# Physical Review Fluids

### Richtmyer-Meshkov instability of an imploding flow with a two-fluid plasma model

Author(s): Y. Li, R. Samtaney, D. Bond, and V. Wheatley

The Richtmyer-Meshkov instability of a cylindrical light-heavy density interface is investigated in the framework of a two-fluid plasma model. Interfacial perturbations are enhanced by the induced Lorentz force. The Biermann battery effect is an important source of the self-generated magnetic field.

[Phys. Rev. Fluids 5, 113701] Published Fri Nov 20, 2020

### Vortex rings drive entrainment and cooling in flow induced by a spark discharge

Author(s): Bhavini Singh, Lalit K. Rajendran, Jiacheng Zhang, Pavlos P. Vlachos, and Sally P. M. Bane

In spark plasma discharges, vortex rings are shown to control the expansion and convective cooling of the hot gas kernel. The rates of both processes increase with the electrical energy deposited. This has implications on momentum transport and passive scalar mixing in plasma-based flow and combustion control applications.

[Phys. Rev. Fluids 5, 114501] Published Fri Nov 20, 2020

### Effect of precipitation mineralization reactions on convective dissolution of ${\mathrm{CO}}_{2}$: An experimental study

Author(s): C. Thomas, S. Dehaeck, and A. De Wit

When CO2 dissolves in a solution of calcium ions, a precipitation mineralization reaction can take place, producing solid calcium carbonate particles that sink to the bottom of the host phase. Convective motions present both above and below the reaction front favor the entrainment of CO2 toward the bottom, which is favorable for the security of carbon sequestration techniques. An experimental study of the influence of such a precipitation reaction on convective dissolution of CO2 is conducted.

[Phys. Rev. Fluids 5, 113505] Published Thu Nov 19, 2020

### Reservoir computing model of two-dimensional turbulent convection

Author(s): Sandeep Pandey and Jörg Schumacher

Reservoir computing models are one possible architecture of recurrent neural networks. Here, a reservoir computing model is applied to reproduce the low-order statistics of a two-dimensional turbulent Rayleigh-Bénard flow without solving the underlying Boussinesq equations.

[Phys. Rev. Fluids 5, 113506] Published Thu Nov 19, 2020

### Sounds of Leidenfrost drops

Author(s): Tanu Singla and M. Rivera

When Leidenfrost drops are confined on a spherical surface, they can oscillate in the form of stars; drops in this configuration are popularly known as Leidenfrost stars. Here, emission of sound in the form of periodic beats from the Leidenfrost stars is studied. It is shown that the vapors escaping from the drop are responsible for sound emission, and a theoretical framework is developed to establish that the frequencies of the sounds depend on the size of the drop, in the same way that frequencies of acoustic modes depend on the length of wind musical instruments.

[Phys. Rev. Fluids 5, 113604] Published Thu Nov 19, 2020

### Deposition of a particle-laden film on the inner wall of a tube

Author(s): Deok-Hoon Jeong, Anezka Kvasnickova, Jean-Baptiste Boutin, David Cébron, and Alban Sauret

The dispensing of liquids in tubing often involves repeated, intermittent flows that leave a thin liquid layer on the inner wall of the tube. The entrainment in the coating film of particles present in the liquid can lead to the contamination of the tube. A study demonstrates the conditions under which particles dispersed in a liquid are deposited on the wall of the tube when the liquid is displaced by air.

[Phys. Rev. Fluids 5, 114004] Published Thu Nov 19, 2020

### Size-dependent particle migration and trapping in three-dimensional microbubble streaming flows

Author(s): Andreas Volk, Massimiliano Rossi, Bhargav Rallabandi, Christian J. Kähler, Sascha Hilgenfeldt, and Alvaro Marin

Finite-sized particles in complex flow fields often experience migration and trapping. Using three-dimensional particle tracking and numerical simulations, it is shown that even density-matched microparticles can experience migration and trapping because of their interaction with boundaries. This effect is particularly sound when particles are being advected in the complex three-dimensional flow generated by oscillating microbubbles confined in a microchannel.

