New Papers in Fluid Mechanics

Author(s): Adrien Lefauve and Miles M. P. Couchman

Our understanding of fluid turbulence has traditionally relied on a few canonical laboratory experiments. In this paper, we present a relatively new canonical experiment, the stratified inclined duct, whose density stratification allows for the study of coherent and intermittent states at higher Reynolds numbers than in unstratified flows. Applying a novel data-driven technique to a large experimental database of shadowgraph visualizations, we automatically identify distinct turbulent states and transitions between them, paving the way for the reduced-order modeling of stratified turbulence.

[Phys. Rev. Fluids 9, 034603] Published Fri Mar 08, 2024

Author(s): Gopal Verma, Ashwini Kumar, Sapna Soni, Kapil Yadav, and Wei Li

We introduce a pump-probe laser setup to explore the interaction of light momentum and fluid mechanics in a two-layer liquid system. Creating a nanometric bulge in the upper layer reveals a transient bulge on the liquid-liquid interface propelled by viscous stress towards the higher refractive index liquid. Noninvasive measurements and numerical simulations validate our findings, unraveling the intricate interplay between light momentum theories (Minkowski and Abraham) and fluid mechanics. The transient deformation height serves as a precise indicator of surface tension and viscosity, enabling nanoscale manipulation with potential applications in sensors, actuators, and optical devices.

[Phys. Rev. Fluids 9, 034801] Published Fri Mar 08, 2024

Author(s): Jianyi Zheng, Yu Guan, Liangliang Xu, Xi Xia, Larry K. B. Li, and Fei Qi

We explore the vortical interactions in a swirling combustion system via the construction of time-varying weighted spatial turbulence networks whose node strength distribution is derived from the Biot-Savart law. We find widespread evidence of scale-free topology in the vortical networks, with the most coherent flow structures acting as the primary network hubs. Crucially, we find that even after the onset of thermoacoustic instability, the scale-free topology can persist continuously in time, contrary to some suggestions from the literature. This discovery could have important implications for the design of flow controllers that rely on destroying the primary hubs of vortical networks.

[Phys. Rev. Fluids 9, 033202] Published Thu Mar 07, 2024

Author(s): Enwei Zhang, Zhan Wang, and Qingquan Liu

This study focuses on the turbulent channel flow over three-dimensional wavy walls. Through temporal-spatial averaging decomposition, the momentum flux and kinetic energy transfers by mean, time-averaged, dispersive, and turbulent motions are revealed. We find a notable correlation between dispersive shear stress and vorticity enhancement. Another finding is that the dispersion-turbulence exchange significantly contributes to turbulent kinetic energy production.

[Phys. Rev. Fluids 9, 034602] Published Thu Mar 07, 2024

Author(s): Niklas Dusch, Victor Avsarkisov, Michael Gerding, Claudia Stolle, and Jens Faber

In this study, we evaluate the effect of kinetic helicity on the slope of the vertical spectrum of kinetic energy in stratified turbulence. Our theoretical approach allows us to define energy-dominated, helicity-dominated, and joint dual cascade regimes in turbulent flows at various stratification rates. Some of them are verified with the balloon measurements from the Troposphere and Lower Stratosphere. To summarize, one of the conclusions of this work states that domination of helicity flattens the spectrum while an increase in the stratification makes it steeper.

[Phys. Rev. Fluids 9, 033801] Published Wed Mar 06, 2024

Author(s): S. Jackson and S. He

Idealized nonuniform body force profiles are used to explain the root cause of turbulence enhancement in various physical flows encountered within such fields as mixed convection, magnetohydrodynamics, and flow control. A recent theory used to explain laminarization is extended to include turbulence enhancement and it is demonstrated that turbulence enhancement can be explained by an increased “apparent Reynolds number”.

[Phys. Rev. Fluids 9, 034601] Published Tue Mar 05, 2024

Author(s): Yuxuan Chen, Tianwei Yang, Hua Zhou, Xingsi Han, and Zhuyin Ren

Theoretical and numerical exploration of the transported Filtered Density Function (FDF) in the framework of Self-Adaptive Turbulence Eddy Simulation (SATES) was conducted, encompassing fundamental definitions and a model for the scalar mixing timescale. To address the model inconsistency in terms of the scalar mixing timescale between RANS and LES modes, a novel model was proposed. Subsequently, a posteriori testing showcased the merits of this novel approach, highlighting its potential to be employed in SATES-FDF simulations of turbulent reacting flows.

