New Papers in Fluid Mechanics

Study on transition to turbulence of rotating-disk boundary layer in a rotor-stator cavity with temperature gradient

Physical Review Fluids - Wed, 05/15/2024 - 11:00

Author(s): Qiang Du, Yaguang Xie, Lei Xie, and Ruonan Wang

We integrated theoretical analysis and numerical simulations to investigate the turbulence transition through a crossflow instability in the boundary layer of a cooler rotating disk within a rotor-stator cavity, influenced by a temperature gradient. This gradient induces centrifugal buoyancy forces that alter the radial inflection points in the mean flow. These changes lead to premature bifurcation of spiral waves, crucial in the transition process, resulting in an early onset of turbulence in the boundary layer of the rotating disk. Our findings underscore the importance of manipulating boundary layer stability via temperature gradients to control turbulent transitions.

[Phys. Rev. Fluids 9, 053908] Published Wed May 15, 2024

Eddy self-similarity in turbulent pipe flow

Physical Review Fluids - Wed, 05/15/2024 - 11:00

Author(s): L. H. O. Hellström, T. Van Buren, J. C. Vaccaro, and A. J. Smits

To investigate the existence of geometrically self-similar eddies in fully developed turbulent pipe flow, stereoscopic particle image velocimetry measurements were performed in two parallel cross-sectional planes, for friction Reynolds numbers Reτ = 1310, 2430, and 3810. The instantaneous turbulence structures are sorted by width using an azimuthal Fourier decomposition, then azimuthally aligned to create a set of average eddy velocity profiles. The streamwise similarity is investigated using two-point correlations. Over the range of scales examined, the candidate structures establish full three-dimensional geometric self-similarity.

[Phys. Rev. Fluids 9, 054607] Published Wed May 15, 2024

Scraping of a thin layer of viscoplastic fluid

Physical Review Fluids - Tue, 05/14/2024 - 11:00

Author(s): J. J. Taylor-West and A. J. Hogg

Scraping of a thin layer of viscoplastic fluid from a horizontal surface by a translating rigid scraper generates a mound of fluid upstream of the scraper and a residual layer behind it. We compute numerical solutions for the system modeled via viscoplastic shallow-layer theory. The unsteady dynamics of this system exhibit a variety of self-similar regimes, for which we construct solutions explicitly and identify key scalings for the temporal development of the mound. We further report experimental results, which are compared with predictions from the shallow-layer theory, obtaining reasonable agreement once a slip boundary condition is included in the model.

[Phys. Rev. Fluids 9, 053301] Published Tue May 14, 2024

Free object in a confined active contractile nematic fluid: Fixed-point and limit-cycle behaviors

Physical Review Fluids - Tue, 05/14/2024 - 11:00

Author(s): Jonathan B. Freund

The dynamics of a free object in an active nematic suspension in a circular container are simulated. For ranges of parameters, unstable chaotic wanderings eventually reach either a fixed-point or limit-cycle (shown) behavior. These flows are analyzed, and similar behaviors confirmed to also occur in more complex geometries.

[Phys. Rev. Fluids 9, 053302] Published Tue May 14, 2024

Free-space and near-wall dynamics of a flexible sheet sedimenting in Stokes flow

Physical Review Fluids - Tue, 05/14/2024 - 11:00

Author(s): Yijiang Yu and Michael D. Graham

We present a numerical study of a thin elastic sheet with small extensibility sedimenting in a viscous fluid in free space or near a wall. The interplay between gravity and the elastic response of sheets gives rise to complex deformation and reorientation dynamics. Near a vertical wall, sheets exhibit asymmetric conformations that cause the sheet to drift toward or away from the wall. Near an inclined wall, sheets show qualitatively different dynamics when the wall angle is large: they either deposit on or slide along the wall with a fixed wall-normal distance.

