859 (May 22, 2007): 2553–85. http://dx.doi.org/10.1098/rsta.2007.2021.
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This paper reviews the development of computational fluid dynamics (CFD) specifically for turbomachinery simulations and with a particular focus on application to problems with complex geometry. The review is structured by considering this development as a series of paradigm shifts, followed by asymptotes. The original S1–S2 blade–blade-throughflow model is briefly described, followed by the development of two-dimensional then three-dimensional blade–blade analysis. This in turn evolved from inviscid to viscous analysis and then from steady to unsteady flow simulations. This development trajectory led over a surprisingly small number of years to an accepted approach—a ‘CFD orthodoxy’. A very important current area of intense interest and activity in turbomachinery simulation is in accounting for real geometry effects, not just in the secondary air and turbine cooling systems but also associated with the primary path. The requirements here are threefold: capturing and representing these geometries in a computer model; making rapid design changes to these complex geometries; and managing the very large associated computational models on PC clusters. Accordingly, the challenges in the application of the current CFD orthodoxy to complex geometries are described in some detail. The main aim of this paper is to argue that the current CFD orthodoxy is on a new asymptote and is not in fact suited for application to complex geometries and that a paradigm shift must be sought. In particular, the new paradigm must be geometry centric and inherently parallel without serial bottlenecks. The main contribution of this paper is to describe such a potential paradigm shift, inspired by the animation industry, based on a fundamental shift in perspective from explicit to implicit geometry and then illustrate this with a number of applications to turbomachinery.
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Zhu, Jianjun, Hanjun Zhao, Guangqiang Cao, Hattan Banjar, Haiwen Zhu, Jianlin Peng, and Hong-Quan Zhang. "A New Mechanistic Model for Emulsion Rheology and Boosting Pressure Prediction in Electrical Submersible Pumps (ESPs) under Oil-Water Two-Phase Flow." SPE Journal 26, no. 02 (January 22, 2021): 667–84. http://dx.doi.org/10.2118/196155-pa.
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Summary As the second most widely used artificial lift method in the petroleum industry, electrical submersible pumps (ESPs) maintain or increase flow rates by converting the kinetic energy to hydraulic pressure. As oilfields age, water is invariably produced with crude oil. The increase of water cut generates oil-water emulsions due to the high-shearing effects inside a rotating ESP. Emulsions can be stabilized by natural surfactants or fine solids existing in the reservoir fluids. The formation of emulsions during oil production creates a high viscous mixture, resulting in costly problems and flow assurance issues, such as increasing pressure drop and reducing production rates. This paper, for the first time, proposes a new rheology model to predict the oil-water emulsion effective viscosities and establishes a link of fluid rheology and its effect with the stage pressure increment of ESPs. Based on Brinkman's (1952) correlation, a new rheology model, accounting for ESP rotational speed, stage number, fluid properties, and so on, is developed, which can also predict the phase inversion in oil-water emulsions. For the new mechanistic model to calculate ESP boosting pressure, a conceptual best-match flow rate (QBM) is introduced. QBM corresponds to the flow rate whose direction at the ESP impeller outlet matches the designed flow direction. Induced by the liquid flow rates changing, various pressure losses can be derived from QBM, including recirculation losses, and losses due to friction, leakage, sudden change of flow directions, and so on. Incorporating the new rheology model into the mechanistic model, the ESP boosting pressure under oil-water emulsion flow can be calculated. To validate the proposed model, the experimental data from two different types of ESPs were compared with the model predictions in terms of ESP boosting pressure. Under both high-viscosity single-phase fluid flow and oil-water emulsion flow, the model predicted ESP pressure increment matches the experimental measurements well. From medium to high flow rates with varying oil viscosities and water cuts, the prediction error is less than 15%.
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Hui, Mun-Hong, Dengen Zhou, Xian-Huan Wen, and Louis J. Durlofsky. "Development and Application of a New Technique for Upscaling Miscible Displacements." SPE Reservoir Evaluation & Engineering 8, no. 03 (June 1, 2005): 189–95. http://dx.doi.org/10.2118/89435-pa.
