Physical Review Fluids

Author(s): Mohammed G. Alhashim and Michael P. Brenner

Recent advancements in automatic differentiation, which played a pivotal role in deep learning, offer a promising approach to addressing challenges in controlling fluid flow behavior. We demonstrate the power of the method by optimizing the packing of a polydisperse system of periodically arranged circular rods to minimize the pressure drop across the media. We show how the optimum topology of the porous media changes with changing the packing fraction.

[Phys. Rev. Fluids 9, 054103] Published Fri May 10, 2024

Author(s): Panayiota Katsamba, Matthew D. Butler, Lyndon Koens, and Thomas D. Montenegro-Johnson

We present an asymptotic theory for the dynamics of slender chemically propelled loops and knots. It is valid for nonintersecting three-dimensional centerlines, with arbitrary chemical patterning and varying (circular) cross-sectional radius, allowing many slender active loops and knots to be studied. The theory has closed-form solutions in simpler cases, enabling us to derive the swimming speeds of chemically patterned tori, and the pumping strength (stresslet) of uniformly active slender tori. Using numerical solutions, we find the behavior of exotic active particle geometries, such as a bumpy uniformly active torus that spins and a Janus trefoil knot, which rotates as it swims forwards.

[Phys. Rev. Fluids 9, 054201] Published Fri May 10, 2024

Author(s): Xianyang Chen and Andrea Prosperetti

500 resolved particles, colored by their temperature, are suspended in Rayleigh-Bénard convection at a Rayleigh number of 107. The lines are streamlines colored according to the fluid vertical velocity. Near the cell bottom, the fluid circulation pushes the particles from the base of the descending to that of the ascending plume where they accumulate into a dune. The particles that follow are dragged up the dune acquiring a vertical velocity component which promotes their resuspension. The lift force plays no role in this process. Depending on the particle number (from 500 to 3000) up to 20% of the fluid gravitational energy can be transferred to the particles.

[Phys. Rev. Fluids 9, 054301] Published Fri May 10, 2024

Author(s): Tian Liang, Cheng Cheng, and Lin Fu

The space-time correlations of both wall-shear fluctuations and the streamwise velocity fluctuations carried by wall-attached eddies are investigated in a multiscale manner, by coupling the inner-outer interaction model (IOIM) with the attached eddy hypothesis. The present results demonstrate that the space-time correlations for the wall-shear stress fluctuation are mainly dominated by near-wall small-scale motions, and wall-attached eddies at a given length scale feature distinctly different space-time properties as compared to those of ensembled eddies with multiple length scales, which provides a new perspective for analyzing the decorrelation mechanisms in turbulence theory.

[Phys. Rev. Fluids 9, 054606] Published Fri May 10, 2024

Author(s): Eyal Heifetz, Nimrod Bratspiess, Anirban Guha, and Leo Maas

Super-currents, tunneling across insulators in Josephson junctions, have a one-to-one classical analog to action-at-a-distance between two interfacial Rossby waves in shear flows. Quantum avoided crossing between eigenstates, described by the Klein-Gordon equation, is obtained as well for the Rossby wave normal modes. Both the quantum and the classical dynamics are formulated as coupled two-state systems and presented on a Bloch sphere, where the Hadamard gate transforms the two normal modes into an intuitive computational basis of two single Rossby waves. Yet, lacking analogs to quantum collapse and entanglement, the Rossby wave system cannot serve as a qubit prototype, even in principle.

[Phys. Rev. Fluids 9, 054802] Published Fri May 10, 2024

Author(s): Jianlin Huang, Jingzhu Wang, Wenlu Guo, and Yiwei Wang

Wall vortex occurs when a cavitation bubble oscillates far from a single rigid wall (at a dimensionless standoff distance γr>1.3). This study finds that a wall vortex in an expanded new regime forms instead of a free vortex at a smaller γr value, when introducing a water surface. Criteria for vortex flow patterns are proposed based on the direction of the bubble centroid migration at the beginning of the second cycle tc though a theoretical model developed with a Lagrangian formulation. Numerical analysis reveals that the wall vortex flow with the influence of the water surface contributes to a greater wall shear stress and larger area, thus increasing the surface cleaning potential.

