Latest papers in fluid mechanics

Author(s): Nandita Pan and Supratik Banerjee

Below critical temperature, turbulence prevents the spontaneous phase separation of binary mixtures, resulting in a phase arrested state of emulsion. The current study explores if a Kolmogorov-like energy cascade exists in fully developed binary fluid turbulence. Using exact relations and direct numerical simulations with up to 10243 grid points, we show that the combined kinetic and interfacial energy exhibits a cascade with a constant transfer rate across the inertial scales. In addition, the cascade rates computed from the three exact laws in divergence, alternative and correlator forms show excellent agreement, thus confirming the equivalence between the three formulations.

[Phys. Rev. Fluids 10, 064615] Published Tue Jun 17, 2025

Author(s): J. C. Muñoz-Hervás, B. Semin, M. Lorite-Díez, G. J. Michon, J. D'Adamo, J. I. Jiménez-González, and R. Godoy-Diana

Passive flow control strategies for bluff bodies consisting in rigid and flexible appendages has been previously studied, but segmented structures remain less well understood. This study investigates wake modification behind a canonical D-shaped body using arrays of rigid and flexible filaments. Combining PIV and deformation measurements, it is shown that passive 2-D reconfiguration of flexible filaments dominates the reduction of the recirculation bubble, velocity deficit, and drag. The results suggest that wake shaping with flexible or pre-curved rigid appendages offers a promising passive strategy for flow control around blunt bodies

[Phys. Rev. Fluids 10, 063903] Published Mon Jun 16, 2025

Author(s): Yuyang Lai, Sina Heydari, On Shun Pak, and Yi Man

Microswimmers must adapt their motion to navigate complex and dynamic environments. This study uses reinforcement learning (RL) to train a three-link swimmer to develop adaptive stroke patterns for target-directed navigation. Two learning strategies are developed, optimizing either swimming speed or energy efficiency. Our results reveal that RL not only recovers patterns similar to classical optimization but also adapts to diverse navigation tasks with remarkable flexibility.

[Phys. Rev. Fluids 10, 064103] Published Mon Jun 16, 2025

Author(s): R. A. Heinonen, L. Biferale, A. Celani, and M. Vergassola

Bayesian approaches to olfactory search, the problem of tracking a source of passive scalars in a turbulent flow, have been very successful but remain understudied in realistic, correlated flows. By searching in realistic direct numerical simulations data, we study the effects of correlations (i.e., structure in the scalar field) on the performance of Bayesian strategies. We find that short-range correlations impede performance but can be mitigated with prior knowledge and additional optimization; meanwhile, large-scale structure typical of windy flows helps the agent reach the target faster, without need for prior knowledge. We also argue that there are optimal values for the observation rate and threshold for detection.

[Phys. Rev. Fluids 10, 064614] Published Mon Jun 16, 2025

Author(s): Jan Turczynowicz, Radost Waszkiewicz, and Łukasz Gładczuk

A metal disk placed on the water surface normally sinks; however, it has been observed that the disk can remain afloat when a vertical water jet is directed at it from above. The jet displaces water from the disk’s upper surface and, by a mechanism analogous to a hydraulic jump, enlarges the effective immersed volume. The resulting increase in buoyant force offsets the disk’s weight, enabling flotation. A theoretical model based on scaling laws specifies the conditions under which this occurs. Experiments on both flotation and sinking confirm the model’s predictions. A brief video demonstration is available at https://youtu.be/as0wRQj1Zws.

[Phys. Rev. Fluids 10, L062801] Published Mon Jun 16, 2025

Author(s): Katsunori Yoshimatsu and Yukio Kaneda

We study the small-scale anisotropy of a passive scalar field in homogeneous isotropic turbulence with a uniform mean scalar gradient. We extend linear response theory of turbulence to predict how the scalar gradient induces anisotropy, focusing on second- and third-order mixed velocity-scalar structure functions. The theoretical predictions generally agree with results by direct numerical simulation.

