The impact of the urban canyon geometry in the nocturnal heat island intensity: analysis by a simplified model adapted to a GIS

A geometria urbana é um dos fatores de maior influência na intensidade da ilha de calor urbana. Seu estudo requer a caracterização de cânions urbanos, geralmente medidos pela relação entre a altura dos edifícios e a largura da rua (H/W), conceito aplicado no modelo numérico de Oke em 1981. O objetivo deste artigo é verificar o impacto da geometria do cânion urbano na intensidade de ilhas de calor noturna. Para isso, foram realizados levantamento de dados climáticos e de geometria urbana em duas cidades brasileiras. Os valores de intensidade de ilha de calor foram confrontados com os simulados pelo modelo original de Oke (1981), o qual foi calibrado e adaptado à plataforma SIG, de forma a possibilitar a incorporação de outro parâmetro de geometria, além da relação H/W: o comprimento de rugosidade. Esse processo gerou uma nova ferramenta de cálculo, que é denominda THIS (Tool for Heat Island Simulation). Aplicou-se o novo modelo para simular alguns cenários urbanos hipotéticos, que representam vários tipos de cânions urbanos. Os resultados demonstraram que cânions urbanos de maior rugosidade amenizam as intensidades de ilha de calor noturna em relação a um cânion de mesmo valor de relação H/W e menor rugosidade.Urban geometry is one of the main factors influencing the development of urban heat islands. The study of urban geometry requires a characterization of urban canyons, which can be usually measured by the H/W ratio (a relationship between the height and the width of a street), a concept applied in a numerical model by Oke in 1981. The aim of this paper is to verify the impact of the canyon geometry on the intensity of the nocturnal urban heat islands. For this purpose, measurements of climate data and urban geometry were conducted in two Brazilian cities. The values of heat island intensity were cross-examined to those generated with the application of the original Oke's model. Therefore, this latter was calibrated and adapted to run in a GIS platform, allowing the incorporation of a geometric parameter other than the H/W ratio - the roughness length. Then, this process produced a new calculation tool, which is called THIS (Tool for Heat Island Simulation). The new model was applied to simulate some hypothetical urban scenarios representing several urban canyons types. The results showed that the urban canyons with the largest roughness reduce the nocturnal heat island intensities in relation to an urban canyon of the same H/W value, but presenting lower roughness rates instead.Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

A multiscale analysis of the urban heat island effect: from city averaged temperatures to the energy demand of individual buildings

Designing the climates of citie

A following car influences cyclist drag: CFD simulations and wind tunnel measurements

It is well-known in elite cycling that a cyclist riding behind a car experiences a substantial reduction in aerodynamic resistance or drag. However, the upstream effect by a following car on the cyclist in front of it is not well-known and has, to the best of our knowledge, not yet been reported in the scientific literature. It is also not taken into account in elite cycling, as for individual time trials, the rules of the International Cycling Union (UCI) only specify a minimum distance between rider and car of 10 m because of safety reasons. Furthermore, during actual races, this limit is often not kept and not strictly enforced. Nevertheless, during individual time trials, there is always at least one, but often more, following cars, potentially influencing the cyclist drag. This study presents the results of CFD simulations and wind tunnel measurements to ascertain and quantify the upstream effect by a following car on the drag of the cyclist in front of it. CFD simulations are performed based on the steady-state Reynolds-Averaged Navier-Stokes equations with the standard k-e model for closure. The simulations are validated based on a series of wind tunnel measurements. The drag reduction for the cyclist ranges from 3.7% over 1.4% to 0.2% for realistic separation distances of 3, 5 and 10 m, respectively. For a typical 50 km individual time trial, the potential time reduction by exploiting this effect (e.g. by a car following the rider at this short distance versus no car behind) is 62.4s, 24.1s and 3.9 s, respectively. As elite cyclist time trials are often won based on seconds or sometimes even less, these differences can be decisive for who wins the stage. Therefore, it is recommended that the UCI not only raises its current minimum separation distance of 10 m to at least 30 m, but also strictly enforces it, to avoid this unwanted aerodynamic effect that can influence the outcome of the race

A following car influences cyclist drag: CFD simulations and wind tunnel measurements

It is well-known in elite cycling that a cyclist riding behind a car experiences a substantial reduction in aerodynamic resistance or drag. However, the upstream effect by a following car on the cyclist in front of it is not well-known and has, to the best of our knowledge, not yet been reported in the scientific literature. It is also not taken into account in elite cycling, as for individual time trials, the rules of the International Cycling Union (UCI) only specify a minimum distance between rider and car of 10 m because of safety reasons. Furthermore, during actual races, this limit is often not kept and not strictly enforced. Nevertheless, during individual time trials, there is always at least one, but often more, following cars, potentially influencing the cyclist drag. This study presents the results of CFD simulations and wind tunnel measurements to ascertain and quantify the upstream effect by a following car on the drag of the cyclist in front of it. CFD simulations are performed based on the steady-state Reynolds-Averaged Navier-Stokes equations with the standard k-e model for closure. The simulations are validated based on a series of wind tunnel measurements. The drag reduction for the cyclist ranges from 3.7% over 1.4% to 0.2% for realistic separation distances of 3, 5 and 10 m, respectively. For a typical 50 km individual time trial, the potential time reduction by exploiting this effect (e.g. by a car following the rider at this short distance versus no car behind) is 62.4s, 24.1s and 3.9 s, respectively. As elite cyclist time trials are often won based on seconds or sometimes even less, these differences can be decisive for who wins the stage. Therefore, it is recommended that the UCI not only raises its current minimum separation distance of 10 m to at least 30 m, but also strictly enforces it, to avoid this unwanted aerodynamic effect that can influence the outcome of the race

an analysis of cases

Social roblems! and public image of the housing estates of 1960\u27s in Spai