On May 29 at noon ET, Michalis Chatzimanolakis (Harvard University) will sit down with the Physical Review Journal Club to discuss their recently published research, “Learning in two dimensions and controlling in three: Generalizable drag reduction strategies for flows past circular cylinders through deep reinforcement learning.” Please register here. Registration is free and a video recording will be provided to all registrants.

We are greatly saddened by the sudden passing on April 14 of Keith Julien, Chair and Professor of Applied Mathematics at the University of Colorado, Boulder, Fellow of the American Physical Society, and a member of the Editorial Board of Physical Review Fluids.

Physical Review Fluids publishes a collection of papers associated with the 2022 Gallery of Fluid Motion. These award winning works were presented at the annual meeting of the APS Division of Fluid Dynamics.

See the 2022 Gallery for the original entries.

The Collection is based on presentations at the 2022 meeting of the APS Division of Fluid Dynamics in Indianapolis, Indiana. Each year the editors of Physical Review Fluids invite the authors of selected presentations made at the Annual meeting of the APS Division of Fluid Dynamics to submit a paper based on their talk to the journal. The selections are made based on the importance and interest of the talk and the submitted papers are peer reviewed. The current set of invited papers is based on presentations made at the 75th Annual meeting of the APS Division of Fluid Dynamics in November 2022. The papers may contain both original research as well as a perspective on the field they cover.

Browse outstanding papers by early career researchers who have received the Frenkiel Award in recognition of their significant contributions to fluid dynamics.

In this paper, we investigate the exit dynamics of a sphere launched underneath a liquid bath surface at a prescribed impact velocity. Spheres with radii approximate or smaller than the capillary length are considered. The process can be sequenced into a partial exit stage that forms a coated layer, and a full exit stage with an attached ligament. A bouncing-off regime, a lower pinch-off penetration regime, and an upper pinch-off penetration regime are identified, separating by a penetration Weber number and a switching Weber number. The phase diagram is revealed, where the two critical Weber numbers are functions of the Bond number.

To investigate the existence of geometrically self-similar eddies in fully developed turbulent pipe flow, stereoscopic particle image velocimetry measurements were performed in two parallel cross-sectional planes, for friction Reynolds numbers Re${}_{\tau }$ = 1310, 2430, and 3810. The instantaneous turbulence structures are sorted by width using an azimuthal Fourier decomposition, then azimuthally aligned to create a set of average eddy velocity profiles. The streamwise similarity is investigated using two-point correlations. Over the range of scales examined, the candidate structures establish full three-dimensional geometric self-similarity.

We integrated theoretical analysis and numerical simulations to investigate the turbulence transition through a crossflow instability in the boundary layer of a cooler rotating disk within a rotor-stator cavity, influenced by a temperature gradient. This gradient induces centrifugal buoyancy forces that alter the radial inflection points in the mean flow. These changes lead to premature bifurcation of spiral waves, crucial in the transition process, resulting in an early onset of turbulence in the boundary layer of the rotating disk. Our findings underscore the importance of manipulating boundary layer stability via temperature gradients to control turbulent transitions.

The dynamics of a free object in an active nematic suspension in a circular container are simulated. For ranges of parameters, unstable chaotic wanderings eventually reach either a fixed-point or limit-cycle (shown) behavior. These flows are analyzed, and similar behaviors confirmed to also occur in more complex geometries.

We present a numerical study of a thin elastic sheet with small extensibility sedimenting in a viscous fluid in free space or near a wall. The interplay between gravity and the elastic response of sheets gives rise to complex deformation and reorientation dynamics. Near a vertical wall, sheets exhibit asymmetric conformations that cause the sheet to drift toward or away from the wall. Near an inclined wall, sheets show qualitatively different dynamics when the wall angle is large: they either deposit on or slide along the wall with a fixed wall-normal distance.

