On April 30 Jin-Qiang Zhong (School of Physics Science and Engineering, Tongji University, and Department of Aeronautics and Astronautics, Fudan University, Shanghai, China) will sit down with Physical Review Journal Club to discuss their recently published paper, “Model for the dynamics of the large-scale circulations in two-layer turbulent convection.”

In their research, Zhong and colleagues present a physically motivated low-dimensional model for the dynamics of two interacting large-scale circulations (LSC) in two-layer turbulent convection. Inspired by previous experimental results of the flow dynamics and coupling in two-layer turbulent convection, the model extended previous studies of single-LSC dynamics to incorporate four stochastic ordinary differential equations describing the strength and azimuthal orientations of two vertically aligned LSCs. The interaction terms of the two LSCs, i.e., thermal and viscous coupling terms, are predicted based on the influence of the fluid temperature by the other LSC through heat advection and thermal diffusion, and the enhanced (reduced) viscous damping across the interface between the two LSCs. This reduced-order model is able to provide accurate predictions for the enhanced occurrence frequency of flow reversals observed experimentally, and suggests a new dynamical process of flow reversals in multilayer turbulent convection. After the presentation, in which Zhong will summarize the modeling approach proposed in the paper, all authors will be available to answer attendee questions in a live Q&A session.

Registration is free and a video recording will be provided to all registrants.

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.

The impact and freezing process of a water droplet are studied experimentally, incorporating the presence of frost and salt. A distinct transition of the spreading dynamics is observed, altering from the well-known 1/2 inertial scaling law to a 1/10 capillary-viscous scaling law. By considering the effect of impact inertia, partial-wetting behavior, and salinity, the mechanism of this transition is elucidated, and a unified model for predicting the droplet arrested diameter is proposed.

Turbulent flows comprise a multitude of scales which make them extremely difficult to analyze and simulate. In this work, we study homogeneous isotropic turbulence using a novel approach which solves the Navier-Sokes equations on a reduced set of modes that are sampled stochastically. The complementary set are solved using trivial dynamics. This method, called Selected Eddy Simulations, is able to capture broad dynamics of turbulence with just 10% of resolved modes, suggesting the turbulence attractor may be smaller or more robust to modeling than previously thought. This result also holds promise for developing alternative low-cost numerical approaches to study turbulent flows.

Electrocapillary flows in a classical experiment of Melcher and Taylor are studied. The computed streamlines qualitatively represent the experimental image. With the increase of electrocapillary forcing, the main circulation localizes near a boundary with a larger electric potential. When a dielectric liquid is replaced by a poorly conducting one, the system becomes non-isothermal owing to the Joule heating, and the flow is driven also by buoyancy and thermocapillary convection. The results show that consideration of the two-phase model is mandatory. The Lippmann equation, connecting electrically induced surface tension with nonuniform surface electric potential, is numerically verified.

The presence of a dispersed phase substantially modifies small-scale turbulence. Here we present a comprehensive mechanistically based model to predict turbulence modulation, the predictions of which, compared with particle-resolved simulations and experiments, is shown.

Acoustic fields are used in numerous applications to induce movement of suspended particles. We develop a rigorous theory that systematically unifies inviscid acoustophoresis with viscous streaming. The theory connects particle motion to a generalized form of the secondary radiation force, which depends on the Stokes layer thickness around the particle, and the contrast of density and compressibility between the particle and the fluid. We identify a reversal of particle motion when inertial and viscous forces are comparable, validated with numerical solutions. This has significant implications for applications involving particle sorting or focusing based on size or material properties.

Shear flows in contact with compliant boundaries exhibit a rich dynamics involving traveling-wave-flutter, Tollmien-Schlichting, as well as divergence instabilities. In this context, maximum transient growth effects are the result of optimal energy exchanges during the fluid-structure interaction process. The present investigation studies the detailed contribution of the different interacting modes. In particular, it is found that the optimal gain may be associated with a large-amplitude oscillatory behavior and that wall-compliance enhances this phenomenon.

We propose a novel approach to accurately model complex flow, ultimately predicting the behavior of a turbulent jet by molding a set of velocity signals input from an idealized flow (readily available from numerical databases online). The model uses fundamental properties of the jet, such as velocity means and standard deviations, easily accessible from textbooks, experiments, or low-order simulations (RANS, LES). The modeled jet reproduces many subtle and intricate properties of the turbulent flow, including the intermittent extreme events known to exist in turbulent flows, which have been typically thought of as not capable of being captured with current modeling techniques.

