Latest papers in fluid mechanics

Artificially thickened boundary layer turbulence due to trip wires of varying diameter

Physical Review Fluids - Mon, 02/26/2024 - 10:00

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

Superflow passing over a rough surface: Vortex nucleation

Physical Review Fluids - Mon, 02/26/2024 - 10:00

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

Impact of hydraulic tortuosity on microporous and nanoporous media flow

Physical Review E - Fri, 02/23/2024 - 10:00

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

Measurement of an eddy diffusivity for chaotic electroconvection using combined computational and experimental techniques

Physical Review Fluids - Fri, 02/23/2024 - 10:00

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

Plume-surface interaction during lunar landing using a two-way coupled DSMC-DEM approach

Physical Review Fluids - Fri, 02/23/2024 - 10:00

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

Trapping of inertial particles in a two-dimensional unequal-strength counterrotating vortex pair flow

Physical Review Fluids - Fri, 02/23/2024 - 10:00

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

Bounded flows of dense gases

Physical Review Fluids - Thu, 02/22/2024 - 10:00

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

Nanoscale electrohydrodynamic ion transport: Influences of channel geometry and polarization-induced surface charges

Physical Review E - Wed, 02/21/2024 - 10:00

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

Numerical analysis of flow anisotropy in rotated-square deterministic lateral displacement devices at moderate Reynolds number

Physical Review Fluids - Wed, 02/21/2024 - 10:00

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

Statistical state dynamics-based study of the stability of the mean statistical state of wall-bounded turbulence

Physical Review Fluids - Wed, 02/21/2024 - 10:00

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

Flow mode and global transport of liquid metal thermal convection in a cavity with $\mathrm{Γ}=1/3$

Physical Review Fluids - Tue, 02/20/2024 - 10:00

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

Role of flow structures on the deposition of low-inertia particles in turbulent pipe flow

Physical Review Fluids - Tue, 02/20/2024 - 10:00

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

From discrete to continuum description of weakly inertial bedload transport

Physical Review Fluids - Tue, 02/20/2024 - 10:00

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

Shear-induced particle migration in viscous suspensions with continuous size distribution

Physical Review Fluids - Tue, 02/20/2024 - 10:00

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

Data-assisted, physics-informed propagators for recurrent flows

Physical Review Fluids - Tue, 02/20/2024 - 10:00

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

Predicting unavailable parameters from existing velocity fields of turbulent flows using a GAN-based model

Physical Review Fluids - Tue, 02/20/2024 - 10:00

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

Internal gravity waves in stratified flows with and without vortical modes

Physical Review Fluids - Tue, 02/20/2024 - 10:00

Author(s): Vincent Labarre, Pierre Augier, Giorgio Krstulovic, and Sergey Nazarenko

We analyze direct numerical simulations of stratified turbulence without shear modes, and with or without vortical modes at various Froude and buoyancy Reynolds numbers. It allows us to investigate the effects of vortical modes on the dynamics of stratified flows. A spatiotemporal analysis reveals slow internal gravity waves interacting by triadic resonance instabilities in our strongly stratified flow simulations such as the one in the figure. We observe that removing vortical modes helps to concentrate the energy around the wave frequency, but it is not enough to observe a weak internal gravity wave’s turbulence regime.

[Phys. Rev. Fluids 9, 024604] Published Tue Feb 20, 2024

Bolgiano-Obukhov scaling in two-dimensional Rayleigh-Bénard convection at extreme Rayleigh numbers

Physical Review Fluids - Fri, 02/16/2024 - 10:00

Author(s): Roshan Samuel and Mahendra K. Verma

Through high-resolution direct numerical simulations, we demonstrate that energy transfers in two-dimensional (2D) thermal convection exhibit Bolgiano-Obukhov scaling. This is in contrast with convection in three dimensions which follows the Kolmogorov-Obukhov phenomenology. This difference arises from the presence of inverse cascade in 2D which leads to a negative kinetic energy flux at small wavenumbers. The magnitude of this flux decreases with wavenumber due to the effect of buoyancy. We also demonstrate that entropy dissipation in the thermal boundary layers displays a scaling law that is observable from the entropy flux curves.

[Phys. Rev. Fluids 9, 023502] Published Fri Feb 16, 2024

Mathematical modeling of erosion and deposition in porous media

Physical Review Fluids - Fri, 02/16/2024 - 10:00

Author(s): Hamad El Kahza and Pejman Sanaei

Using the Stokes equation for fluid flow and the advection-diffusion equation for the transport of solids, alongside threshold laws governing erosion and deposition, we present a model aimed at conducting a comprehensive analysis of both erosion and deposition processes within a porous medium composed of axisymmetric channels.

[Phys. Rev. Fluids 9, 024301] Published Fri Feb 16, 2024

Caustic formation in a non-Gaussian model for turbulent aerosols

Physical Review Fluids - Fri, 02/16/2024 - 10:00

Author(s): J. Meibohm, L. Sundberg, B. Mehlig, and K. Gustavsson

Caustic singularities of the spatial distribution of particles in turbulent aerosols enhance collision rates and accelerate coagulation. The rate of caustic formation depends sensitively on the particle inertia. We study caustic formation in a non-Gaussian statistical model to understand why there is a significant difference in formation rates between direct numerical simulations and Gaussian models. In the limit of small inertia, caustics form due to an optimal fluctuation of the Lagrangian fluid-velocity gradients, and we show that the formation rate depends sensitively on the tails of the gradient distribution, explaining the observed mismatch

[Phys. Rev. Fluids 9, 024302] Published Fri Feb 16, 2024


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