Relationships between vortex stretching and its elongating feature among several scale vortices in an isotropic homogeneous turbulence*

The present study investigates the detail effect of the vortex stretching in terms of the interaction of vortices in the different flow scales in an isotropic homogeneous turbulence in low Reynolds number. The formulation of the vortex stretching associated with the swirl plane specifies its effect in detail, and complete-inflow vortices has been shown to have effective stretching that increases vorticity for swirling and decreases inclination of a vortical axis in this turbulence [K. Nakayama, Phys. Rev. Fluids (2017)]. We apply this formulation in the analysis and show that the vortex stretching in complete-inflow vortex has more intense interactional effect where the parallel stretching component to the swirl plane of a vortex in a scale strengthens the vorticity for swirling of a smaller scale vortex than that of average-inflow vortex. However, the vortex stretching in the outflow vortices in a scale weakens not only the vorticity for swirling themselves but also vorticity for swirling in a smaller scale vortex.