Studying Lagrangian dynamics of turbulence using on-demand fluid particle tracking in a public turbulence database

Yu, Huidan; Kanov, Kalin; Perlman, Eric; Graham, John H.; Frederix, E.M.A.; Burns, Randal; Szalay, Alexander S.; Eyink, Gregory L.; Meneveau, Charles

doi:10.1080/14685248.2012.674643

Cited by 71 publications

(54 citation statements)

References 45 publications

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“…The velocities and accelerations have negligible mean (not shown) that only affect the statistics reported in this work by no more than 1%. Also not shown are the second-order Lagrangian velocity structure function and the acceleration probability distribution of the flow, which we have compared and are fully in agreement with the results published by the JHU database [34] and elsewhere.…”

Section: Methodssupporting

confidence: 81%

Turbulent pair dispersion in the presence of gravity

2015

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Turbulent pair dispersion of heavy particles is strongly altered when particles of two different Stokes numbers (bidisperse) are considered, and this is further compounded when a uniform gravitational acceleration is present. Lagrangian trajectories of fluid tracers, and bidisperse heavy particles with and without gravity were calculated from a direct numerical simulation of homogeneous, isotropic turbulence. Particle pair dispersion shows a short-time, ballistic (Batchelor) regime and a transition to super-ballistic dispersion that is suggestive of the emergence of Richardson scaling. A simple equation of motion for inertial, sedimenting particles captures the essential features of the pair dispersion at very short time and length scales. Kolmogorov scaling arguments are able to qualitatively describe the competition between gravity-induced and fluid-induced relative motion in modifying the amount of time the heavy particles spend in the ballistic regime. The transition from ballistic to super-ballistic dispersion for fluid tracers and monodisperse inertial particles exhibits a pronounced sub-ballistic behavior that can be attributed to the mixed velocity-acceleration structure function. The sub-ballistic behavior is strongly suppressed for bidisperse particles, both in the presence or absence of gravity, primarily because of a reduction in the correlation between velocity and acceleration increments. inherent aesthetic and intellectual merit. The parameter space corresponding to the inertial particle dispersion problem is enormous, so we use atmospheric clouds as a context for restricting the region of study within that space: particles small compared to the Kolmogorov length scale, heavy compared to the surrounding fluid, and obeying to good approximation a linear (Stokes) drag law. Significantly, from the point of view of this study, clouds consist of a population of condensing or evaporating water droplets advected by turbulent air flow in a thermodynamically varying environment, with the result that the size distribution of droplets can be quite broad [14]. There is considerable computational and experimental evidence already that different sizes and therefore different inertial response, can lead to significant changes in the behavior of inertial particles. For example, the tendency to cluster weakens in the case of inertial particles with a broad size distribution (e.g. [15,16]). Furthermore, the dynamics of this polydisperse population of particles can be significantly modified by the presence of a gravitational acceleration that results in particle decoupling from the fluid motions, and perhaps more importantly, a relative velocity of different-sized particles falling at terminal speed [17,18]. Simple Kolmogorov dissipative range scaling arguments (e.g. [19]) suggest that the mean turbulent acceleration in clouds is in the approximate range of 0.1-1 m s −2 , much less than gravitational acceleration. This has the consequence that gravity very likely has an immediate effect on the dispersion of polydispe...

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Section: Methodssupporting

confidence: 81%

Turbulent pair dispersion in the presence of gravity

2015

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“…Also shown is TrO 2 t S t . In agreement with the calculations and arguments outlined above, rods align and disks tumble strongly when TrO 2 t S t is large and a rod (red) in turbulent flow as a function of time, using the JHTDB [17,18]. Also shown is TrO 2 t S t (green).…”

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confidence: 83%

Tumbling of Small Axisymmetric Particles in Random and Turbulent Flows

2014

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We analyze the tumbling of small nonspherical, axisymmetric particles in random and turbulent flows. We compute the orientational dynamics in terms of a perturbation expansion in the Kubo number, and obtain the tumbling rate in terms of Lagrangian correlation functions. These capture preferential sampling of the fluid gradients, which in turn can give rise to differences in the tumbling rates of disks and rods. We show that this is a weak effect in Gaussian random flows. But in turbulent flows persistent regions of high vorticity cause disks to tumble much faster than rods, as observed in direct numerical simulations [S. Parsa, E. Calzavarini, F. Toschi, and G. A. Voth, Phys. Rev. Lett. 109, 134501 (2012)]. For larger particles (at finite Stokes numbers), rotational and translational inertia affects the tumbling rate and the angle at which particles collide, due to the formation of rotational caustics.

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“…12(a) are likely dominated by real deformations caused by the turbulence. Figure 13(a) shows the deformation of the arms of a triad simulated in turbulence from the Johns Hopkins turbulence database [16,31]. We simulate the motion of a deformable triad in forced isotropic turbulence on a 1024 3 triply periodic box.…”

Section: B 3d Resultsmentioning

confidence: 99%

Using deformable particles for single-particle measurements of velocity gradient tensors

2019

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We measure the deformation of particles made of several slender arms in a two-dimensional (2D) linear shear and a three-dimensional (3D) turbulent flow. We show how these measurements of arm deformations along with the rotation rate of the particle allow us to extract the velocity gradient tensor of the flow. The particles used in the experiments have three symmetric arms in a plane (triads) and are fabricated using 3D printing of a flexible polymeric material. Deformation measurements of a particle free to rotate about a fixed axis in a 2D simple shear flow are used to validate our model relating particle deformations to the fluid strain. We then examine deformable particles in a 3D turbulent flow created by a jet array in a vertical water tunnel. Particle orientations and deformations are measured with high precision using four high speed cameras and have an uncertainty on the order of 10 −4 radians. Measured deformations in 3D turbulence are small and only slightly larger than our orientation measurement uncertainty. Simulation results for triads in turbulence show deformations similar to the experimental observations. Deformable particles offer a promising method for measuring the full local velocity gradient tensor from measurements of a single particle where traditionally a high concentration of tracer particles would be required.

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Studying Lagrangian dynamics of turbulence using on-demand fluid particle tracking in a public turbulence database

Cited by 71 publications

References 45 publications

Turbulent pair dispersion in the presence of gravity

Turbulent pair dispersion in the presence of gravity

Tumbling of Small Axisymmetric Particles in Random and Turbulent Flows

Using deformable particles for single-particle measurements of velocity gradient tensors

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