Latest papers in fluid mechanics

Experiments and reduced order modeling of symmetry breaking in Rayleigh-Taylor mixing

Physical Review Fluids - Mon, 10/30/2023 - 10:00

Author(s): Mohammadjavad Mohammadi, Mohammad Khalifi, Nasser Sabet, and Hassan Hassanzadeh

We report the observation of asymmetrical fingering instabilities unfolding across an upward-moving dissolution interface while downward fingers also evolve. We tackled complexities characterized by large viscosity ratios (M) and Rayleigh (Ra) numbers - phenomena often challenging to replicate experimentally and simulate numerically. We present our Rayleigh-Taylor mixing experiments conducted at a substantial viscosity ratio (M≈5×105) and high Rayleigh numbers (Ra~105−3×106). Our experiments have confirmed the emergence of asymmetric growth in fingering instabilities along an upward-moving interface, accompanied by significant downward finger evolution.

[Phys. Rev. Fluids 8, 103504] Published Mon Oct 30, 2023

Strongly superadiabatic and stratified limits of compressible convection

Physical Review Fluids - Mon, 10/30/2023 - 10:00

Author(s): John Panickacheril John and Jörg Schumacher

We identify the limit behaviors of fully compressible convection going beyond the anelastic and Boussinesq approximations. This is done in terms of the governing parameters, the dissipation number and the superadiabaticity. We demonstrate the asymmetry between the top and bottom boundary layers with respect to these parameters; other results include the common characteristics of compressible convection despite seemingly different physical conditions. Finally we show that Mach number alone is inadequate to elucidate the complex system and more importantly, the strongly stratified case has features that resemble solar surface convection.

[Phys. Rev. Fluids 8, 103505] Published Mon Oct 30, 2023

Transition from wall modes to multimodality in liquid gallium magnetoconvection

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

Author(s): Yufan Xu (徐宇凡), Susanne Horn (苏珊娜 · 霍恩), and Jonathan M. Aurnou (乔纳森 · 奥诺)

Revealing insights into liquid metal magnetoconvection: Our study delves into the dynamics of Rayleigh-Baposenard convection within liquid gallium under the influence of a vertical magnetic field. Employing a combination of laboratory experiments and numerical simulations, we elucidate the transitions and heat transfer phenomena within this complex system. This investigation not only enhances our understanding of magnetoconvection from convective onset to supercriticality, but also provides a close comparison with liquid metal rotating convection.

[Phys. Rev. Fluids 8, 103503] Published Fri Oct 27, 2023

Data-driven modeling for drop size distributions

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

Author(s): T. Traverso, T. Abadie, O. K. Matar, and L. Magri

High-fidelity multiphase fluid dynamics data are scarce and expensive. We propose a Bayesian data-driven method to predict the drop size distribution of a liquid jet from sparse measurements. The proposed method provides uncertainty estimation, and it can be used for the optimal design of experiments.

[Phys. Rev. Fluids 8, 104302] Published Fri Oct 27, 2023

Multiscale analysis of a very long wind turbine wake in an atmospheric boundary layer

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

Author(s): Fengshun Zhang, Xiaolei Yang, and Guowei He

In this work, we investigate the dynamics of very long wind turbine wakes (up to 215 rotor diameters), which includes the entire wake recovery process, for three ground surface roughness lengths. The focus is on how the flow structures of different scales vary as they pass through a wind turbine and travel to further downwind locations. Particularly, we examine the energy density in scale space and its evolution in the streamwise direction, providing insights into the range of scales influenced by a wind turbine and its wake.

[Phys. Rev. Fluids 8, 104605] Published Fri Oct 27, 2023

Hard-constrained neural networks for modeling nonlinear acoustics

Physical Review Fluids - Wed, 10/25/2023 - 11:00

Author(s): Defne E. Ozan and Luca Magri

In this work, we model acoustic and thermoacoustic pressure and velocity oscillations from synthetic data. The synthetic data captures the rich nonlinear behavior of thermoacoustic oscillations observed in propulsion and power generation. We develop acoustic neural networks, in which prior physical knowledge is embedded as both soft and hard constraints. We predict and extrapolate in time thermoacoustic oscillations, reconstruct pressure and velocity over the entire domain from pressure sensors only, and obtain a model that is robust to noise and generalizable to unseen scenarios.

[Phys. Rev. Fluids 8, 103201] Published Wed Oct 25, 2023

Microfluidic elongation of viscous droplets at vanishing interfacial tension

Physical Review Fluids - Wed, 10/25/2023 - 11:00

Author(s): Thomas Cubaud

The dynamic response of viscous droplets to a sudden change of interfacial tension with the external phase is systematically examined in microchannels. A two-step hydrodynamic focusing section is employed to continuously generate high-viscosity oil droplets in immiscible alcohols at the first junction and inject droplets into miscible alcohol phases at the second junction. Upon entering stratifications, droplets are seen to strongly elongate depending on fluid properties and flow conditions. Functional relationships are developed to characterize droplet dynamics in a variety of solvents and examine out-of-equilibrium behavior of ternary systems at short-time scales.

