Calculation of the primary trajectories of spores ejected into still air and laminar flow

Abstract

The plane ballistic trajectories followed by small spherical particles representing a variety of spores ejected into still air are determined for motion in a constant gravitational field and resisted according to the Stokes law of viscous friction. These trajectories are presented in terms of a universal one-parameter formula together with a family of curves defining the ground ranges likely to be achieved in a majority of practical cases. Consideration is also given to the movement of spores ejected into linear laminar boundary-layer flows that are both steady and periodic in time in the downstream velocity. The solutions show that projection to the largest possible vertical and downstream altitude, and also the presence of temporal periodic horizontal wind motion of low frequency and favourable phasing, are both factors of significance in augmenting the ground range achieved.