Physical Review Fluids

Author(s): Ram Sudhir Sharma, Wladimir Sarlin, Langqi Xing, Cyprien Morize, Philippe Gondret, and Alban Sauret

Cohesive forces occur at the particle scale and have effects up to the macroscopic scale. Using the canonical configuration of a column of grains collapsing under its own weight in air, this paper reports that a bulk description framework of cohesive effects can account for the macroscopic observations. Experiments are reported with two different cohesion sources, capillary bridges or a polymer coating, for the collapse of rectangular and cylindrical granular columns. The bulk framework is shown to capture the effects of cohesion on the final deposit for both sources of cohesion.

[Phys. Rev. Fluids 9, 074301] Published Mon Jul 15, 2024

Author(s): Axel Tassigny, Maria Eletta Negretti, and Achim Wirth

Laboratory experiments of ocean gravity currents show laminar transport supplemented by spontaneous and intermittent cascading of dense water. Statistical analysis reveals self organized criticality of the downward transport. Cascading intrusions are a major contributor of turbulence and vorticity in the ocean interior.

[Phys. Rev. Fluids 9, 074605] Published Mon Jul 15, 2024

Author(s): Subharthi Chowdhuri and Tirtha Banerjee

The verification of small-scale isotropy requires three-dimensional information of the flow field, a condition rarely satisfied in experiments. To examine this we develop a framework that considers how the presence of bursts at smaller flow scales generates turbulent kinetic energy differently between the horizontal and vertical directions. This framework can be applied both to flow fields obtained via numerical simulations, and to data from field and laboratory measurements. Moreover, a universal relationship emerges to predict small-scale anisotropy from large-scale flow conditions, thus contributing towards the development of next-generation closure models of wall turbulence.

[Phys. Rev. Fluids 9, 074604] Published Wed Jul 10, 2024

Author(s): Qiang Zhu

The dynamics and energy-harvesting performance of piezoelectric plates in oscillatory flows have been studied numerically. The simulations show that when these plates are arranged in an array with certain distance between neighbors, the average energy-harvesting capacity of each individual plate may be increased by as much as 110% within the range of parameters considered. The underlying physical mechanism has been identified as wake energy recovery - a plate in such a formation is able to extract energy from the wakes of its neighbors that will otherwise be dissipated. This finding can be used in the development of environmental-friendly soft-body wave energy harvesters.

[Phys. Rev. Fluids 9, 074101] Published Mon Jul 08, 2024

Author(s): György Tegze and Frigyes Podmaniczky

This study is establishing a new method to characterize the thermal boundary layer in turbulent Rayleigh-Bénard convection. Transition from the convection dominated bulk domain to the diffusion dominated boundary layer can be identified by extrema in the time-variation of the temperature along the fluid-parcel pathlines. We demonstrate that our method reveals the spatiotemporal structure of the boundary layer.

[Phys. Rev. Fluids 9, 074602] Published Mon Jul 08, 2024

Author(s): Masoumeh Gharaati, Shuolin Xiao, Luis A. Martínez-Tossas, Daniel B. Araya, and Di Yang

We use large-eddy simulations to study the effects of helical-shaped blades on the wake flow characteristics of vertical axis wind turbines (VAWTs) at low tip speed ratios. Compared with the straight-bladed VAWT, our study shows that the helical-bladed VAWT generates near-wake flow structures with more three-dimensional features, which accelerate the wake transition to turbulence, enhance the small-scale turbulent dissipation, and result in a more rapid decay of the wake turbulence intensity. Moreover, the helical-bladed VAWT also exhibits much smaller temporal variations for the torque and power coefficients than the straight-bladed VAWT, resulting in smoother wind power generation.

[Phys. Rev. Fluids 9, 074603] Published Mon Jul 08, 2024

Author(s): Andrea Del Gaudio, George Constantinescu, Cristiana Di Cristo, Francesco De Paola, and Andrea Vacca

In this study, we explore the complex dynamics of a dam break wave comprising a clay-water mixture under turbulent flow conditions as it interacts with a vertical rigid wall. Utilizing advanced three-dimensional Large Eddy Simulations (LES), we investigate the evolution of the dam break over time as a function of fluid rheology. The study aims to provide useful information for the development of risk mitigation strategies and the design of protective structures by examining the influence of clay concentration and initial fluid depth on the wave’s behavior, bed shear stresses, and impact forces.

