Boundary layer

LUCID: the intelligent design of cities

The Development of a Local Urban Climate Model and its Application to the Intelligent Design of Cities project (LUCID) is a 3-year research project investigating how cities are able to adapt to a changing climate.

CERC is working on this project, with partners in the academic sector (University College London, London School of Hygiene and Tropical Medicine, University of Reading and Brunel University) as well as other consultancies. It began in June 2007.

The role of CERC within the project is to develop a tool that is able model local changes in temperature and specific humidity on a neighbourhood scale (i.e. over areas of a few square kilometres) due to changing land use. This has been achieved by modifying the CERC model FLOWSTAR to calculate local perturbations to the upwind temperature and humidity fields based on local land use parameters, specifically: surface roughness, surface resistance to evaporation parameter, albedo, thermal admittance and a normalised building volume parameter. In addition, for the purpose of full model validation against temperature measurements, anthropogenic heat from traffic and buildings are also being modelled.

Funded by the UK Engineering and Physical Sciences Research Council (EPSRC).

Learn more

• Further details of this project can be found on the LUCID website.

Dispersion around buildings: comparison with wind tunnel and CFD[top]

Mitsubishi Heavy Industries Ltd (MHI) of Japan contracted CERC to assist in evaluating the CFD dispersion model HYPACT, interpreting results, and improving the model for the case of an accidental release in the vicinity of a single block building. The flow field around the building was calculated using the RAMS model.

HYPACT was evaluated against wind tunnel data and results were interpreted by using the COST-732 Model Evaluation Guidelines (http://www.mi.uni-hamburg.de/Home.484.0.html). Based on the results and performance achieved, CERC used their expertise to suggest improvements to the model.

In the comparison exercise, ADMS 4 was used to model the concentration from an area source placed in the lee of an isolated building, at ground level. Mean concentration results from ADMS 4 were compared against wind tunnel and HYPACT, showing satisfactory agreement.

Supported by Mitsubishi Heavy Industries Ltd.

Mesoscale modification of FLOWSTAR for sharp changes in surface roughness

Coastal meteorology is complex and of great practical importance, for instance for coastal wind farms and flooding predictions. In 2005 and 2006 CERC developed modelling tools to compute wind flows in coastal regions, where there are sharp changes in surface roughness. These tools extend CERC's FLOWSTAR model and produce results in high spatial resolution on a standard Windows PC. The work built on the research of CERC's technical director Professor Julian Hunt.

The mathematical model is a general linearized shallow-layer perturbation model, where the approximately neutral lower layer of thickness h₀ is situated below a stable upper layer (i.e. an inversion with temperature change ΔT), is developed for steady, mesoscale atmospheric flows over low-lying topography whose height is less than h₀. With the Coriolis parameter f, sharp changes in surface conditions (surface roughness, terrain elevation, heat flux) are modelled as a distributed body force through the lower layer. The Froude number of this layer is small.

The project was supported by Mitsubishi Heavy Industries and Kyoto University.

Learn more

• Hunt JCR, Orr A, Rottman JW, and Capon R,2004:Coriolis effects in mesoscale flows with sharp changes in surface conditions.Q. J. R. Meteorol. Soc., 130:2703-2731. (Abstract)
• Orr A, Hunt JCR, Capon R, Sommeria J, Cresswell D, and Owinoh A,2005:Coriolis effects on wind jets and cloudiness along coasts.R. Meteorol. Soc. Weather, 60:10:291-299. (Abstract)

Parameterisation of the atmospheric boundary layer for offshore dispersion

Under a contract with the UK Department for Trade & Industry, CERC developed a marine boundary layer scheme for calculating surface roughness and heat fluxes over the sea that can be used, for example, for dispersion modelling of stacks on oil extraction platforms. To use this scheme all sources and receptors should be over the sea; it is not suitable for coastal modelling.

The scheme has been incorporated into ADMS 4 as the marine boundary layer option which is described in Section 8.9 of the ADMS 4 User Guide (see the Model documentation page).

Supported by the UK Department of Trade and Industry (DTI).