Latest papers in fluid mechanics

Author(s): Anton Glazkov, Miguel Fosas de Pando, Peter J. Schmid, and Li He

Aeroacoustic effects are commonly neglected in the design of high-performance turbomachinery. This study concentrates on the role of acoustic feedback mechanisms for compressible flow through a single-blade configuration. It uses global and adjoint stability tools, together with impulse responses and structural sensitivities, to quantify the impact of propagating sound waves on the overall flow dynamics.

[Phys. Rev. Fluids 8, 103903] Published Wed Oct 11, 2023

Author(s): Anton Glazkov, Miguel Fosas de Pando, Peter J. Schmid, and Li He

This study generalizes the previous investigation (Part I) to multiple-blade passages, focusing in particular on synchronization and phase-locking effects across several neighboring blades. Arising large-scale low-frequency structures, spanning multiple identical flow units, are described and analyzed, and their role within the overall stability framework is determined.

[Phys. Rev. Fluids 8, 103904] Published Wed Oct 11, 2023

Author(s): J. Zhang, A. Hector, M. Rabaud, and F. Moisy

Understanding the process of wave generation by the wind remains a formidable challenge for scientists. While the majority of research has concentrated on the air-water interface, where viscous effects are minimal, our study focuses on the influence of liquid viscosity on the development of mechanically generated waves. Using Synthetic-Schlieren measurements of wind-generated waves over silicon oils 20 and 50 times more viscous than water, we show that Miles’ model, conventionally applied to water waves, also provides an accurate description of wave growth in more viscous liquids. We further explore the dependence of the maximum growth rate and critical wind velocity with the liquid viscosity.

[Phys. Rev. Fluids 8, 104801] Published Wed Oct 11, 2023

Author(s): Beinan Jia and Yongjun Jian

We report the stability of a falling incompressible odd viscosity fluid on flexible substrates when the time-reversal symmetry is broken. The flexible wall equation incorporates the contribution of odd viscosity, where the stress at an interface is determined by the viscosities of the adjacent fluid…

[Phys. Rev. E 108, 045104] Published Tue Oct 10, 2023

Author(s): K. Lüdemann and A. Tilgner

We simulate numerically convection in a rectangular cell filled with an ideal gas rotating about an axis perpendicular to the direction of gravity, corresponding to an experiment with a convection cell placed in a rapidly rotating centrifuge in which the centrifugal force plays the role of gravity. The compressibility of the gas in combination with the rotation of the cell leads to a drifting mode at the onset of convection even in the presence of sidewalls. The temporal variation of this mode is rapid enough to cause the anelastic approximation to fail at parameters typical of realizable laboratory experiments. We also investigate the heat transport in such a convection cell.

[Phys. Rev. Fluids 8, 103502] Published Tue Oct 10, 2023

Author(s): Jean-Lou Pierson

The settling of rods is ubiquitous in nature and industry. In inertial regimes, the body’s orientation is coupled to the translational equation of motion which makes the problem unsteady and very hard to solve analytically. In this article, we focus on two regimes: the very short-time and long-time dynamic of an arbitrarily oriented cylinder settling under gravity.

[Phys. Rev. Fluids 8, 104301] Published Tue Oct 10, 2023

Author(s): Akhilesh Kumar Verma, Sanjay Shukla, Vishwanath Shukla, Abhik Basu, and Rahul Pandit

We obtain the von Kármán–Howarth relation for the stochastically forced three-dimensional (3D) Hall-Vinen-Bekharevich-Khalatnikov (HVBK) model of superfluid turbulence in helium (He4) by using the generating-functional approach. We combine direct numerical simulations (DNSs) and analytical studies t…

[Phys. Rev. E 108, 045103] Published Mon Oct 09, 2023

Author(s): Valentin Dorel, Patrice Le Gal, and Michael Le Bars

Penetrative convection is the interaction between a lower turbulent convective layer of fluid and an upper stably-stratified one. It plays a key role in the atmosphere’s dynamics and in stellar interiors. In this study, we built an experiment of penetrative convection in gases which is closer to the geophysical applications. The internal gravity waves field is studied, as well as the growth of the convective layer. In our setup, the convective layer grows quadratically in time which is strikingly different from the 1/2 exponent obtained with classical models and salted water experiments.

[Phys. Rev. Fluids 8, 103501] Published Mon Oct 09, 2023

Author(s): Daniele Massaro, Fulvio Martinelli, Peter Schmid, and Maurizio Quadrio

Methods for reducing turbulent skin-friction drag are seldom employed in the context of laminar flows, where the level of frictional drag is already low. This work explores the possibility that such technologies may affect a laminar flow during transition. Here we consider a parallel shear flow. Its temporal stability is studied when a standing wave of spanwise wall velocity alters the base flow, making it three-dimensional. It is found that the spanwise forcing has a profound and positive effect on the stability of the flow, with a significant reduction of the nonmodal instability.

[Phys. Rev. Fluids 8, 103902] Published Mon Oct 09, 2023

Author(s): Ryo Enoki, Tomoaki Watanabe, and Koji Nagata

Velocity fields induced by small-scale shear layers and vortex tubes in turbulence are investigated with the triple decomposition of a velocity gradient tensor. The velocity fields are reconstructed with the Biot-Savart law applied to the vorticity vectors of shear and rigid-body rotation. The key image shows a mean flow pattern of small-scale shear layers in isotropic turbulence. The velocity associated with the shear layers dominates the turbulent kinetic energy budget, scalar transport, and energy cascade in isotropic turbulence and planar jets.

