Vorticity dynamics around a straight vortex tube in a simple smear flow

The mechanism of wrap, tilt and stretch of vorticity lines around a strong thin straight tubular vortex in a simple shear flow is investigated analytically. An asymptotic expression of the vorticity field around a vortex which starts with a filament is derived at large vortex Reynolds numbers and at short times of evolution. An oblique vortex, which inclines from the streamwise direction both to the vertical and the spanwise, wraps and stretches the simple shear vorticity to form double spiral vortex layers of high azimuthal vorticity of alternating sign in adjacent spirals. These spirals induce axial shear flows of the same spiral shape and sign which in turn tilt the simple shear vorticity toward the axial direction. Vorticity lines wind helically around the vortex, which results in conversion of the simple sheer vorticity to the axial direction. The effects of system rotation on this interaction are also discussed.