Article
Mechanics
Xiaolei Han, Jiawei Li, Hiroka Rinoshika, Yuyang Zhou, Yan Zheng, Lin Dong, Akira Rinoshika
Summary: This study investigates the multi-scale vortical structures and vortex dynamics around a fixed-bed barchan dune using particle image velocimetry technique, wavelet transform, and the finite-time Lyapunov exponent method. The results show that large- and intermediate-scale coherent structures dominate the dynamic characteristics of the dune wake. Ejection and sweep events contribute the most to the entire field, while outward and inward interaction events mainly occur near the dune crest. The development process of different wavelet scale structures in the shear layer is visualized in the Lagrangian framework, where small-scale waves grow into larger-scale vortices downstream until the reattachment point.
Article
Mechanics
Dmitriy Zhigunov, Roman O. Grigoriev
Summary: This paper presents new classes of unstable recurrent solutions of the two-dimensional Euler equation with periodic boundary conditions. These solutions resemble the recurrent solutions of the Navier-Stokes equation, known as exact coherent structures. The Euler equation solutions come in infinite-dimensional continuous families, are connected to different types of solutions, and exhibit weak instability, leading to the frequent occurrence of these solutions in fully developed turbulence.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Geosciences, Multidisciplinary
R. J. Hardy, J. L. Best, T. Marjoribanks, D. R. Parsons, P. J. Ashworth
Summary: Dunes are common bedforms in sand-bedded rivers, with a complex three-dimensional morphology that influences flow dynamics and sediment transport. The study found that flow over three-dimensional bedforms generates more turbulent vortices compared to two-dimensional bedforms, with these vortices being longer, wider, and taller. Turbulence is dominated by hairpin-shaped vortices and Kelvin-Helmholtz instabilities that interact with the bed, generating high shear stresses for long durations.
JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE
(2021)
Article
Mechanics
Brodie C. Pearson, Jenna L. Pearson, Baylor Fox-Kemper
Summary: The study proposes new relations to diagnose energy and enstrophy dissipation rates in anisotropic two-dimensional turbulence, using second-order advective structure functions. These new relations show improvement over existing methods through increased accuracy, insensitivity to sampling direction, and lower temporal and spatial variability. Advective structure functions have benefits under weakly anisotropic conditions, becoming increasingly important as third-order structure functions become inappropriate.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Christopher J. Camobreco, Alban Potherat, Gregory J. Sheard
Summary: The transition to turbulence in conduits has been a long-standing problem in fluid mechanics, and understanding how to promote or suppress turbulence is crucial for energy production and conservation. While a global picture of three-dimensional (3-D) turbulence is emerging, subcritical turbulence in flows approaching two dimensions has not been observed. However, stability analysis and simulations have shown a subcritical quasi-two-dimensional (quasi-2-D) transition from laminar flow to turbulence, driven by nonlinear Tollmien-Schlichting waves. This alternative scenario calls for new thinking and strategies to control transition in rotating devices and nuclear fusion reactor blankets.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Linsen Zhang, Jianjun Tao
Summary: This paper investigates the decay and growth of localized wave packets in a two-dimensional plane-Poiseuille flow numerically and theoretically. A pattern preservation approximation is proposed to transform the disturbance kinetic energy equation into a classical differential equation for saddle-node bifurcation, predicting the lifetimes of decaying LWPs. The study also successfully predicts the Reynolds number and disturbance kinetic energy of different LWPs under certain conditions.
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
Physics, Multidisciplinary
Adam Griffin, Giorgio Krstulovic, Victor S. L'vov, Sergey Nazarenko
Summary: We present an exact unique constant-flux power-law analytical solution for the wave kinetic equation, applicable for ak << 1. Our theory describes acoustic turbulence in 2D Bose-Einstein condensates, and the corresponding spectrum is confirmed through numerical simulations.
PHYSICAL REVIEW LETTERS
(2022)
Article
Mechanics
Nikolay A. Ivchenko, Sergey S. Vergeles
Summary: The study focuses on time-averaged properties of coherent vortices in two-dimensional turbulence, classifying weak perturbations as waves of condensate propagating in the radial direction. The dispersion law and propagation length of these waves are dependent on the radial position inside the vortex flow, with variations between saturated condensate and viscous condensate cases.
