New Papers in Fluid Mechanics

Large-eddy simulations of turbulent wake flows behind helical- and straight-bladed vertical axis wind turbines rotating at low tip speed ratios

Physical Review Fluids - Mon, 07/08/2024 - 11:00

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

Large eddy simulation of power-law fluid dam break wave impacting against a vertical wall

Physical Review Fluids - Mon, 07/08/2024 - 11:00

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

Settling of nonuniform cylinders at intermediate Reynolds numbers

Physical Review Fluids - Wed, 07/03/2024 - 11:00

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

Simulating shock interaction with a cavity-embedded cylinder/droplet using a real-fluid hybrid scheme at near-critical conditions

Physical Review Fluids - Wed, 07/03/2024 - 11:00

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

Enhancement of ice melting in isotropic turbulence

Physical Review Fluids - Tue, 07/02/2024 - 11:00

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

Transport-induced-charge electroosmosis in nanopores

Physical Review Fluids - Tue, 07/02/2024 - 11:00

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

Balanced proper-orthogonal-decomposition-based feedback control of vortex-induced vibration

Physical Review Fluids - Mon, 07/01/2024 - 11:00

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

Capillary-lubrication force between rotating cylinders separated by a fluid interface

Physical Review Fluids - Mon, 07/01/2024 - 11:00

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

Unusual bifurcation scenario in a stably stratified, valley-shaped enclosure heated from below

Physical Review Fluids - Mon, 07/01/2024 - 11:00

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

Investigation of an overlap of heating peaks in the hypersonic boundary layer over a blunt cone

Physical Review Fluids - Mon, 07/01/2024 - 11:00

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

Vertical-supercooling-controlled interfacial instability for a spreading liquid film

Physical Review Fluids - Mon, 07/01/2024 - 11:00

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

One-dimensional models for supercritical and subcritical transitions in rotating convection

Physical Review Fluids - Thu, 06/27/2024 - 11:00

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

Fluctuation-induced transitions in anisotropic two-dimensional turbulence

Physical Review Fluids - Thu, 06/27/2024 - 11:00

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

Thermal convection of viscoelastic fluids in concentric rotating cylinders: Elastic turbulence and kinetic energy budget analysis

Physical Review Fluids - Tue, 06/25/2024 - 11:00

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

Numerical simulation study on the interaction between hydrogen flame and particle flame in scramjet

Physical Review Fluids - Mon, 06/24/2024 - 11:00

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

Active control of the free surface of a rivulet of a nematic liquid crystal with an electric field

Physical Review Fluids - Mon, 06/24/2024 - 11:00

Author(s): Akhshay S. Bhadwal, Joseph R. L. Cousins, Nigel J. Mottram, Stephen K. Wilson, Brian R. Duffy, Ian C. Sage, and Carl V. Brown

We demonstrate control of the free surface profile of a rivulet of a nematic liquid crystal through the electric field-induced local increase of the effective viscosity of the rivulet. This resulting increase in rivulet height is studied experimentally, and is described theoretically in terms of the volume flux and the electric field strength. The localized effective viscosity change of the flow in this study occurs under isothermal conditions with the other physical properties of the liquid kept constant. The reported effect contrasts with temperature-dependent viscosity control techniques, which involve changes to the physical properties of the liquid.


[Phys. Rev. Fluids 9, 064002] Published Mon Jun 24, 2024

Hydraulic failure of granular materials with artificial cementation

Physical Review Fluids - Mon, 06/24/2024 - 11:00

Author(s): Abbas Farhat, Pierre Philippe, Li-Hua Luu, Alexis Doghmane, and Pablo Cuéllar

Experiments based on hydraulic loading of artificial cemented granular layers by a localized upward water flow revealed the existence of three failure modes: (i) Overall block uplift; (ii) Block rupture by median crack at the inflow zone; (iii) Progressive excavation of a fluidized path along the walls. Despite these distinct scenarios driven by the boundary conditions, the critical flow values at breakpoint are consistent with each other, underlining the local character of the instability, and can be rationalized by extending Archimedes’ number to the present case involving adhesion between grains. Agreement is then established with the purely granular case.


[Phys. Rev. Fluids 9, 064305] Published Mon Jun 24, 2024

Turbulence modulation in dense liquid-solid channel flow

Physical Review Fluids - Mon, 06/24/2024 - 11:00

Author(s): Jonathan S. Van Doren and M. Houssem Kasbaoui

Inertial solid particles suspended in dense turbulent channels modulate turbulence and fluid mass flow rate through two mechanisms: (I) the increase of the suspension’s apparent kinematic viscosity with increasing solid volume fraction and (II) turbulence modulation through the particle feedback force. For particle volume fractions below 3%, the increase in suspensions apparent viscosity accounts for most of the modulation. As the volume fraction increases, the particle feedback force drives additional modulation beyond what the increased viscosity accounts for. Namely, this is a reduction in the bulk fluid velocity, reduction of turbulent fluctuations, and increased coefficient of friction.


[Phys. Rev. Fluids 9, 064306] Published Mon Jun 24, 2024

Influence of wind direction on flow over a cliff and its interaction with a wind turbine wake

Physical Review Fluids - Mon, 06/24/2024 - 11:00

Author(s): Arslan Salim Dar and Fernando Porté-Agel

Most of the literature on flow over cliffs and its interaction with a wind turbine wake deals with wind direction perpendicular to the cliff. As wind direction can be oblique in reality, it is important to understand how the flow over a cliff can change with wind direction and what implications it can have for a wind turbine wake. In this study, we showed that above a certain wind direction, streamwise flow recirculation is replaced by a spanwise one, affecting flow shear and turbulence. In addition, we explored the complex interactions between flow over a cliff and a wind turbine wake, affecting its characteristics such as shape, recovery rate, and turbulence level in a nontrivial manner.


[Phys. Rev. Fluids 9, 064604] Published Mon Jun 24, 2024

Poles, shocks, and tygers: The time-reversible Burgers equation 

Physical Review E - Tue, 06/18/2024 - 11:00

Author(s): Arunava Das, Pinaki Dutta, and Vishwanath Shukla

We construct a formally time-reversible, one-dimensional forced Burgers equation by imposing a global constraint of energy conservation, wherein the constant viscosity is modified to a fluctuating state-dependent dissipation coefficient. The system exhibits dynamical properties which bear strong sim…


[Phys. Rev. E 109, 065108] Published Tue Jun 18, 2024

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