When determining the authorship list for your next paper, be generous yet disciplined.

On July 26, Donovan Allum (University of Saskatchewan) will sit down with the Physical Review Journal Club to discuss their recently published research, “Simulations of buoyant flows driven by variations in solar radiation beneath ice cover”.

Spatial variations in ice and snow characteristics imply that radiative forcing in late winter lakes is spatially heterogeneous. In this work, idealized, three-dimensional simulations of buoyancy-driven flows driven with heterogeneous solar radiation intensity were performed. The radiative forcing in fresh water at temperatures below 4◦C initiates an unstable stratification near the surface, leading to Rayleigh-Taylor instabilities. The variations in radiative forcing intensity generates gravity current-like flow along the surface. In the published paper, the authors provide an in-depth analysis of the development and death of the gravity current-like flow and link their results to possible melt rate variations associated with the spatial variability of the radiative forcing.

After the presentation, Allum and co-author Marek Stastna (University of Waterloo) will be available to answer attendee questions in a live Q&A session moderated by Phys. Rev. Fluids Board Member, Pascale Garaud (UC Santa Cruz).

A statistical tool tests the long-held assumption that small-scale turbulence is isotropic.

Synopsis on:
Subharthi Chowdhuri and Tirtha Banerjee
Phys. Rev. Fluids 9, 074604 (2024)

The verification of small-scale isotropy requires three-dimensional information of the flow field, a condition rarely satisfied in experiments. To examine this we develop a framework that considers how the presence of bursts at smaller flow scales generates turbulent kinetic energy differently between the horizontal and vertical directions. This framework can be applied both to flow fields obtained via numerical simulations, and to data from field and laboratory measurements. Moreover, a universal relationship emerges to predict small-scale anisotropy from large-scale flow conditions, thus contributing towards the development of next-generation closure models of wall turbulence.

We use large-eddy simulations to study the effects of helical-shaped blades on the wake flow characteristics of vertical axis wind turbines (VAWTs) at low tip speed ratios. Compared with the straight-bladed VAWT, our study shows that the helical-bladed VAWT generates near-wake flow structures with more three-dimensional features, which accelerate the wake transition to turbulence, enhance the small-scale turbulent dissipation, and result in a more rapid decay of the wake turbulence intensity. Moreover, the helical-bladed VAWT also exhibits much smaller temporal variations for the torque and power coefficients than the straight-bladed VAWT, resulting in smoother wind power generation.

In this study, we explore the complex dynamics of a dam break wave comprising a clay-water mixture under turbulent flow conditions as it interacts with a vertical rigid wall. Utilizing advanced three-dimensional Large Eddy Simulations (LES), we investigate the evolution of the dam break over time as a function of fluid rheology. The study aims to provide useful information for the development of risk mitigation strategies and the design of protective structures by examining the influence of clay concentration and initial fluid depth on the wave’s behavior, bed shear stresses, and impact forces.

The dynamics and energy-harvesting performance of piezoelectric plates in oscillatory flows have been studied numerically. The simulations show that when these plates are arranged in an array with certain distance between neighbors, the average energy-harvesting capacity of each individual plate may be increased by as much as 110% within the range of parameters considered. The underlying physical mechanism has been identified as wake energy recovery - a plate in such a formation is able to extract energy from the wakes of its neighbors that will otherwise be dissipated. This finding can be used in the development of environmental-friendly soft-body wave energy harvesters.

For sedimenting nonspherical particles at finite Reynolds numbers, very small offsets in the center of mass (less than 0.05% of particle length) can dramatically alter settling behavior. Nonuniformity in mass distribution enhances lateral dispersion and alters overall settling velocity; small changes in particle orientation lead to the onset of wake features which can either stabilize or destabilize the particle’s trajectory, bifurcating over a relatively narrow range of Reynolds number. These results carry implications for a variety of natural and engineered processes, such as the transport and settling of microplastics and/or multimaterial aggregates in the environment.

How does a cavity-embedded n-dodecane droplet behave under near-critical thermodynamic conditions? We present a comprehensive three-dimensional simulation of such a droplet subjected to a normal shock wave, utilizing an effective resolution of 0.87 billion finite volumes. This represents the largest simulation of its kind to date. A novel configuration is introduced to incorporate the influence of the cavity on the droplet dynamics. This study advances our understanding of droplet behavior under extreme conditions, potentially aiding in resolving specific transcritical flow challenges encountered in scramjets, ramjets, and liquid rocket engines.

