NCAS-supported studies in urban meteorology issues - other than those solely concerned with air quality - are concentrated largely at the Universities of Reading (PI Prof. SE Belcher) and Southampton (PI Prof. IP Castro); the two groups work closely together and summaries of their work can be seen in the two sections given below.

Urban Meteorology at Reading

The interpretation of measured data from field experiments in urban areas is often not straightforward owing to a lack of basic understanding of turbulent flow characteristics over groups of buildings. Moreover, recent interest in urban air quality has made it important to understand unsteady turbulent processes on small spatial and time scales. High resolution numerical modelling has been used to elucidate the dominant turbulent processes that occur in urban areas. Turbulent eddies generated by the edges of buildings are shown to be important in mixing within the urban canopy. In particular, shear layers at the rooftops of buildings impact intermittently upon buildings further downstream and drive a recirculation in front of the buildings. Hence, they may play an important role in ventilation within the building canopy.

For further information, see the Urban Meteorology pages at the University of Reading.

Staff involved in this activity are:

Dr Omduth Coceal.

Snapshot showing the structure of the shear layer over building tops, visualised by contours of spanwise vorticity in a vertical plane through the middle of a building. Instantaneous wind vectors are also shown. Note the recirculation in front of the next building (just on the right of the domain shown), caused by intermittent impinging of the shear layer. Vectors are plotted at reduced resolution for clarity. Mean flow is from left to right.

Some of the DNS codes used at Reading were originally developed by Dr Glyn Thomas of Southampton University.

Urban Meteorology at Southampton

The Southampton group aims to advance fundamental understanding of fluid flow, turbulence and dispersion phenomena using numerical simulation (e.g. large-eddy simulation and direct numerical simulation) and wind tunnel experiments, and then use improved understanding and better models for more applied problems, e.g. scalar dispersion and heat transfer within and above typical urban environments. The group is also currently investigating the coupling between weather-scale flows and the urban boundary layer, in which meso-scale flows (e.g. UM data at BADC) are used to drive street-scale computations.

Wind tunnel experiments are undertaken using HWA, LDA and PIV for flows over generic rough walls or, in particular, flows within and above urban-like groups of obstacles. The data provide both fundamental insight into physics and appropriate validation for numerical simulations, which are conducted at Southampton and at Reading.

Commercial CFD codes and an in-house DNS/LES code (originally developed by Dr Glyn Thomas and modified for scalar dispersion by Dr Sergey Yakovenko) are used for numerical simulations of flows and scalar transfer over generic arrays of obstacles in collaboration with the Reading BL group. At Southampton a typical real urban geometry is being studied – the DAPPLE site in central London - and codes for scalar transport from an area surface source (which is in an analogy of weak heat transfer) are being validated by comparisons with dispersion experiments. We are also studying the importance of the oncoming wind direction on in-canopy urban flows. The group is responsible for installing one of the LES codes on HECToR making it accessible to the other NCAS users.

Staff involved in this activity are:

Prof. Ian Castro, Dr Glyn Thomas, Dr Zheng-Tong Xie and Dr Barathi Boppana.