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- Shukla, Sanjay, et al.
(författare)
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Inertial particles in superfluid turbulence : Coflow and counterflow
- 2023
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 35:1, s. 015153-
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Tidskriftsartikel (refereegranskat)abstract
- We use pseudospectral direct numerical simulations to solve the three-dimensional (3D) Hall-Vinen-Bekharevich-Khalatnikov (HVBK) model of superfluid helium. We then explore the statistical properties of inertial particles, in both coflow and counterflow superfluid turbulence (ST) in the 3D HVBK system; particle motion is governed by a generalization of the Maxey-Riley-Gatignol equations. We first characterize the anisotropy of counterflow ST by showing that there exist large vortical columns. The light particles show confined motion as they are attracted toward these columns, and they form large clusters; by contrast, heavy particles are expelled from these vortical regions. We characterize the statistics of such inertial particles in 3D HVBK ST: (1) The mean angle (SIC)(tau) between particle positions, separated by the time lag r, exhibits two different scaling regions in (a) dissipation and (b) inertial ranges, for different values of the parameters in our model; in particular, the value of (SIC)(tau), at large r, depends on the magnitude of U-ns. (2) The irreversibility of 3D HVBK turbulence is quantified by computing the statistics of energy increments for inertial particles. (3) The probability distribution function (PDF) of energy increments is of direct relevance to recent experimental studies of irreversibility in superfluid turbulence; we find, in agreement with these experiments, that, for counterflow ST, the skewness of this PDF is less pronounced than its counterparts for coflow ST or for classical fluid turbulence.
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| 2. |
- Verma, Akhilesh Kumar, et al.
(författare)
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First-passage-time problem for tracers in turbulent flows applied to virus spreading
- 2020
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Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- We study the spreading of viruses, such as SARS-CoV-2, by airborne aerosols, via a first-passage-time problem for Lagrangian tracers that are advected by a turbulent flow: By direct numerical simulations of the three-dimensional (3D) incompressible Navier-Stokes equation, we obtain the time t(R) at which a tracer, initially at the origin of a sphere of radius R, crosses the surface of the sphere for the first time. We obtain the probability distribution function P(R, t(R)) and show that it displays two qualitatively different behaviors: (a) for R << L-I, P(R, t(R)) has a power-law tail similar to t(R)(-alpha), with the exponent alpha = 4 and L-I the integral scale of the turbulent flow; (b) for L-I less than or similar to R, the tail of P(R, t(R)) decays exponentially. We develop models that allow us to obtain these asymptotic behaviors analytically. We show how to use P(R, t(R)) to develop social-distancing guidelines for the mitigation of the spreading of airborne aerosols with viruses such as SARS-CoV-2.
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