Quantification of the influence of geometry on the flow developed over and through fractal and non-fractal groups of obstacles.

Air quality has a major impact on human health and ecosystems. Thus, the improvement of our understanding and the modelling of how urban geometry can modify the natural ventilation of cities has become a crucial issue for the sustainable development of the United Kingdom (UK). According to DEFRA, the cost from the impacts of air pollution in the UK can be estimated to be between £ 9-19 billion every year, this is comparable to the economic cost of obesity (over £ 10 billion).

Cities can be viewed as a complex collection of structures of different scales (buildings of different size, large factories etc.). Research in the field of regional planning has shown that large urban areas have important fractal characteristics and there is evidence that non-fractal, but expanding, cities have also a tendency towards fractality. This project aims to create the foundations for a long-term research approach involving the development of environmental models able to quantify the relation between the fractal geometry of urban forms and their environmental performance. Large amounts of research have contributed towards the modelling and description of the fractal spatial characteristics of cities; however there is no evidence of how the reported fractal geometry can be related to flow characteristics and ventilation rates.

This project will experimentally quantify the relationship between a multi-scale group of obstacles, which could be a generic group of buildings, and the flow structure developed within and over a large group of obstacles. It is expected that the results obtained from this project will facilitate innovative approaches to tackling the current scientific and applied challenges involved in the modelling of urban flows, but will also provide results generic enough to trigger the development of similar approaches in the wider context of environmental fluid mechanics.

The research will act as an important stepping stone to the development, in subsequent projects, of tools to manage the dangerous effects of pollution in large urban centres. Hence, there will be a direct benefit to human health and society.

The results of this projects need to be properly disseminated across different research areas to ensure that the outputs can be applied to the real geometries found in urban areas. The project includes close interaction with Cambridge Environmental Research Consultants (CERC), a world-class engineering company, as well as with Sheffield City Council. The execution and outputs of the project will be discussed and analysed with these partners to optimise the process of knowledge transfer from basic research towards practice. In this context, a one-day workshop will be organised to disseminate the results, and also to obtain feedback from practitioners (City Councils, DEFRA, Met-office etc.) for future research activities. Some of the expected applied results of a follow-up project are the identification of poor ventilation zones, based on their fractal geometry, the creation of guidelines to balance demographic demands and environmental performance, and the determination of the maximum ventilation capacity of current urban layouts. Also the development of tools for urban planers to optimise ventilation rates, which can have an important effect on the reduction of energy consumption of buildings (which currently contribute with about 45% of the total CO2 emissions of the UK)