Physical Review Fluids

Author(s): Bauyrzhan K. Primkulov, Davis J. Evans, Joel B. Been, and John W. M. Bush

Pilot-wave hydrodynamics concerns the dynamics of droplets walking on a vibrating liquid bath, and forms the basis for the field of hydrodynamic quantum analogs. We here investigate a theoretical model that captures both vertical and horizontal drop dynamics. The model provides new rationale for a number of phenomena, including colinear swaying, intermittent walking, and chaotic speed oscillations, all of which are linked to variability in the droplet’s impact phase. Our study also highlights the degeneracy in the droplet’s vertical dynamics, consideration of which is essential for understanding the dynamics of droplets in confined geometries and interacting with standing Faraday waves.

[Phys. Rev. Fluids 10, 013601] Published Mon Jan 06, 2025

Author(s): Mathieu Brasseur, Georges Jourdan, Christian Mariani, Diogo C. Barros, Marc Vandenboomgaerde, and Denis Souffland

An experimental investigation of the Richtmyer-Meshkov instability is conducted in spherical geometry where the displacement and the growth of the perturbations at the interface are given and compared to numerical simulations and new theoretical predictions. The results show that the instability amplitude initially grows, stabilizes, and then reduces before the arrival of the reflected shock wave. The theoretical model developed here agrees well with the experiments, although a time shift is observed in the stabilization regime. Furthermore, we show that convergent Rayleigh-Taylor effects are the main stabilizing mechanisms, and that compressibility has a negligible effect.

[Phys. Rev. Fluids 10, 014001] Published Mon Jan 06, 2025

Author(s): Andy Wu and Sanjiva K. Lele

Neural networks applied to turbulence modeling often do not learn locality or generalize to very high Reynolds number reasonably. Here, a two neural network architecture is introduced that learns the relevant neighborhood needed for sub-filter stress modeling through convolutions and the U-net architecture while generalizing reasonably to Reynolds numbers far larger than the training set on forced homogeneous isotropic turbulence and channel flow.

[Phys. Rev. Fluids 10, 014601] Published Mon Jan 06, 2025

Author(s): A. Leonid Heide and Maziar S. Hemati

This paper introduces an optimization framework for identifying sparse finite-amplitude perturbations that maximize transient growth in nonlinear systems. An iterative direct-adjoint looping algorithm is formulated based on the first-order necessary conditions for optimality. The method is applied to a reduced-order model of sinusoidal shear flow. Our results show that optimal sparse perturbations can achieve comparable energy amplification as the optimal non-sparse solution by triggering many of the same nonlinear modal interactions responsible for driving transient growth. We anticipate the approach will be a useful tool in future investigations into flow stability and control.

[Phys. Rev. Fluids 10, 014401] Published Thu Jan 02, 2025

Author(s): Miao Sun and Yanbo Xie

Previous work showed that a floating liquid bridge can be sustained under DC or high-frequency AC voltage, though the effects of frequency remain unclear. We investigated the stability of a micro-floating liquid bridge under periodic voltage pulses. The recorded current reveals the formation and breakup of the bridge as six distinct states of stability beyond high-speed imaging. Our results show that both pulse frequency and the electrocapillary number are crucial for liquid bridge stability. Considering the charging/discharging process of the system, we corrected the formation and breakup time, which well explained the observed delay in these processes.

[Phys. Rev. Fluids 9, 123701] Published Mon Dec 30, 2024

Author(s): Giulio Foggi Rota, Christian Amor, Soledad Le Clainche, and Marco Edoardo Rosti

Viscoelastic fluids like DNA solutions and polymer melts yield chaotic flows even with small inertial effects (quantified by the Reynolds number). Such turbulent motion is conventionally classified as elasto-inertial turbulence (EIT) or elastic turbulence (ET) when inertial effects are finite or vanishing. Our numerical study investigates the turbulent flow of viscoelastic fluids in planar channel flows over a wide range of Reynolds numbers. We discover that EIT and ET exhibit the same dynamical features and are thus the same. Our finding sheds light on low Reynolds number turbulence, with broader implications for materials science, industrial processes, and biology.

[Phys. Rev. Fluids 9, L122602] Published Mon Dec 30, 2024