Latest papers in fluid mechanics

Analysis of coupled energy and helicity spectra in stratified turbulence: Theory and balloon measurements

Physical Review Fluids - Wed, 03/06/2024 - 10:00

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

Turbulence enhancement in body force opposed flows

Physical Review Fluids - Tue, 03/05/2024 - 10:00

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

Transported filtered density function in self-adaptive turbulence eddy simulation

Physical Review Fluids - Mon, 03/04/2024 - 10:00

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

Parametric study of the dispersion of inertial ellipsoidal particles in a wave-current flow

Physical Review Fluids - Mon, 03/04/2024 - 10:00

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

Turbulence statistics and transport in compressible mixing driven by spherical implosions with narrowband and broadband initial perturbations

Physical Review Fluids - Mon, 03/04/2024 - 10:00

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

Drop encapsulation and bubble bursting in surfactant-laden flows in capillary channels

Physical Review Fluids - Fri, 03/01/2024 - 10:00

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

Effects of the Saffman lift force on particle statistics and turbulence modulation in two-phase flow

Physical Review Fluids - Fri, 03/01/2024 - 10:00

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

Experimental study of a helical acoustic streaming flow

Physical Review Fluids - Thu, 02/29/2024 - 10:00

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

High-fidelity reconstruction of large-area damaged turbulent fields with a physically constrained generative adversarial network

Physical Review Fluids - Thu, 02/29/2024 - 10:00

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

Stable, entropy-consistent, and localized artificial-diffusivity method for capturing discontinuities

Physical Review Fluids - Thu, 02/29/2024 - 10:00

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

Capillary imbibition of shear-thinning fluids: From Lucas-Washburn to oscillatory regimes

Physical Review Fluids - Wed, 02/28/2024 - 10:00

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

Hysteresis and ribbons in Taylor-Couette flow of a semidilute noncolloidal suspension

Physical Review Fluids - Wed, 02/28/2024 - 10:00

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

Spherical thermal counterflow of superfluid $^{4}\mathrm{He}$

Physical Review Fluids - Wed, 02/28/2024 - 10:00

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

Viscoplastic rimming flow inside a rotating cylinder

Physical Review Fluids - Tue, 02/27/2024 - 10:00

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

Neighbor-induced unsteady force in the interaction of a cylindrical shock wave with an annular particle cloud

Physical Review Fluids - Tue, 02/27/2024 - 10:00

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

Grid-generated velocity fields at very small Reynolds numbers

Physical Review Fluids - Tue, 02/27/2024 - 10:00

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

Artificially thickened boundary layer turbulence due to trip wires of varying diameter

Physical Review Fluids - Mon, 02/26/2024 - 10:00

Author(s): Zhanqi Tang, Nan Jiang, Zhiming Lu, and Quan Zhou

Tripping effects are studied in artificially thickened turbulent boundary layers (AT-TBLs) within a finite-length test section. The emergence of the generated large-scale structures highlights the potential of the AT-TBLs to simulate high-Reτ boundary layer turbulence. We examine the noncanonical behaviors and external similarity under over-tripped conditions. The results emphasize the need for caution when pursuing excessive thickening of the boundary layer through leading-edge trips for generating high-Reτ canonical TBLs in a finite-length test section.


[Phys. Rev. Fluids 9, 024606] Published Mon Feb 26, 2024

Superflow passing over a rough surface: Vortex nucleation

Physical Review Fluids - Mon, 02/26/2024 - 10:00

Author(s): Thomas Frisch, Sergey Nazarenko, and Sergio Rica

The dynamics of a superfluid over a surface exhibits significant differences from compressible flow in ordinary fluids. In ordinary fluids, when the local speed exceeds the sound speed, intrinsic dissipation due to viscosity can enable a shock wave. However, in superfluids, lack of dissipation prevents shock waves. Instead, spatial modulation of a wave train of solitons, as in the figure, allows for a smooth transonic transition. This wave train has been observed to eventually become unstable, leading to quantized vortices and an effective drag on a rough surface. The wave train occurs beneath a lambda-shaped structure with a fore and back-front, reminiscent of ordinary compressible fluids.


[Phys. Rev. Fluids 9, 024701] Published Mon Feb 26, 2024

Impact of hydraulic tortuosity on microporous and nanoporous media flow

Physical Review E - Fri, 02/23/2024 - 10:00

Author(s): Shiwani Singh

Using two-dimensional porous structures made up of homogeneously arranged solid obstacles, we examine the effects of rarefaction on the hydraulic tortuosity in the slip and early transition flow regimes via extended lattice Boltzmann method. We observed that modification in either the obstacle's arr…


[Phys. Rev. E 109, 025106] Published Fri Feb 23, 2024

Measurement of an eddy diffusivity for chaotic electroconvection using combined computational and experimental techniques

Physical Review Fluids - Fri, 02/23/2024 - 10:00

Author(s): Arunraj Balaji-Wright, Felix Stockmeier, Richard Dunkel, Matthias Wessling, and Ali Mani

The Poisson-Nernst-Planck-Stokes equations capture the chaotic dynamics of electroconvection accurately, but direct numerical simulation of electroconvection is prohibitively expensive. Furthermore, prediction of the mean fields via application of Reynolds averaging leads to a closure problem. In this work, we combine the macroscopic forcing method, a numerical technique for measurement of closure operators in Reynolds-averaged equations, with high-fidelity experimental data in order to determine a leading order closure for chaotic electroconvection. Simulations of the Reynolds-averaged equations using the leading order closure accurately predict experimental polarization curves.


[Phys. Rev. Fluids 9, 023701] Published Fri Feb 23, 2024

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