[Phys. Rev. Fluids 9, 033201] Published Mon Mar 04, 2024

Author(s): Laura K. C. Sunberg, Michelle H. DiBenedetto, Nicholas T. Ouellette, and Jeffrey R. Koseff

The extent to which particles such as larvae, seagrass pollen, and microplastics are dispersed by waves and currents has many ecological impacts. Here, we systematically examine the effect of a comprehensive set of parameters on the dispersion of ellipsoidal particles in a wave-current flow using a numerical computation approach. Our results show that all of the parameters considered have some effect on the particle dispersion, but that the settling-wave timescale ratio has the greatest effect.

[Phys. Rev. Fluids 9, 034302] Published Mon Mar 04, 2024

Author(s): Moutassem El Rafei and Ben Thornber

We investigate compressible turbulent mixing evolving in spherical implosions with differing initial conditions using high-resolution implicit large eddy simulations. We examine in detail temporal and spatial turbulent transport budgets including density self-correlation, turbulent mass flux, and turbulent kinetic energy. This analysis provides improved understanding of the mixing process initiated by Richtmyer-Meshkov and Rayleigh-Taylor instabilities including quantification of contributions to asymmetries in the mixing layer and numerical dissipation.

[Phys. Rev. Fluids 9, 034501] Published Mon Mar 04, 2024

Author(s): P. Pico, L. Kahouadji, S. Shin, J. Chergui, D. Juric, and O. K. Matar

In this investigation, we dive into the phenomenon of drop encapsulation in elongated bubbles travelling through liquid-filled capillary channels in the presence of surface-active material. Our numerical results reveal that complex interactions between surfactant parameters, Marangoni stresses, viscosity, and inertia are responsible for dramatically altering the pinch-off times, along with the number, size, and velocity of the encapsulated drops. We summarize these interactions in three distinct encapsulation morphological regimes, providing a structured overview of the underlying dynamics.

[Phys. Rev. Fluids 9, 034001] Published Fri Mar 01, 2024

Author(s): Jinchi Li, Ping Wang, and Xiaojing Zheng

The Saffman force is one of the key factors for particle transport and hence the interaction among phases in two-phase wall-bounded turbulence. This numerical work finds that the accumulation of particles near the wall and preferential concentration in low-speed streaks are suppressed by the lift force, leading to destruction of the conditional hairpin vortices and decreasing velocity fluctuations near the wall. However, in the outer layer, the particle-turbulence interaction is increased by the lift force because of higher particle concentration.

[Phys. Rev. Fluids 9, 034301] Published Fri Mar 01, 2024

Author(s): Bjarne Vincent, Sophie Miralles, Daniel Henry, Valéry Botton, and Alban Pothérat

The acoustofluidic helix stirs fluid within a closed container efficiently with only one ultrasound source. The helical shape is obtained by reflecting the acoustic beam on the cavity walls. This acoustic forcing drives multiple descending jets, each impinging a vertical wall and wrapping around the central axis. Time-averaged and low-frequency unsteady flow structures have been obtained by three-dimensional particle tracking velocimetry and Eulerian field reconstructions. Both the velocity amplitudes of the overall time-averaged flow, and the vortex dynamics, depend on the dimensionless acoustic force magnitude called the acoustic Grashof number.

[Phys. Rev. Fluids 9, 024101] Published Thu Feb 29, 2024

Author(s): Qinmin Zheng, Tianyi Li, Benteng Ma, Lin Fu, and Xiaomeng Li

In this work, we propose a novel framework for the high-fidelity reconstruction of large-area damaged turbulent fields with high resolution based on a physically constrained generative adversarial network. The network leverages complete/sparse fields of velocity components as physical constraints and adopts a PatchGAN discriminator network. The proposed reconstruction framework has been shown to achieve excellent reconstruction performance. The reconstructed flow fields are consistent with the raw flow fields in terms of magnitude, power spectrum, and two-point correlation function.

[Phys. Rev. Fluids 9, 024608] Published Thu Feb 29, 2024

Author(s): Suhas S. Jain, Rahul Agrawal, and Parviz Moin

A localized artificial-diffusivity method is developed for capturing discontinuities, such as shocks and contacts, in compressible flows. A new sensor for contact discontinuity makes the method more localized, and a discretely consistent formulation eliminates the need for filtering the solution or filtering the sensors to obtain robust solutions. Improved predictions are observed in canonical shock-tube problems and large-eddy simulations of homogeneous isotropic turbulence.