[Phys. Rev. Fluids 9, 054104] Published Tue May 14, 2024

Increased solidification delays fragmentation and suppresses rebound of impacting drops

Physical Review Fluids - Mon, 05/13/2024 - 11:00

Author(s): Varun Kulkarni, Suhas Tamvada, Nikhil Shirdade, Navid Saneie, Venkata Yashasvi Lolla, Vijayprithiv Batheyrameshbapu, and Sushant Anand

Drops impacting supercooled surfaces adhere to them due to contact line pinning and their solidification. However, distinguishing the influence of each phenomenon on post-impact behavior is challenging since even repellent materials exhibit some drop adhesion. In this study, we examine the impact of water and alkane drops on an omniphobic dry ice surface. We show that the solidification extent within the drop, combined with thermal, elastic, and surface tension forces, dictate outcomes like fragmentation, rebound, or no-bounce. Our findings have critical implications for material design in 3D printing, frost-resistant coatings, and safe biological material transport in cold climates.

[Phys. Rev. Fluids 9, 053604] Published Mon May 13, 2024

Contact-angle hysteresis provides resistance to drainage of liquid-infused surfaces in turbulent flows

Physical Review Fluids - Mon, 05/13/2024 - 11:00

Author(s): Sofia Saoncella, Si Suo, Johan Sundin, Agastya Parikh, Marcus Hultmark, Wouter Metsola van der Wijngaart, Fredrik Lundell, and Shervin Bagheri

Liquid infused surfaces (LISs) are a nature-inspired surface technology that demonstrates multiple functionalities under laminar and controlled flow conditions. We study experimentally the behavior of the infused lubricant under submerged conditions and turbulent flow. When exposed to turbulence, the lubricant layer develops into a pattern of droplets, the length of which depends on the balance between shear and contact force. The stability of the droplets prevents complete drainage of the lubricant and increases the robustness of the LIS in the presence of turbulence. We identify a model that predicts the equilibrium length of the droplets and validate it with numerical simulations.

[Phys. Rev. Fluids 9, 054002] Published Mon May 13, 2024

Energetic inception of breaking in surface gravity waves under wind forcing

Physical Review Fluids - Mon, 05/13/2024 - 11:00

Author(s): Daniel G. Boettger, Shane R. Keating, Michael L. Banner, Russel P. Morison, and Xavier Barthélémy

We examine the influence of wind forcing on the inception of breaking in surface gravity waves using an ensemble of high-resolution numerical simulations. We find that there is a critical point in the energetic evolution of the wave in which the convergence of kinetic energy at the wave crest can no longer be offset by conversion to potential energy, resulting in a rapid growth of kinetic energy up to breaking onset. This energetic signature is shown to consistently differentiate between non-breaking and breaking waves under a range of wind forcing speeds.

[Phys. Rev. Fluids 9, 054803] Published Mon May 13, 2024

Blood flow efficiency in response to red blood cell sphericity

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Mohammed Bendaoud, Mehdi Abbasi, Alexis Darras, Hamid Ez-Zahraouy, Christian Wagner, and Chaouqi Misbah

Exploring how the shape of red blood cells influences their flow properties, this study uses numerical simulations to analyze changes from healthy bi-concave forms to abnormal spherical shapes associated with disorders like spherocytosis. The research reveals complex, non-monotonic relationships between cell shape and flow rate across varying channel widths, and its impact on blood perfusion.

[Phys. Rev. Fluids 9, 053603] Published Fri May 10, 2024

Longitudinal and azimuthal thermoacoustic modes in a pressurized annular combustor with bluff-body-stabilized methane-hydrogen flames

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Byeonguk Ahn, Håkon T. Nygård, Nicholas A. Worth, Zhijian Yang, and Larry K. B. Li

To explore the dynamics of annular combustors, we investigate azimuthal thermoacoustic instabilities under a range of hydrogen power fractions and operating conditions. Using time-series analysis and mode detection techniques, we examine the relationship between longitudinal and azimuthal modes, identifying a transition from chaos to high-amplitude periodic states. Our research sheds light on how hydrogen enrichment affects combustor stability and presents the first identification of type-II Pomeau–Manneville intermittency in annular combustors. These findings contribute to knowledge of the modal dynamics within combustors, with implications for the design and operation of future systems.