Unsteady flows in curved pipes are ubiquitous in science and engineering but their stability characteristics are not well understood in most cases of practical interest. We study the linear stability of pulsatile flow in the archetypal configuration of a toroidal pipe, which appears e.g. in aortic blood flow. The Floquet stability analysis of the harmonically forced system reveals that the curvature leads to nonlinear interactions in the baseflow andconsiderable stabilization that can be orders of magnitude larger than in the corresponding planar case. The figure shows a typical snapshot of the streamwise velocity field in a torus subject to a pulsating pressure gradient.

We develop a model that describes the permeance of simple fluids as well as small hydrocarbon molecules through nanoporous, atomically thin membranes. The model is in agreement with molecular dynamics simulations for a wide range of pore sizes, including pores approaching the steric exclusion limit, as needed for understanding separation processes using such membranes.

In stars and planets natural processes heat convective flows in the bulk of a convective region rather than at hard boundaries. Internally heated convection has been studied extensively in incompressible fluids, but the effects of stratification and compressibility have not been examined in detail. In this work, we study fully compressible convection driven by a spatially uniform heating source in a suite of two- and three-dimensional Cartesian, hydrodynamic simulations. We characterize how Mach, Reynolds, and Nusselt numbers scale with the characteristic strength of the internal heat source. We also measure kinetic energy power spectra and discuss the flow morphologies.

This study focuses on how Lagrangian coherent structures (LCSs) control solute dispersion in heterogeneous poroelastic media (HPM). We show how interactions between medium compressibility, conductivity heterogeneity, and periodic forcing give rise to complex flows and diverse LCS types (KAM islands, chaotic saddles, etc) that have profound impacts on diffusive solute transport (main image) that do not arise in the steady counterpart (inset). Strongly anomalous transport impacts both spatial moments and residence time distributions and persists at low Péclet numbers. This study reveals the complex transport phenomena that can arise in HPM and shows how LCSs govern solute dispersion.

In this work, we experimentally investigate turbulence ingesting rotor noise under various thrusting states. The broadband noise caused by turbulence ingestion is found to dominate at the normalized frequency range of $fR/U_{\mathrm{\infty }}$ = 20 to 80 when the rotor is under low-thrusting conditions. Results also suggest that the turbulence ingestion broadband noise can be scaled by Mach number scaling of $M_{\mathrm{\infty }}^2$$M_c^4$, where $M_{\mathrm{\infty }}$ is the freestream Mach number, and $M_c$ is the corresponding blade tip Mach number.

We combine experiments and numerical simulations to investigate the interaction between a rigid fiber and a triangular obstacle in a microfluidic channel. We find different dynamics depending on the initial position and orientation of the fiber. We show that these dynamics are dictated by the fiber configuration in the vicinity of the obstacle. Some dynamics induce a cross-stream migration which grows with the fiber length. Our findings could in the future be used to design and optimize microfluidic sorting devices to sort rigid fibers by length.

This numerical simulation investigates the vertical convection of liquid metal with varying magnetic fields and wall conductivities. The applied horizontal magnetic field alters plume dynamics and topology, leading to a more coherent large-scale flow structure but weakening convection through Joule dissipation. This competition between rectification and magnetic damping determines the magnetic field’s impact on heat transfer, with the quasi-two-dimensional state being the threshold. Our analysis demonstrates that while the plume area remains constant, condensation of coherent structures enhances horizontal heat transport per unit area, significantly improving overall heat transfer.

In this work, we developed a novel framework for incorporating the near-wall non-overlapping domain decomposition (NDD) method with the machine learning technique. It allows the solution to be calculated with a Robin-type (slip) wall boundary condition on a relatively coarse mesh and then be corrected in the near-wall region by solving the thin boundary-layer equations on a fine subgrid. Through an estimated turbulent viscosity profile provided by a neural network, the proposed method can be easily extended to different turbulence models and achieve commendable accuracy for the test cases of turbulent wall-bounded flows at various Reynolds numbers.

A flow progression from laminar flow slippage to rotational vortices in cavitied microchannels is shown to cause a reversal of flow resistance, i.e. a reduced flow resistance at low Reynolds numbers compared to an unmodified microchannel but a comparatively higher flow resistance at high Reynolds numbers. Furthermore, an earlier transition of initial laminar flow to turbulent flow is suggested to be triggered by instabilities generated along shear layers, formed between the mainstream flow and rotational vortices in each cavity that modifies the sidewalls of microchannels.

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.