47,123 research outputs found
A local lattice Boltzmann method for multiple immiscible fluids and dense suspensions of drops
The lattice Boltzmann method (LBM) for computational fluid dynamics benefits from a simple, explicit, completely local computational algorithm making it highly efficient. We extend LBM to recover hydrodynamics of multi-component immiscible fluids, whilst retaining a completely local, explicit and simple algorithm. Hence, no computationally expensive lattice gradients, interaction potentials or curvatures, that use information from neighbouring lattice sites, need be calculated, which makes the method highly scalable and suitable for high performance parallel computing. The method is analytic and is shown to recover correct continuum hydrodynamic equations of motion and interfacial boundary conditions. This LBM may be further extended to situations containing a high number (O(100)) of individually immiscible drops. We make comparisons of the emergent non-Newtonian behaviour with a power-law fluid model. We anticipate our method will have a range applications in engineering, industrial and biological sciences
Recommended from our members
Constant depth microfluidic networks based on a generalised Murray’s law for Newtonian and power-law fluids
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Microfluidic bifurcating networks of rectangular cross-sectional channels are designed
using a novel biomimetic rule, based on Murray’s law. Murray’s principle is extended to
consider the flow of power-law fluids in planar geometries (i.e. of constant depth rectangular
cross-section) typical of lab-on-a-chip applications. The proposed design offers the ability to
control precisely the shear-stress distributions and to predict the flow resistance along the network.
We use an in-house code to perform computational fluid dynamics simulations in order
to assess the extent of the validity of the proposed design for Newtonian, shear-thinning and
shear-thickening fluids under different flow conditions
Substellar fragmentation in self-gravitating fluids with a major phase transition
The existence of substellar cold H2 globules in planetary nebulae and the
mere existence of comets suggest that the physics of cold interstellar gas
might be much richer than usually envisioned.
We study the case of a cold gaseous medium in ISM conditions which is subject
to a gas-liquid/solid phase transition.
First the equilibrium of general non-ideal fluids is studied using the virial
theorem and linear stability analysis. Then the non-linear dynamics is studied
by using simulations to characterize the expected formation of solid bodies
analogous to comets. The simulations are run with a state of the art molecular
dynamics code (LAMMPS). The long-range gravitational forces can be taken into
account with short-range molecular forces with finite limited computational
resources by using super-molecules, provided the right scaling is followed.
The concept of super-molecule is tested with simulations, allowing us to
correctly satisfy the Jeans instability criterion for one-phase fluids. The
simulations show that fluids presenting a phase transition are gravitationally
unstable as well, independent of the strength of the gravitational potential,
producing two distinct kinds of sub-stellar bodies, those dominated by gravity
("planetoids") and those dominated by molecular attractive force ("comets").
Observations, formal analysis and computer simulations suggest the
possibility of the formation of substellar H2 clumps in cold molecular clouds
due to the combination of phase transition and gravity. Fluids presenting a
phase transition are gravitationally unstable, independent of the strength of
the gravitational potential. Arbitrarily small H2 clumps may form even at
relatively high temperatures up to 400 - 600K, according to virial analysis.
The combination of phase transition and gravity may be relevant for a wider
range of astrophysical situations, such as proto-planetary disks.Comment: 24 pages, 44 figures. accepted for publication in A&
Mobility of Power-law and Carreau Fluids through Fibrous Media
The flow of generalized Newtonian fluids with a rate-dependent viscosity
through fibrous media is studied with a focus on developing relationships for
evaluating the effective fluid mobility. Three different methods have been used
here: i) a numerical solution of the Cauchy momentum equation with the Carreau
or power-law constitutive equations for pressure-driven flow in a fiber bed
consisting of a periodic array of cylindrical fibers, ii) an analytical
solution for a unit cell model representing the flow characteristics of a
periodic fibrous medium, and iii) a scaling analysis of characteristic bulk
parameters such as the effective shear rate, the effective viscosity,
geometrical parameters of the system, and the fluid rheology. Our scaling
analysis yields simple expressions for evaluating the transverse mobility
functions for each model, which can be used for a wide range of medium porosity
and fluid rheological parameters. While the dimensionless mobility is, in
general, a function of the Carreau number and the medium porosity, our results
show that for porosities less than , the dimensionless
mobility becomes independent of the Carreau number and the mobility function
exhibits power-law characteristics as a result of high shear rates at the pore
scale. We derive a suitable criterion for determining the flow regime and the
transition from a constant viscosity Newtonian response to a power-law regime
in terms of a new Carreau number rescaled with a dimensionless function which
incorporates the medium porosity and the arrangement of fibers
Hydrodynamics and Metzner-Otto correlation in stirred vessels for yield stress fluids
This paper investigates the hydrodynamics and power consumption in laminar stirred vessel flowusing numerical computation. The Metzner–Otto correlation was established for mixing in power-law fluids. This paper focuses on its application to yield stress fluids. Distributions of shear rates and their link to power consumption for helical and anchor agitators are discussed. Insight is sought from the analytical formula for Taylor–Couette flows. Laws are established for Bingham, Herschel-Bulkley and Casson fluids and reveal similar results. Fully or partially sheared flow situations with plug regions are considered. Depending on the fluid model, the concept is valid or constitutes a satisfactory approximation for fully sheared flows. When the flow is partially sheared, the expression depends on the Bingham number and the concept must be adapted. The results of the numerical simulations are interpreted in the light of this analysis and results from the literature
Wall effects on the transportation of a cylindrical particle in power-law fluids
The present work deals with the numerical calculation of the Stokes-type drag undergone by a cylindrical particle perpendicularly to its axis in a power-law fluid. In unbounded medium, as all data are not available yet, we provide a numerical solution for the pseudoplastic fluid. Indeed, the Stokes-type solution exists because the Stokes’ paradox does not take place anymore. We show a high sensitivity of the solution to the confinement, and the appearance of the inertia in the proximity of the Newtonian case, where the Stokes’ paradox takes place. For unbounded medium, avoiding these traps, we show that the drag is zero for Newtonian and dilatant fluids. But in the bounded one, the Stokes-type regime is recovered for Newtonian and dilatant fluids. We give also a physical explanation of this effect which is due to the reduction of the hydrodynamic screen length, for pseudoplastic fluids. Once the solution of the unbounded medium has been obtained, we give a solution for the confined medium numerically and asymptotically. We also highlight the consequence of the confinement and the backflow on the settling velocity of a fiber perpendicularly to its axis in a slit. Using the dynamic mesh technique, we give the actual transportation velocity in a power-law “Poiseuille flow”, versus the confinement parameter and the fluidity index, induced by the hydrodynamic interactions
A Kolmogorov-Like Exact Relation for Compressible Polytropic Turbulence
Compressible hydrodynamic turbulence is studied under the assumption of a
polytropic closure. Following Kolmogorov, we derive an exact relation for some
two-point correlation functions in the asymptotic limit of a high Reynolds
number
- …