[Phys. Rev. Fluids 9, 053907] Published Fri May 10, 2024

Engineering of polydisperse porous media for enhanced fluid flows through systematic topology tuning via differentiable direct numerical simulation

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Mohammed G. Alhashim and Michael P. Brenner

Recent advancements in automatic differentiation, which played a pivotal role in deep learning, offer a promising approach to addressing challenges in controlling fluid flow behavior. We demonstrate the power of the method by optimizing the packing of a polydisperse system of periodically arranged circular rods to minimize the pressure drop across the media. We show how the optimum topology of the porous media changes with changing the packing fraction.

[Phys. Rev. Fluids 9, 054103] Published Fri May 10, 2024

Slender phoretic loops and knots

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Panayiota Katsamba, Matthew D. Butler, Lyndon Koens, and Thomas D. Montenegro-Johnson

We present an asymptotic theory for the dynamics of slender chemically propelled loops and knots. It is valid for nonintersecting three-dimensional centerlines, with arbitrary chemical patterning and varying (circular) cross-sectional radius, allowing many slender active loops and knots to be studied. The theory has closed-form solutions in simpler cases, enabling us to derive the swimming speeds of chemically patterned tori, and the pumping strength (stresslet) of uniformly active slender tori. Using numerical solutions, we find the behavior of exotic active particle geometries, such as a bumpy uniformly active torus that spins and a Janus trefoil knot, which rotates as it swims forwards.

[Phys. Rev. Fluids 9, 054201] Published Fri May 10, 2024

Particle-resolved multiphase Rayleigh-Bénard convection

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Xianyang Chen and Andrea Prosperetti

500 resolved particles, colored by their temperature, are suspended in Rayleigh-Bénard convection at a Rayleigh number of 107. The lines are streamlines colored according to the fluid vertical velocity. Near the cell bottom, the fluid circulation pushes the particles from the base of the descending to that of the ascending plume where they accumulate into a dune. The particles that follow are dragged up the dune acquiring a vertical velocity component which promotes their resuspension. The lift force plays no role in this process. Depending on the particle number (from 500 to 3000) up to 20% of the fluid gravitational energy can be transferred to the particles.

[Phys. Rev. Fluids 9, 054301] Published Fri May 10, 2024

Multiscale analysis of the space-time properties in incompressible wall-bounded turbulence

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Tian Liang, Cheng Cheng, and Lin Fu

The space-time correlations of both wall-shear fluctuations and the streamwise velocity fluctuations carried by wall-attached eddies are investigated in a multiscale manner, by coupling the inner-outer interaction model (IOIM) with the attached eddy hypothesis. The present results demonstrate that the space-time correlations for the wall-shear stress fluctuation are mainly dominated by near-wall small-scale motions, and wall-attached eddies at a given length scale feature distinctly different space-time properties as compared to those of ensembled eddies with multiple length scales, which provides a new perspective for analyzing the decorrelation mechanisms in turbulence theory.

[Phys. Rev. Fluids 9, 054606] Published Fri May 10, 2024

Relating interfacial Rossby wave interaction in shear flows with Feynman's two-state coupled quantum system model for the Josephson junction

Physical Review Fluids - Fri, 05/10/2024 - 11:00

Author(s): Eyal Heifetz, Nimrod Bratspiess, Anirban Guha, and Leo Maas

Super-currents, tunneling across insulators in Josephson junctions, have a one-to-one classical analog to action-at-a-distance between two interfacial Rossby waves in shear flows. Quantum avoided crossing between eigenstates, described by the Klein-Gordon equation, is obtained as well for the Rossby wave normal modes. Both the quantum and the classical dynamics are formulated as coupled two-state systems and presented on a Bloch sphere, where the Hadamard gate transforms the two normal modes into an intuitive computational basis of two single Rossby waves. Yet, lacking analogs to quantum collapse and entanglement, the Rossby wave system cannot serve as a qubit prototype, even in principle.

