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
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
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
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
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
Qinmin Zheng, Jianchun Wang, Md Mahbub Alam, Bernd R. Noack, Hui Li, Shiyi Chen
Summary: In this study, the transfer of internal energy fluctuation in stationary compressible isotropic turbulence was numerically investigated, where the spectra of velocity, pressure, density, and temperature exhibited scaling laws in the inertial range. The dominance of the solenoidal component over the dilatational component, and the roles of thermal conduction and vibrational relaxation in the dissipation of energy fluctuations were highlighted.
JOURNAL OF FLUID MECHANICS
(2021)
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
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
A. Gorbunova, G. Balarac, L. Canet, G. Eyink, V. Rossetto
Summary: The study uses direct numerical simulations to test recent theoretical predictions in a three-dimensional incompressible fluid. Results show agreement with predictions from the Functional Renormalization Group (FRG) and can be explained as a consequence of sweeping. Additionally, there is a crossover in the two-point spatiotemporal correlations of the velocity modulus from Gaussian to exponential decay.
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
Damiano Capocci, Perry L. Johnson, Sean Oughton, Luca Biferale, Moritz Linkmann
Summary: In this study, the relative contributions of different physical mechanisms to the energy cascade and helicity transfer in turbulence are quantified. It is found that scale-local vortex flattening and twisting dominate the helicity transfer, accounting for approximately 50% of the mean flux. A new exact relation between these effects is derived, showing the dominance of vortex flattening over twisting. The remaining 50% of the mean flux is attributed to multi-scale vortex flattening, twisting, and entangling.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
P. Baj, F. Alves Portela, D. W. Carter
Summary: In this study, we characterize the incompressible turbulence cascade by examining the inter-scale and inter-space exchanges of scale-by-scale energy, helicity, and enstrophy. We derive governing equations for scale-by-scale helicity and enstrophy similar to the second order structure function. Our analysis focuses on forced periodic turbulence and von Karman flow at different scales. We observe the random sweeping effect in all three individual budgets and between energy and enstrophy transfers. Additionally, we find a kinematic connection between the energy cascade and helicity. Overall, this work extends a classic framework and provides novel insights into turbulence dynamics.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Rishita Das, Sharath S. Girimaji
Summary: By examining the effects of large-scale forcing on small-scale velocity-gradient (VG) dynamics, we found that forcing has subtle but crucial implications on the local streamline geometry, VG magnitude, and dissipation intensity. The interplay between forcing and inertia, pressure, and viscous effects leads to different balance outcomes under different topology conditions. These findings contribute to a better understanding of small-scale processes in turbulence and offer guidance for the development of VG models.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
K. Osawa, Y. Minamoto, M. Shimura, M. Tanahashi
Summary: A new technique based on the Voronoi diagram is used to quantify the clustering of fine-scale dissipative vortices. It is found that velocity gradient events are more intense and intermittent with a higher number density of fine-scale vortices. Fine-scale vortex clusters accumulate among stronger vortices rather than accumulating all vortices in the flow.
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)