A study in tornado like vortex dynamics.

Fine resolution calculations using an axisymmetric numerical model of the flow within a Ward type vortex chamber is discussed. Particular attention is paid to the vortex ground interaction. Variations in the swirl ratio S from zero to unity lead to radically differnt vortex structure in the 'corner' region (i.e., near r z 0). For S1, a concentrated vortex forms in the upper chamber but not in the corner. At moderate S, vortex breakdown was observed, also large amplitude inertial waves, and very intense swirling motion in the corner. When S 1, the central downdraft penetrates to the lower surface and the vortex breakdown occurs within the boundary layer. These results are consistent with experimental observations and suggest the explanation of a number of observed facets of tornadoes. (A)