| 1. |
- Bhatnagar, Akshay, et al.
(författare)
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Deviation-angle and trajectory statistics for inertial particles in turbulence
- 2016
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1539-3755 .- 1550-2376. ; 94:6
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Tidskriftsartikel (refereegranskat)abstract
- Small particles in suspension in a turbulent fluid have trajectories that do not follow the pathlines of the flow exactly. We investigate the statistics of the angle of deviation φ between the particle and fluid velocities. We show that, when the effects of particle inertia are small, the probability distribution function (PDF) Pφ of this deviation angle shows a power-law region in which Pφ∼φ-4. We also find that the PDFs of the trajectory curvature κ and modulus θ of the torsion have power-law tails that scale, respectively, as Pκ∼κ-5/2, as κ→∞, and Pθ∼θ-3, as θ→∞: These exponents are in agreement with those previously observed for fluid pathlines. We propose a way to measure the complexity of heavy-particle trajectories by the number NI(t,St) of points (up until time t) at which the torsion changes sign. We present numerical evidence that nI(St)≡limt→∞NI(t,St)t∼St-Δ for large St, with Δ≃0.5.
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| 2. |
- Bhatnagar, A., et al.
(författare)
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Universal statistical properties of inertial-particle trajectories in three-dimensional, homogeneous, isotropic, fluid turbulence
- 2015
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Ingår i: Proceedings - 15th European Turbulence Conference, ETC 2015. - : TU Delft.
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Konferensbidrag (refereegranskat)abstract
- We obtain new universal statistical properties of heavy-particle trajectories in three-dimensional, statistically steady, homogeneous, and isotropic turbulent flows by direct numerical simulations. We show that the probability distribution functions (PDFs) P(φ), of the angle φ between the Eulerian velocity u and the particle velocity v, at a point and time, scales as P(φ) ∼ φ−γ, with a new universal exponent γ ≃ 4. The PDFs of the trajectory curvature κ and modulus θ of the torsion ϑ scale, respectively, as P(κ) ∼ κ−hκ, as κ → ∞, and P(θ) ∼ θ−hθ, as θ → ∞, with exponents hκ ≃ 2.5 and hθ ≃ 3 that do not depend on the Stokes number St. We also show that γ, hκ and hθ can be obtained by using simple stochastic models. We show that the number NI(t,St) of points (up until time t), at which ϑ changes sign, is such that nI(St) ≡ limt→∞ NI(tSt) ∼ St−∆, with ∆ ≃ 0.4 a universal exponent. t
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| 3. |
- Meibohm, Jan, et al.
(författare)
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Paths to caustic formation in turbulent aerosols
- 2021
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Ingår i: Physical Review Fluids. - : American Physical Society (APS). - 2469-990X. ; 6:6
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of small, yet heavy, identical particles in turbulence exhibits singularities, called caustics, that lead to large fluctuations in the spatial particle-number density, and in collision velocities. For large particle inertia, the fluid velocity at the particle position is essentially a white-noise signal and caustic formation is analogous to Kramers escape. Here we show that caustic formation at small particle inertia is different. Caustics tend to form in the vicinity of particle trajectories that experience a specific history of fluid-velocity gradients, characterized by low vorticity and a violent strain exceeding a large threshold. We develop a theory that explains our findings in terms of an optimal path to caustic formation that is approached in the small inertia limit.
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| 4. |
- Pandit, R., et al.
(författare)
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An overview of the statistical properties of two-dimensional turbulence in fluids with particles, conducting fluids, fluids with polymer additives, binary-fluid mixtures, and superfluids
- 2017
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Ingår i: Physics of fluids. - : American Institute of Physics (AIP). - 1070-6631 .- 1089-7666. ; 29:11
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Tidskriftsartikel (refereegranskat)abstract
- We present an overview of the statistical properties of turbulence in two-dimensional (2D) fluids. After a brief recapitulation of well-known results for statistically homogeneous and isotropic 2D fluid turbulence, we give an overview of recent progress in this field for such 2D turbulence in conducting fluids, fluids with polymer additives, binary-fluid mixtures, and superfluids; we also discuss the statistical properties of particles advected by 2D turbulent fluids.
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