[Phys. Rev. Fluids 9, 074801] Published Mon Jul 08, 2024

Author(s): Brandon R. Angle, Matthew J. Rau, and Margaret L. Byron

For sedimenting nonspherical particles at finite Reynolds numbers, very small offsets in the center of mass (less than 0.05% of particle length) can dramatically alter settling behavior. Nonuniformity in mass distribution enhances lateral dispersion and alters overall settling velocity; small changes in particle orientation lead to the onset of wake features which can either stabilize or destabilize the particle’s trajectory, bifurcating over a relatively narrow range of Reynolds number. These results carry implications for a variety of natural and engineered processes, such as the transport and settling of microplastics and/or multimaterial aggregates in the environment.

[Phys. Rev. Fluids 9, 070501] Published Wed Jul 03, 2024

Author(s): Yu Jiao, Steffen J. Schmidt, and Nikolaus A. Adams

How does a cavity-embedded n-dodecane droplet behave under near-critical thermodynamic conditions? We present a comprehensive three-dimensional simulation of such a droplet subjected to a normal shock wave, utilizing an effective resolution of 0.87 billion finite volumes. This represents the largest simulation of its kind to date. A novel configuration is introduced to incorporate the influence of the cavity on the droplet dynamics. This study advances our understanding of droplet behavior under extreme conditions, potentially aiding in resolving specific transcritical flow challenges encountered in scramjets, ramjets, and liquid rocket engines.

[Phys. Rev. Fluids 9, 074002] Published Wed Jul 03, 2024

Author(s): Aubrey L. McCutchan, Colin R. Meyer, and Blair A. Johnson

Our experimental study explores ice melting rates in quiescent water and in turbulent flow. Particle image velocimetry measurements allow us to visualize and characterize flows generated by meltwater plumes and to non-invasively measure melt rate of an ice sphere fixed in place in the center of our isotropic turbulence tank, in which randomly actuated synthetic jets produce a core of homogeneous isotropic turbulence. We present relationships between ambient water temperature and turbulent kinetic energy on melt rates.

[Phys. Rev. Fluids 9, 074601] Published Tue Jul 02, 2024

Author(s): Wei-Lun Hsu, Zhixuan Wang, Soumyadeep Paul, and Hirofumi Daiguji

In this work, we derive analytical solutions for a unique electrokinetic phenomenon, being termed as transport-induced-charge electroosmosis (TICEO), which does not originate from electric double layers, but is due to the local ion separation in a nanopore filled with an electrolyte solution in the presence of a salinity gradient. We show that the direction of TICEO is independent of the applied electric field, and thus suitable for alternating current (AC) pumping applications. Using a transient model, we examine the time scale, length scale, and operating frequency range for TICEO in a thin nanopore, providing useful guidance for nanopore design in AC nanofluidic technology.

[Phys. Rev. Fluids 9, L071701] Published Tue Jul 02, 2024

Author(s): Haokui Jiang and Shunxiang Cao

This work presents a reduced-order model-based feedback control strategy for suppressing vortex-induced vibration (VIV) of a spring-mounted cylinder using the balanced proper orthogonal decomposition (BPOD) method. The BPOD model, closely aligned with the full-order model (FOM), is employed to design an active flow control strategy with blowing and suction actuators, effectively suppressing VIV up to Re = 100 by adjusting or eliminating unstable eigenmodes. The optimal control strategies, robust to variations in Reynolds numbers, highlight significant gain margins when positioning velocity probes near x/D = 3.0, though probe placement in wavemaker regions might be suboptimal.

[Phys. Rev. Fluids 9, 073901] Published Mon Jul 01, 2024

Author(s): Aditya Jha, Yacine Amarouchene, and Thomas Salez

In highly viscous environments, an object’s dynamics is perturbed in the presence of soft confining boundaries due to the coupling of the lubricated flow with the boundary’s elasticity. Since the deformability of the boundary is central to the elastohydrodynamic forces induced, altering its material nature to that of a capillary fluid interface can drastically alter the magnitude and direction of these forces. Based on a model system with two infinite cylinders rotating near a fluid interface, such changes are theoretically and numerically explored in detail. New scaling results and a reversal in the sign of the generated normal forces, unseen with classical elastic substrates, are revealed.

