Latest papers in fluid mechanics

Author(s): Dipin S. Pillai and Kirti Chandra Sahu

Electrified sessile droplets on solid surfaces are ubiquitous in nature as well as in several practical applications. Although the influence of electric field on pinned sessile droplets and soap bubbles has been investigated experimentally, the theoretical understanding of the stability limit of gen…

[Phys. Rev. E 109, L013101] Published Tue Jan 09, 2024

Author(s): Paolo Valentini, Maninder S. Grover, and Nicholas J. Bisek

The accurate characterization of molecular transport properties is essential for high-fidelity simulations of reactive, hypersonic flows. The correct prediction of energy and mass diffusion in the laminar, high-temperature, multicomponent boundary layer of a hyper-velocity flow has profound implications for the accurate modeling of gas-surface interactions and thermal loads on the aeroshell. In this work, molecular transport is investigated by solely using ab initio potential energy surfaces. Our approach removes the empiricism associated with simplified molecular interactions models used in previous studies and is applicable to arbitrary gas mixtures.

[Phys. Rev. Fluids 9, 013401] Published Tue Jan 09, 2024

Author(s): Xuemin Liu and Jonathan F. MacArt

We develop neural-network active flow controllers through a deep learning PDE augmentation method (DPM). In two-dimensional, incompressible, confined cylinder flow with Re = 100, we compare drag-reduction performance and optimization cost of adjoint-based controllers and deep reinforcement learning (DRL)-based controllers. The DRL-based controller demands 4,229 times the model complexity of the DPM-based one. The DPM-based controller is 4.85 times more effective and 63.2 times less computationally intensive to train than the DRL-based counterpart. In laminar compressible flows, successful extrapolation of the controller to out-of-sample flows demonstrates the robustness of the learning approach.

[Phys. Rev. Fluids 9, 013901] Published Tue Jan 09, 2024

Author(s): Xinglong Shang, Zhengyuan Luo, Bofeng Bai, Long He, and Guoqing Hu

Comprehensive numerical investigations of droplet displacement in soluble surfactant driven flows using the front-tracking method are presented. Surfactant transport in the bulk and at interfaces shapes droplet displacement and determines the transition conditions between steady-state sliding and detachment. Detachment is highly dependent on surfactant replenishment at interfaces, especially at receding contact lines where the nonuniform concentration induced Marangoni flow impedes movement. The critical effective capillary number can be used as a criterion to evaluate the ability of the surfactant to detach the droplet, giving a unique logarithmic relationship with detachment time.

[Phys. Rev. Fluids 9, 014002] Published Tue Jan 09, 2024

Author(s): Anu V. S. Nath, Anubhab Roy, S. Ravichandran, and Rama Govindarajan

The dispersion of heavy inertial particles in a cellular flow made of Taylor-Green vortices is found to display non-ergodicity and sensitive dependence on initial particle location. Even more surprising is the sensitive and non-monotonic dependence on Stokes number. The large time dispersion of particles can be ballistic (red), diffusive (green) or trapped (blue), depending on where they have started in the flow. Diffusive particles show chaotic dynamics. Here the mutually exclusive group of initial particle locations form a non-ergodic set (as in the figure), unlike a turbulent flow, which is known to be ergodic.

[Phys. Rev. Fluids 9, 014302] Published Tue Jan 09, 2024

Author(s): Edward W. G. Skevington and Andrew J. Hogg

Density-driven flows climb out of topographic depressions if they are sufficiently energetic. We investigate the inertial dynamics of these unsteady flows theoretically as fluid climbs from a lower to an upper plateau and then simultaneously propagates away from and drains back into the depression. The volume of fluid that escapes the confinement diminishes with a power-law dependence upon time; the draining flow becomes self-similar, and the self-similarity is of the second kind, featuring an exponent which is a function of the frontal Froude number. The volume continues to decrease even when viscous processes are non-negligible and ultimately none of the fluid escapes from the depression.

[Phys. Rev. Fluids 9, 014802] Published Tue Jan 09, 2024

Author(s): Jin-bo Cheng, Qi-you Liu, Li-jun Yang, Jun-xue Ren, Hai-bin Tang, Qing-fei Fu, and Luo Xie

Using a needle-plate electro-atomization experimental device, and applying a single pulse disturbance voltage signal, the response of the Taylor cone to a disturbance signal was explored. At the experimental level, the coupling relationship between polarization charge relaxation time and the oscillation period of the Taylor cone was uncovered, revealing the oscillation mechanism of the Taylor cone under this voltage disturbance.

[Phys. Rev. Fluids 9, 013701] Published Mon Jan 08, 2024

Author(s): Z. F. Li, G. X. Wu, and Y. Y. Shi

In the Arctic region, with the reduction of ice extent and thickness, a shipping route may become possible. We theoretically derive the wave motions induced by a point source pulsating and advancing at the marginal ice zone. It is found that when a ship navigates along the edge of an ice sheet, the free surface wave pattern has two V-shaped components. The outer V-wave is very similar to the common free surface wave without the ice sheet, while the inner V-wave is mainly due to the reflection of the outer V-wave by the ice sheet.

[Phys. Rev. Fluids 9, 014801] Published Fri Jan 05, 2024

Author(s): Ian Williams, Patrick B. Warren, Richard P. Sear, and Joseph L. Keddie

In an externally imposed electrolyte (salt) concentration gradient, charged colloids drift at speeds of order one micrometre per second. This phenomenon is known as diffusiophoresis. In systems with multiple salts and “crossed” salt gradients, a nonlocal component of the electric field associated wi…

[Phys. Rev. Fluids 9, 014201] Published Thu Jan 04, 2024

Author(s): Yutaro Fujiki, Hideto Awai, Yutaro Motoori, and Susumu Goto

Deformable elastic particles can accumulate around a vortex center even if the particle is neutrally buoyant. The angle between the deformed particle and the pathline plays important roles in this accumulation process. In this paper, we propose a simple model to explain this interesting accumulation phenomenon.

[Phys. Rev. Fluids 9, 014301] Published Thu Jan 04, 2024