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Summary To better design and manage miscible gas injection, a fast and accurate coarse-scale miscible simulation capability is required. In this paper, we present a new technique for the upscaling of first-contact miscible displacements. The method comprises two components: effective flux boundary conditions (EFBCs) and the extended Todd and Longstaff with upscaled relative permeabilities (ETLU) formulation. The former accounts approximately for the effects of the global flow field on the local upscaling problems, while the latter modifies the way that effective fluid properties and upscaled relative permeabilities are computed so that effectively residual oil is properly represented. For a sequence of partially layered, synthetic 2D permeability fields, the technique is shown to be successful in reproducing reference fine-scale solutions. The method is also shown to outperform other upscaling techniques over a wide range of coarsening factors. The upscaling procedure is then applied to a 3D simulation of a miscible gas-injection field study. A near-well upscaling technique is also incorporated into the methodology. We show that the new approach provides coarse-scale simulation results that match the reference solutions closely. In addition, the technique is shown to be very efficient computationally. Introduction In many oil fields with significant amounts of associated gas, miscible gas injection is a potentially attractive recovery method because it can yield high local displacement efficiencies and may also offer a solution for gas handling. For an accurate estimation of the displacement efficiency, complex phenomenalike viscous fingering need to be modeled properly. There are two broad categories of approaches to modeling miscible displacements: fully compositional (FC) and limited compositional (LC). For multicontact miscible processes, FC simulations are generally required. However, fine-scale FC simulations of miscible processes are prohibitively time-consuming. While compositional streamline techniques may eventually address many of the computational difficulties, several issues (e.g., gravity, compressibility, and streamline updating) have yet to be fully resolved. When first-contact miscibility is applicable, the LC formulation may be preferable because of its computational efficiency. The LC formulation allows the simulator to model miscibility within a black-oil framework and empirically accounts for viscous fingering by modifying the fluid properties of the pseudophases. However, because fine-scale LC simulations are still computationally demanding, there remains a clear need for a robust miscible upscaling technique. In this work, we present a novel upscaling technique for the fast and accurate coarse-scale simulation of first-contact miscible displacements. Our method is an LC approach that has two components: the use of EFBCs for the calculation of upscaled (pseudo-) relative permeabilities and the ETLU formulation. EFBCs incorporate some approximate global flow information into the local upscaling calculations and appropriately suppress the flux through high-permeability streaks that are not continuous throughout the domain. As a result, EFBCs address the problem of premature breakthrough of injected fluid, which can occur because of the overestimation of flux that results from the use of standard boundary conditions. Our ETLU formulation extends the Todd and Longstaff method by accounting for the fact that, within reservoir-simulation length scales, there exists an amount of oil that is practically immobile and not available for mixing (Sorb). The computation of effective fluid properties and upscaled relative permeabilities, therefore, should not include this Sorb. This concept in fact leads to the improved behavior of the upscaled relative permeabilities. Previous miscible upscaling approaches entailing upscaled relative permeabilities neither included the Sorb concept nor used any specialized boundary conditions such as EFBCs.
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Ju, J. W., and Tsung-Muh Chen. "Micromechanics and Effective Elastoplastic Behavior of Two-Phase Metal Matrix Composites." Journal of Engineering Materials and Technology 116, no. 3 (July 1, 1994): 310–18. http://dx.doi.org/10.1115/1.2904293.
