Laboratory measurements of axial pressures in two-celled tornado-like vortices

An experimental study of two-celled vortex flows was conducted in a Ward-type tornado vortex chamber (TVC). Time-averaged, stream-static pressure measurements on the vortex axis and observations of the visualized flow in two-celled vortices are reported. The static pressure measured on the vortex axis increases with height downstream of the vortex breakdown, with the axial pressure gradient tending to zero only well aloft. Visualization indicates that the flow downstream of the breakdown in the TVC is everywhere two-celled, with the strongest axial downflow occurring at middle levels. Analysis of the vertical momentum equation strengthens the argument that the turbulent stresses can play an important role in the axial momentum balance of two-celled vortices by opposing the ``filling'' of the vortex core with higher stagnation pressure fluid from aloft, therefore helping to maintain low pressure and high velocities near the surface.