渦コア領域における軸線バンドルの特性

（渦軸線の旋回特性について）

抄録

The present study analyses the bundle features of vortical axis-lines in an isotropic homogeneous turbulence in Direct Numerical Simulation (DNS). The vorticity line and eigen-vortical axis line defined by the real eigenvector of the velocity gradient tensor are analysed in terms of the geometrical characteristic in the vortical region. We apply the theory of local axis geometry that specifies quantitatively the characteristics of the bundle of axis-lines with respect to the passage of vortical region. The analysis method focuses on the gradient tensor of the subjected vector field with respect to the swirl plane and evaluates the physical quantities such as swirlity and sourcity that specify the unidirectionality and the intensity of the respective azimuthal and radial vector (flow) components in the swirl plane. The bundles and distributions of these vectors of the two lines show that the most of eigen-vortical axis lines do not have swirling feature whereas the vorticity lines swirls. While the vorticity lines or vorticity vector have an effect of the vortex stretching to swirl, the relationship between the two vectors of these lines in the swirl plane, expressed as a linear transformation, seems to restrain swirling of the eigen-vortical axis line.