Latest papers in fluid mechanics

Author(s): F. Novotný, Y. Huang, J. Kvorka, Š Midlik, D. Schmoranzer, Z. Xie, and L. Skrbek

Spherically symmetric thermal counterflow of superfluid 4He driven by a central heater is unaffected by shear thanks to the absence of walls. This quantum flow displays a two-fluid behavior and upon increasing drive undergoes a complex process of transition to quantum turbulence that involves formation of normal fluid turbulence above a certain critical threshold, drawing energy from a preexisting random tangle of quantized vortices. Spherically symmetric thermal counterflow can serve as a model flow for cosmological phenomena relating cosmic strings to quantized vortices, for processes occurring in neutron stars, or cosmological structure formation within superfluid models of dark matter.

[Phys. Rev. Fluids 9, L022601] Published Wed Feb 28, 2024

Author(s): Thomasina V. Ball and Neil J. Balmforth

When a small fraction of viscoplastic fluid is placed into a rotating cylinder, steady states can be reached with pool at the bottom of the cylinder and a residual coating elsewhere. Lubrication theory used to model the film thickness builds on previous models by bridging between two asymptotic limits, incorporating both the gravitational force along the cylinder and the hydrostatic pressure gradients. The model predicts steady states are reached after a small number of rotations and allows exploration of drainage when the cylinder comes to a halt. Experiments using a Carbopol suspension provide a suitable comparison to test the thin film theory.

[Phys. Rev. Fluids 9, 023304] Published Tue Feb 27, 2024

Author(s): Sam Briney, Andreas N. Osnes, Magnus Vartdal, Thomas L. Jackson, and S. Balachandar

A shock propagating through a cloud of particles results in highly unsteady forces on each particle in the cloud. In such a finite particle volume fraction scenario, reflected shocks from neighboring particles perturb the force on each particle from its value in the dilute limit. These forces have a delayed onset since the reflected shocks travel at finite speeds. This phenomenon is explored in detail using three-dimensional particle resolved simulations and a model is proposed to account for the unsteady nature of these forces.

[Phys. Rev. Fluids 9, 024308] Published Tue Feb 27, 2024

Author(s): Dana Duong and Stavros Tavoularis

This article is the first to investigate velocity fields behind grids at very small Reynolds numbers that include flows with negligible fluctuations. Measurements were taken behind four square-mesh grids with varying designs, mesh sizes and solidities. We have documented and quantified the weakening of turbulent behavior as the Reynolds number diminishes and identified trends and patterns of the large- and small-scale anisotropies, the skewness and flatness factors of the velocity derivative and the dissipation parameter that have not been reported previously.

[Phys. Rev. Fluids 9, 024607] Published Tue Feb 27, 2024

Author(s): Zhanqi Tang, Nan Jiang, Zhiming Lu, and Quan Zhou

Tripping effects are studied in artificially thickened turbulent boundary layers (AT-TBLs) within a finite-length test section. The emergence of the generated large-scale structures highlights the potential of the AT-TBLs to simulate high-Reτ boundary layer turbulence. We examine the noncanonical behaviors and external similarity under over-tripped conditions. The results emphasize the need for caution when pursuing excessive thickening of the boundary layer through leading-edge trips for generating high-Reτ canonical TBLs in a finite-length test section.

[Phys. Rev. Fluids 9, 024606] Published Mon Feb 26, 2024

Author(s): Thomas Frisch, Sergey Nazarenko, and Sergio Rica

The dynamics of a superfluid over a surface exhibits significant differences from compressible flow in ordinary fluids. In ordinary fluids, when the local speed exceeds the sound speed, intrinsic dissipation due to viscosity can enable a shock wave. However, in superfluids, lack of dissipation prevents shock waves. Instead, spatial modulation of a wave train of solitons, as in the figure, allows for a smooth transonic transition. This wave train has been observed to eventually become unstable, leading to quantized vortices and an effective drag on a rough surface. The wave train occurs beneath a lambda-shaped structure with a fore and back-front, reminiscent of ordinary compressible fluids.