[Phys. Rev. Fluids 10, 064613] Published Fri Jun 13, 2025

Author(s): Richard Cobos and Aditya S. Khair

We present numerical computations of the dynamic electrophoretic velocity of a charged spherical colloid in unsteady electric fields. Focusing on moderate surface charges and Debye lengths comparable to particle size, we find that when a field is suddenly applied, the electrophoretic mobility initially rises independently of field strength on the momentum diffusion timescale. Over longer times, ion diffusion reshapes the Debye cloud, as the mobility reaches its field-dependent steady state. Under oscillatory fields, the mobility amplitude and phase lag strongly depend on field frequency, which governs the cloud’s ability to adjust within each cycle

[Phys. Rev. Fluids 10, 063702] Published Thu Jun 12, 2025

Author(s): Qinyuan Li, Yongkai Chen, Dandan Xiao, Xuerui Mao, and Jie Yao

This study investigates the structure and dynamics of the quiescent momentum core (QMC) and introduces its thermal counterpart—the quiescent thermal core (QTC)—in compressible channel flows using direct numerical simulations at moderate to high Reynolds and Mach numbers. While the QMC retains features observed in incompressible flows, such as low turbulence and sharp interfacial layers, the newly identified QTC displays distinct thermal characteristics, including enhanced thickness and strong temperature gradients. These findings clarify how compressibility modifies core region dynamics and energy transport, extending the concept of core-layer structures to thermal fields in high-speed turbulent flows.

[Phys. Rev. Fluids 10, 064612] Published Thu Jun 12, 2025

Author(s): Joachim Falck Brodin, Kevin Pierce, Paula Reis, Per Arne Rikvold, Marcel Moura, Mihailo Jankov, and Knut Jørgen Måløy

Using a custom-built three-dimensional scanner, this study reveals how immiscible fluid interfaces destabilize during invasion through disordered porous media. As the flow rate is changed, the interface transitions from stable sheets to tangled, unstable fingers. A stability criterion incorporating pressure dynamics and relative permeability is introduced. The findings bridge two-dimensional theory with complex three-dimensional reality, advancing our understanding of multiscale interactions between flow, structure, and interface dynamics.

[Phys. Rev. Fluids 10, 064003] Published Wed Jun 11, 2025

Author(s): Zichen Liu, Bowen Zhu, and Gaojin Li

Synchronized locomotion of undulatory swimmers occurs ubiquitously in nature, ranging from microorganisms such as sperms to larger aquatic animals such as eels and knifefish. To develop a unified understanding of this phenomenon, we use Taylor's two-dimensional infinitely long undulatory sheet model…

[Phys. Rev. E 111, 065103] Published Tue Jun 10, 2025

Author(s): Ivan Smolyanov and Oleg Zikanov

Transient plasma events, such as plasma disruptions, are anticipated in the future magnetic-confinement nuclear fusion reactors. The events are accompanied by a rapid change in the magnetic field generated by the plasma current and, accordingly, induction of strong eddy currents and Lorentz forces w…

[Phys. Rev. E 111, 065104] Published Tue Jun 10, 2025

Author(s): Dinesh Kumar Kinjangi and Daniel Foti

Two distinct hypotheses, related to upwind and turbine scales, for the formation of wake meandering —the large-scale, periodic oscillating motion of the far wake of a wind turbine —are tested via LES by varying the incoming scales. Wake meandering is observed throughout the range of scales but exhibits variation in turbulence and spectral characteristics. Two wake meandering scales are observed: (1) turbine influenced scale with regular Strouhal number, St ≈ 0.3 and corresponding harmonics, with a similar wake center distribution across all upwind conditions, and (2) upwind produced scale if low upwind scales are present, St < 0.1 with irregular wake center distributions.

[Phys. Rev. Fluids 10, 064611] Published Tue Jun 10, 2025

Author(s): Anna Frishman and Daniel Lecoanet

A slowly stretched fluid bridge is destined to break, leaving behind a satellite droplet. Combining experiments and one-dimensional simulations, the size of this droplet is shown to be highly reproducible. It is demonstrated to follow a simple formula depending only on the normalized volume of the bridge and the Weber number, so by stretching the bridge faster or increasing its volume the droplet size can be dramatically increased. The robustness of the satellite size is revealed to be due to an underlying universal dynamical solution.

