Physical Review Fluids

Author(s): Irmak T. Karpuzcu and Deborah A. Levin

Axial symmetry is a common assumption in hypersonic flows over conical geometries, yet many exhibit unsteady, three-dimensional instabilities. Using triple-deck theory, linear stability analysis, and direct simulation Monte Carlo, we examine non-axisymmetric azimuthal eigenmodes in Mach 16 flows. The strongest amplification occurs for azimuthal wavenumber n=1 near the cone tip due to interactions between the conical shock and the viscous shear layer. In double-cone flows, these three-dimensional effects alter the surface properties where the transmitted conical shock hits the wall, challenging axial symmetry assumptions and laminar-to-turbulent transition.

[Phys. Rev. Fluids 10, 033901] Published Fri Mar 07, 2025

Author(s): Yaxing Li, Henri Sanness Salmon, Roumaissa Hassaini, Kelken Chang, Claudio Mucignat, and Filippo Coletti

This study examines how underwater turbulence shapes the movement and clustering of floating particles with relevance to environmental processes like micro-plastic dispersion or oil spills. Experiments in water tunnels were conducted, generating controlled turbulence beneath a flat surface. We find that floating particles form clusters matching the size and duration of large underwater swirls, persisting as long as these turbulent structures exist. While the water surface appears calm, hidden three-dimensional turbulence below creates surface flows with two-dimensional-like features, trapping particles in long-lived vortices.

[Phys. Rev. Fluids 10, 034602] Published Fri Mar 07, 2025

Author(s): J. V. Roggeveen and H. A. Stone

In low-Reynolds-number flows, active swimmers can create non-reciprocal swimming strategies to achieve sustained propulsion. However, by virtue of their geometry and deformability, it is also possible for passive particles to drift or move in directions different from the mean background flow. We study hinge-shaped particles and demonstrate that adding elasticity leads to symmetry breaking and drift in oscillating flows and characterize the influence of deformability on drift.

[Phys. Rev. Fluids 10, 034401] Published Thu Mar 06, 2025

Author(s): J. V. Roggeveen and H. A. Stone

In low-Reynolds-number flows, active swimmers can create non-reciprocal swimming strategies to achieve sustained propulsion. However, by virtue of their geometry and deformability, it is also possible for passive particles to drift or move in directions different from the mean background flow. We study hinge-shaped particles and demonstrate that adding elasticity leads to symmetry breaking and drift in oscillating flows and characterize the influence of deformability on drift.

[Phys. Rev. Fluids 10, 034401] Published Thu Mar 06, 2025

Author(s): Sergei Badulin, Vladimir Gnevyshev, and Yury Stepanyants

Wave wakes produced by a finite-size source uniformly moving on an ice plate overlying deep water is studied. The kinematic and amplitude characteristics of source-generated flexural-gravity waves are presented in terms of isophase patterns; the wave patterns are determined by ad hoc defined analogues of Mach and Bond numbers. The Reference Solution Approach is used to describe the distribution of wave amplitudes in the wake accounting for the source size and shape. This approach agrees with the Stationary Phase Method in the far-field zone and reproduces also specific wave dynamics at short and intermediate distances from the source.

[Phys. Rev. Fluids 10, 034801] Published Tue Mar 04, 2025

Author(s): Yaxin Mo and Luca Magri

Measurements taken from fluid flows are often sparse, noisy, and from a mix of pressure and velocity data. In this paper, we develop a physics-constrained neural network to reconstruct the full flow field from incomplete measurements. We propose a new loss function specifically for reconstructing flows from noisy, sparse measurements. We reconstruct a laminar bluff body wake and a chaotic Kolmogorov flow from sparse measurements and stochastic noise.

[Phys. Rev. Fluids 10, 034901] Published Tue Mar 04, 2025

Author(s): Yaxin Mo and Luca Magri

Measurements taken from fluid flows are often sparse, noisy, and from a mix of pressure and velocity data. In this paper, we develop a physics-constrained neural network to reconstruct the full flow field from incomplete measurements. We propose a new loss function specifically for reconstructing flows from noisy, sparse measurements. We reconstruct a laminar bluff body wake and a chaotic Kolmogorov flow from sparse measurements and stochastic noise.

