NEW ARTICLE
Which direction matters more for subgrid-scale (SGS) turbulence? Our analysis reveals that the essence of dynamic SGS models is often condensed in only a few (sometimes, just one) special directions, offering new insights into the success of dynamic large-eddy simulation models.
Xiaohan Hu, Keshav Vedula, and George Ilhwan Park
Phys. Rev. Fluids 9, 074607 (2024)
NEW ARTICLE
We address coherent pressure structures in turbulent channel flows through SPOD and resolvent analysis with and without an eddy-viscosity model. The spectral analysis revealed energetic structures in the near-wall region, as well as large-scale and spanwise-coherent structures. Pressure structures are targeted in both SPOD and resolvent analysis by selecting an adequate norm through the quadrature weights and observation operator, respectively. The first SPOD and the leading resolvent modes closely agree and show low-ranking behavior. The analyzed modes comprise quasi-streamwise (for near-wall and large-scale structures) and spanwise vortices with pressure peaking at vortex centers.
Filipe R. do Amaral and André V. G. Cavalieri
Phys. Rev. Fluids 9, 074606 (2024)
NEW ARTICLE
Uncharged micron-sized water droplets flying toward each other do not always coalesce due to the cushioning effect of the air between them.For oppositely charged droplets, we discover a regime for which droplets always collide when they move inside the stable manifolds of a saddle point of the relative droplet dynamics. A consequence is that only for small electrical charges does the droplet coalescence rate depend primarily upon the Knudsen number (Kn), the ratio of the mean-free-path of air to the mean droplet radius. For much larger charges, coalescence does not depend upon Kn. Our theory predicts the critical charge at which the transition between the two regimes occurs.
A. Dubey, G. P. Bewley, K. Gustavsson, and B. Mehlig
Phys. Rev. Fluids 9, 074302 (2024)
NEW ARTICLE
We show that the apparent relaxation time inferred from the exponential thinning regime in viscoelastic pinch-off is not necessarily a material property, as was assumed so far, but depends on the system size for various polymer solutions and filament thinning techniques. It depends on the plate size in Capillary Breakup Extensional Rheometry (CaBER) with both slow and fast plate separation protocols, and on the nozzle size in Dripping-onto-Substrate (DoS), corroborating recent observations with the dripping technique. It is not due to artifacts such as solvent evaporation or polymer degradation and it cannot always be rationalized by finite extensibility effects.
A. Gaillard et al.
Phys. Rev. Fluids 9, 073302 (2024)
NEW ARTICLE
Novel formulations involving a control surface at a distance from the body are developed to compute drift loads on structures composed of an impermeable hull and a perforated surface accurately and efficiently. The developed formulation can not only give all six components of the mean wave drift force and moment, but also determine the drift loads on each individual body of a multi-body system.
Peiwen Cong, Hui Liang, Yingyi Liu, and Bin Teng
Phys. Rev. Fluids 9, 074802 (2024)
LETTER
A viscous fluid in contact with a solid channel that has a preferential affinity with respect to a second fluid embedded in the channel leads to a spontaneous imbibition process. Due to the increasing friction of the invading phase, the invading fluid scales diffusively in time. What happens when a third liquid is a lubricant coating the channel? We show that when the lubricant viscosity is decreased, dissipation switches from being localized in the bulk of the invading phase, to the lubricant layers. This leads to a new crossover, below which diffusive dynamics are not observed. Our results open up the possibility of using this mechanism in SLIPS and LIS to control capillary flows.
Sergi G. Leyva, Ignacio Pagonabarraga, Aurora Hernández-Machado, and Rodrigo Ledesma-Aguilar
Phys. Rev. Fluids 9, L072002 (2024)
NEW ARTICLE
Our experiments demonstrate that pancake-shaped bubbles in thin tilted Hele-Shaw cells rise slower than what is expected by simply correcting the effective gravity. This effect is shown to be more important for larger inclination. A careful study highlights an asymmetry for the lubrication film between the bubble and the top and bottom walls. As the cell inclination increases, this asymmetry also increases. We propose that it induces an additional “friction” due to fluid motion between the surrounding of the bubble and the Poiseuille flow further away.
