Article
Mechanics
L. Djenidi, R. A. Antonia
Summary: The study shows that there are differences in the solutions of the Karman-Howarth equation between forced turbulence and decaying turbulence, mainly due to the generation of large-scale motions in forced turbulence. As the Reynolds number increases, the impact of forcing on small scales decreases, allowing the KHEq solutions to agree well with spectrally based solutions at scales unaffected by forcing.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Hanxun Yao, Tamer A. Zaki, Charles Meneveau
Summary: Based on the generalized local Kolmogorov-Hill equation, this study examines the definition of entropy and entropy generation for turbulence. The results from direct numerical simulations confirm the validity of the fluctuation relation in non-equilibrium thermodynamics for turbulent flows in the inertial range.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Maurizio Carbone, Michael Wilczek
Summary: Statistically homogeneous flows follow exact kinematic relations, with the Betchov homogeneity constraints being one of the most well-known and extensively used homogeneity relations. These relations have significant implications for the dynamics of fluids and turbulent energy cascade.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Daniel Clark, Andres Armua, Richard D. J. G. Ho, Arjun Berera
Summary: Through numerical simulations, the study explores homogeneous and isotropic turbulence in higher spatial dimensions, focusing on chaos and predictability. The results reveal a transition to a non-chaotic regime above a critical dimension of approximately 5.88, highlighting the significance of Kolmogorov's 1941 theory in the context of turbulence properties.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Alberto Vela-Martin, Javier Jimenez
Summary: This paper analyzes the turbulent energy cascade from the perspective of statistical mechanics, testing the microscopical reversibility of the cascade and studying the origin of statistical irreversibility and the prevalence of direct and inverse energy cascades.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Miguel P. Encinar
Summary: Three-dimensional turbulent flows enhance velocity gradients through strong nonlinear interactions. The 'Betchov' relations define a length scale, and it is found that isotropic cascade models need not distinguish between vortex stretching and strain self-amplification.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Miguel P. Encinar, Javier Jimenez
Summary: The algorithm introduced by Jimenez (J. Fluid Mech., vol. 854, 2018, R1) is used to identify the flow patterns of causal significance in three-dimensional isotropic turbulence. The study finds that the dimensions of the perturbations introduced in the flow are controlled by the kinetic energy content and the enstrophy and dissipation, and affect their significance in the flow. Strain is found to be more efficient than vorticity in propagating the perturbation contents to other regions of the flow. The findings suggest that manipulating strain-dominated vortex clusters is more effective in controlling turbulent flows.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Takeshi Matsumoto, Michio Otsuki, Takeshi Ooshida, Susumu Goto
Summary: We studied the correlation function and mean linear response function of velocity Fourier mode of statistically steady-state, homogeneous and isotropic turbulence in Eulerian and Lagrangian coordinates through direct numerical simulation. The relation between the two functions was found to be disproportional, contrary to the fluctuation-dissipation theorem. Characteristic times associated with the functions were identified and compared between Eulerian and Lagrangian coordinates, showing different scalings in the inertial range.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Kazuhiro Inagaki
Summary: This study investigates the impact of helicity on scale-similar structures of turbulence, revealing that the energy cascade process in the scale-similar range is completely independent of helicity. Additionally, it is found that the helicity cascade is slightly non-local in scales compared to the energy cascade.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Xiangjun Wang, Minping Wang, Luca Biferale
Summary: This study investigates the accelerations of tracer and light particles in compressible homogeneous isotropic turbulence. The results show that the characteristics of acceleration vary for tracer particles and bubbles, and are closely related to the flow structures.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
A. Ababaei, B. Rosa, J. Pozorski, L. -P. Wang
Summary: This study investigates the dynamics of inertial particles in turbulence and found that considering lubrication forces and gravity can affect the relative velocities and distribution functions of particles in the near-contact region. However, the effect is minimal away from contact regions, and mass loading significantly impacts collision statistics.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
John B. Bell, Andrew Nonaka, Alejandro L. Garcia, Gregory Eyink
Summary: The study investigates the effect of thermal fluctuations in the dissipation range of homogeneous isotropic turbulence using fluctuating hydrodynamics. It confirms theoretical predictions regarding the dominance of these fluctuations in the energy spectrum at length scales comparable to the Kolmogorov length and the presence of Gaussian thermal equipartition in the far-dissipation range.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Sualeh Khurshid, Diego A. Donzis, Katepalli R. Sreenivasan
Summary: This study utilized a database of highly resolved direct numerical simulations of three-dimensional isotropic turbulence to analyze the temporal behaviors of spectral transfer and energy. The results showed that energy transfer fluctuates by an order of magnitude around its temporal average in the inertial range, with only slow fluctuations having unidirectional properties.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Alberto Vela-Martin
Summary: This investigation questions the importance of inverse interscale energy fluxes for the modelling of the energy cascade in large-eddy simulations. It explores alternative representations of the local subgrid-scale (SGS) energy fluxes that produce negligible backscatter. These findings suggest that the energy cascade is strongly unidirectional locally and can be modelled as an irreversible sink of energy.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jin-Han Xie, Shi-Di Huang
