Article
Mechanics
Xuan Zhang, Robert E. Ecke, Olga Shishkina
Summary: In rapidly rotating turbulent Rayleigh-Benard convection with a small Prandtl number fluid in slender cylindrical containers, a boundary zonal flow (BZF) is found to develop near the sidewall, carrying a disproportionate amount of heat transport for Pr < 1 but decreasing abruptly for larger Pr. The BZF is robust and appears in containers of different aspect ratios and over a broad range of Pr and Ra values.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Geert Brethouwer
Summary: The study shows that rotation can significantly influence passive tracer transport in shear flows, making it much faster than momentum transport, in violation of the Reynolds analogy. This dissimilarity is observed in steady flows with large counter-rotating vortices at low Reynolds numbers as well as in fully turbulent flows at higher Reynolds numbers. The Coriolis force induced by rotation dampens velocity fluctuations more strongly than tracer fluctuations near the neutral stability limit, breaking the Reynolds analogy.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Yufeng Lin, Andrew Jackson
Summary: This study focuses on the dynamics of Boussinesq convection in a rotating full sphere, particularly on the development of large-scale coherent structures and mean zonal flows. The research reveals the critical role of the convective Rossby number in the formation and transition of large-scale vortices.
JOURNAL OF FLUID MECHANICS
(2021)
Review
Mathematics, Applied
Artur Perevalov, Ruben E. Rojas, Daniel P. Lathrop
Summary: In this experiment, the dissipation of kinetic energy to heat in rotating turbulent shear flows was studied by torque measurements. The purpose was to understand rotating turbulence in atmospheres, oceans, and liquid planetary cores, as well as the role of viscosity in the Kolmogorov-Constantin-Doering limit. The findings showed that differential rotation in cylindrical and spherical Couette flows could either enhance or reduce dissipation. Additionally, new results regarding increased scaling exponents in rough spherical Couette flows were documented.
PHYSICA D-NONLINEAR PHENOMENA
(2023)
Article
Mechanics
Mohammed Hussein Hamede, Sebastian Merbold, Christoph Egbers
Summary: This experiment studies the turbulent Taylor-Couette flow between two concentric independently rotating cylinders with a radius ratio of 0.1. The flow patterns are observed to depend on the rotation ratio, showing a more pronounced axial dependence. The angular momentum transport is calculated using recorded flow fields and exhibits a maximum for low counter-rotating cases. The space-time behavior of the turbulent flow reveals patterns propagating from both the inner and outer regions, enhancing the angular momentum transport.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Astronomy & Astrophysics
A. Barekat, M. J. Kaepylae, P. J. Kaepylae, E. P. Gilson, H. Ji
Summary: The study found that a negative radial gradient of the mean flow is only generated at the equator, where meridional flows are absent. At other latitudes, the meridional flow is comparable to the mean flow corresponding to differential rotation. Additionally, it was observed that the meridional components of the Reynolds stress cannot be ignored, and the turbulent viscosity is quenched by rotation by about 50% from the surface to the bottom of the NSSL.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Geochemistry & Geophysics
Taylor L. Lonner, Ashna Aggarwal, Jonathan M. Aurnou
Summary: This study simulates turbulent convection in a planet's outer core using a thermally-driven, free surface paraboloidal laboratory annulus. The researchers found that the dynamics of rapidly rotating convection in free-surface paraboloidal annuli are similar to those in planetary spherical shell geometries. The experiments showed the presence of thermal Rossby waves and multiple azimuthal jets, with more jets forming at higher rotation rates. The migration of the jets and the flux of energy into larger-scale zonal flow structures were also observed. The effects of ambient magnetic fields on such turbulent flows remain unknown.
