Latest papers in fluid mechanics

Study of the vortex structure in compressible wall-bounded turbulence

Physical Review Fluids - Wed, 12/06/2023 - 10:00

Author(s): Tianyi Bai, Cheng Cheng, Kevin P. Griffin, Xinliang Li, and Lin Fu

Compressible turbulent channel flows exhibit a multitude of vortex structures dispersed throughout the boundary layer. Although the structural similarity between compressible and incompressible flows has been well established, most of these observations are concluded through merely visualizations of instantaneous fields. We dissect the statistical features of vortices in compressible channel flows comprehensively and show a quantitative consistency with incompressible flows by applying semi-local scaling. This work fills a gap in our knowledge about vortex structures in compressible channel flows and first applies Morkovin’s hypothesis to statistics of instantaneous vortex features.


[Phys. Rev. Fluids 8, 124603] Published Wed Dec 06, 2023

Estimates of mode-1 internal tide harmonic generation in the global ocean

Physical Review Fluids - Wed, 12/06/2023 - 10:00

Author(s): Scott Wunsch and F. Joseph Marcellino

Internal waves play an important role in the dynamics of the ocean. When propagating in vertically varying stratification, they generate harmonic modes through a nonlinear effect. In this work, measured ocean stratification profiles are analyzed to estimate the propensity of oceanic internal tides to exhibit this effect. As seen in the figure, nonlinear harmonic generation could plausibly occur in the Equatorial Indo-Pacific, but not elsewhere, in the global ocean.


[Phys. Rev. Fluids 8, 124801] Published Wed Dec 06, 2023

Investigation of the influence of the dimensionless centrifugal work number on spanwise rotating channel low-speed compressible flow

Physical Review Fluids - Wed, 12/06/2023 - 10:00

Author(s): Junxin Che, Ruquan You, Fei Zeng, Haiwang Li, Wenbin Chen, and Zhi Tao

We introduce a novel dimensionless parameter, termed the centrifugal work number, which is derived from the rotational energy equation. This parameter quantifies the ratio of centrifugal force work to gas enthalpy in the flow within rotating channels. Large eddy simulation was employed to validate the influence of this parameter on rotating channel flow. The flow similarity theory considering the fluid compression characteristics inside the rotating channel has been established.


[Phys. Rev. Fluids 8, L121401] Published Wed Dec 06, 2023

Interaction between trefoil knotted flame and vortex

Physical Review Fluids - Tue, 12/05/2023 - 10:00

Author(s): Yunde Su (苏运德) and Yue Yang (杨越)

We present a novel three-dimensional configuration for the numerical study of the flame-vortex interaction. The premixed flame is initially located within a vortex tube with the same trefoil knotted centerline, and it propagates outward and interacts with the knotted vortex tube. This configuration allows the study of flame extinction, flame-flame interaction, and suppression of the vortex reconnection. Using direct numerical simulations, we show that the asymmetric flame propagation along the vortex axis generates helicity, and the baroclinic effect arising from the misalignment between the local density gradient and nonlocal pressure gradient flattens the vortex/flame tubes.


[Phys. Rev. Fluids 8, 123201] Published Tue Dec 05, 2023

Subcritical transition to turbulence triggered by a magnetic dynamo

Physical Review Fluids - Tue, 12/05/2023 - 10:00

Author(s): F. Daniel, L. Petitdemange, and C. Gissinger

The numerical simulations reported here show that the significant slowdown of many stars can be understood as a subcritical transition to turbulence. It is sustained by a nonlinear mechanism involving the emergence of a strong magnetic field in the radiative region of stars. This turbulence provides a new source of angular momentum transport that persists at very low differential shear, arbitrarily far from any hydrodynamic instability. This scenario is captured by a simple nonlinear model that provides a general description of the transition to turbulence in astrophysical flows, as long as it involves competition between a large-scale magnetic field and a small-scale magnetic instability.


[Phys. Rev. Fluids 8, 123701] Published Tue Dec 05, 2023

Integral relation in zero-pressure-gradient boundary layer flows

Physical Review Fluids - Tue, 12/05/2023 - 10:00

Author(s): Tie Wei and Joseph Klewicki

A precise relationship between the boundary layer edge velocity components, Ue and Ve, and the friction velocity, uτ, is derived from the integral of the continuity and momentum equations for flow over a flat plate. This relationship is validated using experimental and numerical data across a wide range of Reynolds numbers. At higher Reynolds numbers, the integral relation can be approximated as UeVe/uτ2≈H12, where H12 represents the shape factor.


[Phys. Rev. Fluids 8, 124601] Published Tue Dec 05, 2023

Wall shear stress and wall heat flux in a supersonic turbulent boundary layer subjected to concave surface curvature

Physical Review Fluids - Tue, 12/05/2023 - 10:00

Author(s): Fulin Tong (童福林), Junyi Duan (段俊亦), Xiangxin Ji (纪相鑫), Siwei Dong (董思卫), Xianxu Yuan (袁先旭), and Xinliang Li (李新亮)

Compressible turbulent boundary layers over concave surface curvature are of major interest in the design of high-speed aircraft and propulsion systems. In this work, we investigate the effect of longitudinal concave surface curvature on the statistical and structural properties of the fluctuating wall shear stress and wall heat flux, including probability density function, space-time correlations, and frequency spectra. We also quantitatively demonstrate that the significantly energized outer large-scale structures make an increasingly important contribution to the mean wall shear stress and wall heat flux generation.