[Phys. Rev. Fluids 9, 074001] Published Mon Jul 01, 2024

Author(s): Patrick J. Stofanak, Cheng-Nian Xiao, and Inanc Senocak

We explore stably stratified flows in V-shaped triangular cavities, following Prandtl’s mountain and valley flow model. Our study identifies five distinct steady states. A zero-flow state bifurcates into symmetry-conjugated asymmetric circulation states forming a pitchfork bifurcation. Additionally, we identify two symmetric states characterized by upslope and downslope flows, respectively. These states, although not symmetry-conjugated, originate from the same eigenmode, leading to a novel bifurcation pattern that deviates from traditional canonical forms. Our findings illuminate the complex bifurcation structure of stratified flows in such cavities, which has previously been overlooked.

[Phys. Rev. Fluids 9, 074401] Published Mon Jul 01, 2024

Author(s): Zhenghao Feng, Chong Cai, Cunbiao Lee, and Daoning Yang

In this Letter, we report a phenomenon where two overlapping heating peaks are observed over a slightly blunted cone instead of just one in a hypersonic flow. Through optical measurements and direct numerical simulations, we confirm that the former peak originates from dilatational effects of second mode while the latter emerges due to high shear viscous dissipation. The convergence between the saturation location of second mode and onset location of transition leads to the overlap of peaks. This study not only highlights the additional heating regions over blunt models brought by the second mode, but also suggests employing designed bluntness strategies to control them.

[Phys. Rev. Fluids 9, L071901] Published Mon Jul 01, 2024

Author(s): Li Chen, Feng Wang, Yingrui Wang, Peng Huo, Yuqi Li, Xi Gu, Man Hu, and Daosheng Deng

The authors explore how solidification and thermo-instability could produce the sunflower shape of paraffin wax confined within a Hele-Shaw cell.

[Phys. Rev. Fluids 9, L072001] Published Mon Jul 01, 2024

Author(s): Sutapa Mandal, Snehashish Sarkar, and Pinaki Pal

The phenomenon of supercritical and subcritical transitions from one state to another with the variation of a control parameter is widely observed across a variety of natural as well as artificial systems. This paper investigates those transitions in the rotating Rayleigh-Bénard convection (RRBC) system. However, the complexity of RRBC so far hindered the simplest possible description of these transitions. Here, a very simple description of the phenomenon is presented using a pair of one dimensional reduced order models of the system in the presence of free-slip and no-slip boundary conditions. The results of the models are then validated with that of the direct numerical simulations.

[Phys. Rev. Fluids 9, 063503] Published Thu Jun 27, 2024

Author(s): Lichuan Xu, Adrian van Kan, Chang Liu, and Edgar Knobloch

We study turbulent fluctuation-induced transitions between hurricane-like large-scale vortices and unidirectional jets in stochastically forced, viscously damped two-dimensional turbulence within an elongated periodic domain. Using direct numerical simulations of unprecedented duration, lasting up to 10000 viscous time units, we collect detailed statistical data on the lifetimes of these metastable structures and quantify the impact of the domain aspect ratio, the forcing scale, and the Reynolds number. We also uncover irreversible transition paths between jets and vortices, which consist of two stages: a rapid change in structure and a subsequent slow viscous adjustment of kinetic energy.

[Phys. Rev. Fluids 9, 064605] Published Thu Jun 27, 2024

Author(s): A. Chauhan and C. Sasmal

We perform a comprehensive numerical study on all three modes of thermal convection (forced, free, and mixed) within a system comprising two concentric horizontal cylinders filled with viscoelastic fluids, with the inner cylinder rotating. In forced convection, the flow field remains stable, while in free and mixed convection, an increase in the Weissenberg number leads to a transition from steady to unsteady periodic, quasiperiodic, and finally, an aperiodic and chaotic behavior. This transition arises due to the presence of elastic instability and the subsequent appearance of elastic turbulence in viscoelastic fluids with the increasing Weissenberg number.

[Phys. Rev. Fluids 9, 063303] Published Tue Jun 25, 2024

Author(s): Junjie Li, Suofeng Han, Wenxue Han, Ronggang Wei, Chunbo Hu, and Chao Li

To study the effects of powder injection on hydrogen flame flow field parameters in scramjet, numerical simulation methods are employed. The study focuses on the influence of particle injection expansion angle and particle injection swirl on hydrogen flame flow field parameters. The computational results indicate that injecting powder fuel into the hydrogen flame leads to a decrease in flame flow field temperature.

[Phys. Rev. Fluids 9, 063201] Published Mon Jun 24, 2024