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A micromechanical framework is presented to predict effective (overall) elasto-(visco-)plastic behavior of two-phase particle-reinforced metal matrix composites (PRMMC). In particular, the inclusion phase (particle) is assumed to be elastic and the matrix material is elasto-(visco-)plastic. Emanating from Ju and Chen’s (1994a,b) work on effective elastic properties of composites containing many randomly dispersed inhomogeneities, effective elastoplastic deformations and responses of PRMMC are estimated by means of the “effective yield criterion” derived micromechanically by considering effects due to elastic particles embedded in the elastoplastic matrix. The matrix material is elastic or plastic, depending on local stress and deformation, and obeys general plastic flow rule and hardening law. Arbitrary (general) loadings and unloadings are permitted in our framework through the elastic predictor-plastic corrector two-step operator splitting methodology. The proposed combined micromechanical and computational approach allows us to estimate overall elastoplastic responses of PRMMCs by accounting for the microstructural information (such as the spatial distribution and micro-geometry of particles), elastic properties of constituent phases, and the plastic behavior of the matrix-only materials. Comparison between our theoretical predictions and experimental data on uniaxial elastoplastic tests for PRMMCs is also presented to illustrate the capability of the proposed framework. A straightforward extension to accommodate viscoplastic matrix material is also presented to further enhance the applicability of the proposed method.
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POZDEREC, MIHA, and DUNJA ŠAJN GORJANC. "Permeability properties of woven fabrics containing two-ply fancy yarns." Industria Textila 72, no. 02 (April 22, 2021): 156–67. http://dx.doi.org/10.35530/it.072.02.1712.
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The basic intention of the presented research is to analyse the permeability properties of woven fabrics containing two-ply fancy yarns in the weft direction. Within the framework of presented research, two-ply fancy yarns were analysed. Because of their structure, they are classified as fancy yarns with structural effects. The first analysed two-ply fancy yarn is made of the mixture of 81% cotton and 19% viscose. The second is made of the mixture of 67% viscose and 33% flax. For the purpose of the presented research, woven fabrics containing two-ply fancy yarn were made in three different densities in weft (10 threads per cm, 13 threads per cm, and 16 threads per cm) in the twill weave T 1/3 Z. The theoretical part includes the historical development of the production of the fancy yarns, a detailed discussion of the ring production processes, the types and the structure of the fancy yarns, their use, and the global and European market of the fancy yarns. The experimental part consists of three parts. In the first part, the structural properties of the analysed fancy yarns were researched (the fineness of the fancy yarn, the frequency of repeating the effects per one meter of the yarn, the direction of twisting the fancy yarn, the number of the twists of the basic and the effective part, the diameter of the fibers, the diameter of the basic and the effective part, the fineness of individual components, the direction of the twist of individual components, and the percentage of the inside twist of individual components). In the second part, constructional properties of the analysed woven fabrics with the fancy yarn in the weft were researched (mass, thickness, the density of the warp and weft threads, and openness of the surface). In the third part, permeability properties of the analysed woven fabrics with the fancy yarn in the weft were researched where greater attention was paid to air permeability and water vapour permeability. The results of the research showed that the samples with the first two-ply fancy yarn in the weft (81% cotton and 19% viscose) have greater air permeability and water vapour permeability. Meanwhile, the samples with the second two-ply fancy yarn in the weft (67% viscose and 33% flax) have lesser abrasion resistance and poorer dimensional stability while being washed.
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Zappulla, Matthew L. S., and Brian G. Thomas. "Surface Defect Formation in Steel Continuous Casting." Materials Science Forum 941 (December 2018): 112–17. http://dx.doi.org/10.4028/www.scientific.net/msf.941.112.
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Serious defects in the continuous casting of steel, including surface cracks and depressions, are often related to thermal mechanical behavior during solidification in the mold. A finite-element model has been developed to simulate the temperature, shape, and stress of the steel shell, as it moves down the mold in a state of generalized plane strain at the casting speed. The thermal model simulates transient heat transfer in the solidifying steel and between the shell and mold wall. The thermal model is coupled with a stress model that features temperature-, composition-, and phase dependent elastic-visco-plastic constitutive behavior of the steel, accounting for liquid, δ-ferrite, and γ-austenite behavior. Depressions are predicted to form when the shell is subjected to either excessive compression or tension, but the shapes, severity, and appearance differ with conditions. Cracks appearing without depressions are suggested to form in the lower ductility trough when the shell is colder but more brittle. The local thickness of the shell and austenite layer appears to have major effects as well. The model reveals new insights into the formation mechanisms and behavior of surface depressions and longitudinal cracks in the continuous casting process.
