Numerical modeling of the three-dimensional flows in the ground boundary layer of a maintained axisymmetrical vortex

The three-dimensional flow in the ground boundary-layer beneath an intense Rankine vortex is studied, using a numerical technique. Equations of motion in terms of dimensionless vorticity, stream function and circulation have been derived and generalized. Upwind instead of the usual central difference scheme has been used. The method was found to be stable for the range of Reynolds numbers for the natural tornado. The results predict the known physical characteristics of the three-dimensional bound-arylayer of intense vortices, namely: The distribution of horizontal velocities in the vertical direction is oscillatory in the outer region; and the motion in the core region is upward, whilst there is weak descending motion in the outer region. The predicted pressure distribution also falls within the range observed for the natural tornado.