A Feature of Vortical Axis in Coalescence of Vortical Regions in a Homogeneous Isotropic Turbulence*

The present study analyses the dynamics of coalescence of vortical regions with the behavior of vorticity lines in a homogeneous isotropic turbulence. A process of coalescence of several vortical regions shows that two vortical regions approach and coalesce, and that another vortical region coalesces with them. While a single and large vortical region is formed by the coalescences, all vortical regions do not coalesce and the core regions of respective vortices with intense swirling remain separately. Then the bundle of vorticity lines exist in the organized vortical region that pass respective regions of the coalesced vorticies. On the other hand, the bundles of vorticity lines in the core regions of respective vortices tend to pass through non intense core region of coalesced vortex. It is noted that vorticity vectors of two vortical regions to coalesce have the same direction. It shows that the characteristics of two vortical regions in the coalescence of vortical regions are different from these of anti-parallel vortex tubes in the reconnection of vortex.