[Phys. Rev. Fluids 10, 034901] Published Tue Mar 04, 2025

Author(s): Weiqi Sun, Jimmy Philip, Wolfgang Schröder, and Joseph Klewicki

We numerically investigate the evolution of small-scale synthetic streamwise vortices in low-friction-Reynolds-number turbulent boundary layers. After analyzing statistical structures associated with these near-wall synthetic and naturally occurring streamwise vortices, we observe the similarities regarding their scales and the signature of kinetic energy transport. These similarities indicate that embedded small synthetic streamwise vortices of a spanwise scale comparable to those in canonical turbulent boundary layers are self-contained in the near-wall region and directly interact with the structures in this area toinfluence the associated turbulent transport.

[Phys. Rev. Fluids 10, 034601] Published Mon Mar 03, 2025

Author(s): H. D. Lim, B. Zang, Junfei Ding, Shengxian Shi, and T. H. New

In this study, we show that side jets can be produced by introducing strong forcing on V-notched nozzle jets. We demonstrate that the plane along which the side jets are formed can be controlled by varying the forcing frequency, where the side jets can drastically increase the spread rate and enhance mixing.

[Phys. Rev. Fluids 10, 034701] Published Mon Mar 03, 2025

Author(s): Brett A. Meyers and Pavlos P. Vlachos

Echocardiography and cardiac MRI have helped expand understanding of complex fluid dynamics within the heart’s chambers. However, many of the advances have yet to be fully used in clinical practice. We explore the role of fluid mechanics in intracardiac flow analysis and in assessing cardiac function and diagnosing diseases. Emerging trends include a shift from pressure-based assessments to more detailed analyses of flow energy and vortex dynamics, and the use of machine learning. Reproducibility and standardization remain challenging. Critical research needs are identified, including validating fluid mechanics measurements and developing a unified framework for intracardiac flow analysis.

[Phys. Rev. Fluids 10, 020501] Published Fri Feb 28, 2025

Author(s): Brett A. Meyers and Pavlos P. Vlachos

Echocardiography and cardiac MRI have helped expand understanding of complex fluid dynamics within the heart’s chambers. However, many of the advances have yet to be fully used in clinical practice. We explore the role of fluid mechanics in intracardiac flow analysis and in assessing cardiac function and diagnosing diseases. Emerging trends include a shift from pressure-based assessments to more detailed analyses of flow energy and vortex dynamics, and the use of machine learning. Reproducibility and standardization remain challenging. Critical research needs are identified, including validating fluid mechanics measurements and developing a unified framework for intracardiac flow analysis.

[Phys. Rev. Fluids 10, 020501] Published Fri Feb 28, 2025

Author(s): Ming Yu, Yibin Du, Qian Wang, Siwei Dong, and Xianxu Yuan

This paper employs direct numerical simulations at Mach 2 to reveal how particles with infinite thermal inertia, acting as persistent heat sinks or sources, drastically alter turbulence statistics and coherent structures. Hot particles suppress turbulence by weakening velocity streaks and vortical motions, whereas cold particles amplify Reynolds shear stress and skin friction. Crucially, particle feedback forces inhibit wall-normal fluctuations, with heat transfer aligning coherently with ejection and sweeping events.

[Phys. Rev. Fluids 10, 024606] Published Fri Feb 28, 2025

Author(s): Ming Yu, Yibin Du, Qian Wang, Siwei Dong, and Xianxu Yuan

This paper employs direct numerical simulations at Mach 2 to reveal how particles with infinite thermal inertia, acting as persistent heat sinks or sources, drastically alter turbulence statistics and coherent structures. Hot particles suppress turbulence by weakening velocity streaks and vortical motions, whereas cold particles amplify Reynolds shear stress and skin friction. Crucially, particle feedback forces inhibit wall-normal fluctuations, with heat transfer aligning coherently with ejection and sweeping events.

[Phys. Rev. Fluids 10, 024606] Published Fri Feb 28, 2025

Author(s): Qing Gong (龚庆), Yi-Fei Huang (黄逸飞), Juan-Cheng Yang (阳倦成), and Ming-Jiu Ni (倪明玖)

The transition from zigzag mode to B-interface instability mode is experimentally observed in a Hele-Shaw cell filled with three liquid layers. The interface coupling effect is considered to be the determinant factor triggering this Faraday instability. Considering the zero-order interface coupling effect, we identify that the mode transition can be promoted by increasing the wave number and thickness of the middle layer liquid. Furthermore, by including the impact of first-order interface coupling, it is evident that a decrease in vibration acceleration and an increase in viscosity can promote mode transition from the dispersion relation.

