# Latest papers in fluid mechanics

### Superfluid helium-4 hydrodynamics with discrete topological defects

Author(s): Demosthenes Kivotides

A model of normal-fluid dynamics and its coupling with superfluid vortices is formulated. The role of axial flow instabilities of superfluid vortices in energy transfer from normal-fluid to superfluid turbulence is indicated.

[Phys. Rev. Fluids 3, 104701] Published Mon Oct 08, 2018

### Spontaneous capillary propulsion of liquid droplets on substrates with nonuniform curvature

Author(s): P. Galatola

A liquid droplet spread on a solid substrate with nonuniform curvature, such as a conical surface, spontaneously moves. By assuming that the only source of dissipation is the contact line viscosity, we perturbatively determine the speed of the droplet and the total capillary force acting on it.

[Phys. Rev. Fluids 3, 103601] Published Fri Oct 05, 2018

### Self-assembly of a drop pattern from a two-dimensional grid of nanometric metallic filaments

Author(s): Ingrith Cuellar, Pablo D. Ravazzoli, Javier A. Diez, Alejandro G. González, Nicholas A. Roberts, Jason D. Fowlkes, Philip D. Rack, and Lou Kondic

We report experiments, modeling, and numerical simulations of the self–assembly of particle patterns obtained from a nanometric metallic square grid. Initially, nickel filaments of rectangular cross section are patterned on a SiO2 flat surface, and then they are melted by laser irradiation with ∼18-...

[Phys. Rev. E 98, 043101] Published Thu Oct 04, 2018

### Inertial forces for particle manipulation near oscillating interfaces

Author(s): Siddhansh Agarwal, Bhargav Rallabandi, and Sascha Hilgenfeldt

Oscillating microscale interfaces give rise not only to steady flows, but also steady inertial forces on particles. Our efficient theoretical description of these forces, which can be attractive or repulsive, provides a toolbox for separating and sorting microscale objects like biological cells.

[Phys. Rev. Fluids 3, 104201] Published Thu Oct 04, 2018

### Large-scale structure of velocity and passive scalar fields in freely decaying homogeneous anisotropic turbulence

Author(s): Katsunori Yoshimatsu and Yukio Kaneda

It is shown that there are an inﬁnite number of invariants characterizing the large-scale structure in certain kinds of freely-decaying homogeneous turbulent velocity and passive scalar ﬁelds. A self-similarity assumption suggests that the large-scale anisotropy of the fields is persistent.

[Phys. Rev. Fluids 3, 104601] Published Thu Oct 04, 2018

### Numerical investigation of breaking internal solitary waves

Author(s): Giovanni la Forgia, Talia Tokyay, Claudia Adduce, and George Constantinescu

With high-resolution 3D large Eddy Simulations we study internal solitary waves differently breaking over a sloping boundary. The entrainment parameter and mixing efficiency pry apart two effects of turbulent instabilities occurring in stratified fluid in terms of changes in bulk density profile.

[Phys. Rev. Fluids 3, 104801] Published Thu Oct 04, 2018

### Generalization of Taylor's formula to particles of arbitrary inertia

Author(s): S. Boi, A. Mazzino, P. Muratore-Ginanneschi, and S. Olivieri

In the early 1920s Sir G. I. Taylor derived a formula that can be fairly considered one of the cornerstones of large-scale tracer transport. Here, we extend Taylor’s formula to particles of any inertia including Basset and Faxèn corrections, plus other forces in the particle dynamics.

[Phys. Rev. Fluids 3, 104501] Published Tue Oct 02, 2018

### Growth of clogs in parallel microchannels

Author(s): Alban Sauret, Katarzyna Somszor, Emmanuel Villermaux, and Emilie Dressaire

When suspensions flow in microchannels or porous media, particles can get trapped and form clogs. A new model predicts the clogging dynamics and flow rate in simple porous media. The results are relevant to describe the aging of water filters and the influence of proppants on flow through rocks.

[Phys. Rev. Fluids 3, 104301] Published Mon Oct 01, 2018

### Transition to turbulence scaling in Rayleigh-Bénard convection

Author(s): Jörg Schumacher, Ambrish Pandey, Victor Yakhot, and Katepalli R. Sreenivasan

If a fluid flow is driven by a weak Gaussian random force, the nonlinearity in the Navier-Stokes equations is negligibly small and the resulting velocity field obeys Gaussian statistics. Nonlinear effects become important as the driving becomes stronger and a transition occurs to turbulence with ano...

[Phys. Rev. E 98, 033120] Published Fri Sep 28, 2018

### Nonlinear thermal effects in unsteady shear flows of a rarefied gas

Author(s): Y. Ben-Ami and A. Manela

We study the response of a rarefied gas in a slab to the motion of its boundaries in the tangential direction. Different from previous investigations, we consider boundaries displacements at nonsmall Mach (Ma) numbers, coupling the dynamic and thermodynamic gas states, and deviating the system from ...