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
(2022)
Article
Thermodynamics
Geert Brethouwer
Summary: Rotation has a significant impact on flows and transport processes in engineering applications, but its effects are not fully understood. In this study, numerical simulations are used to investigate the influence of rotation on heat and momentum transfer in Couette and Taylor-Couette flows. It is found that anti-cyclonic rotation initially increases the Nusselt numbers for momentum and heat transfer, but they decrease and approach unity at high rotation rates. The Reynolds analogy factor also increases with rotation, indicating that the heat transfer can become faster than momentum transfer.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2023)
Article
Mechanics
Running Hu, Xinliang Li, Changping Yu
Summary: The multiscale dynamics of streamwise-rotating channel turbulence is studied using direct numerical simulations. It is found that stronger rotation weakens the turbulence in the buffer layer, while other layers experience enhanced turbulence. Additionally, small- and large-scale inclined structures exhibit different angles with the streamwise direction, with the difference becoming more pronounced at higher rotation rates. The Coriolis force and pressure-velocity correlation are identified as important factors in sustaining the inclined structures.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Running Hu, Xinliang Li, Changping Yu
Summary: This paper studies the energy and helicity transfers of helical rotating turbulence and discusses their antisymmetry and conservation. Three expressions for helicity transfers are presented and their relationships are discussed. Direct numerical simulations show that helicity can reduce inverse energy cascades, mainly due to transhelical energy fluxes and the interactions of two-dimensional modes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Al Habib Ullah, Braden L. Rostad, Jordi Estevadeordal
Summary: The study reports the effects of turbulence levels created by a three-cylinder rotating system on the flow over a dimpled surface of an airfoil. Different angles of attack on a NACA0015 airfoil were tested at Reynolds numbers of 0.5 x 10(5) and 1.0 x 10(5) in a low-speed wind tunnel. The results show complex unsteady and turbulent flows generated by the rotating system, which interact with the airfoil flow and lead to significant effects on separation region and turbulence levels.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2021)
Article
Mechanics
X. Q. He, A. D. Bragg, Y. L. Xiong, P. Fischer
Summary: This study used direct numerical simulations to investigate the behavior of a rotating two-dimensional flow that is heated at its equator, where buoyancy and Coriolis forces lead to rich flow behavior. The research found a non-monotonic dependence of flow properties on the Rossby number for a given Rayleigh number, and large-scale mean circulations strongly influenced by rotation.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
S. L. Tang, R. A. Antonia, L. Djenidi
Summary: In this study, we analyze the approach towards local isotropy in statistically stationary turbulent shear flows using the transport equations for the fourth-order moments of the velocity derivative. It is found that, as the Taylor microscale Reynolds number increases, the large-scale contribution gradually decreases and the small-scale motion becomes more locally isotropic. The rate at which local isotropy is approached depends on the weakening of the large-scale forcing, which is controlled by the magnitude of the non-dimensional velocity shear parameter.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Astronomy & Astrophysics
Subham Ghosh, Banibrata Mukhopadhyay
Summary: Research demonstrates that rotation stabilizes plane Couette flow, while destabilizing plane Poiseuille flow faster, leading to turbulence in forced local accretion disks.
ASTROPHYSICAL JOURNAL
(2021)
Article
Mechanics
Dario Vincenzi, Takeshi Watanabe, Samriddhi Sankar Ray, Jason R. Picardo
Summary: This paper investigates polymer scission in turbulent flows through stochastic modeling and direct numerical simulations, studying the characteristics of both passive and active polymers. The results show that the reduction of kinetic energy dissipation is maximized by an intermediate polymer relaxation time, where polymers stretch significantly but do not break too quickly.
JOURNAL OF FLUID MECHANICS
(2021)
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
Mechanics
Adrian van Kan, Alexandros Alexakis
JOURNAL OF FLUID MECHANICS
(2020)
Article
Physics, Fluids & Plasmas
Basile Poujol, Adrian van Kan, Alexandros Alexakis
PHYSICAL REVIEW FLUIDS
(2020)
Article
Physics, Fluids & Plasmas
P. Clark Di Leoni, A. Alexakis, L. Biferale, M. Buzzicotti
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, 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.