[Phys. Rev. Fluids 8, 104201] Published Wed Oct 25, 2023

Observation of inertia-gravity wave attractors in an axisymmetric enclosed basin

Physical Review Fluids - Wed, 10/25/2023 - 11:00

Author(s): Corentin Pacary, Thierry Dauxois, Evgeny Ermanyuk, Pascal Metz, Marc Moulin, and Sylvain Joubaud

The peculiar reflection of internal waves in rotating stratified fluids enables the concentration of energy on a limit cycle, called an attractor. In this work, the existence of internal gravity wave attractors for rotating stratified fluids is predicted in three-dimensional axisymmetric geometry. This information is used to design experiments using a truncated conical shaped tank in order to form an inertia-gravity waves attractor. We highlight an important difference in the nonlinear regime between the stratification-only and the rotation-only cases.

[Phys. Rev. Fluids 8, 104802] Published Wed Oct 25, 2023

Wavelet-based modeling of subgrid scales in large-eddy simulation of particle-laden turbulent flows

Physical Review Fluids - Tue, 10/24/2023 - 11:00

Author(s): M. Hausmann, F. Evrard, and B. van Wachem

In this paper, we present a model for large eddy simulations (LES) which reconstructs the unresolved subgrid-scale velocity, by representing it with wavelet basis functions. Exploiting the compact support of the wavelet basis, accurate statistically inhomogeneous and anisotropic subgrid-scale velocity statistics can be generated. We apply the model to LES of single-phase and particle-laden turbulent flows. The generated subgrid-scale velocity possesses the correct characteristic features of turbulence, such as the correct spatial correlations, and improves the description of the behavior of particle clustering and the particle pair dispersion, which are poorly predicted in classical LES.

[Phys. Rev. Fluids 8, 104604] Published Tue Oct 24, 2023

Analysis of anisotropic subgrid-scale stress for coarse large-eddy simulation

Physical Review Fluids - Mon, 10/23/2023 - 11:00

Author(s): Kazuhiro Inagaki (稲垣 和寛) and Hiromichi Kobayashi (小林 宏充)

This study discusses the necessity of anisotropic subgrid-scale (SGS) stress separated from the energy transfer in large-eddy simulations (LESs). We investigate the budget equation for grid-scale (GS) Reynolds stress in turbulent channel flows. The anisotropic stress has a large and nondissipative contribution to the streamwise and spanwise components of GS Reynolds stress when the filter size is large. The positive contribution is prominent at a scale consistent with the spacing of streaks in the near-wall region. Therefore, we infer that anisotropic stress contributes to the generation mechanism of coherent structures, which is key to further improving SGS models.

[Phys. Rev. Fluids 8, 104603] Published Mon Oct 23, 2023

Thermorelaxing multicomponent flows investigated with a Baer-Nunziato-type model

Physical Review E - Fri, 10/20/2023 - 11:00

Author(s): Chao Zhang and Lifeng Wang

In inertial confinement fusion (ICF) implosions, mixing the ablator into the fuel and the hot spot is one of the most adverse factors that lead to ignition degradation. Recent experiments in the Marble campaign at the Omega laser facility and the National Ignition Facility demonstrate the significan…

[Phys. Rev. E 108, 045108] Published Fri Oct 20, 2023

Elastic hoops jumping on water

Physical Review Fluids - Fri, 10/20/2023 - 11:00

Author(s): Han Bi Jeong, Ji-Sung Park, Eunjin Yang, Yunsuk Jeung, Juliette Amauger, and Ho-Young Kim

Elastic hoops can jump on water by harnessing the reaction force from water’s form drag, much like fishing spiders. These artificial jumpers allow us to mathematically understand the drag-based water jumps, which can achieve greater velocities than the surface-tension-based jumps seen in water striders and springtails.

[Phys. Rev. Fluids 8, 100503] Published Fri Oct 20, 2023

Droplets sliding on single and multiple vertical fibers

Physical Review Fluids - Thu, 10/19/2023 - 11:00

Author(s): M. Leonard, J. Van Hulle, F. Weyer, D. Terwagne, and N. Vandewalle

Exploring droplet dynamics: This study sheds light on the behavior of droplets sliding down vertical fibers, a key issue in microfluidics and fog harvesting. Using real-time tracking, the research covers single and multi-fiber systems. A standout finding is that multiple vertical fibers increase droplet speed but also lead to greater liquid loss in grooves. This discovery is captured in a detailed theoretical model, offering valuable insights for optimizing droplet-based technologies.