[Phys. Rev. Fluids 5, 114201] Published Thu Nov 19, 2020

### Preferential concentration in the particle-induced convective instability

Author(s): Sara Nasab and Pascale Garaud

Direct numerical simulations are used to study preferential concentration of heavy inertial particles in the particle-induced convective instability. This process and the resulting significant particle concentration enhancement are investigated using the two-fluid equations. Motivated by dominant balance arguments, the scaling of the particle concentration enhancement over the mean is found; the maximum scales as urms2τp/κp, and the typical as (urms2τp/κp)1/2, where urms is the rms of the fluid velocity, τp is the particle stopping time, and κp is the assumed particle diffusivity.

[Phys. Rev. Fluids 5, 114308] Published Thu Nov 19, 2020

### Dynamic subgrid-scale scalar-flux model based on the exact rate of production of turbulent fluxes

Author(s): Shujaut H. Bader and Paul A. Durbin

“We propose a dynamic subgrid scale (SGS) scalar flux model based on the exact turbulent flux production rate. The model incorporates a tensor diffusivity explicitly dependent on subgrid stresses and the resolved velocity gradient. Representing diffusivity by a tensor allows the scalar flux vector to be misaligned with the filtered temperature gradient. Since modeling the subgrid scales represents their influence on resolved scales as an average of small scales, we show that extending RANS type closures to an LES framework is a promising route to cost effective and robust subgrid modeling.

[Phys. Rev. Fluids 5, 114609] Published Thu Nov 19, 2020

### Editorial: Promoting Inclusive and Respectful Communications

Author(s): Michael Thoennessen

[Phys. Rev. Fluids 5, 110002] Published Wed Nov 18, 2020

### Acoustic stability of nonadiabatic high-energy-density shocks

Author(s): César Huete, Francisco Cobos-Campos, Ernazar Abdikamalov, and Serge Bouquet

Shock waves are very efficient at compressing fluid. Ideally, the maximum mass compression ratio is f+1, where f accounts for molecular degrees of freedom. Sufficiently strong shocks, those that induce very high temperatures downstream, may alter f by adding vibrational modes or promoting molecular dissociation. In addition, the nonadiabaticity of these effects, and others like ionization and/or radiation, also affect the mass compression ratio and other shock properties. These changes ultimately modify the D’yakov-Kontorovich limits associated with the acoustic stability of planar isolated shocks.

[Phys. Rev. Fluids 5, 113403] Published Wed Nov 18, 2020

### Coupled population balance and large eddy simulation model for polydisperse droplet evolution in a turbulent round jet

Author(s): Aditya Aiyer and Charles Meneveau

A hybrid approach is developed to simulate the transport and breakup of droplets in a turbulent round jet. The inflow size distribution is obtained from a one-dimensional parcel model that is coupled to a coarse large-eddy simulation (LES) of a turbulent jet. The LES results are compared to experimental data and show good agreement. Additionally, LES allows us to quantify the distributions of the mean and variability of key quantities of the polydisperse distribution.

[Phys. Rev. Fluids 5, 114305] Published Wed Nov 18, 2020

### Mobility of bidisperse mixtures during bedload transport

Author(s): Rémi Chassagne, Philippe Frey, Raphaël Maurin, and Julien Chauchat

The mobility of bidisperse segregated beds is studied numerically with a coupled fluid discrete element method model in the bedload regime. The transport is observed to be higher when small particles are buried below large ones. This is interpreted as a granular process and a new simple explanation is given in the framework of the μ(I) rheology. A predictive model for the increase of transport is proposed based on granular rheological arguments.

[Phys. Rev. Fluids 5, 114307] Published Wed Nov 18, 2020

### Roughness effects on scalar transport

Author(s): Zvi Hantsis and Ugo Piomelli

In the flow over a smooth wall, the statistics of velocity and temperature, properly normalized, collapse (Reynolds’ analogy); when the wall is rough, this analogy fails. Its failure has long been known to be due to the pressure gradient, which is absent in the scalar transport equation. A study examines how the geometrical features of the roughness affect the failure of the Reynolds’ analogy, by focusing on the transport equations for temperature variance and turbulent kinetic energy.