[Phys. Rev. Fluids 9, 053602] Published Wed May 08, 2024

Author(s): W. Sun, A. Yalcin, and M. Oberlack

The instability behavior of plane Couette flow is notoriously difficult, because it has no classical unstable modes, and this for any high Reynolds number. Here, the plane Couette flow is modified by means of a constant wall transpiration, i.e. simultaneous blowing from below, which has a destabilizing effect, and suction from above, which has a stabilizing effect. These opposing effects led to a changed in an unpredictable way, i.e. a destabilization at a certain point with increasing transpiration rate, the increase in instability then reaches a maximum and then leads to a slow stabilization again as the transpiration rate increases further. The destabilizing effects clearly dominate here.

[Phys. Rev. Fluids 9, 053906] Published Wed May 08, 2024

Author(s): L. Reynier, B. Di Pierro, and F. Alizard

The effects of density variations on structures developing in an isotropic incompressible turbulence flow are investigated. Statistical analyses are carried out on datasets obtained from direct numerical simulations of forced turbulence. Numerical evidence shows that the introduction of a variable-density field into a turbulent field modifies the coherent structures and the energy spectrum in the inertial range.

[Phys. Rev. Fluids 9, 054604] Published Wed May 08, 2024

Author(s): Robert A. Handler, Richard J. Watkins, Silvia Matt, and K. P. Judd

Kolmogorov scaling is used to derive a model for the structure function constant associated with index of refraction fluctuations in Rayleigh-Benard turbulence. The model predicts that the normalized structure function constant depends on the heat flux to the four-thirds power, and is independent of the Rayleigh number. The model agrees with the results of numerical simulations, thereby lending support to the assumptions underlying the theory.

[Phys. Rev. Fluids 9, 054605] Published Wed May 08, 2024

Author(s): Steven Soriano and Rodolfo Ostilla-Mónico

The interaction between a vortex and an impacting body is complex due to the interaction of inviscid and viscous mechanisms. We conduct the first three-dimensional direct numerical simulations of this process and vary the relative impact velocity of the cylinder to explore the parameter space and analyze this process in detail. Strong vortices lead to ejection and interaction of secondary vorticity from the cylinder’s boundary layer, while weak vortices lead to approximately inviscid interaction of the cylinder with the primary vortex through deformations.

[Phys. Rev. Fluids 9, 054701] Published Wed May 08, 2024

Author(s): Alessandro Ceci, Andrea Palumbo, Johan Larsson, and Sergio Pirozzoli

We carry out a numerical study of swept shock wave/turbulent boundary layer interaction (SBLI) in the hypersonic regime, where a crossflow velocity component is added to the incoming flow to mimic three-dimensional interactions with cylindrical symmetry. The spatiotemporal dynamics of wall pressure well conform with the previously introduced formula for swept supersonic interactions, extending the validity of the model to SBLIs in the hypersonic regime.

[Phys. Rev. Fluids 9, 054603] Published Tue May 07, 2024

Author(s): Saurabh Nath and David Quéré

A viscous drop spreads slowly on a solid at a velocity selected by its viscosity. We show here that liquid-infused solids – a class of materials with properties in between a solid and a liquid – can expedite the spreading dynamics due to interfacial slip, which we investigate at short time.

[Phys. Rev. Fluids 9, 054001] Published Mon May 06, 2024

Author(s): N. Hanevy, J. Ferguson, P. M. J. Trevelyan, and P. T. Griffiths

In this paper a formulation of the incompressible Navier-Stokes equations is introduced which allows one to model boundary-layer flows induced by the motion of a deforming surface. Such a formulation may be used to model flows relevant in a wide variety of industries from polymer processing to glass manufacturing. We show that for particular sheet geometries and velocities, similarity solutions may be obtained that account for sheet thinning (or thickening) and roughness patterns observed in extrusion-type processes.

[Phys. Rev. Fluids 9, 054101] Published Mon May 06, 2024

Author(s): Ying Wu, Fue-Sang Lien, Eugene Yee, and Guang Chen

We report numerical simulations for the transverse flow-induced vibration (FIV) of an elastically supported elliptical cylinder-plate assembly in the regime of low Reynolds number. We investigate the combined effect of the aspect ratio of the elliptical cylinder (namely, AR = 0.5-2), the reduced velocity (namely, Ur = 2-30), and the splitter-plate length (namely, LSP/D = 0.75 and 2.5). Among numerous factors that exert impacts on the assembly’s FIV over an unlimited range of reduced velocity, the aspect ratio determines the nature and width of the synchronization branch in the amplitude response.

