Latest papers in fluid mechanics

Author(s): Xiaofeng Wei, Dege Li, Jing Lei, Jinglu Li, Javier Rivero-Rodríguez, Fangye Lin, Dongyun Wang, and Benoit Scheid

In this paper, we investigate the exit dynamics of a sphere launched underneath a liquid bath surface at a prescribed impact velocity. Spheres with radii approximate or smaller than the capillary length are considered. The process can be sequenced into a partial exit stage that forms a coated layer, and a full exit stage with an attached ligament. A bouncing-off regime, a lower pinch-off penetration regime, and an upper pinch-off penetration regime are identified, separating by a penetration Weber number and a switching Weber number. The phase diagram is revealed, where the two critical Weber numbers are functions of the Bond number.

[Phys. Rev. Fluids 9, 054003] Published Fri May 17, 2024

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

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

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

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

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

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

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

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