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Mansura, Dmytro A., Nicholas H. Thom, and Hartmut J. Beckedahl. "Numerical and Experimental Predictions of Texture-Related Influences on Rolling Resistance." Transportation Research Record: Journal of the Transportation Research Board 2672, no. 40 (May 30, 2018): 430–39. http://dx.doi.org/10.1177/0361198118776114.
Повний текст джерелаАнотація:
To overcome rolling resistance (RR) a typical vehicle on average consumes 4152 MJ/119 L of fuel annually as a result of both vehicle and pavement factors. A slight improvement in surface texture arrangement may therefore decrease fuel consumption bringing substantial long-term socio-economic benefits. This aligns with ever-tighter limits on CO2 in the USA (163 g/km until 2025) fostering sustainable construction/exploitation of tires/pavements. This paper describes a multi-scale 3-D numerical methodology to calculate micro-distortional RR and contact indentations of surface aggregates into visco-elastic tread compound accounting for loading, velocity, temperature, and compound properties. It consists of a micro-scale tread block single aggregate model and a macro-scale car tire finite element model, rolling in steady-state mode over a rigid smooth surface. The surface texture is idealized in terms of hemispherical indenters. The micro-distortional RR estimates are based on contact force and energy lost per single stone. The computed contact/normal forces peak significantly due to visco-elastic effects at the beginning of the tire–surface contact phase, followed by a gradually relaxing stress region with a sudden release at the end of the interaction. The contact forces appear to be of a reasonable distribution and magnitude. It is found that micro-distortional RR is higher on a rougher and sparsely packed surface compared with a smoother and more tightly packed case. To determine the total tire-related RR, macro-distortional RR can then be added. The predictions were qualitatively confirmed and adjusted against real bituminous mixes by experimental testing, showing a reasonable agreement.
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Delage, Timmy N., Satoshi Okuzumi, Mario Flock, Paola Pinilla, and Natalia Dzyurkevich. "Steady-state accretion in magnetized protoplanetary disks." Astronomy & Astrophysics 658 (February 2022): A97. http://dx.doi.org/10.1051/0004-6361/202141689.
Повний текст джерелаАнотація:
Context. The transition between magnetorotational instability (MRI)-active and magnetically dead regions corresponds to a sharp change in the disk turbulence level, where pressure maxima may form, hence potentially trapping dust particles and explaining some of the observed disk substructures. Aims. We aim to provide the first building blocks toward a self-consistent approach to assess the dead zone outer edge as a viable location for dust trapping, under the framework of viscously driven accretion. Methods. We present a 1+1D global magnetically driven disk accretion model that captures the essence of the MRI-driven accretion, without resorting to 3D global nonideal magnetohydrodynamic (MHD) simulations. The gas dynamics is assumed to be solely controlled by the MRI and hydrodynamic instabilities. For given stellar and disk parameters, the Shakura–Sunyaev viscosity parameter, α, is determined self-consistently under the adopted framework from detailed considerations of the MRI with nonideal MHD effects (Ohmic resistivity and ambipolar diffusion), accounting for disk heating by stellar irradiation, nonthermal sources of ionization, and dust effects on the ionization chemistry. Additionally, the magnetic field strength is numerically constrained to maximize the MRI activity. Results. We demonstrate the use of our framework by investigating steady-state MRI-driven accretion in a fiducial protoplanetary disk model around a solar-type star. We find that the equilibrium solution displays no pressure maximum at the dead zone outer edge, except if a sufficient amount of dust particles has accumulated there before the disk reaches a steady-state accretion regime. Furthermore, the steady-state accretion solution describes a disk that displays a spatially extended long-lived inner disk gas reservoir (the dead zone) that accretes a few times 10−9 M⊙ yr−1. By conducting a detailed parameter study, we find that the extent to which the MRI can drive efficient accretion is primarily determined by the total disk gas mass, the representative grain size, the vertically integrated dust-to-gas mass ratio, and the stellar X-ray luminosity. Conclusions. A self-consistent time-dependent coupling between gas, dust, stellar evolution models, and our general framework on million-year timescales is required to fully understand the formation of dead zones and their potential to trap dust particles.
