New Papers in Fluid Mechanics

Author(s): Smiron Varghese, Benjamin Miquel, and Wouter J. T. Bos

We present an analytical investigation of the global helicity budget associated with the salt-fingering instability within the two-dimensional, three-component framework. Our analysis shows that in the region of parameter space corresponding to salt fingering, helicity amplification occurs when the …

[Phys. Rev. E 114, L023101] Published Thu Aug 27, 2026

Author(s): Huifeng Chen (陈慧锋), Yixin Yang (杨揖心), Mingbo Sun (孙明波), Hongbo Wang (汪洪波), Dapeng Xiong (熊大鹏), Changhai Liang (梁昌海), Wenxiao Long (龙文骁), and Wenming Li (李文明)

This paper uses direct numerical simulations to systematically investigate supersonic flows in a bent pipe with a developing turbulent boundary layer and a core flow region. The results reveals that boundary layers experience intricate flow patterns at different azimuthal angles: secondary flows that drives the streaks move from the lower to the upper side; separation triggered by the combined effects of the adverse pressure gradient and flow deceleration on the upper wall; and the increase of the Görtler instability on the lower wall inducing the clustering and uplift of low-momentum fluids, the presence of Görtler-like vortices, and the baroclinic effect of turbulent transport processes.

[Phys. Rev. Fluids 11, 083401] Published Thu Aug 27, 2026

Author(s): Yu Cheng and Tianle Liu

Turbulent transport in large-eddy simulations relies on subgrid-scale (SGS) closures, yet conventional models typically assume that SGS stresses are uniquely determined by the resolved flow. We introduce a conditional diffusion model that learns the conditional distribution of SGS stresses from high-resolution atmospheric boundary layer simulations. By representing conditional variability rather than a single deterministic mapping, the proposed framework accurately reproduces SGS stress statistics, generalizes across unseen stability regimes and grid resolutions, and provides a new probabilistic framework for SGS turbulence modeling.

[Phys. Rev. Fluids 11, 084610] Published Wed Aug 26, 2026

Author(s): Pranav Hegde, Wietze Herreman, Jorge César Brändle de Motta, Romain Canu, Marie-Charlotte Renoult, and Gerrit Maik Horstmann

Metal-pad-roll instabilities limit the safe and efficient operation of aluminum reduction cells, yet laboratory-scale models fall outside the assumptions of most existing theories. We develop an analytical stability theory for small rectangular two-layer cells that captures finite-depth, viscous, and capillary effects, including a parameter-free description of interfacial-wave damping. Validated against direct numerical simulations and experiments, the theory provides quantitative benchmarks for designing and interpreting small-scale MHD experiments and multiphase simulations.

[Phys. Rev. Fluids 11, 084803] Published Wed Aug 26, 2026

Author(s): Johnathan Hoggarth, Daniel M. Harris, John W. M. Bush, and Bauyrzhan K. Primkulov

We introduce a simple droplet generation technique that rapidly stretches a liquid ligament on both quiescent and vibrating baths. By systematically varying the stretching distance and the radius of the cylindrical probe used to form the ligament, we map the parameter space in which the ligament pinches off and collapses into a single droplet. The resulting droplet size follows the volume-conservation scaling R∼a2/3L1/3 , with excellent reproducibility (radius variation below 5%).

[Phys. Rev. Fluids 11, L082001] Published Wed Aug 26, 2026

Author(s): Mehdi Riahi and Mohamed Hayani Choujaa

Previous studies dealing with Floquet stability analysis of non-zero-mean time-modulated Rayleigh-Bénard convection have shown the existence of only harmonic and subharmonic instability modes. Here, we emphasize the existence of quasiperiodic instabilities that have not yet been reported in the lite…

[Phys. Rev. E 114, 025108] Published Mon Aug 24, 2026

Author(s): Chien-Chia Liu and Jui-Yin Lin

Wall roughness plays a central role in determining turbulent friction in pipe flows, yet most predictive frameworks continue to characterize the wall by a single effective roughness scale. Classical datasets—notably Nikuradse's sand-grain experiments and the rough-pipe measurements of Colebrook and …

