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
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
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
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
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
Mathematics, Applied
Feng Liu, Hantao Liu, Hongkai Zhao, Pengfei Lyu
Summary: The inverse energy cascade in homogeneous isotropic turbulence is described using an eigenvalue method, quantitatively capturing the backward energy transfer process and applicable to both isotropic turbulence and resolved velocity fields. This method, based on the product of eigenvalues of the rate-of-strain tensor, is easier to obtain compared to traditional velocity derivative skewness S-k, and has potential for extension to anisotropic turbulence. The presented description aims to inspire future research on modeling the backward energy transfer process and improve the accurate prediction of complex flows.
APPLIED MATHEMATICS AND MECHANICS-ENGLISH EDITION
(2021)
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
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
Acoustics
Wei Wang, Steven A. E. Miller
Summary: In this study, Eulerian-Lagrangian direct numerical simulations were used to investigate the impact of suspended particles on noise in decaying homogeneous isotropic turbulence. The results show that as the number of particles and their diameter increase, noise is dominated by monopole and dipole terms.
Article
Computer Science, Interdisciplinary Applications
Shang-Gui Cai, Johan Degrigny, Jean-Francois Boussuge, Pierre Sagaut
Summary: An improved coupling method of immersed boundary method and turbulence wall models on Cartesian grids is proposed to generate smooth wall surface pressure and skin friction at high Reynolds numbers. Various modifications are presented to enhance the near wall solution, and the validity of the method is demonstrated through numerical benchmark tests.
JOURNAL OF COMPUTATIONAL PHYSICS
(2021)
Article
Mechanics
H. Yoo, M. L. Bahlali, J. Favier, P. Sagaut
Summary: Simulating rotating geometries in fluid flows for industrial applications poses challenges for general fluid solvers, including the lattice Boltzmann method. This study introduces a novel approach integrating overset grids and an optimized collision operator to enhance stability and accuracy in LBM simulations. The robustness and second order accuracy of the overset HRR algorithm are demonstrated in various flow configurations with mid-to-high Reynolds numbers.
Article
Mechanics
Jeremie Janin, Fabien Duval, Christophe Friess, Pierre Sagaut
Summary: Turbulence is a common feature in all flows around us, but it is difficult to provide a mathematical framework for the generation of turbulent eddies. Several methods have been proposed to reproduce realistic features for velocity fluctuations, and their performance is evaluated through large-eddy simulations. These methods can efficiently control resolved turbulent energy and maintain the integral length scale independent of domain size.
Article
Mechanics
Y. Feng, J. Miranda-Fuentes, J. Jacob, P. Sagaut
Summary: The study developed a lattice Boltzmann method for atmospheric dynamics based on the anelastic approximation, introducing reference base state values and constructing an LB model in an anelastic framework. The model effectively simulates atmospheric flows by solving mass and momentum conservation equations with a regularization procedure and simulating temperature field through a finite volume method.
Article
Mechanics
M. L. Bahlali, H. Yoo, J. Favier, P. Sagaut
Summary: The study introduces a new direct coupling scheme based on the overset technique to address moving boundary problems within the lattice Boltzmann framework. The method interpolates distribution functions instead of moments, ensuring mass and momentum conservation at the interface nodes between fixed and moving grids. The results show that the direct coupling method improves the accuracy of the lattice Boltzmann overset algorithm for aeroacoustics, particularly in conserving vortex structures over time and reducing spurious acoustic distortions at fixed/moving interfaces.
Article
Computer Science, Interdisciplinary Applications
Gauthier Wissocq, Pierre Sagaut
Summary: This article proposes a method for studying the numerical properties of the lattice Boltzmann method (LBM), which reveals the deviations from the Navier-Stokes equations through the derivation of its hydrodynamic limits. The errors and dissipation characteristics of different collision models are explained through detailed analysis.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Mechanics
B. Bugeat, J-Ch Robinet, J-C Chassaing, P. Sagaut
Summary: Resolvent analysis is used to study the low-frequency behavior of the laminar oblique shock wave/boundary layer interaction (SWBLI). The computed optimal gain follows a first-order low-pass filter equation, consistent with previous findings. The damping rate scales with the scale, resulting in a constant Strouhal number. The study supports the idea that the low-frequency dynamics of the SWBLI is a forced dynamics, with background perturbations continuously exciting the flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Guanxiong Wang, Song Zhao, Pierre Boivin, Eric Serre, Pierre Sagaut
Summary: A new low-Mach algorithm is proposed to reduce the computational cost of thermal flow simulations in the low Mach number limit. The method accelerates simulations by enlarging the time step through re-scaling the pseudoacoustic speed. It overcomes the drawbacks of classical methods and shows excellent agreement with reference data and high computational efficiency in various test cases.
