Clustering of vector nulls in homogeneous isotropic turbulence

We analyze the vector nulls of velocity, Lagrangian acceleration, and vorticity, coming from direct numerical simulations of forced homogeneous isotropic turbulence at Re lambda is an element of O([40-600]). We show that the clustering of velocity nulls is much stronger than those of acceleration and vorticity nulls. These acceleration and vorticity nulls, however, are denser than the velocity nulls. We study the scaling of clusters of these null points with Re lambda and with characteristic turbulence lengthscales. We also analyze datasets of point inertial particles with Stokes numbers St = 0.5, 3, and 6, at Re lambda = 240. Inertial particles display preferential concentration with a degree of clustering that resembles some properties of the clustering of the Lagrangian acceleration nulls, in agreement with the proposed sweep-stick mechanism of clustering formation.

Automated summary

Through numerical simulations, it was found that clusters of velocity, acceleration, and vorticity null points in turbulence tend to cluster together, with velocity nulls showing the strongest clustering. The denser acceleration and vorticity null points were also observed. The scaling relationships of these null points clusters with Re lambda and turbulence length scales were studied, as well as the preferential concentration of inertial particles with properties resembling Lagrangian acceleration null clustering.