Physical understanding of gas-liquid annular flow and its transition to dispersed droplets
Transformation from annular to droplet flow is investigated for co-current, upward gas-liquid
flow through a cylindrical tube using grid based volume of fluid framework. Three transitional routes, namely, orificing, rolling, and undercutting are observed for flow transformation at different range of relative velocities between the fluids. Physics behind these three exclusive phenomena is described using circulation patterns of gaseous phase in the vicinity of a liquid film which subsequently sheds drop leading towards transition. Orifice amplitude is found to grow exponentially towards the core whereas it p...
Source: Physics of Fluids - July 7, 2016 Category: Physics Authors: Parmod Kumar, Arup Kumar Das and Sushanta K. Mitra Source Type: research
Sliding Couette flow in a ribbed annulus
The flow in an annulus driven by the axial movement of one of the cylinders has been studied. The stationary cylinder has been fitted with axisymmetric ribs resulting in the appearance of the centrifugal-force-driven instability which leads to the formation of axial vortices. The critical stability conditions have been determined for a wide range of geometries of practical interest; these conditions include the critical Reynolds number as well as the best vortex packing. It has been shown that a sufficiently large increase of the ribs’ wavelength leads to a flow stabilization as the flow becomes nearly rectilinear, thus ...
Source: Physics of Fluids - July 7, 2016 Category: Physics Authors: H. V. Moradi and J. M. Floryan Source Type: research
Hydrodynamics of sediment threshold
This study shows that for a hindrance coefficient of 0.3, the threshold curve (threshold Shields parameter versus shear Reynolds number) has an excellent agreement with the experimental data of uniform sediments. However, most of the experimental data are bounded by the upper and lower limiting threshold curves, corresponding to the hindrance coefficients of 0.2 and 0.4, respectively. The threshold curve of this study is compared with those of previous researchers. The present model also agrees satisfactorily with the experimental data of nonuniform sediments. (Source: Physics of Fluids)
Source: Physics of Fluids - July 6, 2016 Category: Physics Authors: Sk Zeeshan Ali and Subhasish Dey Source Type: research
Breakup modes of fluid drops in confined shear flows
Using a conservative level set method we investigate the deformation behavior of isolated spherical fluid drops in a fluid channel subjected to simple shear flows, accounting the following three non-dimensional parameters: (1) degree of confinement (Wc = 2a/h, where a is the drop radius and h is the channel thickness); (2) viscosity ratio between the two fluids (λ = μd/μm, where μd is the drop viscosity and μm is the matrix viscosity); and (3) capillary number (Ca). For a given Wc, a drop steadily deforms to attain a stable geometry (Taylor number and inclination of its long axis to the shear direction) when Ca < 0.3....
Source: Physics of Fluids - July 6, 2016 Category: Physics Authors: Nilkamal Barai and Nibir Mandal Source Type: research
Analysis of homogeneous/non-homogeneous nanofluid models accounting for nanofluid-surface interactions
This article reports an unbiased analysis for the water based rod shaped alumina nanoparticles by considering both the homogeneous and non-homogeneous nanofluid models over the coupled nanofluid-surface interface. The mechanics of the surface are found for both the homogeneous and non-homogeneous models, which were ignored in previous studies. The viscosity and thermal conductivity data are implemented from the international nanofluid property benchmark exercise. All the simulations are being done by using the experimentally verified results. By considering the homogeneous and non-homogeneous models, the precise movement o...
Source: Physics of Fluids - July 6, 2016 Category: Physics Authors: R. Ahmad Source Type: research
Particle mobility between two planar elastic membranes: Brownian motion and membrane deformation
We study the motion of a solid particle immersed in a Newtonian fluid and confined between two parallel
elastic
membranes possessing shear and bending rigidity. The hydrodynamic mobility depends on the frequency of the particle motion due to the elastic energy stored in the membrane. Unlike the single-membrane case, a coupling between shearing and bending exists. The commonly used approximation of superposing two single-membrane contributions is found to give reasonable results only for motions in the parallel direction, but not in the perpendicular direction. We also compute analytically th...
Source: Physics of Fluids - July 6, 2016 Category: Physics Authors: Abdallah Daddi-Moussa-Ider, Achim Guckenberger and Stephan Gekle Source Type: research
Investigation of full and partial ground effects on a flapping foil hovering above a finite-sized platform
The full and partial ground effects on the lift generation of a flapping airfoil in normal hovering mode are investigated numerically using the discrete vortex method in two dimensions. To achieve full ground effect, the airfoil of chord c is made to hover above the center of a finite-sized platform of length 10c. We have observed the force-enhancement, force-reduction, and force-recovery regimes at low, medium, and high ground clearances in line with the existing literature. This paper puts special focus on partial ground effect when the airfoil is hovering near the edge of the platform. Lift-modifying mechanisms not prev...
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: Lu Wang and Ronald W. Yeung Source Type: research
Oscillating flow and separation of species in rectangular channels
The mass transfer and separation of species in a tube using oscillatory flows are strongly affected by the fluid flow profiles in the tube. It has been well established that oscillatory motion in a one-dimensional flow configuration leads to a single tuning dimensionless frequency, where optimum separation may be effected. In this work, the effect on species separation by two-dimensional laminar flow arising in a rectangular cross section is studied and a surprising result is that a second tuning frequency may occur at lower dimensionless oscillation frequencies. The physics reveals that this new optimum disappears when th...