[Phys. Rev. Fluids 8, 124602] Published Tue Dec 05, 2023

Symmetry properties and bifurcations of viscoelastic thermovibrational convection in a square cavity

Physical Review E - Fri, 12/01/2023 - 10:00

Author(s): Alessio Boaro, Gregor MacDowall, and Marcello Lappa

To fill a gap in the literature about the specific dynamics of thermovibrational flow in a square cavity filled with a viscoelastic fluid when vibrations and the imposed temperature gradient are concurrent, a parametric investigation has been conducted to investigate the response of this system over…


[Phys. Rev. E 108, 065101] Published Fri Dec 01, 2023

Statistics of inhomogeneous turbulence in large-scale quasigeostrophic dynamics

Physical Review E - Fri, 12/01/2023 - 10:00

Author(s): Anton Svirsky, Corentin Herbert, and Anna Frishman

A remarkable feature of two-dimensional turbulence is the transfer of energy from small to large scales. This process can result in the self-organization of the flow into large, coherent structures due to energy condensation at the largest scales. We investigate the formation of this condensate in a…


[Phys. Rev. E 108, 065102] Published Fri Dec 01, 2023

Effects of atmospheric stratification and jet position on the properties of early aircraft contrails

Physical Review Fluids - Thu, 11/30/2023 - 10:00

Author(s): Pierre Saulgeot, Vincent Brion, Nicolas Bonne, Emmanuel Dormy, and Laurent Jacquin

We are interested in the dilution of exhaust gases in aircraft wakes due to the combined effect of wake, mixing, and atmospheric stratification. The aim is to predict the properties of early contrails as a function of the aircraft’s main properties and the state of the atmosphere. Two-dimensional simulations of a passive scalar field representing jets under the action of wake vortices are carried out in a framework that allows a wide parametric study of aircraft and atmospheric parameters. The figure shows the evolution of vortex position (dashed lines) and ice mass (solid colors) for a B777 with a relative humidity of 140% and two atmospheric stratification conditions.


[Phys. Rev. Fluids 8, 114702] Published Thu Nov 30, 2023

Compression-driven viscous fingering in a radial Hele-Shaw cell

Physical Review Fluids - Wed, 11/29/2023 - 10:00

Author(s): Callum Cuttle, Liam C. Morrow, and Christopher W. MacMinn

The viscous-fingering instability that emerges when gas is injected into a liquid-filled Hele-Shaw cell is a paradigm of pattern formation that has been extensively studied. Here, we examine a previously neglected aspect of the problem: The compressibility of the injected gas. We use experiments, numerical simulations, and an axisymmetric model to show that gas compression controls the time-dependent injection rate and systematically delays the onset of viscous fingering at high capillary number. We quantify the importance of gas compression with a single dimensionless compressibility number.


[Phys. Rev. Fluids 8, 113904] Published Wed Nov 29, 2023

Shape-induced pairing of spheroidal squirmers

Physical Review Fluids - Mon, 11/27/2023 - 10:00

Author(s): Ruben Poehnl and William E. Uspal

We consider the conditions needed to obtain stable bound states of two spheroidal squirmers. We find that the particles must have oblate shape and non-axisymmetric distribution of surface slip in order to obtain immotile “head-to-head” pairs of identical particles. For motile “head-to-tail” pairs, the particles cannot be identical, and must satisfy certain conditions involving their self-propulsion velocities, stresslets, and shape. Overall, our results demonstrate that introducing heterogeneity in shape and interfacial actuation opens new possibilities for realizing self-organization in systems of interfacially driven microswimmers.


[Phys. Rev. Fluids 8, 113103] Published Mon Nov 27, 2023

Linear stability of thermocapillary flow in a droplet attached to a hot or cold substrate

Physical Review Fluids - Mon, 11/27/2023 - 10:00

Author(s): Lukas Babor and Hendrik C. Kuhlmann

Thermocapillary flow in droplets attached to a heated or cooled wall can undergo various hydrodynamic instabilities. In this work, we explain these instabilities by means of linear stability analysis and present their dependence on the contact angle, Prandtl number, and the heating or cooling mode of operation.


[Phys. Rev. Fluids 8, 114003] Published Mon Nov 27, 2023

Convection rolls and three-dimensional particle dynamics in merging solute streams

Physical Review Fluids - Mon, 11/27/2023 - 10:00

Author(s): Robben E. Migacz, Guillaume Durey, and Jesse T. Ault

Microparticles migrate in gradients of solute concentration through a process known as diffusiophoresis. Several classic works have examined the phenomenon in two dimensions in microfluidic devices where streams of distinct solute concentration meet. We expand on such works by considering, experimentally, numerically, and theoretically, the dynamics of fluid, solute, and particles in three dimensions. We find that diffusioosmotic flow along walls of nonzero surface charge, which yields structures we call “convection rolls,” can be significant to the dynamics.


[Phys. Rev. Fluids 8, 114201] Published Mon Nov 27, 2023

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