[Phys. Rev. Fluids 9, 024609] Published Thu Feb 29, 2024

Author(s): Camille Steinik, Davide Picchi, Gianluca Lavalle, and Pietro Poesio

We studied the filling dynamics of a shear-thinning fluid in a capillary tube. In regimes where inertial effects can be neglected, we generalize the Lucas-Washburn scaling relation to shear-thinning fluids, showing that the classical 1/2 scaling law holds only if an ad hoc time-dependent effective viscosity that applies to both Newtonian and shear-thinning fluids is introduced. In regimes where inertia competes with viscous and gravity effects, the system shows an oscillating behavior. The shear-thinning effect acts on the system, favoring such oscillating behavior.

[Phys. Rev. Fluids 9, 023305] Published Wed Feb 28, 2024

Author(s): Changwoo Kang, Michael F. Schatz, and Parisa Mirbod

Flow states in dispersed particle flow determine the performance in industrial applications such as chemical mixers and bioreactors. Hysteresis in flow transitions can modify the flow condition and thus can affect the efficiency. We numerically show hysteretic behaviors in the Taylor-Couette flow of a noncolloidal suspension with a rotating inner cylinder and a stationary outer one. We also examine a standing wave of weak counterrotating vortices, known as ribbons, that occurs as the primary instability.

[Phys. Rev. Fluids 9, 023901] Published Wed Feb 28, 2024

Author(s): F. Novotný, Y. Huang, J. Kvorka, Š Midlik, D. Schmoranzer, Z. Xie, and L. Skrbek

Spherically symmetric thermal counterflow of superfluid 4He driven by a central heater is unaffected by shear thanks to the absence of walls. This quantum flow displays a two-fluid behavior and upon increasing drive undergoes a complex process of transition to quantum turbulence that involves formation of normal fluid turbulence above a certain critical threshold, drawing energy from a preexisting random tangle of quantized vortices. Spherically symmetric thermal counterflow can serve as a model flow for cosmological phenomena relating cosmic strings to quantized vortices, for processes occurring in neutron stars, or cosmological structure formation within superfluid models of dark matter.

[Phys. Rev. Fluids 9, L022601] Published Wed Feb 28, 2024

Author(s): Thomasina V. Ball and Neil J. Balmforth

When a small fraction of viscoplastic fluid is placed into a rotating cylinder, steady states can be reached with pool at the bottom of the cylinder and a residual coating elsewhere. Lubrication theory used to model the film thickness builds on previous models by bridging between two asymptotic limits, incorporating both the gravitational force along the cylinder and the hydrostatic pressure gradients. The model predicts steady states are reached after a small number of rotations and allows exploration of drainage when the cylinder comes to a halt. Experiments using a Carbopol suspension provide a suitable comparison to test the thin film theory.

[Phys. Rev. Fluids 9, 023304] Published Tue Feb 27, 2024

Author(s): Sam Briney, Andreas N. Osnes, Magnus Vartdal, Thomas L. Jackson, and S. Balachandar

A shock propagating through a cloud of particles results in highly unsteady forces on each particle in the cloud. In such a finite particle volume fraction scenario, reflected shocks from neighboring particles perturb the force on each particle from its value in the dilute limit. These forces have a delayed onset since the reflected shocks travel at finite speeds. This phenomenon is explored in detail using three-dimensional particle resolved simulations and a model is proposed to account for the unsteady nature of these forces.

[Phys. Rev. Fluids 9, 024308] Published Tue Feb 27, 2024

Author(s): Dana Duong and Stavros Tavoularis

This article is the first to investigate velocity fields behind grids at very small Reynolds numbers that include flows with negligible fluctuations. Measurements were taken behind four square-mesh grids with varying designs, mesh sizes and solidities. We have documented and quantified the weakening of turbulent behavior as the Reynolds number diminishes and identified trends and patterns of the large- and small-scale anisotropies, the skewness and flatness factors of the velocity derivative and the dissipation parameter that have not been reported previously.

[Phys. Rev. Fluids 9, 024607] Published Tue Feb 27, 2024