Summary: Through simulations of an idealized isotropic convection system, we provide evidence for the existence of Bolgiano-Obukhov (BO) scaling in Rayleigh-Benard convection (RBC) and establish its association with the inverse kinetic energy cascade. We also observe strong intermittent effects in the buoyancy field, but not in the velocity.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Alexandros Alexakis, Marc-Etienne Brachet
JOURNAL OF FLUID MECHANICS
(2020)
Article
Physics, Fluids & Plasmas
Rahul Agrawal, Alexandros Alexakis, Marc E. Brachet, Laurette S. Tuckerman
PHYSICAL REVIEW FLUIDS
(2020)
Article
Physics, Fluids & Plasmas
Alexandros Alexakis, Sergio Chibbaro
PHYSICAL REVIEW FLUIDS
(2020)
Article
Mechanics
Takahiro Nemoto, Alexandros Alexakis
Summary: The study reveals that the decay time scale of turbulence in pipe flows increases double-exponentially as Reynolds number approaches its critical value, influenced by the transition between stable turbulence and metastable states.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Fluids & Plasmas
Alexandros Alexakis, Francois Petrelis, Santiago J. Benavides, Kannabiran Seshasayanan
Summary: This study investigates symmetry breaking in a turbulent environment, showcasing the transition from a symmetric state to a symmetry-breaking state through two examples. The critical behavior of these transitions is shown to be related to the multiplicative nature of fluctuations and can be predicted in certain limits using results from statistical properties of random interfaces. The results suggest the existence of a new class of out-of-equilibrium phase transitions controlled by multiplicative noise.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Mechanics
Adrian van Kan, Alexandros Alexakis
Summary: This study investigates forced, rapidly rotating and stably stratified turbulence using an asymptotic expansion method, focusing on a region that is difficult to attain through direct numerical simulations. The study reveals the occurrence of forward and split energy cascades in this region, and presents theoretical arguments supporting the observed energy cascade phenomena.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Xander M. de Wit, Adrian van Kan, Alexandros Alexakis
Summary: In this study, direct numerical simulations of thin-layer flow were used to investigate whether the bistable range survives as the domain size and turbulence intensity are increased. The research found that the bistable range grows as the box size and/or Reynolds number Re are increased.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Fluids & Plasmas
Alexandros Alexakis, Sergio Chibbaro
Summary: In this study, the statistical properties of the local energy flux rate towards small scales in three isotropic turbulent magnetohydrodynamic flows with different magnetic field strengths and structures were examined using highly resolved direct numerical simulations. The results showed that the probability distribution of the local energy flux exhibited long tails related to extreme events, similar to the hydrodynamic case. The different terms of the energy flux displayed different properties and showed sensitivity to the type of flow examined. Furthermore, a correlation was observed between the local energy flux and the gradients of the involved fields, with a stronger dispersion than in hydrodynamic flows. Additionally, the local energy flux was found to depend on the local amplitude of the magnetic field to some extent.
JOURNAL OF PLASMA PHYSICS
(2022)
Article
Physics, Multidisciplinary
Guillaume Bermudez, Alexandros Alexakis
Summary: The presence of large scale magnetic fields in nature is often attributed to the inverse cascade of magnetic helicity driven by turbulent helical dynamos. In this study, the authors show that the inverse flux of magnetic helicity toward the large scales is bounded by a certain constant and decreases with the magnetic Reynolds number. Numerical simulations demonstrate that the nonlinear saturation is achieved by a balance between the inverse cascade and dissipation, with the saturation value of the magnetic energy determined by the domain size scales, magnetic Reynolds number, and magnetic Prandtl number. These findings have critical implications for the modeling of astrophysical dynamos.
PHYSICAL REVIEW LETTERS
(2022)
Article
Environmental Sciences
Ben Ajzner, Alexandros Alexakis
Summary: This study examines a turbulence shell model to investigate the probability distributions of velocity modes with changing scales. It demonstrates that while velocity amplitudes are not scale-invariant, their ratios are. Furthermore, the study shows how the probability distributions of velocity modes can be re-scaled to present a scale-independent form using large deviation theory.
Article
Physics, Multidisciplinary
Akhilesh Kumar Verma, Rahul Pandit, Marc E. Brachet
Summary: The study explores the formation of finite-temperature compact objects in self-gravitating bosonic systems through direct numerical simulations. It shows that the system undergoes a thermally driven first-order transition from a collapsed Bose-Einstein condensate to a tenuous Bose gas over a wide range of model parameters, and also obtains a binary condensate comprising a pair of collapsed objects rotating around their center of mass through suitable initial conditions in the GPPE.
PHYSICAL REVIEW RESEARCH
(2021)
Article
Physics, Fluids & Plasmas
Adrian van Kan, Alexandros Alexakis, Marc-Etienne Brachet
Summary: The paper proposes a simple, energy-conserving model to describe the three-dimensional instabilities growing on two-dimensional flows and studies the evolution of the model in different stages. It identifies specific growth patterns and nonlinear phenomena, which are important for understanding and analyzing DNS results and guiding further theoretical developments.
Article
Physics, Fluids & Plasmas
Adrian van Kan, Alexandros Alexakis, Marc-Etienne Brachet
Summary: In this study, Levy on-off intermittency arising from multiplicative alpha-stable white noise close to an instability threshold was investigated in linear and nonlinear regimes for a pitchfork bifurcation with fluctuating growth rate. Different parameter regimes were identified, with critical exponents computed from the stationary distribution. The properties of the system, influenced by nonequilibrium, power-law-distributed fluctuations, were found to be substantially different from Gaussian thermal fluctuations in terms of statistics and critical behavior.