Scraping of a thin layer of viscoplastic fluid from a horizontal surface by a translating rigid scraper generates a mound of fluid upstream of the scraper and a residual layer behind it. We compute numerical solutions for the system modeled via viscoplastic shallow-layer theory. The unsteady dynamics of this system exhibit a variety of self-similar regimes, for which we construct solutions explicitly and identify key scalings for the temporal development of the mound. We further report experimental results, which are compared with predictions from the shallow-layer theory, obtaining reasonable agreement once a slip boundary condition is included in the model.

Liquid infused surfaces (LISs) are a nature-inspired surface technology that demonstrates multiple functionalities under laminar and controlled flow conditions. We study experimentally the behavior of the infused lubricant under submerged conditions and turbulent flow. When exposed to turbulence, the lubricant layer develops into a pattern of droplets, the length of which depends on the balance between shear and contact force. The stability of the droplets prevents complete drainage of the lubricant and increases the robustness of the LIS in the presence of turbulence. We identify a model that predicts the equilibrium length of the droplets and validate it with numerical simulations.

We examine the influence of wind forcing on the inception of breaking in surface gravity waves using an ensemble of high-resolution numerical simulations. We find that there is a critical point in the energetic evolution of the wave in which the convergence of kinetic energy at the wave crest can no longer be offset by conversion to potential energy, resulting in a rapid growth of kinetic energy up to breaking onset. This energetic signature is shown to consistently differentiate between non-breaking and breaking waves under a range of wind forcing speeds.

Drops impacting supercooled surfaces adhere to them due to contact line pinning and their solidification. However, distinguishing the influence of each phenomenon on post-impact behavior is challenging since even repellent materials exhibit some drop adhesion. In this study, we examine the impact of water and alkane drops on an omniphobic dry ice surface. We show that the solidification extent within the drop, combined with thermal, elastic, and surface tension forces, dictate outcomes like fragmentation, rebound, or no-bounce. Our findings have critical implications for material design in 3D printing, frost-resistant coatings, and safe biological material transport in cold climates.

500 resolved particles, colored by their temperature, are suspended in Rayleigh-Bénard convection at a Rayleigh number of ${10}^7$. 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.

Exploring how the shape of red blood cells influences their flow properties, this study uses numerical simulations to analyze changes from healthy bi-concave forms to abnormal spherical shapes associated with disorders like spherocytosis. The research reveals complex, non-monotonic relationships between cell shape and flow rate across varying channel widths, and its impact on blood perfusion.

To explore the dynamics of annular combustors, we investigate azimuthal thermoacoustic instabilities under a range of hydrogen power fractions and operating conditions. Using time-series analysis and mode detection techniques, we examine the relationship between longitudinal and azimuthal modes, identifying a transition from chaos to high-amplitude periodic states. Our research sheds light on how hydrogen enrichment affects combustor stability and presents the first identification of type-II Pomeau–Manneville intermittency in annular combustors. These findings contribute to knowledge of the modal dynamics within combustors, with implications for the design and operation of future systems.

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.

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.

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.

Experiments show the effects on combustion of adding hydrogen to natural gas—a fuel mixture that could reduce carbon emissions from power plants.

Focus story on:
Byeonguk Ahn et al.
Phys. Rev. Fluids 9, 053907 (2024)

APS has selected 156 Outstanding Referees for 2024 who have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online.

The recipients of the 40th François Naftali Frenkiel Award for Fluid Mechanics are Aliénor Rivière, Daniel J. Ruth, Wouter Mostert, Luc Deike, and Stéphane Perrard for their paper “Capillary driven fragmentation of large gas bubbles in turbulence” which was published in Physical Review Fluids 7, 083602 (2022).

The 75th Annual Meeting of the American Physical Society (APS) − Division of Fluid Mechanics was held in Indianapolis, IN from November 20–22, 2022.

The Editors of Physical Review Fluids highlight the journal’s achievements, its editorial standards, and its special relationship with the APS Division of Fluid Dynamics (DFD).

Beverley McKeon and Eric Lauga describe their vision as new Co-Lead Editors for Physical Review Fluids, which celebrates its fifth anniversary this year.