The initial vortex aloft and helical structure near the surface

Formation of the helical vortices in different media is an important hydrodynamic problem. To study the evolution of the initial vortex aloft, we use a simple axisymmetric hydrodynamic model. The control parameters of the model are the initial height of the vortex and the turbulent Reynolds number. Simulations show that a vortex having initially only an azimuthal component of velocity is converted into a helical vortex. The initial vorticity drifts downwards to the surface. An external energy source is not included into the model for supporting the initial vortex, so that the energy of the system decreases with time. At sufficiently high turbulent Reynolds numbers, there is enough time to form an intense helical structure near the surface.