Two-dimensional fluid dynamics in a sharply bent channel: Laminar flow, separation bubble, and vortex dynamics
Understanding the hydrodynamic properties of fluidflow in a curving pipe and channel is important for controlling theflow behavior in technologies and biomechanics. The nature of the resultingflow in a bent pipe is extremely complicated because of the presence of a cross-stream secondaryflow. In an attempt to disentangle this complexity, we investigate the fluid dynamics in a bent channel via the direct numerical simulation of theNavier-Stokes equation in two spatial dimensions. We exploit the absence of secondaryflow from our model and systematically investigate theflow structure along the channel as a function of both th...
Source: Physics of Fluids - October 7, 2016 Category: Physics Authors: Daichi Matsumoto, Koji Fukudome and Hirofumi Wada Source Type: research
Flow and dispersion in anisotropic porous media: A lattice-Boltzmann study
Given their capability of spreading active chemical species and collecting electricity,porous media made of carbon fibers are extensively used asdiffusion layers in energy storage systems, such as redox flowbatteries. In spite of this, thedispersion dynamics of species insideporous media is still not well understood and often lends itself to different interpretations. Actually, the microscopic design of efficientporous media, which can potentially and effectively improve the performances of flowbatteries, is still an open challenge. The present study aims to investigate the effect of fibrous media micro-structure ondispers...
Source: Physics of Fluids - October 7, 2016 Category: Physics Authors: D. Maggiolo, F. Picano and M. Guarnieri Source Type: research
The physics of pressure variation in microchannels within corotating or static discs
We formulate a comprehensive analysis for the radial pressure variation in flow through microchannels within corotating (or static) discs, which is important for its fundamental value and application potential in macrofluidic and microfluidic devices. The uniqueness and utility of the present approach emanate from our ability to describe the physics completely in terms of non-dimensional numbers and to determine quantitatively the separate roles of inertia, centrifugal force, Coriolis force, and viscous effects in the overall radial pressure difference ( Δpio). It is established here that the aspect ratio (ratio of inter-...
Source: Physics of Fluids - October 5, 2016 Category: Physics Authors: Abhijit Guha and Sayantan Sengupta Source Type: research
A study of the rheology of planar granular flow of dumbbells using discrete element method simulations
Granular materials handled in industries are typically non-spherical in shape and understanding theflow of such materials is important. The steadyflow of mono-disperse, frictional, inelastic dumbbells in two-dimensions is studied by soft sphere, discrete element method simulations for chuteflow and shear cellflow. The chuteflow data are in the denseflow regime, while the shear cell data span a wide range of solid fractions. Results of a detailed parametric study for both systems are presented. In chuteflow, increase in the aspect ratio of the dumbbells results in significant slowing of theflow at a fixed inclination and in...
Source: Physics of Fluids - October 5, 2016 Category: Physics Authors: Sandip Mandal and D. V. Khakhar Source Type: research
On the shape of large wave-groups on deep water —The influence of bandwidth and spreading
In the openocean, the formation of largewaves isnon-linear. This non-linearity modifies the shape and structure of steepwaves relative to that expected in a linearmodel. Work by Adcocket al. [ “Nonlineardynamics of wave-groups in randomseas: Unexpected walls of water in the open ocean, ” Proc. R. Soc. A471(2184), 20150660 (2015)] used a numericalmodel to show that, for awave spectrum representative of that of astorm in the NorthSea,non-linear dynamics resulted in the following changes to the shape of extremewave groups relative to a linearmodel: expansion of the wave-crest laterally, contraction of the wave-group in th...
Source: Physics of Fluids - October 4, 2016 Category: Physics Authors: T. A. A. Adcock, P. H. Taylor and S. Draper Source Type: research
Drag measurements in laterally confined 2D canopies: Reconfiguration and sheltering effect
Plants in aquatic canopies deform when subjected to awater flow and so, unlike a rigid bluff body, the resultingdrag forceFD grows sub-quadratically with the flow velocityŪ. In this article, the effect of density on the canopy reconfiguration and the correspondingdrag reduction is experimentally investigated for simple 2D synthetic canopies in an inclinable, narrowwater channel. Thedrag acting on the canopy, and also on individualsheets, is systematicallymeasured via two independent techniques. Simultaneousdrag and reconfigurationmeasurements demonstrate that data for differentReynolds numbers (400 –2200), irrespective...
Source: Physics of Fluids - October 4, 2016 Category: Physics Authors: Sylvie Barsu, Delphine Doppler, J. John Soundar Jerome, Nicolas Rivi ère and Michel Lance Source Type: research
Vorticity isotropy in high Karlovitz number premixed flames
The isotropy of the smallestturbulent scales is investigated in premixedturbulent combustion by analyzing the vorticity vector in a series of high Karlovitz number premixedflame direct numerical simulations. It is found that increasing the Karlovitz number and the ratio of the integral length scale to theflame thickness both reduce the level ofanisotropy. By analyzing the vorticity transport equation, it is determined that thevortex stretching term is primarily responsible for the development of anyanisotropy. The local dynamics of thevortex stretching term and vorticity resemble that of homogeneousisotropic turbulence to ...
Source: Physics of Fluids - October 4, 2016 Category: Physics Authors: Brock Bobbitt and Guillaume Blanquart Source Type: research
Stability of viscosity stratified flows down an incline: Role of miscibility and wall slip
The effects of wall velocity slip on the linear stability of a gravity-drivenmiscible two-fluidflow down an incline are examined. Thefluids have the matched density but differentviscosity. A smoothviscosity stratification is achieved due to the presence of a thin mixed layer between thefluids. The results show that the presence of slip exhibits a promise for stabilizing themiscibleflow system by raising the criticalReynolds number at the onset and decreasing the bandwidth of unstable wave numbers beyond the threshold of the dominant instability. This is different from its role in the case of a singlefluid down a slippery s...
