Helicoidal particles in turbulent flows with multi-scale helical injection
arXiv:1812.01962 · doi:10.1017/jfm.2019.237
Abstract
We present numerical and theoretical results concerning the properties of turbulent flows with strong multi-scale helical injection. We perform direct numerical simulations of the Navier-Stokes equations under a random helical stirring with power-law spectrum and with different intensities of energy and helicity injections. We show that there exists three 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 and helicity transfer is sub-leading and (iii) both are sub-leading and helicity is maximal at all scales. As a result, the cases (ii-iii) give flows with Kolmogorov-like inertial energy cascade and tuneable helicity transfers/contents. We further explore regime (iii) by studying its effect on the kinetics of point-like isotropic helicoids, particles whose dynamics is isotropic but breaks parity invariance. We investigate small-scale fractal clustering and preferential sampling of intense helical flow structures. Depending on their structural parameters, the isotropic helicoids either preferentially sample co-chiral or anti-chiral flow structures. We explain these findings in limiting cases in terms of what is known for spherical particles of different densities and degrees of inertia. Furthermore, we present theoretical and numerical results for a stochastic model where dynamical properties can be calculated using analytical perturbation theory. Our study shows that a suitable tuning of the stirring mechanism can strongly modify the small-scale turbulent helical properties and demonstrates that isotropic helicoids are the simplest particles able to preferentially sense helical properties in turbulence.
References in corpus (24)
- Cascades and transitions in turbulent flows
- Heavy particle concentration in turbulence at dissipative and inertial scales
- Inverse energy cascade in three-dimensional isotropic turbulence
- The Joint Cascade of Energy and Helicity in Three-Dimensional Turbulence
- Hyperviscosity, Galerkin truncation and bottlenecks in turbulence
- Fractal clustering of inertial particles in random flows
- Statistical models for spatial patterns of heavy particles in turbulence
- Sling effect in collisions of water droplets in turbulent clouds
- Acceleration statistics of finite-sized particles in turbulent flow: the role of Faxen forces
- Helicity conservation by flow across scales in reconnecting vortex links and knots
- Multifractal concentrations of inertial particles in smooth random flows
- Intermittency in the Joint Cascade of Energy and Helicity
- Non-Kolmogorov cascade of helicity driven turbulence
- Preferential sampling and small-scale clustering of gyrotactic microswimmers in turbulence
- Weaving knotted vector fields with tunable helicity
- Turbulence and Multiscaling in the Randomly Forced Navier Stokes Equation
- Ergodic and non-ergodic clustering of inertial particles
- Statistical model for the orientation of non-spherical particles settling in turbulence
- Effects of forcing in three dimensional turbulent flows
- Role of helicity for large- and small-scale turbulent fluctuations
- On the Global Regularity of a Helical-decimated Version of the 3D Navier-Stokes Equations
- Effects of helicity on dissipation in homogeneous box turbulence
- Small-scale anisotropy induced by spectral forcing and by rotation in non-helical and helical turbulence
- Simulated Navier-Stokes trefoil reconnection