[Phys. Rev. E 98, 033121] Published Fri Sep 28, 2018

### Reynolds number effects in pipe flow turbulence of generalized Newtonian fluids

Author(s): J. Singh, M. Rudman, and H. M. Blackburn

Direct numerical simulations of turbulent pipe flow of power-law fluids show that the effect of shear thinning on turbulence statistics in the inner-wall region does not disappear as Re is increased. A log-law mean viscosity profile is also predicted that is self-similar in the inner region.

[Phys. Rev. Fluids 3, 094607] Published Fri Sep 28, 2018

### Multiscaling analysis of the mean thermal energy balance equation in fully developed turbulent channel flow

Author(s): Tie Wei

Properly accounting for the intricate Prandtl number dependence in different layers of turbulent channel flows, a multiscaling analysis is developed for the mean thermal energy balance (MHB) equations. A formal analogy is established between the MHB equation and the mean momentum balance equation.

[Phys. Rev. Fluids 3, 094608] Published Fri Sep 28, 2018

### Solutal convection in porous media: Comparison between boundary conditions of constant concentration and constant flux

Author(s): Mohammad Amin Amooie, Mohamad Reza Soltanian, and Joachim Moortgat

We numerically examine solutal convection in porous media, driven by the dissolution of carbon dioxide (CO2) into water—an effective mechanism for CO2 storage in saline aquifers. Dissolution is associated with slow diffusion of free-phase CO2 into the underlying aqueous phase followed by density-dri...

[Phys. Rev. E 98, 033118] Published Thu Sep 27, 2018

### Modeling sphere suspension microstructure and stress

Author(s): J. J. J. Gillissen and H. J. Wilson

We develop a model for the microstructure and the stress, in dense suspensions of non-Brownian, perfectly smooth spheres at vanishing particle Reynolds number. These quantities are defined in terms of the second-order moment a of the distribution function of the orientation unit vector between hydro...

[Phys. Rev. E 98, 033119] Published Thu Sep 27, 2018

### Dynamics of a simple model microswimmer in an anisotropic fluid: Implications for alignment behavior and active transport in a nematic liquid crystal

Author(s): Abdallah Daddi-Moussa-Ider and Andreas M. Menzel

Simple model microswimmers in an oriented uniaxially anisotropic fluid, such as a nematic liquid crystal, can show rich alignment behavior due to purely hydrodynamic effects. The type of propulsion mechanism and the relative magnitudes of the different involved viscosities play a crucial role.

[Phys. Rev. Fluids 3, 094102] Published Thu Sep 27, 2018

### Mean kinetic energy replenishment mechanisms in vertical-axis wind turbine farms

Author(s): Seyed Hossein Hezaveh and Elie Bou-Zeid

We study mean kinetic energy replenishment in a clustered farm of vertical axis wind turbines using an actuator line model in a large eddy simulation. We find that clustered designs are benefical for improving overall performance but suggest that irregular designs may have even more promise.

[Phys. Rev. Fluids 3, 094606] Published Wed Sep 26, 2018

### Formation number of confined vortex rings

Author(s): I. Danaila, F. Luddens, F. Kaplanski, A. Papoutsakis, and S. S. Sazhin

The formation number of confined vortex rings is studied using direct numerical simulations. The structure of the vortex ring at pinch-off depends on the injection program and the confinement ratio. The value of the formation time is predicted using a model for the viscous confined vortex ring.

[Phys. Rev. Fluids 3, 094701] Published Wed Sep 26, 2018

### Spectral energy cascade and decay in nonlinear acoustic waves

Author(s): Prateek Gupta and Carlo Scalo

We present a numerical and theoretical investigation of the nonlinear spectral energy cascade of decaying finite-amplitude planar acoustic waves in a single-component ideal gas at standard temperature and pressure. We analyze various one-dimensional canonical flow configurations: a propagating trave...

[Phys. Rev. E 98, 033117] Published Tue Sep 25, 2018

### Diffuse interface model to simulate the rise of a fluid droplet across a cloud of particles

Author(s): Gregory Lecrivain, Yuki Kotani, Ryoichi Yamamoto, Uwe Hampel, and Takashi Taniguchi

We simulate a fluid droplet with suspended particles rising in another fluid with a diffuse interface model in which phase boundaries are replaced with smooth spreading interfaces. We find that at low Reynolds number the droplet terminal velocity decreases exponentially with particle concentration.

[Phys. Rev. Fluids 3, 094002] Published Tue Sep 25, 2018

### Current-voltage response for unipolar funnel-shaped nanochannel diodes

Author(s): Yoav Green

Permselective nanochannels can rectify the electric current transported through them similar to solid-state diodes. The rectification is due to symmetry breaking related to distribution of the nanochannels’ surface charge as well as the geometry. Thus far, most of the works related to the asymmetric...

[Phys. Rev. E 98, 033114] Published Mon Sep 24, 2018