Fluid dynamics of Urban Tall-building clUsters for Resilient built Environments (FUTURE)

The world is witnessing rapid urbanisation, where a large percentage of its population is expected to live within urban environments - circa 70% - by 2050 [1]. The main solution to urban immigration has been to construct tall buildings (TBs), which allow for a high-density population (and commercial activities) to reside in the hearts of our cities. However, recent years have witnessed increasing concerns regarding public health and wellbeing in dense urban environments. For instance, it is known that the urban heat island effect, where urban areas are typically some degrees hotter than the surrounding rural areas, can contribute to death rates during heatwaves [2]. To exacerbate these issues, as recognised by the London Plan [3], ''some climate change is inevitable..." and this is likely to increase the frequency and severity of extreme weather events, and the consequent urban health risks. The current COVID-19 crisis has also highlighted the importance of predicting pathogen dispersion and of efficient indoor/outdoor ventilation in urban areas [4]. It is, therefore, in the public interest to build healthy and sustainable urban environments by ensuring that air quality, transport of pollutant emissions, and the microclimate within cities (e.g. winds, temperatures, pollutant concentrations, and anthropogenic heat) do not reach unsustainable levels from poor urban development planning and lack of strategic directions. Recent initiatives are now promoting research on urban environmental health and sustainability (e.g. Public Health England's project Healthy-Polis).

Despite the likely effects of the proliferation of tall structures in exacerbating some of the problems discussed above, current weather and air quality models do not cater for TBs and their long-lasting effects on the winds and temperature fields within urban neighbourhoods. This mostly relates to the dominant small scales of the phenomena under examination, in contrast to the spatial resolution that these models typically achieve (i.e. of the order of hundreds of metres) within the constraints of state-of-the-art computer power, resource availability, and turnaround time. On the other hand, the spatial resolution of computational fluid dynamics methods used in academia is much higher i.e. appropriate to resolve the presence of these urban towers. However, these research simulations often lack much of the physics needed to adequately capture real environmental flows (e.g. atmospheric conditions, heat exchange), and are generally run over much smaller domains. Hence, there is a dual need for more realistic detailed simulations and better parametrisations for larger-scale operational models, with the former informing development of the latter.

To overcome these limitations, this project will employ a synergy of wind-tunnel tests, field observations, high-fidelity computer-aided analysis, and theoretical models. This will allow us to (i) understand the dependence of wind and temperature fields on the geometric parameters describing TBs both in isolation and as a cluster, and (ii) to develop parametrisations and open-source models that can be readily available to policymakers and regulators to assist them in building more resilient urban environments. The aim is to develop publicly available fast turnaround models that describe the effect of TBs on the quantities of interest for users with different levels of sophistication. This will include "rule-of-thumb" design principles aimed at local authorities and technical model parametrisations suitable for implementation in larger numerical weather prediction and air quality software to serve the professional and operational modelling community.

References
[1] Revision of World Urbanization Prospect (2018). DESA, UN.
[2] Vardoulakis et al. (2016). Environmental Health 15, S30.
[3] The London Plan (2017). Greater London Authority.
[4] ECDC Tech. Report (2020). European Centre for Disease Prevention and Control.