Showing papers by "Alan Robins published in 2004"

Short communication Sustainable development of urban transport systems and human exposure to air pollution

Abstract: DAPPLE (Dispersion of Air Pollution and Penetration into the Local Environment, http://www.dapple.org.uk) is a major research project that will provide the understanding necessary to assess the sustainability of urban road transport in terms of exposure to traffic-related air pollution as an alternative to current indicators based on emissions, roadside, or far-fromroad air pollution levels. The methodology is described, which combines on-street and laboratory measurement with modelling of the movement of air, vehicles, and vehicle exhaust emissions. The relationship between this kind of assessment and more realistic indicators of sustainability is discussed. The value of large-scale interdisciplinary research in this area is thus demonstrated. D 2004 Elsevier B.V. All rights reserved.

A comparison of wind-tunnel experiments and numerical simulations of neutral and stratified flow over a hill

Abstract: A comparison is made of numerical and experimental results for flow over two-dimensional hills in both neutral and stably stratified flow. The numerical simulations are carried out using a range of one-and-a-half order and second-order closure schemes. The performance of the various turbulence schemes in predicting both the mean and turbulent quantities over the hill is assessed by comparing the results with new wind-tunnel measurements. The wind-tunnel experiments include both neutral and stably stratified flow over two different hills with different slopes, one of which is steep enough to induce flow separation. The dataset includes measurements of the mean and turbulent parts of the flow using laser Doppler anemometry. Pressure measurements are also made across the surface of the hill. These features make the dataset an excellent test of the model performance. In general second-order turbulence schemes provide the best agreement with the experimental data, however, they can be numerically unstable for steep hills. Some modifications can be made to the standard one-and-a-half order closure scheme, which results in improved performance at a fraction of the computation cost of the second-order schemes.

Large-eddy simulation of dispersion: comparison between elevated and ground-level sources

Abstract: Large-eddy simulation (LES) is used to calculate the concentration fluctuations of passive plumes from an elevated source (ES) and a ground-level source (GLS) in a turbulent boundary layer over a rough wall The mean concentration, relative fluctuations and spectra are found to be in good agreement with the wind-tunnel measurements for both ES and GLS In particular, the calculated relative fluctuation level for GLS is quite satisfactory, suggesting that the LES is reliable and the calculated instantaneous data can be used for further post-processing Animations are shown of the meandering of the plumes, which is one of the main features to the numerical simulations Extreme value theory (EVT), in the form of the generalized Pareto distribution (GPD), is applied to model the upper tail of the probability density function of the concentration time series collected at many typical locations for GLS and ES from both LES and experiments The relative maxima (defined as maximum concentration normalized by the local mean concentration) and return levels estimated from the numerical data are in good agreement with those from the experimental data The relative maxima can be larger than 50 The success of the comparisons suggests that we can achieve significant insight into the physics of dispersion in turbulent flows by combining LES and EVT

Large-Eddy Simulation of Turbulent Flow Over a Rough Surface

Abstract: A family of wall models is proposed that exhibits more satisfactory performance than previous models for the large-eddy simulation (LES) of the turbulent boundary layer over a rough surface. The time and horizontally averaged statistics such as mean vertical profiles of wind velocity, Reynolds stress, turbulent intensities, turbulent kinetic energy and also spectra are compared with wind-tunnel experimental data. The purpose of the present study is to obtain simulated turbulent flows that are comparable with wind-tunnel measurements for use as the wind environment for the numerical prediction by LES of source dispersion in the neutral atmospheric boundary layer.

LES and Extreme Value Theory

Abstract: Using large-eddy simulation (LES), we calculate the concentration fluctuations of passive plumes from an elevated (ES) and a ground-level source (GLS) in a turbulent boundary layer over a rough wall. The mean concentration, relative fluctuations and spectra are found in good agreement with the wind-tunnel measurements. The Generalised Pareto Distribution (GPD) is applied to model the upper tail of the probability density function of concentration time series, collected at many typical locations for GLS and ES from both LES and experiments. The relative maxima and return levels against downstream distance, which are estimated from numerical data, are in good agreement with those from experimental data.

Personal exposure to air pollution at a street canyon intersection: implications for air quality management in the context of sustainable development

Abstract: R.N. Colvile, S. Kaur, S. Belcher, M. Bell, R. Britter, M. Nieuwenhuijsen, A. Robins, A. Tomlin, D. Shallcross Imperial College London, Department of Environmental Science & Technology, London, UK University of Reading Department of Meteorology, Reading, UK University of Leeds Institute for Transport Studies, Leeds, UK University of Cambridge, Department of Engineering, Cambridge, UK University of Surrey, School of Mechanical Engineering, Guildford, UK University of Leeds Department of Fuel & Energy, Leeds, UK University of Bristol Department of Chemistry Bristol, UK