Ian Eames

A one-dimensional model framework of unsteady free-surface flow through a blocking-drag region is developed, tested, and applied to understand the dam-break flow past a rectangular building. This is achieved by studying the steady-state, adjustment to steady-state, and the unsteady response of a blocking-drag region. Three steady flow regimes are identified based on the Froude number upstream and downstream of a blocking-drag region: a subcritical state, a choked state with a subcritical-supercritical transition, and a supercritical state. The interaction between a dam-break flow and a blocking-drag region can be mostly understood from the quasi-steady analysis using the variation of the Froude number with time, and comparing the upstream and downstream Froude number scatter plots against the steady curve. The force time-series depends on the height of the precursor layer and the position of the blocking-drag region relative to the lock-length. This model provides considerable insight into the types of flow characteristics observed at low/high Froude numbers and goes some way to clarifying the relationship between the drag force and the dam-break flow properties.

The fluid mechanical processes that govern the spread of infectious agents through the air in complex spaces are reviewed and the scientific gaps and challenges identified and discussed. Air, expelled from the nose and mouth, creates turbulent jets that form loosely coherent structures which quickly slow. For the transport and dispersion of aerosols, the suitability of the Eulerian as well as the Lagrangian approaches are brought into context. The effects of buoyancy and external turbulence are explored and shown to influence the horizontal extent of expulsion through distinct mechanisms which both inhibit penetration and enhance mixing. The general influence of inhomogeneous turbulence and stratification on the spread of infectious agents in enclosed complex spaces is discussed.