[Phys. Rev. Fluids 9, 054102] Published Mon May 06, 2024

Author(s): Aseel Farhat, Adam Larios, Vincent R. Martinez, and Jared P. Whitehead

An algorithm is developed, rigorously justified, and numerically implemented that is capable of determining the full body force used to generate chaotic, turbulent dynamics in two-dimensional Navier-Stokes fluid dynamics. The primary contribution of this result is that the accurate reconstruction of the force requires only partial observation of the state, i.e. sparse observations of the state are sufficient to recover not only the state itself but the unknown forcing function as well even in the fully developed turbulent setting.

[Phys. Rev. Fluids 9, 054602] Published Mon May 06, 2024

Author(s): Gerrit Maik Horstmann, Yakov Nezihovski, Thomas Gundrum, and Alexander Gelfgat

We present an experimental and theoretical study of interfacial waves generated in a two-phase swirling flow by a low-frequency (1 - 10 Hz) rotating magnetic field (RMF) oriented parallel to the interface. In contrast to surface waves excited by axial magnetic fields, we find that the first and dominant wave mode resembles a hyperbolic paraboloid. A good agreement of experiment with a linearized model was obtained. These results can have important implications for metallurgical processes and point the way to further research in the dynamics of the swirl flow, particularly by extending into the nonlinear regime.

[Phys. Rev. Fluids 9, 054801] Published Mon May 06, 2024

Author(s): Gabriel Hadjerci and Basile Gallet

While heat transport by baroclinic turbulence in oceans and planetary atmospheres is well described by a two-layer model, the relative depth of the two layers varies greatly depending on the situation of interest, making it an important parameter governing the transport properties of the system. Focusing on the low-drag turbulent regime, we extend the vortex-gas scaling theory to address the case of arbitrary layer depths.

[Phys. Rev. Fluids 9, L051802] Published Mon May 06, 2024

Author(s): Damien P. Huet, Antoine Morente, Guodong Gai, and Anthony Wachs

We investigate the inertial and noninertial dynamics of three-dimensional elastic capsules flowing through a square channel presenting a sharp corner. The channel Reynolds number Re ranges from 0.01 to 50 and the Capillary number Ca, which measures the ratio of the viscous and elastic stresses, ranges from 0.075 to 0.35. We report trajectory, surface area, velocity and membrane stress in the case of a single capsule, two capsules and a train of ten capsules released upstream of the corner. This study contributes to the elaboration of practical guidelines for controlling capsule breakup and predicting throughput in both inertial and noninertial microfluidic experiments.

[Phys. Rev. Fluids 9, 053601] Published Fri May 03, 2024

Author(s): Thomas J. Lambert, Bojan Vukasinovic, and Ari Glezer

The reciprocal coupled interactions between a forebody gimbaled axisymmetric bluff body, free to precess in pitch, yaw, and roll, and the body’s near wake are exploited for prescribing its attitude using fluidic actuation. It was shown that closed-loop control of pitch and yaw can significantly attenuate the inherent model’s baseline oscillations by more than 80%, or the control could be tuned to achieve a rapid large-amplitude response to amplify the natural yaw or pitch oscillations by more than 225% of the baseline motion. Either suppression or amplification of the natural oscillations of the model are associated with induced changes in the symmetry of the primary dynamical wake modes.

[Phys. Rev. Fluids 9, 053904] Published Fri May 03, 2024

Author(s): Yves-Marie Ducimetière, Edouard Boujo, and François Gallaire

We consider flows subject to a steady symmetry-breaking bifurcation and forced by a weak noise acting on a slow timescale. By employing a multiple-scale weakly nonlinear expansion technique, we derive a stochastically forced Stuart-Landau equation for the dominant symmetry-breaking mode. The probability density function of the solution, and of the escape time from one attractor to the other, are then determined by solving the associated Fokker-Planck equation, which is made possible by the extremely low dimensionality of the amplitude equation. The validity of this reduced order model is then tested on the flow past a planar sudden expansion.

[Phys. Rev. Fluids 9, 053905] Published Fri May 03, 2024