Latest papers in fluid mechanics

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

Prediction of the reaction yield in a X-micromixer given the mixing degree and the kinetic constant

Physical Review Fluids - Thu, 02/15/2024 - 10:00

Author(s): S. Tomasi Masoni, A. Mariotti, M. Antognoli, C. Galletti, R. Mauri, M. V. Salvetti, and E. Brunazzi

Understanding flow regimes and mixing in microreactors is crucial for achieving high reaction yields. This study combines simulations and experiments in an X-microreactor up to Reynolds number (Re) 600. For Re > 375, an unsteady periodic regime is observed with a collapsing central vortical structure and symmetric vorticity shedding. Counterrotating vortices form, merge, and recreate the central vortex. Despite increased mixing in this regime, reaction yield remains similar due to reduced reactant residence time. A model predicting reaction yield based on mixing degree and nominal kinetic constant is developed, successfully encompassing all flow regimes and Damköhler numbers (0.1 < Da < 103).


[Phys. Rev. Fluids 9, 024202] Published Thu Feb 15, 2024

Validation of symmetry-induced high moment velocity and temperature scaling laws in a turbulent channel flow

Physical Review E - Wed, 02/14/2024 - 10:00

Author(s): Francisco Alcántara-Ávila, Luis Miguel García-Raffi, Sergio Hoyas, and Martin Oberlack

The symmetry-based turbulence theory has been used to derive new scaling laws for the streamwise velocity and temperature moments of arbitrary order. For this, it has been applied to an incompressible turbulent channel flow driven by a pressure gradient with a passive scalar equation coupled in. To …


[Phys. Rev. E 109, 025104] Published Wed Feb 14, 2024

Stochastic reorientations and the hydrodynamics of microswimmers near deformable interfaces

Physical Review Fluids - Wed, 02/14/2024 - 10:00

Author(s): Sankalp Nambiar and J. S. Wettlaufer

We study the fluid mediated hydrodynamics of an orientable microscopic swimmer that is near a deformable boundary, and that can intrinsically execute random orientation changes. Accounting for swimmer reorientations via orientation tumbles or active Brownian rotations on time scales comparable to the boundary deformations, we find that a pusher-type swimmer can rotate away from the interface, while its attraction towards the interface is enhanced. Depending on the viscosity of the fluids on either side of the interface, the swimmer can experience a stronger migration towards the interface at short times, and away from the interface in the long-time limit.


[Phys. Rev. Fluids 9, 023102] Published Wed Feb 14, 2024

Arresting of interfacial phase separation with an imposed flow

Physical Review Fluids - Wed, 02/14/2024 - 10:00

Author(s): Ryuta X. Suzuki, Shoji Seya, Takahiko Ban, Manoranjan Mishra, and Yuichiro Nagatsu

We experimentally investigate displacement of a more viscous liquid by a less viscous one in a Hele-Shaw cell using an aqueous two phase system, where phase separation occurs in the growing liquid-liquid interfacial region, by varying the injection flow rate and the phase separation rate. We show that the degree of the interfacial phase separation scales as a unique function of the ratio of the flow and phase separation rates and it decreases with the ratio. These results demonstrate that the interfacial phase separation is arrested by the imposed flow and determined by competition between the flow and phase separation rates. The arresting effect and the mechanism are numerically verified.


[Phys. Rev. Fluids 9, 024003] Published Wed Feb 14, 2024

Experimental and numerical investigation of three-dimensional shock train topology with differently oriented background waves

Physical Review E - Tue, 02/13/2024 - 10:00

Author(s): Dayi Wang, Ziao Wang, Juntao Chang, Lianjie Yue, Gang Wang, and Hao Chen

To better understand the three-dimensional topology of the interaction between the shock train and the background wave, the steady and dynamic characteristics of a shock train were investigated using wind-tunnel experiments and numerical simulation. A 14° wedge placed at the bottom and sidewalls was…


[Phys. Rev. E 109, 025103] Published Tue Feb 13, 2024

Effects of symmetry-breaking mechanisms on the flow field around magnetic-responsive material appendages that mimic swimming strokes

Physical Review Fluids - Tue, 02/13/2024 - 10:00

Author(s): Mohammad Mohaghar, Angelica A. Connor, Shuai Wu, Ruike Renee Zhao, and Donald R. Webster

This study quantifies the effects of breaking the symmetry of magnetic-responsive material appendage motion. Asymmetry is achieved through distinct shape changes and asymmetric cycle periods. The appendage with an asymmetric joint and asymmetric cycle demonstrates significantly faster downward motion (and enhances swimming efficiency) by reducing the vorticity strength and viscous energy dissipation in the surrounding fluid. The study provides insights into the induced flow and opens avenues for bio-inspired aquatic robots made from magnetic-responsive soft materials with the potential for fostering underwater propulsion and exploration in aquatic environments.