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Giannokostas, Konstantinos, Yannis Dimakopoulos, Andreas Anayiotos, and John Tsamopoulos. "Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes." Materials 14, no. 2 (January 13, 2021): 367. http://dx.doi.org/10.3390/ma14020367.
Повний текст джерелаАнотація:
The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that describes the level of the local blood structure at any instance. The constitutive model is enhanced by the non-Newtonian modeling of the plasma phase, which features bulk viscoelasticity. Incorporating microcirculation phenomena such as the cell-free layer (CFL) formation or the Fåhraeus and the Fåhraeus-Lindqvist effects is an indispensable part of the blood flow investigation. The coupling between them and the momentum balance is achieved through correlations based on experimental observations. Notably, we propose a new simplified form for the dependence of the apparent viscosity on the hematocrit that predicts the CFL thickness correctly. Our investigation focuses on the impact of the microtube diameter and the pressure-gradient on velocity profiles, normal and shear viscoelastic stresses, and thixotropic properties. We demonstrate the microstructural configuration of blood in steady-state conditions, revealing that blood is highly aggregated in narrow tubes, promoting a flat velocity profile. Additionally, the proper accounting of the CFL thickness shows that for narrow microtubes, the reduction of discharged hematocrit is significant, which in some cases is up to 70%. At high pressure-gradients, the plasmatic proteins in both regions are extended in the flow direction, developing large axial normal stresses, which are more significant in the core region. We also provide normal stress predictions at both the blood/plasma interface (INS) and the tube wall (WNS), which are difficult to measure experimentally. Both decrease with the tube radius; however, they exhibit significant differences in magnitude and type of variation. INS varies linearly from 4.5 to 2 Pa, while WNS exhibits an exponential decrease taking values from 50 mPa to zero.
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Lin, Ting-Yu, and Satish G. Kandlikar. "Heat Transfer Investigation of Air Flow in Microtubes—Part I: Effects of Heat Loss, Viscous Heating, and Axial Conduction." Journal of Heat Transfer 135, no. 3 (February 11, 2013). http://dx.doi.org/10.1115/1.4007876.
Повний текст джерелаАнотація:
Experiments were conducted to investigate local heat transfer coefficients and flow characteristics of air flow in a 962 μm inner diameter stainless steel microtube (minichannel). The effects of heat loss, axial heat conduction and viscous heating were systematically analyzed. Heat losses during the experiments with gas flow in small diameter tubes vary considerably along the flow length, causing the uncertainties to be very large in the downstream region. Axial heat conduction was found to have a significant effect on heat transfer at low Re. Viscous heating was negligible at low Re, but the effect was found to be significant at higher Re. After accounting for varying heat losses, viscous heating and axial conduction, Nu was found to agree very well with the predictions from conventional heat transfer correlations both in laminar and turbulent flow regions. No early transition to turbulent flow was found in the present study.
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Natali, Arturo N., Emanuele L. Carniel, Piero G. Pavan, Franz G. Sander, Christina Dorow, and Martin Geiger. "A Visco-Hyperelastic-Damage Constitutive Model for the Analysis of the Biomechanical Response of the Periodontal Ligament." Journal of Biomechanical Engineering 130, no. 3 (April 22, 2008). http://dx.doi.org/10.1115/1.2900415.
Повний текст джерелаАнотація:
The periodontal ligament (PDL), as other soft biological tissues, shows a strongly non-linear and time-dependent mechanical response and can undergo large strains under physiological loads. Therefore, the characterization of the mechanical behavior of soft tissues entails the definition of constitutive models capable of accounting for geometric and material non-linearity. The microstructural arrangement determines specific anisotropic properties. A hyperelastic anisotropic formulation is adopted as the basis for the development of constitutive models for the PDL and properly arranged for investigating the viscous and damage phenomena as well to interpret significant aspects pertaining to ordinary and degenerative conditions. Visco-hyperelastic models are used to analyze the time-dependent mechanical response, while elasto-damage models account for the stiffness and strength decrease that can develop under significant loading or degenerative conditions. Experimental testing points out that damage response is affected by the strain rate associated with loading, showing a decrease in the damage limits as the strain rate increases. These phenomena can be investigated by means of a model capable of accounting for damage phenomena in relation to viscous effects. The visco-hyperelastic-damage model developed is defined on the basis of a Helmholtz free energy function depending on the strain-damage history. In particular, a specific damage criterion is formulated in order to evaluate the influence of the strain rate on damage. The model can be implemented in a general purpose finite element code. The accuracy of the formulation is evaluated by using results of experimental tests performed on animal model, accounting for different strain rates and for strain states capable of inducing damage phenomena. The comparison shows a good agreement between numerical results and experimental data.