[Phys. Rev. Fluids 9, 024701] Published Mon Feb 26, 2024

Author(s): Shiwani Singh

Using two-dimensional porous structures made up of homogeneously arranged solid obstacles, we examine the effects of rarefaction on the hydraulic tortuosity in the slip and early transition flow regimes via extended lattice Boltzmann method. We observed that modification in either the obstacle's arr…

[Phys. Rev. E 109, 025106] Published Fri Feb 23, 2024

Author(s): Arunraj Balaji-Wright, Felix Stockmeier, Richard Dunkel, Matthias Wessling, and Ali Mani

The Poisson-Nernst-Planck-Stokes equations capture the chaotic dynamics of electroconvection accurately, but direct numerical simulation of electroconvection is prohibitively expensive. Furthermore, prediction of the mean fields via application of Reynolds averaging leads to a closure problem. In this work, we combine the macroscopic forcing method, a numerical technique for measurement of closure operators in Reynolds-averaged equations, with high-fidelity experimental data in order to determine a leading order closure for chaotic electroconvection. Simulations of the Reynolds-averaged equations using the leading order closure accurately predict experimental polarization curves.

[Phys. Rev. Fluids 9, 023701] Published Fri Feb 23, 2024

Author(s): A. Bajpai, A. Bhateja, and R. Kumar

In this investigation, a novel two-way coupled gas-granular solver is developed, incorporating direct simulation Monte Carlo (DSMC) for gas particle collisions and discrete element method (DEM) for granular particle interactions. Gas-grain interaction model consists of momentum and energy exchange between the two phases. Using this framework, we have performed a comprehensive study of dust dispersion due to plume impingement on a lunar surface. We have predicted not only the velocity field of gas and grain phases, but also their temperature field, which can be meaningful information for spacecraft designers.

[Phys. Rev. Fluids 9, 024306] Published Fri Feb 23, 2024

Author(s): Zilong Zhao, Zhiwei Guo, Zhigang Zuo, and Zhongdong Qian

This study indicates that small inertia particles can be trapped in a two-dimensional unequal-strength counter-rotating vortex pair (CVP) flow. Through analytical derivations of the particle motion in the potential CVP flow, this study first identifies a particle-attracting ring S0.

[Phys. Rev. Fluids 9, 024307] Published Fri Feb 23, 2024

Author(s): Sergiu Busuioc and Victor Sofonea

Numerical solutions of the Enskog equation obtained employing a Finite-Difference Lattice Boltzmann (FDLB) with half-range Gauss-Hermite quadratures and a Direct Simulation Monte Carlo (DSMC)-like particle method (PM), are systematically compared to determine the range of applicability of the simplified Enskog collision operator implemented in the Lattice Boltzmann framework. For low to moderate reduced density, the proposed FDLB model exhibits commendable accuracy for all bounded flows tested in this study, with substantially lower computational cost than the PM method.

[Phys. Rev. Fluids 9, 023401] Published Thu Feb 22, 2024

Author(s): Arghyadeep Paul and N. R. Aluru

Electrohydrodynamic ion transport has been studied in nanotubes, nanoslits, and nanopores to mimic the advanced functionalities of biological ion channels. However, probing how the intricate interplay between the electrical and mechanical interactions affects ion conduction in asymmetric nanoconduit…

[Phys. Rev. E 109, 025105] Published Wed Feb 21, 2024

Author(s): Calum Mallorie, Rohan Vernekar, Benjamin Owen, David W. Inglis, and Timm Krüger

Deterministic lateral displacement (DLD) is a common method of separating suspensions of particles by their physical properties. DLD devices are typically limited to operation in the Stokes flow regime, which leads to high processing times, because their behavior becomes unpredictable at flow rates where fluid inertia is important. In this study, we show that the average flow direction in a typical DLD device can diverge from the direction of the applied pressure drop due to inertial effects, and present an explanation for why this happens. This new understanding may contribute to improved DLD designs for operation at high flow rates.

[Phys. Rev. Fluids 9, 024203] Published Wed Feb 21, 2024

Author(s): Brian F. Farrell and Petros J. Ioannou

In wall turbulence, the time-mean flow is returned to after almost any disturbance, which indicates that it is a stable statistical feature underlying the disorder of turbulence. However, the stability of this statistical feature can not be determined directly from the stability of the time-mean flow itself. What is required is a statistical stability analysis method. We determine the statistical stability of the time-mean state by averaging the dynamics of the return to the time-mean state over the turbulent attractor using the linear inverse model method.