[Phys. Rev. Fluids 10, 024005] Published Wed Feb 26, 2025

Author(s): Qing Gong (龚庆), Yi-Fei Huang (黄逸飞), Juan-Cheng Yang (阳倦成), and Ming-Jiu Ni (倪明玖)

The transition from zigzag mode to B-interface instability mode is experimentally observed in a Hele-Shaw cell filled with three liquid layers. The interface coupling effect is considered to be the determinant factor triggering this Faraday instability. Considering the zero-order interface coupling effect, we identify that the mode transition can be promoted by increasing the wave number and thickness of the middle layer liquid. Furthermore, by including the impact of first-order interface coupling, it is evident that a decrease in vibration acceleration and an increase in viscosity can promote mode transition from the dispersion relation.

[Phys. Rev. Fluids 10, 024005] Published Wed Feb 26, 2025

Author(s): Varun Shankar, Dibyajyoti Chakraborty, Venkatasubramanian Viswanathan, and Romit Maulik

Improved turbulence closure models for large eddy simulations (LES) have the potential to impact a large variety of societal applications. This work introduces differentiable turbulence, where deep learning is embedded within a differentiable LES solver to enhance closure models given sparse observations of the true flow state. By leveraging physics-informed neural network architectures and solver-in-the-loop optimization, we put forth a technique that allows for the learning of novel closures without the use of high-fidelity numerical simulations - opening a pathway to the development and identification of LES closures in a multifidelity setting.

[Phys. Rev. Fluids 10, 024605] Published Wed Feb 26, 2025

Author(s): Varun Shankar, Dibyajyoti Chakraborty, Venkatasubramanian Viswanathan, and Romit Maulik

Improved turbulence closure models for large eddy simulations (LES) have the potential to impact a large variety of societal applications. This work introduces differentiable turbulence, where deep learning is embedded within a differentiable LES solver to enhance closure models given sparse observations of the true flow state. By leveraging physics-informed neural network architectures and solver-in-the-loop optimization, we put forth a technique that allows for the learning of novel closures without the use of high-fidelity numerical simulations - opening a pathway to the development and identification of LES closures in a multifidelity setting.

[Phys. Rev. Fluids 10, 024605] Published Wed Feb 26, 2025

Author(s): Jiyoung Lee, Leon Chan, Tony Zahtila, Wilson Lu, Gianluca Iaccarino, and Andrew Ooi

We investigate methods for mapping between low- and high-resolution simulations to generate surrogate models, which would significantly reduce the overall computational costs. Our focus is on interpolative decomposition, a rank-revealing matrix decomposition technique that efficiently selects key parameters to minimize the number of required simulation sets. We demonstrate that this approach remains effective even in the presence of multiple flow regimes (mode transitions) and show that the mapping process can also function as a classification tool for identifying different flow modes.

[Phys. Rev. Fluids 10, 024703] Published Wed Feb 26, 2025

Author(s): Jaewuk Jung, Jihoo Moon, and Daegyoum Kim

This study presents a method of generating oscillating jets in conductive fluids with time-varying Lorentz force, which eliminates the need for complex nozzle geometries or active components. A steady jet under constant forcing is modeled as a baseline to examine the effects of electromagnetic and fluid variables on jet deflection. Furthermore, the classification of oscillating jet behaviors with respect to Strouhal number and Stuart number reveals how variations in forcing frequency and electromagnetic parameters modulate jet structure. These findings enhance the understanding of electromagnetically controlled flows with broad implications for flow control and heat transfer.

[Phys. Rev. Fluids 10, 023701] Published Tue Feb 25, 2025

Author(s): Christopher J. Camobreco, Alban Pothérat, and Gregory J. Sheard

This work investigates efficient routes to turbulence in quasi-two-dimensional (Q2D) shear flows. When the base flow is steady, transient growth is modest, as the initial perturbations are two-dimensional. With the addition of an oscillatory base flow component, the transient growth of even two-dimensional initial perturbations increases dramatically. However, as has been shown for three-dimensional flows, this transient growth proves to be almost entirely modal intracyclic growth, rather than non-normal growth, which delays sustained turbulence. Thus, in these Q2D flows, a non-oscillatory driving force sustains turbulence more efficiently than a pulsatile one.

[Phys. Rev. Fluids 10, 023905] Published Tue Feb 25, 2025