[Phys. Rev. Fluids 9, 054802] Published Fri May 10, 2024

Wall vortex induced by the collapse of a near-wall cavitation bubble: Influence of the water surface

Physical Review Fluids - Wed, 05/08/2024 - 11:00

Author(s): Jianlin Huang, Jingzhu Wang, Wenlu Guo, and Yiwei Wang

Wall vortex occurs when a cavitation bubble oscillates far from a single rigid wall (at a dimensionless standoff distance γr>1.3). This study finds that a wall vortex in an expanded new regime forms instead of a free vortex at a smaller γr value, when introducing a water surface. Criteria for vortex flow patterns are proposed based on the direction of the bubble centroid migration at the beginning of the second cycle tc though a theoretical model developed with a Lagrangian formulation. Numerical analysis reveals that the wall vortex flow with the influence of the water surface contributes to a greater wall shear stress and larger area, thus increasing the surface cleaning potential.

[Phys. Rev. Fluids 9, 053602] Published Wed May 08, 2024

Stability of plane Couette flow with constant wall transpiration

Physical Review Fluids - Wed, 05/08/2024 - 11:00

Author(s): W. Sun, A. Yalcin, and M. Oberlack

The instability behavior of plane Couette flow is notoriously difficult, because it has no classical unstable modes, and this for any high Reynolds number. Here, the plane Couette flow is modified by means of a constant wall transpiration, i.e. simultaneous blowing from below, which has a destabilizing effect, and suction from above, which has a stabilizing effect. These opposing effects led to a changed in an unpredictable way, i.e. a destabilization at a certain point with increasing transpiration rate, the increase in instability then reaches a maximum and then leads to a slow stabilization again as the transpiration rate increases further. The destabilizing effects clearly dominate here.

[Phys. Rev. Fluids 9, 053906] Published Wed May 08, 2024

Isotropic turbulence of variable-density incompressible flows

Physical Review Fluids - Wed, 05/08/2024 - 11:00

Author(s): L. Reynier, B. Di Pierro, and F. Alizard

The effects of density variations on structures developing in an isotropic incompressible turbulence flow are investigated. Statistical analyses are carried out on datasets obtained from direct numerical simulations of forced turbulence. Numerical evidence shows that the introduction of a variable-density field into a turbulent field modifies the coherent structures and the energy spectrum in the inertial range.

[Phys. Rev. Fluids 9, 054604] Published Wed May 08, 2024

Model for the structure function constant for index of refraction fluctuations in Rayleigh-Bénard turbulence

Physical Review Fluids - Wed, 05/08/2024 - 11:00

Author(s): Robert A. Handler, Richard J. Watkins, Silvia Matt, and K. P. Judd

Kolmogorov scaling is used to derive a model for the structure function constant associated with index of refraction fluctuations in Rayleigh-Benard turbulence. The model predicts that the normalized structure function constant depends on the heat flux to the four-thirds power, and is independent of the Rayleigh number. The model agrees with the results of numerical simulations, thereby lending support to the assumptions underlying the theory.

[Phys. Rev. Fluids 9, 054605] Published Wed May 08, 2024

Direct numerical simulations of a cylinder cutting a vortex

Physical Review Fluids - Wed, 05/08/2024 - 11:00

Author(s): Steven Soriano and Rodolfo Ostilla-Mónico

The interaction between a vortex and an impacting body is complex due to the interaction of inviscid and viscous mechanisms. We conduct the first three-dimensional direct numerical simulations of this process and vary the relative impact velocity of the cylinder to explore the parameter space and analyze this process in detail. Strong vortices lead to ejection and interaction of secondary vorticity from the cylinder’s boundary layer, while weak vortices lead to approximately inviscid interaction of the cylinder with the primary vortex through deformations.

[Phys. Rev. Fluids 9, 054701] Published Wed May 08, 2024


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