We present numerical and theoretical results concerning the properties of turbulent flowsunder strong multi-scale helical injection. We perform direct numerical simulations ofthe Navier-Stokes equations under a random helical stirring with power-law spectrumand with different intensities of energy and helicity injections. We show that there existsthree different regimes where the forward energy and helicity inertial transfers are: (i)both leading with respect to the external injections, (ii) energy transfer is leading andhelicity transfer is sub-leading, and (iii) both are sub-leading and helicity is maximal atall scales. As a result, the cases (ii-iii) give flows with Kolmogorov-like inertial energycascade and tunable helicity transfers/contents. We further explore regime (iii) in aLagrangian domain, by studying the kinetics of point-like isotropic helicoids, particleswhose dynamics is isotropic but breaks parity invariance. We investigate small-scalefractal clustering and preferential sampling of intense helical flow structures. Dependingon its structural parameters, the isotropic helicoids either preferentially sample co-chiralor anti-chiral flow structures. We explain these findings in limiting cases in terms of whatis known for spherical particles of different densities and inertia. Furthermore, we presenttheoretical and numerical results for a stochastic model where Lagrangian properties canbe calculated using analytical perturbation theory. Our study shows that a suitabletuning of the stirring mechanism can strongly modify the small-scale turbulent helicalproperties and demonstrates that isotropic helicoids are the simplest particles able topreferentially sense helical properties in turbulence

Biferale, L., Gustavsson, K., Scatamacchia, R. (2019). Helicoidal particles in turbulent flows with multi-scale helical injection. JOURNAL OF FLUID MECHANICS, 869, 646-673 [10.1017/jfm.2019.237].

Helicoidal particles in turbulent flows with multi-scale helical injection

Biferale L.;
2019-01-01

Abstract

We present numerical and theoretical results concerning the properties of turbulent flowsunder strong multi-scale helical injection. We perform direct numerical simulations ofthe Navier-Stokes equations under a random helical stirring with power-law spectrumand with different intensities of energy and helicity injections. We show that there existsthree different regimes where the forward energy and helicity inertial transfers are: (i)both leading with respect to the external injections, (ii) energy transfer is leading andhelicity transfer is sub-leading, and (iii) both are sub-leading and helicity is maximal atall scales. As a result, the cases (ii-iii) give flows with Kolmogorov-like inertial energycascade and tunable helicity transfers/contents. We further explore regime (iii) in aLagrangian domain, by studying the kinetics of point-like isotropic helicoids, particleswhose dynamics is isotropic but breaks parity invariance. We investigate small-scalefractal clustering and preferential sampling of intense helical flow structures. Dependingon its structural parameters, the isotropic helicoids either preferentially sample co-chiralor anti-chiral flow structures. We explain these findings in limiting cases in terms of whatis known for spherical particles of different densities and inertia. Furthermore, we presenttheoretical and numerical results for a stochastic model where Lagrangian properties canbe calculated using analytical perturbation theory. Our study shows that a suitabletuning of the stirring mechanism can strongly modify the small-scale turbulent helicalproperties and demonstrates that isotropic helicoids are the simplest particles able topreferentially sense helical properties in turbulence
2019
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore FIS/02 - FISICA TEORICA, MODELLI E METODI MATEMATICI
English
Biferale, L., Gustavsson, K., Scatamacchia, R. (2019). Helicoidal particles in turbulent flows with multi-scale helical injection. JOURNAL OF FLUID MECHANICS, 869, 646-673 [10.1017/jfm.2019.237].
Biferale, L; Gustavsson, K; Scatamacchia, R
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/214777
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