Source: Physics of Fluids - October 4, 2016 Category: Physics Authors: Sukhendu Ghosh and R. Usha Source Type: research
Interfacial waves generated by electrowetting-driven contact line motion
The contact angle of aliquid-fluidinterface can be effectively modulated by the electrowetting-on-dielectric(EWOD) technology. Rapid movement of the contact line can be achieved by swift changes of voltage at the electrodes, which can give rise tointerfacialwaves under the strong influence ofsurface tension. Here we experimentally demonstrate EWOD-driveninterfacialwaves of overlappingliquids and compare their wavelength and decay length with the theoretical results obtained by a perturbation analysis. Our theory also allows us to predict the temporal evolution of theinterfacial profiles in either rectangular or cylindrical...
Source: Physics of Fluids - October 4, 2016 Category: Physics Authors: Jonghyun Ha, Jaebum Park, Yunhee Kim, Bongsu Shin, Jungmok Bae and Ho-Young Kim Source Type: research
Molecular origins of higher harmonics in large-amplitude oscillatory shear flow: Shear stress response
Recent work has focused on deepening our understanding of the molecular origins of the higher harmonics that arise in the shear stress response of polymeric liquids in large-amplitude oscillatory shear flow. For instance, these higher harmonics have been explained by just considering the orientation distribution of rigid dumbbells suspended in a Newtonian solvent. These dumbbells, when in dilute suspension, form the simplest relevant molecular model of polymer viscoelasticity, and this model specifically neglects interactions between the polymer molecules [R. B. Birdet al., “Dilute rigid dumbbell suspensions in large-amp...
Source: Physics of Fluids - October 3, 2016 Category: Physics Authors: P. H. Gilbert and A. J. Giacomin Source Type: research
Spatial instability of viscous double-layer liquid sheets
This paper investigates the spatial instability of a double-layer viscous liquid
sheet moving in a stationary gas medium. A linear stability analysis is conducted and
two situations are considered, an inviscid-gas situation and a viscous-gas situation.
In the inviscid-gas situation, the basic state of the entire gas phase is stationary
and the analytical dispersion relation is derived. Similar to single-layer sheets,
the instability of double-layer sheets presents two unstable modes, the sinuous and
the varicose modes. However, the result of the base-case double-layer sheet i...
Source: Physics of Fluids - October 3, 2016 Category: Physics Authors: Han-Yu Ye, Li-Jun Yang and Qing-Fei Fu Source Type: research
Secondary peak in the Nusselt number distribution of impinging jet flows: A phenomenological analysis
The objectives are here twofold: first, validate theLES results against experimental data available in the literature and second to explore this validated numerical database by the use of high order statistics such as skewness and probability density functions of the temporal distribution of temperature and pressure to identifyflow features at the origin of the second Nusselt peak. Skewness (Sk) of the pressure temporal distribution reveals the rebound of the primaryvortices located near the location of the secondary peak and allows to identify the initiation of the unsteady separation linked to the local minimum in the me...
Source: Physics of Fluids - September 30, 2016 Category: Physics Authors: P. Aillaud, F. Duchaine, L. Y. M. Gicquel and S. Didorally Source Type: research
Breakup process of cylindrical viscous liquid specimens after a strong explosion in the core
Basic understanding andtheoretical description of the expansion and breakup of cylindrical specimens of Newtonianviscousliquid after anexplosion of an explosive material in the core are aimed in this work along with the experimental investigation of the discovered phenomena. The unperturbedmotion is considered first, and then supplemented by the perturbation growth pattern in the linear approximation. It is shown that a special non-trivial case of theRayleigh-Taylor instability sets in being triggered by the gaspressure differential between the inner and outersurfaces of the specimens. The spectrum of the growing perturbat...
Source: Physics of Fluids - September 30, 2016 Category: Physics Authors: B. H. Bang, C. S. Ahn, D. Y. Kim, J. G. Lee, H. M. Kim, J. T. Jeong, W. S. Yoon, S. S. Al-Deyab, J. H. Yoo, S. S. Yoon and A. L. Yarin Source Type: research
Electro-osmotic and pressure-driven flow of viscoelastic fluids in microchannels: Analytical and semi-analytical solutions
In this work, we present a series of solutions for combined electro-osmotic and pressure-driven flows of viscoelastic fluids in microchannels. The solutions are semi-analytical, a feature made possible by the use of the Debye –Hückel approximation for the electrokinetic fields, thus restricted to cases with small electric double-layers, in which the distance between the microfluidic device walls is at least one order of magnitude larger than the electric double-layer thickness. To describe the complex fluid rheology, several viscoelastic differential constitutive models were used, namely, the simplified Phan-Thien–Tan...
Source: Physics of Fluids - September 29, 2016 Category: Physics Authors: L. L. Ferr ás, A. M. Afonso, M. A. Alves, J. M. Nóbrega and F. T. Pinho Source Type: research
Gravity currents in a linearly stratified ambient fluid created by lock release and influx in semi-circular and rectangular channels
We present an experimental investigation, supported by a theoretical model, of the motion of lock-release, constant inflow, and time varying inflow gravitycurrents (GCs) into a linearly stratified ambientfluid at largeReynolds number. The aim is the experimental validation of a simple model able to predict the slumping phase front speed and the asymptotic self-similar front speed for rectangular and circular cross section channels. The first investigated system is of Boussinesq type with the densecurrent (salt water dyed with aniline) released in a circular channel of 19 cm diameter and 400 cm long (605 cm in the inflowexp...
Source: Physics of Fluids - September 29, 2016 Category: Physics Authors: S. Longo, M. Ungarish, V. Di Federico, L. Chiapponi and F. Addona Source Type: research