[Phys. Rev. Fluids 10, 063604] Published Mon Jun 09, 2025

Author(s): Doyel Pandey and Steffen Hardt

An electrolyte-filled nanochannel can promote significant thermo-osmotic flow in the presence of wall slip. This flow augments the thermoelectric response of the channel especially in situations with thin electric double layers (relative to the channel width). For example, for a slip length of 40 nm, the thermoelectric power can increase by more than a factor of 200 due to convective charge transport.

[Phys. Rev. Fluids 10, 063701] Published Mon Jun 09, 2025

Author(s): Bradley Pascoe, Michael Groom, and Ben Thornber

The compression or expansion of turbulent mixing layers often occurs under anisotropic strain rates, causing the mixing layer to compress or expand at different rates in different directions. Anisotropic strain patterns are common in nozzle flows and implosions yet are rarely addressed in turbulence models. The treatment of the turbulent length scale under bulk compression is investigated for a two-equation Reynolds—Averaged Navier—Stokes model. Comparing to strained implicit large eddy simulations, the mixing layer properties are better predicted when accounting for the alignment of the strain rates and the mixing layer growth direction.

[Phys. Rev. Fluids 10, 064609] Published Mon Jun 09, 2025

Author(s): Gregory Eyink and Hao Quan

Weak Euler solutions have been hypothesized to explain the d’Alembert paradox of non-vanishing drag. A difficulty is the “weak-strong uniqueness” property, which requires that an admissible weak Euler solution must coincide with the smooth Euler solution for the same initial data. Using the Josephson-Anderson relation adapted from superfluids, we show that weak-strong uniqueness for d’Alembert’s solution requires mild conditions. To explain drag we therefore predict that these conditions are violated by violent eruption of very thin boundary layers. We discuss observational signatures and explain how the small length-scales involved could threaten the validity of a hydrodynamic description.

[Phys. Rev. Fluids 10, 064610] Published Mon Jun 09, 2025

Author(s): Anjali Vajigi and Subhadeep Roy

We investigate the dynamics of active paths during a two-phase flow of immiscible fluids under an external pressure drop ΔP. We demonstrate that this dynamics of new path opening plays a crucial role in understanding the nonlinear rheology for the one-dimensional capillary fiber bundle model in the …

[Phys. Rev. E 111, 065102] Published Mon Jun 09, 2025

Author(s): Peyman Rostami, Alexander Erb, Reza Azizmalayeri, Johanna Steinmann, Robert W. Stark, and Günter K. Auernhammer

We investigate the coalescence dynamics of two identical polymer solution drops on a solid substrate. Our primary focus is the influence of the elastocapillary number (Ec), which is defined as the ratio of the sample timescale (i.e., the polymer relaxation timescale) to the experimental viscous timescale of drop merging. The dynamics of the liquid bridge depend non-monotonically on Ec. A combination of surface tension, polymer stress, and viscosity shapes the bridge profile during the process.

[Phys. Rev. Fluids 10, 063603] Published Fri Jun 06, 2025

Author(s): Jiacheng Yang, Xinshu Zhang, and Jinyu Yao

In this study, with the prediction directly from the framework based on the Zakharov equation using kernels in Hamiltonian form, instability regions were obtained in different water depths. Extensive numerical simulations were conducted using a higher-order spectral method to investigate the modulational instability. Numerical simulations confirm that sidebands grow exponentially, suggesting that there is noticeable modulational instability in shallow water at dimensionless water depth 0.8. An evident amplification can also be achieved.

[Phys. Rev. Fluids 10, 064801] Published Fri Jun 06, 2025

Author(s): Luke Neville

The steady Stokes flow around two unequally sized parallel cylinders is solved for exactly using tools from complex analysis and conformal mapping, generalizing the known solutions for a cylinder moving by a plane wall, and two equal cylinders. The resulting flows are highly constrained by the condition that the system be force and torque free, with it impossible to move one cylinder independently of the other.

[Phys. Rev. Fluids 10, 064102] Published Thu Jun 05, 2025