# Latest papers in fluid mechanics

### Fluid mixing by an electromagnetically driven floating rotor

Author(s): Saúl Piedra, Josue Flores, Guillermo Ramírez, Aldo Figueroa, Miguel Piñeirua, and Sergio Cuevas

We analyze the mixing properties of a floating stirrer driven electromagnetically in a thin layer of electrolyte, consisting of two free-floating magnets with opposite polarities connected by a rigid coupling. The magnetic rotor is set in circular motion using Lorentz forces created due to the inter…

[Phys. Rev. E 108, 025101] Published Fri Aug 11, 2023

### Late-time draining of a thin liquid film on the outer surface of a circular cylinder

Author(s): Rebecca A. McKinlay, Alexander W. Wray, and Stephen K. Wilson

We use a combination of analytical and numerical techniques to give a complete description of the late-time draining of a thin liquid film on the outer surface of a horizontal cylinder. In this asymptotic limit three regions of qualitatively different behavior emerge, namely a draining region on the upper part of the cylinder and a pendant-drop region on the lower part of the cylinder joined by a narrow inner region in which the film has a surprisingly complicated capillary-ripple structure consisting of an infinite sequence of alternating dimples and ridges.

[Phys. Rev. Fluids 8, 084001] Published Fri Aug 11, 2023

### Physics and modeling of liquid films in pulsating heat pipes

Author(s): Xiaolong Zhang (张晓龙) and Vadim S. Nikolayev

A pulsating heat pipe (PHP) is a capillary meandering between hot spot and cooled area filled with a two-phase fluid that oscillates inside it due to evaporation and condensation. We introduce a one-dimensional physical model, the Oscillating Film Thickness model, that incorporates previously overlooked physics related to liquid film deposition, evaporation, and contact line motion. The model more accurately represents the physics of the phenomena without loss of computational efficiency. Improvements in modeling accuracy and computational efficiency are demonstrated for the case of the simplest, single branch PHP.

[Phys. Rev. Fluids 8, 084002] Published Fri Aug 11, 2023

### Large eddy simulation model for two-way coupled particle-laden turbulent flows

Author(s): M. Hausmann, F. Evrard, and B. van Wachem

In this paper, a new modeling strategy for large eddy simulations (LES) of particle-laden turbulent flows is proposed, which takes the influence of the subgrid-scale fluid velocity on the particle transport and the turbulence modulation by the particles into account. The modeling combines an enrichment of the LES with subgrid-scale fluid velocity and a subgrid-scale model based on a transport equation for the subgrid-scale kinetic energy. The model improves the particle clustering and the kinetic energy spectrum of homogeneous isotropic turbulence laden with two-way coupled particles compared to standard LES.

[Phys. Rev. Fluids 8, 084301] Published Fri Aug 11, 2023

### Dependence of the asymptotic energy dissipation on third-order velocity scaling

Author(s): Kartik P. Iyer

The dissipation of kinetic energy in a turbulent flow is controlled by the competition between the random pushing and pulling of fluid parcels. If the pushing and pulling motions average each other out with increasing turbulence intensity, then the average dissipation must decay and energy will be conserved in the inviscid limit. This work highlights this pivotal dependence of the energy dissipation rate on the small-scale motions in fluid turbulence.

[Phys. Rev. Fluids 8, L082601] Published Fri Aug 11, 2023

### Darcy's law of yield stress fluids on a treelike network

Author(s): Vincenzo Maria Schimmenti, Federico Lanza, Alex Hansen, Silvio Franz, Alberto Rosso, Laurent Talon, and Andrea De Luca

Understanding the flow of yield stress fluids in porous media is a major challenge. In particular, experiments and extensive numerical simulations report a nonlinear Darcy law as a function of the pressure gradient. In this letter we consider a treelike porous structure for which the problem of the …

[Phys. Rev. E 108, L023102] Published Wed Aug 09, 2023

### Hydrodynamic interaction between coaxially rising bubbles in elastoviscoplastic materials: Equal bubbles

Author(s): A. Kordalis, D. Pema, S. Androulakis, Y. Dimakopoulos, and J. Tsamopoulos

We investigate the pair interaction of equal-size, tandem bubbles rising in yield stress fluids with elasticity. This configuration manifests intense attractive dynamics and conforms with experimental reports that, in such materials, a bubble tends to follow the path of a preceding one. We demonstrate that the reason is that the solid-like behavior of the material preserves stresses generated by the passage of the leading bubble and makes the material “softer” for the trailing one. We conduct an extensive parametric study, on the geometric features such as the bubble radius and the initial separation distance, and on the material properties.

[Phys. Rev. Fluids 8, 083301] Published Wed Aug 09, 2023

### Von Kármán vortex street past a permeable circular cylinder: Two-dimensional flow and dynamic-mode-decomposition-based secondary stability analysis

Author(s): F. Caruso Lombardi, A. Bongarzone, G. A. Zampogna, F. Gallaire, S. Camarri, and P. G. Ledda

We explore the role of permeability in modifying the vortex shedding past a permeable circular cylinder. The two-dimensional (2D) von Kármán vortex street sets at progressively larger distances from the body and is eventually suppressed, as permeability increases. Using Dynamic Mode Decomposition we perform a linear stability analysis with respect to three-dimensional perturbations of the 2D periodic vortex shedding. We identify a range of permeability in which the shedding remains 2D, at least for the values of Reynolds number considered here; for larger values of permeability, the wake remains steady and 2D.

[Phys. Rev. Fluids 8, 083901] Published Wed Aug 09, 2023

### Oblique and parallel modes of the bistable bluff body wake

Author(s): Simran Singh Panesar, Hao Xia, and Martin Passmore

Bistability is of significant interest for ground vehicle drag reduction and reduced order modelling of simulated flows. For many bluff bodies, an oblique, asymmetric shedding mode persists with a transient parallel, symmetric state. Base pressure and particle image velocimetry measurements are made in the bistable wake of a surface mounted geometry of semi-circular cross section (half-axisymmetric) at ReD=3.2×105. Using proper orthogonal decomposition and wavelet analysis, we find that bifurcation to an opposing symmetry breaking state is tied to reversal of an oblique mode at the vortex shedding frequency.

[Phys. Rev. Fluids 8, 084601] Published Wed Aug 09, 2023