[Phys. Rev. E 114, 025109] Published Mon Aug 24, 2026

Author(s): Bin Zhang, Yuke Li, Hongna Zhang, Guiren Wang, Rong Liu, Shaowei Wang, and Zijing Ding

Polymer diffusive instability (PDI) provides a unique route to instability in viscoelastic flows at vanishing Reynolds numbers, yet how realistic wall conditions modify its behavior remains unclear. Here, we show that wall slip regulates PDI in viscoelastic Poiseuille flows by altering the dominant instability pathway. Increasing slip weakens the near-wall PDI-1 mechanism and favors a shear-driven PDI-2 regime. Combining linear stability analysis and direct numerical simulations, we reveal the energy-transfer processes underlying this slip-induced transition and provide new insight into controlling polymer-flow instabilities.

[Phys. Rev. Fluids 11, 083905] Published Mon Aug 24, 2026

Author(s): Bodhinanda Chandra, Sachith Dunatunga, and Ken Kamrin

Granular materials dissipate energy through frictional rearrangement and dissipative collisions, yet these mechanisms are often entangled or partially neglected in continuum models. We develop a unified viscoelastic–viscoplastic framework that links the coefficient of restitution e directly to continuum viscosities while preserving the established μ(I) rheology during plastic flow. Implemented within the material point method, the model reproduces the steady-state Bagnold solution, wave propagation, impact, dynamic reposing behavior, and vibration-induced pattern formation. These results emphasize that restitution must be embedded correctly to capture granular flow dynamics accurately.

[Phys. Rev. Fluids 11, 084301] Published Mon Aug 24, 2026

Author(s): Chulan Hu and Xuebo Li

Wall-attached motions leave an intermittent footprint on the near-wall flow, but conventional coherence analyses reveal only its time-averaged behavior. Using synchronized two-point hot-wire measurements in a high-Reynolds-number turbulent boundary layer, we develop a wavelet-based framework that resolves this wall imprint in time and scale while recovering established mean coherence scaling. The results show that the characteristic persistence scale grows with wall distance even as coherence at that scale weakens, and that strongly wall-imprinted events exhibit systematic wall-normal changes in scale-local energy transfer and energy distribution.

[Phys. Rev. Fluids 11, 084609] Published Mon Aug 24, 2026

Author(s): Georg Rempfer, Mae Nesenberend, Chengkai Zhu, Bart Stam, Debabrata Panja, and Joost de Graaf

Numerical studies of viscoelastic Stokes flow often regularize the stress singularities predicted by the Oldroyd-B model, obscuring their underlying structure. We introduce an efficient FFT-based projection solver for incompressible flow and validate it in the classical four-roll mill. By analyzing the polymeric stress directly in Fourier space, we quantify its power-law scaling with resolution and determine the critical Weissenberg number for steady-state convergence without adding artificial stress diffusion.

[Phys. Rev. Fluids 11, 084901] Published Mon Aug 24, 2026

Author(s): John L. Spiesberger and Eugene Terray

A theory inspired by whale tracking suggests that wave interference can make energy travel faster than light.

[Phys. Rev. E 114, 025107] Published Tue Aug 18, 2026

Author(s): Tianquan Tang, Mengjie Wu, and Lixi Huang

The theory of using transducer arrays for the contactless and stable manipulation of Rayleigh objects (ka≪1, where k is the wave number and a is the averaged radius of object) is well established, whereas retrieving the transducer parameters required for the stable and dynamic manipulation of Mie ob…

[Phys. Rev. E 114, 025106] Published Mon Aug 17, 2026

Author(s): A. Bongarzone, C. Content, D. Sipp, and C. Leclercq

Resolvent analysis is a cornerstone tool for predicting how flows respond to external forcing, but for unsteady flows the choice of linear operator is not obvious. The common mean-flow resolvent, linearized about the time-averaged flow, can misidentify the dominant receptivity mechanisms, whereas the statistically optimal mean resolvent correctly captures physically relevant phenomena such as the vortex pairing in jets presented here. This work introduces a projection method that enables mean resolvent analysis at low computational cost without resorting to adjoint equations about the unsteady attractor, thereby opening a path toward more complex flows.

