Physical Models of Atmospheric Boundary Layer Flows: Some Developments and Recent Applications

Experimental studies on wind engineering require the use of different types of physical models of boundary layer flows. Small-scale models obtained in a wind tunnel, for example, attempt to reproduce real atmosphere phenomena like wind loads on structures and pollutant dispersion by the mean flow and turbulent mixing. The quality of the scale model depends on the similarity between the laboratory-generated flow and the atmospheric flow. Different types of neutral atmospheric boundary layer (ABL) including full-depth and part-depth simulations are experimentally evaluated. The Prof. Jacek Gorecki wind tunnel of the UNNE, Argentina, and the Prof. Joaquim Blessmann closed-return wind tunnel of the UFRGS, Brazil, were used to obtain the experimental data. Finally, some recent wind engineering applications of this type of physical wind models are shown

Análise experimental no túnel de vento dos processos de difusão de gases poluentes na atmosfera

The objective of this work is the study of atmospheric pollutants dispersion problems in wind tunnels. The use of a reduced scale model provides the ability to analyze the process of dispersion in complex models. It also allows the study of different situations and alternatives in the source design. The wind tunnel pollutants dispersion simulation requires two sets of similarity criteria; the first established that the wind tunnel flow must be similar to natural wind in the atmospheric boundary layer, and the second, that the model source characteristics must be similar to prototype. In this work, the similarity criteria of the atmospheric flow and the emission source are studied to reproduce dispersion processes and develop a first approach to the experimental study of this phenomenon. Firstly, the results of a visualization dispersion process test performed at the wind tunnel of the Facultad de Ingeniería de la Universidad Nacional del Nordeste, using smoke as a tracer and considering three operation velocities are presented. The study of the plume evolution was made by image digital processing and the plume rise is also discussed by comparison of measurements with theoretical values. Finally, preliminary experiments results are presented to evaluate concentration field from an isolated point emission source using a light gas and reduced scale model.Keywords: atmospheric dispersion, similarity, wind tunnel.O objetivo deste trabalho é o estudo de problemas de dispersão de poluentes na atmosfera em túneis de vento. A utilização de um modelo em escala reduzida fornece a capacidade de analisar o processo de dispersão em situações complexas. Também permite a avaliação de diferentes alternativas para o projeto da fonte de emissão. A simulação do processo de dispersão de poluentes no túnel de vento requer dois conjuntos de critérios de similaridade, o primeiro estabelece que o escoamento no interior do túnel de vento deve ser semelhante ao vento natural na camada limite atmosférica, e o segundo que as características da fonte no modelo devem ser semelhantes às do protótipo. Neste trabalho, são estudados os critérios de semelhança do escoamento atmosférico e a fonte de emissão para reproduzir o processo de dispersão, e fazer uma primeira abordagem ao estudo experimental deste fenômeno. Na primeira parte, são apresentados os resultados de um estudo de visualização de um processo de dispersão realizado no túnel de vento da Facultad de Ingeniería de la Universidad Nacional del Nordeste, utilizando fumaça e considerando três velocidades de operação. O estudo da evolução da pluma simulada foi realizado a partir do processamento digital de imagens obtidas durante o teste. Analisa-se também a elevação da pluma comparando as medições com valores teóricos. Finalmente, são apresentados resultados de medições preliminares de experimentos para avaliar o campo de concentração de uma emissão de gás muito leve, utilizando um modelo em escala reduzida.Palavras-chave: dispersão atmosférica, semelhança, túnel de vento

Wind Tunnel Experiments on Turbulent Boundary Layer Flows

The knowledge and experimental development of boundary layer turbulent flows is extremely important in applications related to the building aerodynamics, wind comfort, atmospheric dispersion, and even aeronautics. The Aerodynamic Laboratories of the UFRGS and UNNE have been making joint activities related to wind engineering such as those mentioned earlier for more than 25 years. In this work, a compilation of different experiments on turbulent boundary layer flows realized in these both laboratories is carried out. The characteristics of flows that develop on a smooth surface of the wind tunnel are experimentally evaluated. Then, reduced-scale models of atmospheric boundary layer flows are analyzed including the effects of turbulence generators and surface roughness. Special attention on the behavior of the turbulent parameters in the case of experimental studies using low mean velocity is paid. Finally, some comments referring to recent studies on thermal effects in turbulent boundary layer flows and the development of reduced-scale models of convective flows are included

Distribuições de Probabilidade das Flutuações de Velocidade e Concentração nos Processos de Dispersão de Poluentes

Testes na atmosfera e num túnel de camada limite foram realizadospara avaliar o comportamento probabilístico das flutuações de velocidadee concentração associadas a um processo de dispersão. Distribuiçõespróximas à Gaussiana foram obtidas na analise das velocidades.Para as flutuações de concentração, diferentes comportamentos podemser determinados, conforme a região do campo das concentrações analisada

Characteristics of Zonda Wind in South American Andes

This paper discusses some features and conditions that characterize the Zonda wind, focusing particularly on the implications for wind engineering applications. This kind of wind, typical of mountainous regions, is far from being adequately characterized for computational simulations andproper modeling in experimental facilities such as boundary layer wind tunnels. The objective of this article is to report the research works that are being developed on this kind of wind, describing the main obtained results, and also to establish some general guidelines for the proper analysis of the Zonda in the wind engineering context. A classification for the Zonda wind is indicated and different cases of structural and environmental effects are described. Available meteorological data is analyzed from the wind engineering point of view to obtain the Zonda wind gust factors, as well as basic wind speeds relevant for structural design. Some considerations and possible directions for the Zonda wind-tunnel and computational modeling are provided. Gust factor values larger than those used for open terrain were obtained, nevertheless, the basic wind speed values obtained are similar to values presented by the Argentinian Wind Code for three-second gust, principally at Mendoza airport.Fil: Loredo Souza, Acir M.. Universidade Federal do Rio Grande do Sul. Laboratório de Aerodinâmica Das Construções; BrasilFil: Wittwer, Adrián Roberto. Universidad Nacional del Nordeste. Facultad de Ingeniería; ArgentinaFil: Castro, Hugo Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina. Universidad Tecnológica Nacional. Facultad Reg. Resistencia; ArgentinaFil: Vallis, Matthew B.. Universidade Federal do Rio Grande do Sul; Brasil. Universidade Federal Do Rio Grande do Sul. Laboratório de Aerodinâmica Das Construções; Brasi