Previous studies on inter-unit dispersion around multi-storey buildings focused mostly on an isolated building. Considering that the presence of an upstream building(s) would significantly modify the airflow pattern around a downstream building, this study intends to investigate the influence of such changed airflow patterns on inter-unit dispersion characteristics around a multi-storey building due to wind effect. Computational fluid dynamics (CFD) method in the framework of Reynolds-averaged Navier-stokes modelling was employed to predict the coupled outdoor and indoor airflow field, and the tracer gas technique was used to simulate the dispersion of infectious agents between units. Based on the predicted concentration field, a mass conservation based parameter, namely re-entry ratio, was used to evaluate quantitatively the inter-unit dispersion possibilities and thus assess risks along different routes. The presence of upstream building(s) could disrupt the strong impingement of approaching flows but brings a more complex and irregular airflow pattern around the downstream multi-storey buildings, leading to a more scattered distribution of re-entry ratio values among different units and uncertain dispersion routes. Generally, the tracer gas concentration in most units was lower than those in an isolated building, although very high concentrations were found in some specific areas.
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