Physical Review Fluids
Statistical state dynamics-based study of the stability of the mean statistical state of wall-bounded turbulence
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 $\mathrm{Γ}=1/3$
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
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
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
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
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
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
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
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
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
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
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
Stochastic reorientations and the hydrodynamics of microswimmers near deformable interfaces
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
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
Effects of symmetry-breaking mechanisms on the flow field around magnetic-responsive material appendages that mimic swimming strokes
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
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
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
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
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
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