[Phys. Rev. Fluids 9, 023101] Published Tue Feb 13, 2024

Electrophoretic maneuvering of nonuniformly charged particles suspended in linear flows: Impact of the medium viscoelasticity

Physical Review Fluids - Tue, 02/13/2024 - 10:00

Author(s): Rajnandan Borthakur and Uddipta Ghosh

Electrophoresis often coexists with imposed background flows in many applications. When particles carry nonuniform surface charge, and the fluid itself is complex, the particles may follow fascinating trajectories, as shown in this work. Indeed, the combined action of a background flow and complex fluidic medium may cause particles to undergo cross-stream migration. However, the very nature of its trajectory and the extent of its migration depends on whether the imposed flow or the electrophoretic propulsion dominates the motion. The insights provided here may be exploited for improving electrophoretic separation and sorting of particles based on their size and surface charge.


[Phys. Rev. Fluids 9, 023302] Published Tue Feb 13, 2024

Flow of a shear-thinning fluid in a rectangular duct

Physical Review Fluids - Tue, 02/13/2024 - 10:00

Author(s): Ilya Barmak, Davide Picchi, Alexander Gelfgat, and Neima Brauner

A rigorous numerical solution for steady laminar flows of shear-thinning fluids in rectangular ducts is presented for the first time. We derive universal scaling laws for the effective viscosity that depends on the dimensionless rheological parameters and the effective channel size that is a function of the aspect ratio of the duct. These allow us to generalize the classical formula for the friction factor of Newtonian flows (12/Re) to Carreau fluids flowing in rectangular ducts of any aspect ratio, where the Reynolds number is based on the effective channel size and the effective viscosity.


[Phys. Rev. Fluids 9, 023303] Published Tue Feb 13, 2024

Thermal boundary layers in turbulent Rayleigh-Bénard convection with rough and smooth plates: A one-to-one comparison

Physical Review Fluids - Tue, 02/13/2024 - 10:00

Author(s): Ronald du Puits

Roughness at a surface hotter or colder than its environment may significantly enhance the convective heat transfer coefficient. This enhancement results from modification of the near-wall flow field. Our work demonstrates how roughness elements deform the temperature field compared to a smooth surface, and, under which conditions the heat transfer coefficient is enhanced.


[Phys. Rev. Fluids 9, 023501] Published Tue Feb 13, 2024

Stability of traveling waves of a thermoviscous liquid film down the outer surface of a cylinder

Physical Review Fluids - Tue, 02/13/2024 - 10:00

Author(s): Garima Singh and Naveen Tiwari

The stability of a traveling wave on the outside of a heated solid vertical cylinder is considered. The axisymmetric traveling wave becomes unstable and leads to the formation of asymmetric droplets over the cylinder. Eigenvalue analysis indicates that at smaller wavenumbers, the gravity mode exists, and a thermocapillary mode also exists but at larger wavenumbers. Patterns generated using nonlinear analysis show that the selected mode is governed by the geometric confinement in the azimuthal direction. Interesting nonlinear patterns are obtained due to an interesting interplay between the gravity mode and thermocapillary mode.


[Phys. Rev. Fluids 9, 024002] Published Tue Feb 13, 2024

Turbulent power theory in heavy-ion plasma of a Jovian magnetosphere

Physical Review Fluids - Tue, 02/13/2024 - 10:00

Author(s): Vitaliy Kaminker

Turbulent power is introduced in to Jupiter’s magnetosphere near the cen- trifugal equator of the plasma disc. Turbulent fluctuations are generated within the plasma fluid. Turbulent energy then travels out of the plasma disc via shear Alfvén waves, dissipating out of the system along the way.


[Phys. Rev. Fluids 9, 024602] Published Tue Feb 13, 2024

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