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
Mechanics
Martin Jacques-Coper, Valentina Ortiz-Guzman, Jorge Zanelli
Summary: This study presents a simplified model of the terrestrial planet atmosphere, describing it as a two-dimensional open system with an ideal gas. The model considers the effects of radiation, matter exchange, diffusion, and dissipation. The dynamics of the atmosphere is governed by non-linear differential equations, and the problem can be solved analytically or numerically depending on the level of non-linearity. The study provides analytical expressions and simulations for the linear regime, allowing exploration of the model's response to parameter changes. Interestingly, a 2.5% reduction in emissivity can lead to a 7-degree Celsius increase in average global temperature.
Article
Engineering, Aerospace
Patrick N. Okolo, Kun Zhao, John Kennedy, Chigbo Mgbemena, Mkpamdi Eke, Gareth J. Bennett
Summary: This study presents a method to accurately characterize the geometries of 3D wire screens as simplified 2D screens for low Reynolds numbers. By comparing numerical flow fields and validating with experimental results, it is found that the simplified 2D models closely match the full 3D results and are more accurate than commonly used flow correlations. The research contributes to design studies by enabling fast analysis of the impact of wire screens in flow or noise control applications.
JOURNAL OF AEROSPACE ENGINEERING
(2021)
Article
Mechanics
Xiaolei Han, Yuyang Zhou, Jiawei Li, Yan Zheng, Akira Rinoshika
Summary: Tomographic particle image velocimetry (PIV) was used to measure and analyze the three-dimensional flow structures and dynamic characteristics behind a fixed-bed barchan dune model. The study found arch-shaped vortex chains and quasi-streamwise vortex structures, and revealed that the arch-shaped vortex system dominates the barchan dune wake.
Article
Mechanics
Erik Lindborg, Arne Nordmark
Summary: This study conducts a spectral analysis of a non-divergent flow on a sphere based on Fjortoft's method. It demonstrates that the spherical harmonic energy spectrum remains invariant under rotations of the polar axis, and derives the spectral energy equation and energy transfer relations. The importance of exploring two-dimensional turbulence through simulations using spherical geometry is highlighted, based on the explanation of relevant theories and hypotheses.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Fluids & Plasmas
Enwei Zhang, Wangxia Wu, Qingquan Liu, Xiaoliang Wang
Summary: This study conducted a large-eddy simulation to investigate the turbulent flow and mass transfer over two-dimensional wavy walls. It found that vortices are generated from separation and reattachment points, and the layout of vortices on the wall is reversed to that at the separation point. The convex wall enhances the spanwise vorticity traced to the upstream trough.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Water Resources
Ignacio J. Moncho-Esteve, Manuel Garcia-Villalba, Yasu Muto, Koji Shiono, Guillermo Palau-Salvador
ADVANCES IN WATER RESOURCES
(2018)
Article
Thermodynamics
Gonzalo Arranz, Alejandro Gonzalo, Markus Uhlmann, Oscar Flores, Manuel Garcia-Villalba
FLOW TURBULENCE AND COMBUSTION
(2018)
Article
Engineering, Mechanical
A. Gonzalo, G. Arranz, M. Moriche, M. Garcia-Villalba, O. Flores
JOURNAL OF FLUIDS AND STRUCTURES
(2018)
Article
Engineering, Aerospace
M. Moriche, M. Raiola, S. Discetti, A. Ianiro, O. Flores, M. Garcia-Villalba
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING
(2020)
Article
Engineering, Mechanical
G. Arranz, O. Flores, M. Garcia-Villalba
JOURNAL OF FLUIDS AND STRUCTURES
(2020)
Article
Engineering, Aerospace
M. Moriche, A. Gonzalo, O. Flores, M. Garcia-Villalba
Summary: Through simulations of large-amplitude plunging maneuvers at different velocity ratios, it was found that the force coefficients follow a similar trend with the main peak amplitude linearly increasing with the velocity ratio. The Reynolds number and three-dimensionality significantly affect the maximum value of the lift coefficient at the end of the maneuver and its subsequent transient decay.
Article
Engineering, Aerospace
Manuel Moriche, Girguis Sedky, Anya R. Jones, Oscar Flores, Manuel Garcia-Villalba
Summary: Experiments and simulations of large-amplitude plunging maneuvers were conducted to explore the effect of airfoil shape on aerodynamics. Results showed that the airfoil shape had a small effect on the lift coefficient but a somewhat larger effect on the drag coefficient. Additionally, force decomposition analysis revealed the impact of vortical structures on peak aerodynamic forces.