Article
Mechanics
Lincheng Xu, Eric Serre, Pierre Sagaut
Summary: This paper proposes an original theoretical investigation of mass leakage at boundaries within the general lattice Boltzmann framework, providing insights into its origins and characteristics. The paper presents a correction scheme based on averaged mass leakage to address the mass leakage problems in lattice Boltzmann simulations. The theoretical analysis is validated through numerical experiments, which show very good agreement with the proposed analysis.
Article
Mechanics
G. Wissocq, T. Coratger, G. Farag, S. Zhao, P. Boivin, P. Sagaut
Summary: A general methodology is presented for constructing conservative numerical models for fluid simulations based on segregated schemes, particularly for the thermal coupling with the lattice Boltzmann method (LBM). The proposed methodology decouples the energy equation with the LBM using a linear equivalence with standard discretizations of the entropy equation. The resulting models are shown to be conservative, stable, and retain the low dissipation of the LBM for isentropic phenomena.
Article
Mechanics
M. Nguyen, J. F. Boussuge, P. Sagaut, J. C. Larroya-Huguet
Summary: In this study, a compressible hybrid lattice Boltzmann method solver was used to perform a wall-resolved large eddy simulation of an isothermal axisymmetric jet. The simulation results were able to reproduce the flow field statistics, Nusselt number profile, and shear stress profile of the jet. The lack of temporal periodicity in the azimuthally averaged Nusselt number at the location of the secondary peak was attributed to the relatively low azimuthal coherence of the primary vortical structures.
Article
Mechanics
Shang-Gui Cai, Sajad Mozaffari, Jerome Jacob, Pierre Sagaut
Summary: This paper applies an immersed boundary-turbulence wall modeling approach to investigate turbulent flows over a generic car geometry, known as the Ahmed body. The study shows that the near-wall solution is significantly deteriorated compared to the body-fitted simulation, but enhanced wall treatments proposed in the literature can effectively address this issue.
Article
Computer Science, Interdisciplinary Applications
G. Moldovan, G. Lehnasch, L. Cordier, M. Meldi
Summary: This article investigates and assesses the essential features of the Multigrid Ensemble Kalman Filter proposed for Data Assimilation of fluid flows, with a focus on the improvement in performance due to the inner loop. The results indicate that the contribution of the inner loop is essential in obtaining accurate flow reconstruction and global parametric optimization.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Mechanics
E. V. Kuidjo Kuidjo, M. G. Rodio, R. Abgrall, P. Sagaut
Summary: This work focuses on 3D simulations of complex bubbly, cap-bubbly, and churn regimes with different bubble shapes and wide bubble size distribution. It investigates and compares various bubble interaction mechanisms of coalescence and fragmentation for the 2-Group Interfacial Area Transport Equation (IATE) model, with the assessment of two models in a CFD code for the first time. It proposes and evaluates a novel model of fragmentation and coalescence. Furthermore, it validates the models against experimental data for different configurations and regimes.
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2023)
Article
Mechanics
G. Farag, P. Boivin, P. Sagaut
Summary: When considering departure from ideal gas behavior, the Noble-Abel stiffened gas model proves to be a simple and appealing candidate. The linear interaction approximation is extended to account for non-ideal gas effects introduced by this equation of state. The changes with respect to ideal gas are analyzed in terms of transfer functions, critical angle, and compression factor, highlighting their impact on damping and transfer of fluctuations across shock waves. This is further demonstrated through the interaction of an entropy spot with a Mach 3 stationary shock wave.