A spotlight on JFM Rapids, a well-established section in the Journal of Fluid Mechanics [JFM] that continues to provide a highly visible venue for short, high-quality, articles addressing timely research challenges of broad interest. In this collection, the Editors of JFM Rapids each explain why they selected one article that presents exciting results with exceptional impact on currently active fluid mechanics research.

Read on to discover the selected articles and the Editors’ insights:

• Particle-resolved simulation of antidunes in free-surface flows by Christoph Schwarzmeier, Christoph Rettinger et al.

Elisabeth Guazzelli: “This JFM Rapids presents new simulations of flow over a granular sediment bed, which aim at reproducing the formation and the development of antidunes in a supercritical flow. The problem is well known to be extremely difficult because of the strongly varying water surface of rapid flows. This paper is a milestone in the development of high-resolution methods as it includes the free-surface dynamics into the granular bed evolution process. It opens new perspectives for detailed studies of morphodynamics in supercritical flows.”

• The Effects of Surfactants on Plunging Breakers by M.A. Erinin, C. Liu et al.

Detlef Lohse: “This is an excellent paper on the effect of surfactants on plunging breaker waves. Most studies on waves have been done with clean water, but in the ocean, water is not clean at all and the wave dynamics is strongly affected by surfactants. This study combines very original large scale experiments with insightful numerical simulations. With this combination, the authors can quantifatively account for the surprising observations and beautifully work out the physics of the effect of the surfactants on the breaking waves.”

• The streaks of wall-bounded turbulence need not be long by Javier Jiménez

Dan Henningson: “The effect of damping the longest streaks in wall-bounded turbulence is explored using numerical experiments. It is found that long streaks are not required for the self-sustenance of the bursting process, which is relatively little affected by their absence. This Rapids paper can be seen as a further step in the simplification of minimal models for wall-turbulence, and as such an interesting contribution to characterise the most important aspects of turbulence.”

• Compressible turbulent convection in highly stratified adiabatic background by John Panickacheril John and Jörg Schumacher

Colm-cille Caulfield: “Rayleigh-Bénard convection is one of the most important (and widely studied) fluid flows where buoyancy forces drive a turbulent heat transport across a fluid layer. Canonically, three simplifying assumptions are made: that the flow is incompressible, with a divergence-free velocity field; that the fluid properties, such as kinematic viscosity and thermal diffusivity are constant; and that the  flow is in the  Oberbeck-Boussinesq regime, with a linear equation of state relating density to temperature, such that density variations are only significant in the buoyancy force coupling the density to the flow velocity. There are many important situations, for example in the convective zone of stars, where these assumptions are not (at all) valid. In this innovative paper describing a series of highly resolved three-dimensional direct numerical simulations, these assumptions are relaxed to allow for fully compressible flow to develop, leading to prominent top-down asymmetry. Though the flow is still highly idealized, a sparse network of thin plume structures are observed, which have at least qualitative resemblance to the Sun’s  well-known granule network. The thin plume structures are also shown to be associated with significantly reduced global heat transport compared to the canonically-considered flow, suggesting many significant implications for such more realistic convection flows.”

• Dynamics and containment of a viscous liquid atop a granular bed by Edward M. Hinton  and Anja C. Slim

Sarah Waters: “This fascinating paper examines the dynamics of a gravity current of viscous fluid on a deformable granular layer of finite depth.   The problem is motivated by the spreading of viscous magma on a granular bed, and the findings have wider fluid mechanics applications, for example in the reworking of sub-glacial tills. The numerical study examines how the viscous fluid can cause the entire granular layer to flow, with potential feedback on the dynamics of the gravity current. The contribution reveals a mechanism by which a viscous liquid can drive levee formation and become trapped during flow atop a granular layer, and opens up new research avenues, such as the possibility of generating instabilities in non-axisymmetric cases.” 

We hope these selected articles will inspire more researchers to submit their results to JFM Rapids.

Read these articles in one collection

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