Keywords: complex terrain, heuristic approach, nuclear accidents, particle flows, nuclear safety, Navier-, Stokes equations, modelling, air pollution, environmental pollution, expert systems, atmospheric dispersion models, airborne radioactive material, atmospheric transport
A heuristic approach to particle flows in complex terrain
A heuristic approach based on emulating the Navier-Stokes equations is proposed for a shorthand description of flows of airborne particle in complex terrain. The exercise is motivated by the need for a simple, computer-inexpensive, yet comprehensive and flexible model to support a software package on nuclear accident consequence assessment, currently in development at IFA-Bucharest. Central to the design is the notion that pollutant particle pathlines do not actually coincide on a point-by-point basis with the air-particle pathlines, airborne solid particles being driven by their inertia to passing from one air-pathline to another, particularly as the air flow undergoes inflexions and/or vorticity. Consequent to this notion, which, inter alia, has fed the literature on 'particle impaction', is a heuristic scaling and parameterisation of the hydrodynamic equations, yielding a set of linear equations linking particle acceleration to terrain-dependent pressure gradient fields, which may also reflect the terrain's nature, canopy, and diurnal/annua1 insolation. It is shown that such equations can (roughly) accommodate most of the typical behaviours featuring cloud/plume motions, including coastal and mountain-slope circulation, large eddies (mechanical and thermal), wake effects, blocking, deflection, channelling, other inversion-dependent and even less common effects noted in observations, at scales ranging from isolated buildings up to the mesoscale, under the control of a reduced number of parameters that may eventually be linked to experiment and measurement.