[Phys. Rev. Fluids 8, 104602] Published Mon Oct 09, 2023

Author(s): Rajat Mittal and Jung Hee Seo

By summarizing the historical trajectory of immersed boundary methods and addressing some frequently asked questions about these methods, this article attempts to empower researchers to innovate in ways that advance the state-of-the-art in these methods.

[Phys. Rev. Fluids 8, 100501] Published Fri Oct 06, 2023

Author(s): Khemraj Gautam Kshetri and Nitesh Nama

Acoustofluidic systems often employ prefabricated acoustic scatterers that perturb the imposed acoustic field to realize the acoustophoresis of immersed microparticles. We present a numerical study to investigate the time-averaged streaming and radiation force fields around a scatterer. Based on the…

[Phys. Rev. E 108, 045102] Published Thu Oct 05, 2023

Author(s): Qing Wang, Feng Qu, Zeyu Wang, Di Sun, and Junqiang Bai

This paper focuses on secondary instabilities in the shear layer of a supersonic jet over a convex wall. The methods of conditional averaging and dynamic mode decomposition analysis are involved to quantitatively investigate the roll-modes and secondary instability modes. Both sinuous- and varicose-type secondary instabilities and their competitions exist in the shear layer. The mechanism of the instability is due to the velocity fluctuations and Reynolds stress parallel to the local mean flow gradient. The local inflection point instability caused by the mean flow gradient is also the source of turbulent energy that sustains the instabilities.

[Phys. Rev. Fluids 8, 103901] Published Thu Oct 05, 2023

Author(s): Jesse Reijtenbagh, Jerry Westerweel, and Willem van de Water

The Lyapunov field measures the sensitivity to small perturbations of the fluctuating flow behind an accelerated plate. Using a robot, we repeat this experiment 42 times and measure the difference between the flows as they turn turbulent. The Lyapunov field of a single experiment (left) mirrors the (logarithmic) difference between its 42 repetitions (right). It is an expression of ergodicity, and a vivid illustration of the butterfly effect.

[Phys. Rev. Fluids 8, 104601] Published Thu Oct 05, 2023

Author(s): Anneline H. Christensen, Ankur Gupta, Guang Chen, Winfried S. Peters, Michael Knoblauch, Howard A. Stone, and Kaare H. Jensen

Molecular diffusion in bulk liquids proceeds according to Fick's law, which stipulates that the particle current is proportional to the conductive area. This constrains the efficiency of filtration systems in which both selectivity and permeability are valued. Previous studies have demonstrated that…

[Phys. Rev. E 108, 045101] Published Wed Oct 04, 2023

Author(s): Gonçalo Coutinho, Ana S. Moita, Massimiliano Rossi, and António L. N. Moreira

Rigid particles in red blood cell (RBC) flows are forced to migrate to the near-wall region, through a phenomenon known as margination. In this work, we use a three-dimensional particle tracking method to provide an experimental perspective into the intricate dynamics of synthetic particles within RBC flows and make a significant departure from the simulation-driven research landscape in microcirculation studies, where experimental data has been notably scarce. The experimental results show the critical role of the physical interactions between synthetic particles and RBCs in triggering margination: A phenomenon characterized by speed, irreversibility, and unpredictability.

[Phys. Rev. Fluids 8, 103101] Published Mon Oct 02, 2023

Author(s): Bjørn G. Winckelmann and Henrik Bruus

Analytical expressions are derived for the time-averaged, quasisteady, acoustic radiation force on a heated, spherical, elastic, solid microparticle suspended in a fluid and located in an axisymmetric incident acoustic wave. The heating is assumed to be spherically symmetric, and the effects of part…

[Phys. Rev. E 108, 035108] Published Fri Sep 29, 2023

Author(s): Darren Crowdy, Michael Mayer, and Marc Hodes

A novel low-Reynolds-number fluid pump architecture is proposed wherein the offset interdigitated teeth of a hot comb and a cold comb in contact with a liquid cause its unidirectional motion due to thermocapillary stresses active along the unequal menisci between the teeth. The pump involves no moving parts, requires no external driving pressure, and pumps a continuous stream of liquid rather than a series of discrete droplets.

[Phys. Rev. Fluids 8, 094201] Published Thu Sep 28, 2023

Author(s): Animesh Biswas, Trinh Huynh, Balaram Desai, Max Moss, and Arshad Kudrolli

We investigate the dynamics of magnetoelastic robots as they move through a water-saturated granular bed with transverse undulation of the body being actuated by an oscillating magnetic field. The robots create dynamic burrows as they fluidize the medium and move with speeds that depend on the field frequency and strength and the sediment depth. A transition from nearly rigid to anguilliform body motion is observed because of a subtle balance of thrust, drag, and elastic forces. The overall trends in the robot’s speed are generally consistent with Lighthill’s theory of elongated body swimming.

[Phys. Rev. Fluids 8, 094304] Published Thu Sep 28, 2023

Author(s): Yuhong Li, Xiangtian Li, Han Wu, Peng Zhou, Xin Zhang, and Siyang Zhong

We investigate the aerodynamic and aeroacoustic characteristics of a small-scale drone rotor operating in axial descending flight. The integrated aerodynamic forces and the far-field noise are measured by wind tunnel experiments. Then, near-field flow structures and corresponding noise source analysis are presented based on computational aeroacoustics (CAA) simulations. We found the unique acoustic feature of descending flight is the haystacking-like spectral humps, possibly caused by the interaction between the blade leading edge and the rotor wake.

[Phys. Rev. Fluids 8, 094803] Published Thu Sep 28, 2023