Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence
We use direct numerical simulations to compute structure functions, scaling exponents, probability density functions, and effective transport coefficients of passive scalars in turbulent rotating helical and nonhelical flows. We show that helicity affects the inertial range scaling of the velocity a...
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todo:paper_24700045_v95_n3_p_Imazio2023-10-03T16:42:18Z Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence Imazio, P.R. Mininni, P.D. Diffusion Scaling laws Anomalous scaling Effective diffusion coefficients Horizontal diffusions Rotating turbulence Structure functions Transport coefficient Velocity fluctuations Vertical diffusion Probability density function We use direct numerical simulations to compute structure functions, scaling exponents, probability density functions, and effective transport coefficients of passive scalars in turbulent rotating helical and nonhelical flows. We show that helicity affects the inertial range scaling of the velocity and of the passive scalar when rotation is present, with a spectral law consistent with ∼k'-1.4 for the passive scalar variance spectrum. This scaling law is consistent with a phenomenological argument [P. Rodriguez Imazio and P. D. Mininni, Phys. Rev. E 83, 066309 (2011)PLEEE81539-375510.1103/PhysRevE.83.066309] for rotating nonhelical flows, which follows directly from Kolmogorov-Obukhov scaling and states that if energy follows a E(k)∼k-n law, then the passive scalar variance follows a law V(k)∼k-nθ with nθ=(5-n)/2. With the second-order scaling exponent obtained from this law, and using the Kraichnan model, we obtain anomalous scaling exponents for the passive scalar that are in good agreement with the numerical results. Multifractal intermittency models are also considered. Intermittency of the passive scalar is stronger than in the nonhelical rotating case, a result that is also confirmed by stronger non-Gaussian tails in the probability density functions of field increments. Finally, Fick's law is used to compute the effective diffusion coefficients in the directions parallel and perpendicular to rotation. Calculations indicate that horizontal diffusion decreases in the presence of helicity in rotating flows, while vertical diffusion increases. A simple mean field argument explains this behavior in terms of the amplitude of velocity fluctuations. © 2017 American Physical Society. Fil:Mininni, P.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_24700045_v95_n3_p_Imazio |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
Diffusion Scaling laws Anomalous scaling Effective diffusion coefficients Horizontal diffusions Rotating turbulence Structure functions Transport coefficient Velocity fluctuations Vertical diffusion Probability density function |
| spellingShingle |
Diffusion Scaling laws Anomalous scaling Effective diffusion coefficients Horizontal diffusions Rotating turbulence Structure functions Transport coefficient Velocity fluctuations Vertical diffusion Probability density function Imazio, P.R. Mininni, P.D. Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| topic_facet |
Diffusion Scaling laws Anomalous scaling Effective diffusion coefficients Horizontal diffusions Rotating turbulence Structure functions Transport coefficient Velocity fluctuations Vertical diffusion Probability density function |
| description |
We use direct numerical simulations to compute structure functions, scaling exponents, probability density functions, and effective transport coefficients of passive scalars in turbulent rotating helical and nonhelical flows. We show that helicity affects the inertial range scaling of the velocity and of the passive scalar when rotation is present, with a spectral law consistent with ∼k'-1.4 for the passive scalar variance spectrum. This scaling law is consistent with a phenomenological argument [P. Rodriguez Imazio and P. D. Mininni, Phys. Rev. E 83, 066309 (2011)PLEEE81539-375510.1103/PhysRevE.83.066309] for rotating nonhelical flows, which follows directly from Kolmogorov-Obukhov scaling and states that if energy follows a E(k)∼k-n law, then the passive scalar variance follows a law V(k)∼k-nθ with nθ=(5-n)/2. With the second-order scaling exponent obtained from this law, and using the Kraichnan model, we obtain anomalous scaling exponents for the passive scalar that are in good agreement with the numerical results. Multifractal intermittency models are also considered. Intermittency of the passive scalar is stronger than in the nonhelical rotating case, a result that is also confirmed by stronger non-Gaussian tails in the probability density functions of field increments. Finally, Fick's law is used to compute the effective diffusion coefficients in the directions parallel and perpendicular to rotation. Calculations indicate that horizontal diffusion decreases in the presence of helicity in rotating flows, while vertical diffusion increases. A simple mean field argument explains this behavior in terms of the amplitude of velocity fluctuations. © 2017 American Physical Society. |
| format |
JOUR |
| author |
Imazio, P.R. Mininni, P.D. |
| author_facet |
Imazio, P.R. Mininni, P.D. |
| author_sort |
Imazio, P.R. |
| title |
Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| title_short |
Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| title_full |
Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| title_fullStr |
Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| title_full_unstemmed |
Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| title_sort |
passive scalars: mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence |
| url |
http://hdl.handle.net/20.500.12110/paper_24700045_v95_n3_p_Imazio |
| work_keys_str_mv |
AT imaziopr passivescalarsmixingdiffusionandintermittencyinhelicalandnonhelicalrotatingturbulence AT mininnipd passivescalarsmixingdiffusionandintermittencyinhelicalandnonhelicalrotatingturbulence |
| _version_ |
1807316096640876544 |