In this work, we derive analytical solutions for a unique electrokinetic phenomenon, being termed as transport-induced-charge electroosmosis (TICEO), which does not originate from electric double layers, but is due to the local ion separation in a nanopore filled with an electrolyte solution in the presence of a salinity gradient. We show that the direction of TICEO is independent of the applied electric field, and thus suitable for alternating current (AC) pumping applications. Using a transient model, we examine the time scale, length scale, and operating frequency range for TICEO in a thin nanopore, providing useful guidance for nanopore design in AC nanofluidic technology.

Our experimental study explores ice melting rates in quiescent water and in turbulent flow. Particle image velocimetry measurements allow us to visualize and characterize flows generated by meltwater plumes and to non-invasively measure melt rate of an ice sphere fixed in place in the center of our isotropic turbulence tank, in which randomly actuated synthetic jets produce a core of homogeneous isotropic turbulence. We present relationships between ambient water temperature and turbulent kinetic energy on melt rates.

In this Letter, we report a phenomenon where two overlapping heating peaks are observed over a slightly blunted cone instead of just one in a hypersonic flow. Through optical measurements and direct numerical simulations, we confirm that the former peak originates from dilatational effects of second mode while the latter emerges due to high shear viscous dissipation. The convergence between the saturation location of second mode and onset location of transition leads to the overlap of peaks. This study not only highlights the additional heating regions over blunt models brought by the second mode, but also suggests employing designed bluntness strategies to control them.

We explore stably stratified flows in V-shaped triangular cavities, following Prandtl’s mountain and valley flow model. Our study identifies five distinct steady states. A zero-flow state bifurcates into symmetry-conjugated asymmetric circulation states forming a pitchfork bifurcation. Additionally, we identify two symmetric states characterized by upslope and downslope flows, respectively. These states, although not symmetry-conjugated, originate from the same eigenmode, leading to a novel bifurcation pattern that deviates from traditional canonical forms. Our findings illuminate the complex bifurcation structure of stratified flows in such cavities, which has previously been overlooked.

The authors explore how solidification and thermo-instability could produce the sunflower shape of paraffin wax confined within a Hele-Shaw cell.

In highly viscous environments, an object’s dynamics is perturbed in the presence of soft confining boundaries due to the coupling of the lubricated flow with the boundary’s elasticity. Since the deformability of the boundary is central to the elastohydrodynamic forces induced, altering its material nature to that of a capillary fluid interface can drastically alter the magnitude and direction of these forces. Based on a model system with two infinite cylinders rotating near a fluid interface, such changes are theoretically and numerically explored in detail. New scaling results and a reversal in the sign of the generated normal forces, unseen with classical elastic substrates, are revealed.

This work presents a reduced-order model-based feedback control strategy for suppressing vortex-induced vibration (VIV) of a spring-mounted cylinder using the balanced proper orthogonal decomposition (BPOD) method. The BPOD model, closely aligned with the full-order model (FOM), is employed to design an active flow control strategy with blowing and suction actuators, effectively suppressing VIV up to Re = 100 by adjusting or eliminating unstable eigenmodes. The optimal control strategies, robust to variations in Reynolds numbers, highlight significant gain margins when positioning velocity probes near x/D = 3.0, though probe placement in wavemaker regions might be suboptimal.

We study turbulent fluctuation-induced transitions between hurricane-like large-scale vortices and unidirectional jets in stochastically forced, viscously damped two-dimensional turbulence within an elongated periodic domain. Using direct numerical simulations of unprecedented duration, lasting up to 10000 viscous time units, we collect detailed statistical data on the lifetimes of these metastable structures and quantify the impact of the domain aspect ratio, the forcing scale, and the Reynolds number. We also uncover irreversible transition paths between jets and vortices, which consist of two stages: a rapid change in structure and a subsequent slow viscous adjustment of kinetic energy.

The phenomenon of supercritical and subcritical transitions from one state to another with the variation of a control parameter is widely observed across a variety of natural as well as artificial systems. This paper investigates those transitions in the rotating Rayleigh-Bénard convection (RRBC) system. However, the complexity of RRBC so far hindered the simplest possible description of these transitions. Here, a very simple description of the phenomenon is presented using a pair of one dimensional reduced order models of the system in the presence of free-slip and no-slip boundary conditions. The results of the models are then validated with that of the direct numerical simulations.

We perform a comprehensive numerical study on all three modes of thermal convection (forced, free, and mixed) within a system comprising two concentric horizontal cylinders filled with viscoelastic fluids, with the inner cylinder rotating. In forced convection, the flow field remains stable, while in free and mixed convection, an increase in the Weissenberg number leads to a transition from steady to unsteady periodic, quasiperiodic, and finally, an aperiodic and chaotic behavior. This transition arises due to the presence of elastic instability and the subsequent appearance of elastic turbulence in viscoelastic fluids with the increasing Weissenberg number.

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).

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

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.

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.