Benjamin Monnet, J. John Soundar Jerome, Valérie Vidal, and Sylvain Joubaud
Phys. Rev. Fluids 9, 073601 (2024)
NEW ARTICLE
Ion selective concentration shocks have been shown to develop in electrochemical cells with homogeneous porous media of low surface charge. Here we demonstrate through a set of simulations that heterogeneity in the porous structure can lead to substantial differences in separation performance. Both variation in surface charge and characteristic pore size, result in vortical flow in the depleted area, affecting multiple metrics such as energy consumption, water recovery, and desalination. These effects can also be observed for hierarchical media and may be exploited in future designs of porous materials in electrochemical applications beyond shock electrodialysis
Alexander D. Sapp, Huanhuan Tian, and Martin Z. Bazant
Phys. Rev. Fluids 9, 073701 (2024)
NEW ARTICLE
Inspired by industrial processes in oil and gas well plugging and abandonment (P&A) operations, this study investigates the injection of heavy, thick fluids into lighter fluids. By experimenting and analyzing flow behaviors using dimensionless numbers such as Reynolds number, Froude number, inclination angle, Bingham number, and viscosity ratio, we identified different flow regimes such as stable and unstable slumping, separation, and mixing. These findings offer valuable insights for improving fluid flow analysis in applications like 3D printing and other industrial processes.
M. Faramarzi, S. Akbari, and S. M. Taghavi
Phys. Rev. Fluids 9, 073301 (2024)
NEW ARTICLE
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.
Ram Sudhir Sharma et al.
Phys. Rev. Fluids 9, 074301 (2024)
NEW ARTICLE
We study numerically and analytically the effect of Navier slip on the orientational dynamics and effective shear viscosity of a semi-dilute suspension of two-dimensional particles with either circular or elongated (plate-like) shape, interacting only via hydrodynamic and contact forces. We show that at dilute concentrations slip causes the elongated particles to align in the flow direction, whilst for large concentrations tumbling of the particles occurs due to particle-particle interactions. We show this change in orientational microstructure directly impacts the effective viscosity of the suspension: a minimum in the effective viscosity occurs at a threshold concentration.
Catherine Kamal and Lorenzo Botto
Phys. Rev. Fluids 9, 074102 (2024)
NEW ARTICLE
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.
Axel Tassigny, Maria Eletta Negretti, and Achim Wirth
Phys. Rev. Fluids 9, 074605 (2024)
NEW ARTICLE
The natural frequency of a fluid overlying on a wavy wall in general reduces. This reduction is observed by a shift in the minimum of the Faraday threshold, i.e., in the parametric acceleration versus frequency plot.
B. Dinesh, N. Brosius, T. Corbin, and R. Narayanan
Phys. Rev. Fluids 9, 073902 (2024)
EDITORS' SUGGESTION
The follower force model is a fundamental model for active filaments, commonly utilized to model microtubule-motor protein complexes and collections of cilia. In this work we perform a thorough analysis of this model, employing techniques from computational dynamical systems, adapted from high Reynolds number fluid dynamics, to map out the bifurcations in the system and classify emergent states. This approach allows us to bridge the gap between 2D and 3D analyses, in particular establishing the initial buckling as a double Hopf bifurcation. Additionally, we identify the existence of a quasiperiodic solution at the second bifurcation, and categorize the dynamics at higher values of forcing.
Bethany Clarke, Yongyun Hwang, and Eric E. Keaveny
Phys. Rev. Fluids 9, 073101 (2024)
NEW ARTICLE
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.
Subharthi Chowdhuri and Tirtha Banerjee
Phys. Rev. Fluids 9, 074604 (2024)
NEW ARTICLE
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.
Qiang Zhu
Phys. Rev. Fluids 9, 074101 (2024)