[Phys. Rev. Fluids 8, 103601] Published Thu Oct 19, 2023

Oscillating Taylor bubble during the emptying of a partially filled water bottle

Physical Review E - Wed, 10/18/2023 - 11:00

Author(s): Olivier Praud, Cyril Vettorello, and Véronique Roig

The oscillatory behavior observed during the emptying of a vertical cylinder partially filled with water has been studied for large neck-to-bottle diameter ratios, d*. For large apertures (d*>0.8), a Taylor bubble invades the cylinder from the bottom, and its rising speed exhibits periodic oscill…

[Phys. Rev. E 108, 045107] Published Wed Oct 18, 2023

Viscoelastic jet instabilities studied by direct numerical simulations

Physical Review Fluids - Tue, 10/17/2023 - 11:00

Author(s): Mateus C. Guimarães, Fernando T. Pinho, and Carlos B. da Silva

The evolution of inertio-elastic shear-layer and jet-column instabilities of submerged jets of viscoelastic polymer solutions is studied by direct numerical simulation. At high Reynolds numbers, viscoelasticity has a destabilizing effect in the linear region of perturbation growth, but stabilizes the jet perturbations at the nonlinear regime. Two competing instability mechanisms are identified and analyzed in order to explain the observed results for the different regimes.

[Phys. Rev. Fluids 8, 103301] Published Tue Oct 17, 2023

Experimental evidence of random shock-wave intermittency

Physical Review E - Mon, 10/16/2023 - 11:00

Author(s): Guillaume Ricard and Eric Falcon

We report the experimental observation of intermittency in a regime dominated by random shock waves on the surface of a fluid. We achieved such a nondispersive surface-wave field using a magnetic fluid subjected to a high external magnetic field. We found that the small-scale intermittency of the wa…

[Phys. Rev. E 108, 045106] Published Mon Oct 16, 2023

High-fidelity model of the human heart: An immersed boundary implementation

Physical Review Fluids - Mon, 10/16/2023 - 11:00

Author(s): Francesco Viola, Giulio Del Corso, and Roberto Verzicco

We present a multi–physics computational model of the human heart accounting for the electrophysiology, elasto-mechanics, and hemodynamics, including their complex interactions. The model is accurate and computationally efficient and, thanks to the implementation on GPU architectures, it allows cardiovascular simulations of physiologic and pathologic configurations within a time–to–solution compatible with clinical practice. Results are shown for healthy conditions and for myocardial infarction with the aim of assessing the reliability and predictive capabilities of the model which can be used to anticipate the outcome of surgical procedures or support clinical decisions.

[Phys. Rev. Fluids 8, 100502] Published Mon Oct 16, 2023

Acoustic tokamak with strongly coupled toroidal bubbles

Physical Review E - Fri, 10/13/2023 - 11:00

Author(s): A. Caumont, O. Stephan, E. Bossy, B. Dollet, C. Quilliet, and P. Marmottant

Gas bubbles stabilized in toroidal 3D-printed cages are good acoustic resonators with an unusual topology. We arrange them in a circular array to obtain what we call an “acoustic tokamak” because of the torus shape of the whole array. We demonstrate experimentally and theoretically that the system f…

[Phys. Rev. E 108, 045105] Published Fri Oct 13, 2023

Polymer diffusive instability leading to elastic turbulence in plane Couette flow

Physical Review Fluids - Fri, 10/13/2023 - 11:00

Author(s): Miguel Beneitez, Jacob Page, and Rich R. Kerswell

Elastic turbulence is a chaotic flow state observed in dilute polymer solutions in the absence of inertia. In this paper we show that an infinitesimal amount of polymer diffusion gives raise to a new wall-mode instability. This instability leads to chaotic dynamics in inertialess Couette flow. This new instability might provide a generic transition pathway to elastic and elasto-inertial turbulence.

[Phys. Rev. Fluids 8, L101901] Published Fri Oct 13, 2023

Pitch perturbation effects on a revolving wing at low Reynolds number

Physical Review Fluids - Thu, 10/12/2023 - 11:00

Author(s): Shantanu S. Bhat, Soudeh Mazharmanesh, Albert Medina, Fang-Bao Tian, John Young, Joseph C. S. Lai, and Sridhar Ravi

Motivated by the potential impact of unsteady kinematics on small turbomachines and propellers, we examine a revolving wing subjected to pitch perturbations. Through experiments and numerical analysis, we find that the wing’s performance during perturbations is mainly influenced by the pitch-rotation velocity and mean angle of attack. Beyond a certain perturbation amplitude, the stable leading-edge vortex that forms on a revolving wing becomes unstable, significantly altering wing-surface pressures. Our study demonstrates that rotational effects dominate the resulting wing performance when the flow structures around the wing are destabilized.

[Phys. Rev. Fluids 8, 104701] Published Thu Oct 12, 2023


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