[Phys. Rev. Fluids 5, 114607] Published Wed Nov 18, 2020

### Decomposition of the mean friction drag in adverse-pressure-gradient turbulent boundary layers

Author(s): Yitong Fan (范钇彤), Weipeng Li (李伟鹏), Marco Atzori, Ramon Pozuelo, Philipp Schlatter, and Ricardo Vinuesa

From an energy budget perspective, the decomposition of mean friction drag in adverse-pressure-gradient turbulent boundary layers is conducted, obtaining contributions associated with dissipation, production, and convection across the boundary layer. In the wall-normal distributions of the decomposed constituents, positions of inner peaks are well scaled in viscous units, whereas outer peaks scale in outer units, regardless of Reynolds number and pressure-gradient magnitude.

[Phys. Rev. Fluids 5, 114608] Published Wed Nov 18, 2020

### Analysis of flame-flame interactions in premixed hydrocarbon and hydrogen flames

Author(s): S. Trivedi, H. Kolla, J. H. Chen, and R. S. Cant

Flame-flame interactions play an important role in altering flame surface area and fuel consumption rate but have received comparatively little attention so far. An investigation into the statistics of flame-flame interaction events in the progress variable space aims to quantify the relative frequency of occurrence of these events and looks at the topology of each type of interaction. Understanding the statistics and the topology can help to identify the overall influence of flame-flame interactions on flame properties and, in future, help to model these effects.

[Phys. Rev. Fluids 5, 113201] Published Tue Nov 17, 2020

### Pipe flow with large particles and their impact on the transition to turbulence

Author(s): Martin Leskovec, Fredrik Lundell, and Fredrik Innings

Large particles disturb a flow more than small particles. Using Magnetic Resonance Imaging (MRI) and pressure drop measurements we find that large spherical and cubic particles in pipe flow promote subcritical turbulent-like flow disturbances (as seen in the radial mean velocity and rms profiles at Re=700). These disturbances lead to significant changes in the laminar-turbulent transition at low particle concentrations (<5% per volume). We suggest these observations can be explained by the relative magnitude of (i) particle interactions, (ii) flow disturbances introduced by the particles and (iii) viscous dissipation in the system.

[Phys. Rev. Fluids 5, 112301(R)] Published Mon Nov 16, 2020

### Heat transfer scaling in natural convection with shear due to rotation

Author(s): R. Vishnu and A. Sameen

Axial vortices are ubiquitous in nature and in engineering, and the breakdown of these vortices can have far-reaching consequences. In the presence of a temperature gradient, topological behavior dramatically changes depending on the various flow parameters. Quantities such as heat transport, scalar mixing, and turbulent correlations are influenced immensely by the interplay between rotation and convection.

[Phys. Rev. Fluids 5, 113504] Published Mon Nov 16, 2020

### Thermoelectrohydrodynamic convection in parallel plate capacitors under dielectric heating conditions

Author(s): Harunori N. Yoshikawa, Changwoo Kang, Inoccent Mutabazi, Florian Zaussinger, Peter Haun, and Christoph Egbers

A theoretical model of thermal convection induced by dielectric heating is developed via further exploitation of the analogy between gravity-driven thermal convection and convection driven by an electrohydrodynamic effect. The model is applied to a horizontal layer of dielectric fluid to determine the conditions of convection generation by the linear stability theory. The competition between gravity and the electrohydrodynamic effect under dielectric heating gives rise to different flow patterns depending on the Rayleigh number.

[Phys. Rev. Fluids 5, 113503] Published Fri Nov 13, 2020

### Analysis of depinning behavior of drop on chemically heterogeneous surface

Author(s): Bing He, Chunyan Qin, Sihao Zhou, and Binghai Wen

Three types of depinning behaviors of a drop on a heterogeneous surface are numerically investigated. Depinning is found to occur due to two processes: slow- and fast-moving. A dynamic equilibrium results from competition between gravity and the capillary force in the whole drop. At the microscopic scale, based on measurement of the real-time contact angle, the local force balance in the contact line region is maintained by the unbalanced Young’s force and the substrate resistance in the slow-moving stage, while the unbalanced Young’s force provides the driving force for contact line motion in the fast-moving stage.

[Phys. Rev. Fluids 5, 114003] Published Fri Nov 13, 2020