Fluctuating plume models provide a useful conceptual paradigm in the understanding of plume dispersion in a turbulent flow. In particular, these models have enabled analytical predictions of higher-order concentration moments, and the form of the one-point concentration probability density function (PDF). In this paper, we extend the traditional formalism of these models, grounded in the theory of homogeneous and isotropic turbulent flow, to two cases: namely, a simple sheared boundary layer and a large array of regular obstacles. Some very high-resolution measurements of plume dispersion in a water channel, obtained using laser-induced fluorescence (LIF) line-scan techniques are utilised. These data enable us to extract time series of plume centroid position (plume meander) and dispersion in the relative frame of reference in unprecedented detail. Consequently, experimentally extracted PDFs are able to be directly compared with various theoretical forms proposed in the literature. This includes the PDF of plume centroid motion, the PDF of concentration in the relative frame, and a variety of concentration moments in the absolute and relative frames of reference. The analysis confirms the accuracy of some previously proposed functional forms of model components used in fluctuating plume models, as well as suggesting some new forms necessary to deal with the complex boundary conditions in the spatial domain.

We report on measurements of the near-field dispersion of contaminant plumes in a large array of building-like obstacles at three scales; namely, at fullscale in a field experiment, at 1:50 scale in a wind-tunnel simulation, and at 1:205 scale in a water-channel simulation. Plume concentration statistics extracted from the physical modelling in the wind-tunnel and water-channel simulations are compared to those obtained from a field experiment. The modification of the detailed structure of the plume as it interacts with the obstacles is investigated. To this purpose, measurements of the evolution of the mean concentration, concentration fluctuation intensity, concentration probability density function, and integral time scale of concentration fluctuations in the array plume obtained from the field experiment and the scaled wind-tunnel and water-channel experiments are reported and compared, as well as measurements of upwind and within-array velocity spectra. Generally, the wind-tunnel and water-channel results on the modification of the detailed plume structure by the obstacles were qualitatively similar to those observed in the field experiments. However, with the appropriate scaling, the water-channel simulations were able to reproduce quantitatively the results of the full-scale field experiments better than the wind-tunnel simulations.

The dispersion of tracers within a large array of obstacles is investigated in a boundary-layer wind-tunnel simulation. The experiment models at 1:50 scale a large outdoor field study that simulated an urban boundary layer with an array of shipping containers, known as MUST (Mock Urban Setting Test -Yee and Biltoft, 2004, Boundary-Layer Meteorology 111, 363-415). The wind-tunnel results are reported and discussed in detail, and some comparisons are drawn to the outdoor field trial and previous studies of plume dispersion within obstacle arrays, as well as open terrain. The analysis covers a wide range of concentration statistics and other quantitative descriptors of plume behaviour, giving a comprehensive treatment of the physical mechanisms involved in the development of a dispersing plume within an 'urban-like' environment. Emphasis is placed on the description and mathematical modelling of concentration fluctuations within the plume, as well as the usual mean concentration results. Some discussion is also centred on the physical similarities and differences between scaled model simulations and full-scale dispersion experiments, and some possibly surprising influences of upwind flow conditioning on obstacle array dispersion that require more careful attention.

In this study, we couple compartment models for indoor air quality and disease transmission to develop a novel SEIR-e model for disease transmission and pathogen exposure. In doing so, we gain insight into the contribution of people-people and people-pathogen interactions to the spread of transmissible diseases. A general modelling framework is used to assess the risk of infection in indoor environments due to people-pathogen interactions via inhalation of viral airborne aerosols, and contact with contaminated surfaces. We couple the indoor environment model with a standard disease transmission model to investigate how both people-people and people-pathogen interactions result in disease transmission. The coupled model is referred to as the SEIR-e model. To demonstrate the applicability of the SEIR-e model and the novel insights it can provide into different exposure pathways, parameter values which describe exposure due to people-people and people-pathogen interactions are inferred using Bayesian techniques and case data relating to the 2020 outbreak of COVID-19 in Victoria (Australia).