Measurements and computations of flow in an urban street system

We present results from laboratory and computational experiments on the turbulent flow over an array of rectangular blocks modelling a typical, asymmetric urban canopy at various orientations to the approach flow. The work forms part of a larger study on dispersion within such arrays (project DIPLOS) and concentrates on the nature of the mean flow and turbulence fields within the canopy region, recognising that unless the flow field is adequately represented in computationalmodels there is no reason to expect realistic simulations of the nature of the dispersion of pollutants emitted within the canopy. Comparisons between the experimental data and those obtained from both large-eddy simulation (LES) and direct numerical simulation (DNS) are shown and it is concluded that careful use of LES can produce generally excellent agreement with laboratory and DNS results, lending further confidence in the use of LES for such situations. Various crucial issues are discussed and advice offered to both experimentalists and those seeking to compute canopy flows with turbulence resolving models

Northern Hemisphere Snow-Cover Trends (1967–2018): A Comparison between Climate Models and Observations

Observed changes in Northern Hemisphere snow cover from satellite records were compared to those predicted by all available Coupled Model Intercomparison Project Phase 5 (“CMIP5”) climate models over the duration of the satellite’s records, i.e., 1967–2018. A total of 196 climate model runs were analyzed (taken from 24 climate models). Separate analyses were conducted for the annual averages and for each of the seasons (winter, spring, summer, and autumn/fall). A longer record (1922–2018) for the spring season which combines ground-based measurements with satellite measurements was also compared to the model outputs. The climate models were found to poorly explain the observed trends. While the models suggest snow cover should have steadily decreased for all four seasons, only spring and summer exhibited a long-term decrease, and the pattern of the observed decreases for these seasons was quite different from the modelled predictions. Moreover, the observed trends for autumn and winter suggest a long-term increase, although these trends were not statistically significant. Possible explanations for the poor performance of the climate models are discussed

Measurements in an urban-type boundary layer.

Wind tunnel measurements of the boundary layer flow over a very rough surface comprising a staggered array of cubes are presented and discussed. Attention is concentrated on the near-wall region, including the canopy region below the tops of the roughness elements. Particle image velocimetry (PIV) and laser Doppler anemometry were used to identify the dominant features of the mean and turbulent flow and these are compared with the better-known features of the flow above the roughness. Spatial correlation data, extracted from the PIV images, are used to provide information about eddy structures and it is shown that these differ in some crucial respects from those typical of more classical boundary layers. The implications of the results are discussed in terms of their relevance to flows within the urban environment

Análise do impacto da morfologia urbana na demanda estimada de energia das edificações: um estudo de caso na cidade de Maceió, AL

International audienceEvaluation of the impact of urban morphology on the estimated energy demand of buildings: a case study in Maceió, Brazil Tathiane Agra de Lemos Martins Marion Bonhomme Luc Adolphe Resumo ste estudo apresenta um método simplificado de análise e mapeamento morfológico do tecido urbano para auxiliar no estudo da climatologia e do impacto da forma urbana na demanda de energia das edificações. Diferentes parâmetros foram empregados na análise da geometria urbana, a fim realizar uma cartografia de áreas morfologicamente homogêneas, cada uma apresentando uma influência diferente na demanda energética das edificações. Numa primeira etapa, os parâmetros morfológicos urbanos foram automatizados e calculados em um sistema de informação geográfica, para diferentes resoluções espaciais. Os resultados morfológicos obtidos para uma aplicação na cidade de Maceió, AL, foram analisados por meio da Análise de Componentes Principais (ACP), a partir da qual foi possível identificar a significância dos parâmetros para o contexto urbano considerado. A análise de agrupamento (Clustering Analysis) permitiu que as diferentes configurações tipológicas fossem agregadas, classificadas e, na sequência, submetidas às simulações computacionais para estimativa da demanda de energia das edificações. Seis indicadores morfológicos foram conservados e cinco classes tipológicas representativas do tecido urbano de Maceió foram destacadas. Observou-se um impacto importante na demanda de energia de três parâmetros morfológicos principais: a densidade total construída, a verticalidade, a compacidade e o prospecto médio. Palavras-chave: Forma urbana. SIG. Clima urbano. Eficiência energética dos edifícios. Abstract This study presents a simplified method of morphological analysis and mapping of the urban fabric to assist in the study of the climatology and impact of the urban form on the energy demand of buildings. Different parameters have been applied in the analysis of the urban geometry in order to make a cartography of morphologically homogeneous areas, each one presenting a different type of influence on the energy demand of buildings. In the first stage of the study, the morphological parameters were automated and calculated using a geographical information system software. The morphological results obtained through a case study in Maceió, Alagoas, were analyzed using Principal Components Analysis (PCA), which allowed the identification of the significance of the parameters for the urban context. Through a Clustering Analysis, different typological configurations were grouped, classified and then submitted to computational simulations to estimate the buildings' energy demand. Six morphological indicators were maintained and five typological classes representative of the urban fabric of Maceió were highlighted. The study indicated that three main morphological parameters have a major impact: total built density, verticality, compactness and the mean prospectus