Join the Physical Review Journal Club and Chong Shen Ng, University of Twente, The Netherlands, for an important discussion of respiratory droplets with details from the recently published Physical Review Fluids paper: “Growth of respiratory droplets in cold and humid air”. The research, summarized here by Physics Magazine, reveals through numerical simulations of a cough, how droplets first grow before evaporating and shrinking in cooler, more humid air—contradicting previous research, which suggested they don’t continuously evaporate.

Ng will provide a short presentation, then answer all questions from participants during a live session, moderated by Emmanuel Villermaux, Aix-Marseille Université, Marseille, France. Registration is free.

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

APS has appointed Beverley McKeon (California Institute of Technology) and Eric Lauga (University of Cambridge) as Lead Editors for the Physical Review Fluids as of February 1, 2021. They take the helm following the journal’s founding Editors John Kim and Gary Leal. Learn More.

We study the propagation of dynamic jamming fronts in a dense cornstarch suspension generated by a towed body. Previous studies have investigated this phenomenon under pushing, pulling, or shearing, separately. In our experiment we are able to show how the front propagates in the full field surrounding the cylinder experiencing pushing, pulling, and shearing simultaneously. Though the fronts propagate symmetrically in the transverse direction to the cylinder movement, we observe a fore-aft asymmetry for the first time.

We explain the turbulent structure of supercritical currents through highly resolved simulations that employ up to a billion grid points. Three families of hairpin vortices dominate the near-bed and interface layers of the current, with their generation mechanisms dictating their shape, orientation, and number density. We observe, for the first time, a feedback loop with a persistent counter-gradient transport induced by the interacting hairpin vortices increasing the local concentration gradient and the local high concentration gradient which then, in turn, modulates turbulent structures in the lower-interface region.

Linear stability analysis about the mean flow of a nonlinear limit cycle has been found to yield a very accurate prediction of its frequency, a property called RZIF (Real Zero Imaginary Frequency). However, although approximating the mean flow via the SCM (Self Consistent Model) is sufficient for the archetypal case of the cylinder wake, it is inadequate for predicting the frequency of thermosolutal traveling waves.

Streaks are considered to be of major importance in near-wall turbulence for their role in the regeneration of turbulent energy. The life cycle of streaks in the buffer layer of wall-bounded turbulence is identified by tracking the time evolution of individual streaks. The results show that streaks are born in the buffer layer, coalescing with each other to create larger streaks that are still attached to the wall. Once the streak becomes large enough, the tall-attached streak eventually splits into wall-attached and wall-detached components, disintegrating further until they dissipate into the turbulent background.

Particle-induced transition is characterized by a smooth laminar-turbulent transition. For large pipe-to-particle diameter ratios (D/d) even dilute systems exhibit this smooth transition. In this study we use particles with a D/d of 5.7, which represents a “sweet spot”, allowing the use of particle image velocimetry to study this particular phenomenon. With direct insight to the velocity fields we show that for this type of transition the velocity fluctuations scale proportionally to the Reynolds number and the particle-to-pipe diameter ratio. Furthermore, elongated streamwise structures are observed during the transition.

We show that as inertial particles settle through a turbulent boundary layer, the mechanism responsible for enhancing their settling rate relative to the Stokes velocity transitions from being the preferential sweeping mechanism to the turbophoretic drift mechanism. We consider the corresponding effect on the particle concentration profiles and discuss how the Rouse model must be modified to account for particle inertia.

Using high-speed imaging, the different stages of drop detachment from a capillary are studied for a viscoelastic suspension of spherical particles dispersed in a dilute polymer solution. The dynamics can be rationalized by recognizing the different contributions the particles and polymer make to the properties of the solution and the way these effects influence different time scales of the deformation and breakup process.

Although a suction vortex is one of the most common vortices appearing in everyday life, its internal structure has not been fully understood yet. We experimentally generate directly a superfluid suction vortex with a superfluid stirring system. A quantum vortex line carries all the microscopic circulation, and the distribution of vortex lines can be measured by combining two acoustic techniques. The results show that the vortex lines accumulate in the narrow region around the axis of symmetry. However, the vortex lines are not a simple bundle of straight vertical lines, but most of them incline in the horizontal direction.

PRFluids held another Physical Review Journal Club session on May 17 where Juliette Pierre, Sorbonne Université, CNRS, France, presented fascinating information from the recently published PRFluids paper: Sound of effervescence. Pierre provided evidence that the unique sound that emanates from champagne is vibrations of the bubble cavity that are triggered by the bursting process. The presentation was followed by a question-and-answer session. View the full video of the Journal Club session here.

This Collection contains seven papers invited by the editors which apply machine learning to fluid mechanics. Some of the papers are based on presentations given at the Machine Learning minisymposium or other sessions held at the 72nd Annual meeting of the APS Division of Fluid Dynamics in Seattle, Washington in November 2019, and others were separately invited. Submission of these papers was invited based on the importance and interest of the work and the papers were subsequently peer reviewed. The papers may contain both original research as well as a perspective on the problems they cover. We believe that these are outstanding papers which contain important advances in the use of machine learning in fluid mechanics and look forward to publishing more excellent papers in machine learning of fluid mechanics in the future.

PRFluids held its first Physical Review Journal Club on April 12 with an exclusive conversation with author Eric W. Hester along with co-authors Claudia Cenedese and Geoffrey Vasil on their recently published PRFluids paper: Aspect ratio affects iceberg melting. In the discussion, Hester demonstrates how the shape of an iceberg seems to have large effects on its melting rate. He also answers questions from the live audience. View the full video of the Journal Club session here.

At the beginning of 2021, eight Physical Review journals began publishing Letters which are intended for the accelerated publication of important new results targeted to the specific readership of each journal.

The recipients of the 37th François Naftali Frenkiel Award for Fluid Mechanics are Matthew Butler, Finn Box, Thomas Robert, and Dominic Vella for their paper “Elasto-capillary adhesion: Effect of deformability on adhesion strength and detachment”.

The collection is based on presentations at the 2019 meeting of the APS Division of Fluid Dynamics. 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. In the current issue nine invited papers based on presentations made at the 72nd Annual meeting of the APS Division of Fluid Dynamics in Seattle, Washington in November 2019 have been published together as a Collection. The papers may contain both original research as well as a perspective on the field they cover. We believe that these are outstanding papers in fluid mechanics and look forward to publishing more excellent papers in the year ahead.

APS Editor in Chief, Michael Thoennessen, discusses a new opportunity for communicating authors to include their pronouns together with their contact email in order to promote a more respectful, inclusive, and equitable environment.

The 37th Annual Gallery of Fluid Motion (GFM) was held at the American Physical Society (APS) Division of Fluid Dynamics Annual Meeting in Seattle, Washington November 23–26, 2019.

Physical Review Fluids publishes a collection of papers associated with the 2019 Gallery of Fluid Motion. These award winning works were presented at the annual meeting of the APS Division of Fluid Dynamics.

See the 2019 Gallery for the original entries.

See the Physics Feature News story on the 2019 Gallery.