Article
Physiology
Manuel Garcia-Villalba, Lorenzo Rossini, Alejandro Gonzalo, Davis Vigneault, Pablo Martinez-Legazpi, Eduardo Duran, Oscar Flores, Javier Bermejo, Elliot McVeigh, Andrew M. Kahn, Juan C. del Alamo
Summary: This study investigated the personalized risk stratification of stroke in AF patients and how LA anatomy and function affect the risk of LAA thrombosis. Through CFD analysis, it was found that LAAT/TIA-pos patients had significant alterations in LAA blood residence time and kinetic energy compared to LAAT/TIA-neg patients. Additionally, the different functions of LA were shown to distinctly impact LA and LAA hemodynamics.
FRONTIERS IN PHYSIOLOGY
(2021)
Article
Mechanics
G. Arranz, O. Flores, M. Garcia-Villalba
Summary: Numerical simulations are used to explore tandem configurations of two self-propelled flexible flappers with finite span. These configurations are characterized by their hydrodynamic performance and topology, with compact and regular configurations observed depending on the vertical offset H and phase shift φ. The upstream flapper's performance is similar to an isolated flapper, while the downstream flapper's performance is significantly affected by the wake of the leader vortex rings.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
R. Jurado, G. Arranz, O. Flores, M. Garcia-Villalba
Summary: This study investigates the effect of aspect ratio on the flow and aerodynamic performance of a pair of wings in horizontal tandem configuration through direct numerical simulations. The results show that the aerodynamic performance of the forewing remains unchanged regardless of the aspect ratio of the hindwing, while the hindwing is clearly affected by the interaction with the forewing's trailing edge vortex.
Article
Engineering, Mechanical
G. Arranz, C. Martinez-Muriel, O. Flores, M. Garcia-Villalba
Summary: We propose a method for computing fluid-structure interaction problems in multi body systems. The method solves the fluid flow equations using Uhlmann's (2005) immersed boundary method and the rigid body equations using Felis's (2017) recursive algorithms. The weakly coupled systems of equations result in a cost-effective method. The accuracy of the method is demonstrated through comparisons with existing literature, and two three-dimensional bioinspired applications are also presented as illustrations of the method's capabilities.
JOURNAL OF FLUIDS AND STRUCTURES
(2022)
Article
Mechanics
Manuel Moriche, Daniel Hettmann, Manuel Garcia-Villalba, Markus Uhlmann
Summary: We conducted numerical simulations of heavy non-spherical particles settling under gravity and observed that oblate spheroids form columnar clusters, resulting in enhanced settling velocity. The behavior of many-particle cases is not qualitatively different from single-particle cases, contrary to previous results for spheres. We also analyzed pairwise interactions of oblate spheroids and spheres, finding similar attraction regions but noticeable differences during drafting and tumbling phases, including longer drafting phases and more collision events for free-to-rotate spheroids.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
C. Martinez-Muriel, G. Arranz, M. Garcia-Villalba, O. Flores
Summary: In this study, we conducted direct numerical simulations of the flow around a spanwise-flexible wing in forward flight. By varying the effective stiffness and keeping the effective inertia constant, we found an optimal aerodynamic performance associated with a damped resonance phenomenon. This enhanced performance is attributed to larger effective angles of attack and a delayed development of the leading edge vortex.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Biology
Eduardo Duran, Manuel Garcia-Villalba, Pablo Martinez-Legazpi, Alejandro Gonzalo, Elliot McVeigh, Andrew M. Kahn, Javier Bermejo, Oscar Flores, Juan Carlos del Alamo
Summary: This study, using a high-fidelity patient-specific computational fluid dynamics (CFD) model, investigated for the first time the influence of changes in pulmonary vein (PV) flow split on left atrial (LA) flow transport, focusing on thrombosis in the left atrial appendage (LAA). The results showed that flow patterns were sensitive to PV flow split variations, particularly in planes parallel to the mitral valve. Changes in PV flow split also had a significant impact on blood stasis and could contribute to increased risk for thrombosis inside the LAA, particularly in patients with atrial fibrillation (AF) and previous LAA thrombus or a history of Transient Ischemic Attacks (TIAs). Our study highlights the importance of considering patient-specific PV flow split variations when assessing LA hemodynamics and identifying patients at increased risk for thrombosis and stroke. This knowledge is relevant to planning clinical procedures such as AF ablation or the implementation of LAA occluders.
COMPUTERS IN BIOLOGY AND MEDICINE
(2023)
Article
Engineering, Multidisciplinary
G. Arranz, M. Moriche, M. Uhlmann, O. Flores, M. Garcia-Villalba
BIOINSPIRATION & BIOMIMETICS
(2018)