TURBULENCE, TOROIDAL CIRCULATION AND DISPERSION OF FALLOUT PARTICLES FROM THE RISING NUCLEAR CLOUD

The entraining-parcel model of the rise and expansion of the nuclear cloud is revised to allow for 1 production of turbulent kinetic energy from kinetic energy of rise during the momentum-conserving, inelastic-collision entrainment, so that total kinetic energy is conserved in entrainment. This production of turbulent energy is in addition to that due to eddy viscosity 2 dissipation of turbulent energy to heat. The resulting nuclear-cloud model is represented as an energy cycle between enthalpy and energy of rise, turbulent energy, and potential energy. Calculations of toroidal circulation and particle motion in the nuclear cloud are discussed, using the cloud model and turbulent similarity theory. If the toroidal circulation is to be represented by a vortex ring superimposed on the parcel-model cloud, the vortex ring can be considered the largest eddy in the turbulent spectrum, containing a fixed fraction of the turbulent energy. This gives an estimate of the circulation without recourse to, but in general agreement with, estimates based on measurements of nuclear cloud films. Alternately, circulation may be calculated by an adaptation of Kelvins theorem. This method assumes neither a particular vortex form nor steady-state flow, and is therefore more consistent with actual cloud conditions.