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Lin, Ting-Yu, and Satish G. Kandlikar. "Heat Transfer Investigation of Air Flow in Microtubes—Part II: Scale and Axial Conduction Effects." Journal of Heat Transfer 135, no. 3 (February 8, 2013). http://dx.doi.org/10.1115/1.4007877.
Повний текст джерелаАнотація:
In this paper, the scale effects are specifically addressed by conducting experiments with air flow in different microtubes. Three stainless steel tubes of 962, 308, and 83 μm inner diameter (ID) are investigated for friction factor, and the first two are investigated for heat transfer. Viscous heating effects are studied in the laminar as well as turbulent flow regimes by varying the air flow rate. The axial conduction effects in microtubes are experimentally explored for the first time by comparing the heat transfer in SS304 tube with a 910 μm ID/2005 μm outer diameter nickel tube specifically fabricated using an electrodeposition technique. After carefully accounting for the variable heat losses along the tube length, it is seen that the viscous heating and the axial conduction effects become more important at microscale and the present models are able to predict these effects accurately. It is concluded that neglecting these effects is the main source of discrepancies in the data reported in the earlier literature.
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Rahman, M. M., Xiaoqing Tian, Huachen Pan, and A. K. M. Sadrul Islam. "Elliptic Blending with One-Equation Model." Global Journal of Science Frontier Research, March 23, 2020, 45–54. http://dx.doi.org/10.34257/gjsfrfvol20is2pg.
Повний текст джерелаАнотація:
A wall-distance-free modification to Wray-Agarwal (WA) one-equation turbulence model is convoked using an elliptic relaxation approach to accurately accounting for non-local characteristics of near-wall turbulence. Model coefficients/functions are parameterized with the elliptic relaxation function to preserve the combined effects of near-wall turbulence and nonequilibrium. The characteristic length scale associated with the elliptic relaxation equation is formulated in terms of viscous and turbulent length scales in conjunction with the invariant of strain-rate tensor. Consequently, non-local effects are explicitly influenced by the mean flow and turbulent variables. A near-wall damping function is introduced to relax the viscous length-scale coefficient adhering to the elliptic relaxation model. Comparisons indicate that the new model improves the accuracy of flow simulations compared to the widely used Spalart-Allmar as model and remains competitive with the SST model.A good correlation is obtained between the current model and DNS/experimental data.
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Padma Devi, M., and Suripeddi Srinivas. "Thermal characteristics on two immiscible fluid flows in a porous space with time dependent pressure gradient." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, May 27, 2022, 095440892210965. http://dx.doi.org/10.1177/09544089221096569.
Повний текст джерелаАнотація:
The present investigation deals with the pulsating magnetohydrodynamic flow of two immiscible conducting incompressible viscous fluids in a channel filled with a porous medium, accounting for the thermal radiation effect. The problem is formulated by employing the balance of linear momentum, energy for both phases. The effects of governing flow parameters on the velocities, temperature, and stresses are studied by the perturbation method. Expressions for velocity and the temperature in both regions are obtained. Graphical results for the velocity, temperature distributions for various emerging parameters, and tabulated results for shear-stress and mass flux are presented and discussed.
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"Hydrodynamics of quantized shape transitions of lipid domains." Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences 448, no. 1932 (January 9, 1995): 97–111. http://dx.doi.org/10.1098/rspa.1995.0007.