[Phys. Rev. Fluids 11, 083903] Published Mon Aug 17, 2026

Author(s): Gourab Chakraborty, Vinod Narayanan, and Uddipta Ghosh

Reactive fronts in porous media are often destabilized by concentration dependent viscosity of the constituent fluids, leading to viscous fingering. These processes are known to be strongly influenced by hydrodynamic dispersion, originating from incomplete mixing at the pore scale. Yet, their impact and the resulting instabilities remain poorly understood. This study combines transient and quasi-steady-state linear stability analysis to reveal how hydrodynamic dispersion and diffusivity contrasts govern the growth and onset of instabilities, providing new physical insights, with potential applications in contaminant remediation, enhanced oil recovery, and carbon sequestration.

[Phys. Rev. Fluids 11, 083904] Published Mon Aug 17, 2026

Author(s): Binjian Ma, Xiaoyu He, Yuexuan Mao, Zixuan Wang, Yonggang Zhu, Huizhu Yang, and Xiaozhou He

Classical similarity theory describes the far field of a laminar jet, but not how a finite Poiseuille inlet loses its memory and reaches that state. We develop a self-consistent two-mode analytical model that predicts this pre-asymptotic evolution without empirical fitting. The theory uncovers a universal Reynolds-scaled centerline decay and shows that the transition length grows linearly with Reynolds number, while reproducing full velocity profiles for both round and slot jets in close agreement with Navier–Stokes simulations.

[Phys. Rev. Fluids 11, 084101] Published Mon Aug 17, 2026

Author(s): Tanmay Agrawal, Vamsi Krishna Chalamalla, and Narsing Kumar Jha

Air curtains restrict buoyancy-driven exchange through building doorways, but sealing effectiveness saturates near about 80 to 85% and the transport pathways fluid takes to leak through have remained unclear. We combine large-eddy simulation with Lagrangian particle tracking to follow individual fluid parcels, classifying their trajectories into three pathways: a gravity current active only before the curtain establishes, and two turbulent-entrainment routes that dominate afterward. Once the curtain is established, the residual leakage is shown to be governed by entrainment at the jet interface rather than by buoyancy.

[Phys. Rev. Fluids 11, 084504] Published Mon Aug 17, 2026

Author(s): Xianliang Chen, Zhiye Zhao, Jianping Gan, and Lin Fu

The velocity law of the wall is a well-known law for wall turbulence. In compressible turbulence, the temperature law of the wall is also of interest, but its overall accuracy is inferior to its velocity counterpart. We propose to construct the compressible law of the wall for heat energy using total enthalpy. A semilocal total enthalpy transformation of no fitted parameters is constructed for channel flows, which is structurally analogous and comparable in accuracy to the Trettel–Larsson velocity transformation. This new transformation can potentially serve as a wall model for energy equations to accurately predict the enthalpy or temperature in compressible turbulence.

[Phys. Rev. Fluids 11, 084608] Published Mon Aug 17, 2026

Author(s): Charlie J. Lloyd and Robert M. Dorrell

The offshore wind industry is expanding in deep, seasonally stratified waters, where infrastructure-induced mixing may alter ocean dynamics and ecosystems. We present the first fully structure-resolved direct numerical simulations of stratified flow past a vertical cylinder as an idealized model for flow interactions with offshore wind foundations. We identify two distinct wake regimes: a weakly stratified regime characterized by a narrow turbulent wake, and a strongly stratified regime characterized by thermocline-spanning recirculation cells and stationary internal waves, providing a new mechanism for far-field energy transport and a possible explanation for wake persistence discrepancies.

[Phys. Rev. Fluids 11, 084802] Published Mon Aug 17, 2026

Author(s): Schahin Akbari, Mostafa Noori, Yongqi Wang, and Martin Oberlack

This study investigates nonaxisymmetric shape oscillations of an inviscid droplet. A highly accurate Galerkin framework is extended to fully three-dimensional droplet oscillations, and modal coupling is examined for different initial configurations, beginning with four nonaxisymmetric initial shapes (see Figure). The results show that the droplet keeps the symmetries of its initial shape and velocity throughout the oscillation. Only those modes that exhibit all symmetries of the initial configuration are excited. Conversely, modes which violate the symmetries are not excited.

[Phys. Rev. Fluids 11, 083602] Published Fri Aug 14, 2026