An Analysis of Three-Dimensional Vortical Flow Structure in a Homogeneous Isotropic Turbulence

The present study investigates velocity structure of vortices in a homogeneous isotropic turbulence with a low Reynolds number. It applies physical quantities that have been proposed to specify the topology of local flow, where swirlity indicates the unidirectionality and intensity of azimuthal flow in arbitrary plane, and symmetry of vortical flow does the skewness of vortical flow. In the analysis of the velocity structure, the vortex center is identified as a maximum points of the swirlity in a vortical region, using its Hessians. If the symmetry of vortical flow does not exhibit the axisymmetric feature in the vortex center, then the elliptic direction of the vortical flow is set to have uniform direction in the statistical flow structure. The results show that the statistical vortical flow is asymmetric, and that the azimuthal flow is dominant in the vortical flow. The radial flow is also asymmetric, and has both inflow and outflow, while the axial flow is weak. These characteristics specify the particular features of a vortex associated with topological stability or pressure minimum.