Повний текст джерелаАнотація:
The time-dependent distortions of nearly circular liquid domains of lipids at the air-water interface are studied analytically by accounting for line tension and electrostatic effects in the monolayer and viscous effects in both the monolayer and subphase fluid. One driving force for the shape changes arises from the electrostatic repulsions between molecular dipoles. This force is opposed by a line tension that favors circular shapes. The growth rate of small amplitude disturbances is determined as a function of the distortion (azimuthal) symmetry number n , the domain radius, the dipole density difference and line tension between the lipid domain and the surrounding lipid layer, and the viscosities of the monolayer and underlying liquid. For representative parameter values, the disturbance growth rate is independent of the monolayer viscosity and depends only on the subphase viscosity.
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Chaussonnet, G., R. Koch, H. J. Bauer, A. Sänger, T. Jakobs, and T. Kolb. "Smoothed Particle Hydrodynamics Simulation of an Air-Assisted Atomizer Operating at High Pressure: Influence of Non-Newtonian Effects." Journal of Fluids Engineering 140, no. 6 (January 30, 2018). http://dx.doi.org/10.1115/1.4038753.
Повний текст джерелаАнотація:
A twin-fluid atomizer configuration is predicted by means of the two-dimensional (2D) weakly compressible smooth particle hydrodynamics (SPH) method and compared to experiments. The setup consists of an axial liquid jet surrounded by a high-speed air stream (Ug ≈ 60 m/s) in a pressurized reactor, which is operated at up to 11 bar. Two types of liquid are investigated: a viscous Newtonian liquid (μl = 200 mPa·s) consisting of glycerol/water mixture and a viscous non-Newtonian liquid (μ1,apparent. ≈ 150 mPa·s), which is a carboxymethyl cellulose solution. Three-dimensional (3D) effects are taken into account in the 2D code by introducing: (i) a surface tension term, (ii) a cylindrical viscosity operator, and (iii) a modified velocity accounting for the divergence of the volume in the radial direction. The numerical results at high pressure show a good qualitative agreement with experiment, i.e., a correct transition of the different atomization regimes with regard to pressure, and similar dynamics and length scales of the generated ligaments. The propagation velocity of the Kelvin–Helmholtz (KH) instability is well predicted, but its frequency needs a correction factor to be globally well recovered for the Newtonian liquid. The Sauter mean diameter (SMD), calculated from the spray size distribution, shows similar trends of the reactor pressure dependency. The simulation of the non-Newtonian liquid at high pressure shows the same breakup regime with finer droplets compared to Newtonian liquids, and the simulation at atmospheric pressure shows an apparent viscosity similar to the experiment.
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Chetti, Boualem, Mohamed Hemis, Othman Tahar, and Moussa Smara. "Combined effects of elastic deformation and piezo-viscous dependency on the performance of a journal bearing operating with a non-Newtonian fluid." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, March 3, 2022, 135065012210802. http://dx.doi.org/10.1177/13506501221080277.
Повний текст джерелаАнотація:
A theoretical study of the effects of elastic deformation and the variation of viscosity with pressure on the performance characteristics of a circular journal bearing lubricated with non-Newtonian fluids. The Barus law and the power law model are used to express the viscosity-pressure variation and the non-Newtonian behavior of fluids respectively. To determine the displacement field at the fluid film bearing liner interface, the elastic thin liner model is used. The modified Reynolds equation accounting the viscosity pressure dependency in the non-Newtonian fluids is mathematically derived and solved using finite difference method, to obtain the fluid film pressure field. The static performance characteristics for finite-width journal bearing are evaluated for various values of pressure-viscosity coefficient, the power law index n, and the elastic deformation coefficient. According to the results obtained, it is found that the hydrodynamic pressure and non-dimensional load-carrying capacity increase as the power law index and pressure-viscosity coefficient increases especially for rigid and heavily loaded bearing case. In addition, the combined effects of the elastic deformation and the viscosity pressure dependency are found to be more pronounced on the performance characteristics of a heavily loaded journal bearing operating with a shear-thickening fluid.