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: A. Hacioglu and R. Narayanan Source Type: research
Two phase flow of liquids in a narrow gap: Phase interference and hysteresis
Co-current flow of two immiscible liquids, such as oil and water in a planar fracture, exhibits nonlinear structures which become important in many natural and engineering systems such as subsurface flows, multiphase flows in lubrication joints, and coating flows. In this context, co-current flow of oil and water with variable rates is experimentally studied in a Hele-Shaw cell, various flow regimes are classified, and relative permeabilities for the phases are analysed thoroughly. Similar to multiphase pipe flows, multiphase flow in planar gaps shows various flow regimes, each having different flow rate/pressure gradient ...
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: Salim Raza, S. Hossein Hejazi and Ian D. Gates Source Type: research
Stokesian swimming of a sphere at low Reynolds number by helical surface distortion
Explicit expressions are derived for the matrices determining the mean translational and rotational swimming velocities and the mean rate of dissipation for Stokesian swimming at low Reynolds number of a distorting sphere in a viscous incompressible fluid. As an application, an efficient helical propeller-type stroke is found and its properties are calculated. (Source: Physics of Fluids)
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: B. U. Felderhof and R. B. Jones Source Type: research
A Brownian dynamics study on ferrofluid colloidal dispersions using an iterative constraint method to satisfy Maxwell’s equations
Ferrofluids are often favored for their ability to be remotely positioned via external magnetic fields. The behavior of particles in ferromagnetic clusters under uniformly applied magnetic fields has been computationally simulated using the Brownian dynamics, Stokesian dynamics, and Monte Carlo methods. However, few methods have been established that effectively handle the basic principles of magnetic materials, namely, Maxwell’s
equations. An iterative constraint method was developed to satisfy Maxwell’s
equations when a uniform magnetic field is imposed on ferrofluids in a heterogeneou...
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: Sean Hyun Dubina and Lewis Edward Wedgewood Source Type: research
Analytical solution for the lubrication force between two spheres in a bi-viscous fluid
An analytical solution for the calculation of the normal lubrication force acting between two moving spheres embedded in a shear-thinning fluid represented by a bi-viscous model is provided. The resulting force between the suspended spheres exhibits a consistent transition between the Newtonian constant-viscosity limits and it reduces to the well-known standard Newtonian lubrication theory for viscosity-ratio approaching one. Effects of several physical parameters of the theory are analyzed under relevant physical conditions, i.e., for a prototypical case of two non-colloidal spheres immersed in a non-Newtonian fluid with ...
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: A. Vázquez-Quesada and M. Ellero Source Type: research
Numerical and experimental investigation of natural flow-induced vibrations of flexible hydrofoils
The objective of this work is to present combined numerical and experimental studies of natural flow-induced vibrations of flexible hydrofoils. The focus is on identifying the dependence of the foil’s vibration frequencies and damping characteristics on the inflow velocity, angle of attack, and solid-to-fluid added mass ratio. Experimental results are shown for a cantilevered polyacetate (POM) hydrofoil tested in the cavitation tunnel at the French Naval Academy Research Institute (IRENav). The foil is observed to primarily behave as a chordwise rigid body and undergoes spanwise bending and twisting deformations, and the...
Source: Physics of Fluids - July 5, 2016 Category: Physics Authors: Eun Jung Chae, Deniz Tolga Akcabay, Alexandra Lelong, Jacques Andre Astolfi and Yin Lu Young Source Type: research
Three-dimensional wake topology and propulsive performance of low-aspect-ratio pitching-rolling plates
The wake topology and propulsive performance of low-aspect-ratio plates undergoing a pitching-rolling motion in a uniform stream were numerically investigated by an in-house immersed-boundary-method-based incompressible Navier-Stokes equation solver. A detailed analysis of the vortical structures indicated that the pitching-rolling plate produced double-loop vortices with alternating signs from its trailing edge every half period. These vortices then shed and further evolved into interconnected “double-C”-shaped vortex rings, which eventually formed a bifurcating wake pattern in the downstream. As the wake convected do...
Source: Physics of Fluids - July 1, 2016 Category: Physics Authors: Chengyu Li and Haibo Dong Source Type: research
Harvesting energy from the sloshing motion of ferrofluids in an externally excited container: Analytical modeling and experimental validation
When a container carrying a magnetized
ferrofluid is subjected to external mechanical stimuli, the sloshing motion of the magnetized
ferrofluid generates a time-varying magnetic flux, which can be used to induce an electromotive force in a coil placed adjacent to the container. This process generates an electric current in the coil, and therewith, can be used to transduce external vibrations into electric energy. In this article, we develop a nonlinear analytical model, which governs the electro-magneto-hydrodynamics of an electromagnetic ferrofluid-based vibratory energy harvester. Using pe...
Source: Physics of Fluids - July 1, 2016 Category: Physics Authors: S. Alazmi, Y. Xu and M. F. Daqaq Source Type: research
