Indoor-outdoor pollutant exchange in a flow through a hollow cube immersed in a turbulent boundary layer

Abstract

Understanding how turbulent processes disperse air pollution inside buildings is crucial for urban planning and occupancy comfort. Driven by this motivation, the present work investigates an idealization of the indoor-outdoor exchange of a passive scalar pollutant in an urban environment, namely, flow-through an isolated hollow cube, a scaled-down (about 40:1) model building immersed in a turbulent boundary layer, with windows in the upstream and downstream faces of the cube. Presently, two cases are investigated where the first one involves an indoor ground-level passive scalar source, and the second one has an outdoor ground-level source placed upstream to the model, with both being studied for a fixed Reynolds number (Re=URefH/ν) of ≈20,000; here URef is the incoming flow velocity at the cube height (H) measured without the cube. The experiments take place in a recirculating water tunnel where Planar Laser-induced Fluorescence (PLIF) measurements are performed to capture the mean and transient behaviours of a scalar and Particle Image Velocimetry (PIV) to capture the velocity fields, with these two being performed simultaneously. Changing the source position significantly alters the scalar transport and distribution inside the model. The indoor injection case shows scalar accumulation in re-circulation flow regions near the top and bottom walls inside the cube, while in the outdoor case, a relatively uniform scalar buildup within the cube is observed. These differences are found to be due to the distinction between the two cases in the advective and turbulent scalar transport mechanisms. The insights from the present results can significantly contribute to our understanding and modelling of pollutant(s) exchange between indoor and outdoor environments in intricate atmospheric boundary layer conditions.

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Identifiers

ORCID for Subhajit Biswas: orcid.org/0000-0002-0357-5796

ORCID for Christina Vanderwel: orcid.org/0000-0002-5114-8377

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