[Phys. Rev. Fluids 9, 024605] Published Wed Feb 21, 2024

Author(s): Xin-Yuan Chen (陈新元), Juan-Cheng Yang (阳倦成), and Ming-Jiu Ni (倪明玖)

In this experimental investigation we examine the dynamics of liquid metal thermal convection within an elongated cuboid cell with aspect ratio 1/3. We highlight the evolution of flow modes, transitioning from single- to double-roll mode, and transitional modes which are reconstructed by visualizing temperature data on the sidewall. As the Rayleigh number surpasses the critical value, the flow state transforms from a multiple-mode coexistence state to a single-roll mode-dominated configuration. Flow modes and global transport properties offer profound insights into the fundamental characteristics of thermal convection in liquid metals under strong lateral geometric confinement.

[Phys. Rev. Fluids 9, 023503] Published Tue Feb 20, 2024

Author(s): Rasmus Korslund Schlander, Stelios Rigopoulos, and George Papadakis

We characterize the role of coherent structures on the transport and wall deposition of low-inertia particles in a turbulent pipe flow using extended proper orthogonal decomposition (EPOD) and spectral analysis. The equilibrium Eulerian approach is employed to model particle velocity and concentration. A new Fukagata-Iwamoto-Kasagi (FIK) identity is derived for the wall deposition rate coefficient (Sherwood number) and employed to quantify the contributions of the mean and fluctuating velocity and particle concentration fields for different Stokes, Froude and Reynolds numbers. New terms appear due to the inertia of the particles that encapsulate the turbophoresis effect.

[Phys. Rev. Fluids 9, 024303] Published Tue Feb 20, 2024

Author(s): Benjamin Fry, Laurent Lacaze, Thomas Bonometti, Pierre Elyakime, and François Charru

Granular bedload plays a crucial role in shaping streams and influencing their development over time. This process involves the movement of grains along the stream bed surface driven by the shear stress from the flowing water. For an accurate model on a practical scale, it is essential to grasp the key properties of the granular layer interacting with the water. Our focus lies in understanding the rheological characteristics of the water grain mixture when grain movement is localized within a thin layer near the bed surface and under a weakly inertial regime. This aims to expand our understanding of viscous-laminar properties mostly described for a thick shear layer in the literature.

[Phys. Rev. Fluids 9, 024304] Published Tue Feb 20, 2024

Author(s): O. M. Lavrenteva, I. Smagin, and A. Nir

A novel approach to study of the shear-induced diffusion of particles in suspensions with continuous particle size distribution is suggested. It addresses the migration of local moments of the size distribution. Particle size distribution at each point is consequently obtained from the resulting moments, by solving inverse problems locally. For a particular example of stationary flow in a circular tube, we present results that include concentration inhomogeneity, moments’ distributions and the consequent local continuous particle size distributions. The similarity and difference from cases of monodispersed suspensions are discussed.

[Phys. Rev. Fluids 9, 024305] Published Tue Feb 20, 2024

Author(s): T. Lichtenegger

Computational fluid dynamics simulations of dynamic flows usually entail large numerical costs. Over the last few years, several data-driven methods, partly of significant complexity, have been devised to mitigate CPU times while still capturing the relevant physics. In this work, a very simple approach with a clear physical interpretation is presented that splits the problem into a linear and a nonlinear part. Based on a database of precomputed reference states, predictions are made using the method of analogues (nonlinear dynamics) together with physics-informed propagators that capture and correct for any deviation from the nearest reference state in a linear fashion.

[Phys. Rev. Fluids 9, 024401] Published Tue Feb 20, 2024

Author(s): Linqi Yu, Mustafa Z. Yousif, Young-Woo Lee, Xiaojue Zhu, Meng Zhang, Paraskovia Kolesova, and Hee-Chang Lim

This study developed a mapping generative adversarial network (M-GAN) to predict unavailable parameters: streamwise velocity, temperature, and pressure from available velocity components. Two-dimensional Rayleigh–Bénard flow and turbulent channel flow are used to evaluate M-GAN performance. The results indicate that the proposed model has good capability to map the available parameters to unavailable parameters. Furthermore, M-GAN also has good generalization to predict the parameters from channel flows at different Reynolds numbers.

[Phys. Rev. Fluids 9, 024603] Published Tue Feb 20, 2024