The flow in a wind tunnel test section must meet high standards to obtain accurate and reliable measurement data.Good flow quality demands a certain degree of spatial uniformity and temporal steadiness of velocity and pressure.In this paper, a set of six new indices is developed and presented that relate spatial aspects of the mean velocity field to flow quality.One index quantifies the degree of uniformity of the velocity field and can be used directly as a flow quality indicator.The five other indices are related to different types of deviations from spatially uniform flow; skewed flow and angularity (up-flow and down-flow, swirl, cross-flow, diverging and converging flow).The indices can be used to evaluate the flow quality in existing tunnels and to assess the impact of design modifications.They can also be used in the CFD-based design of new wind tunnels.
Het KNMI voorspelt dat de temperaturen in Nederland in de toekomst zullen stijgen ten gevolge van de klimaatverandering. Milde winters en hete zomers met hittegolven zullen steeds frequenter optreden (Klein Tank en Lenderink, 2009). Door de klimaatverandering zal de luchttemperatuur in de gebouwde omgeving in de toekomst eveneens gaan stijgen. Deze verwachte stijging zal consequenties hebben voor het binnenklimaat in gebouwen. Terwijl het optreden van milde winters kan leiden tot een lager energieverbruik voor verwarming, kunnen de hete zomers juist leiden tot problemen met respect tot het thermisch comfort en de gezondheid van de gebruikers, en indien actieve koelsystem aanwezig zijn tot een toename van het energieverbruik voor koeling. Passieve adaptatiemaatregelen kunnen worden toegepast op gebouwniveau om het binnenklimaat op peil te houden en het gebruik van actieve koeling zoveel mogelijk te beperken en/of te verminderen.
CFD is applied to evaluate pedestrian wind comfort at outdoor platforms in a high-rise apartment building. Model validation is focused on generic building sub-configurations that are obtained by decomposition of the actual complex building geometry. The comfort study is performed during the design stage, which allows structural design changes to be made for wind comfort improvement. Preliminary simulations are performed to determine the effect of different design modifications. A full wind comfort assessment study is conducted for the final design. Structural remedial measures for this building, aimed at reducing pressure short-circuiting, appear to be successful in bringing the discomfort probability estimates down to acceptable levels. Finally, the importance of one of the main sources of uncertainty in this type of wind comfort studies is illustrated. It is shown that the uncertainty about the terrain roughness classification can strongly influence the outcome of wind comfort studies and can lead to wrong decisions. This problem is present to the same extent in both wind tunnel and CFD wind comfort studies when applying the same particular procedure for terrain relation contributions as used in this paper.
Desempenho higrotermico dos edificios tem sido estudado usando uma variedade de programas de computador, os quais consideram determinados dominios geometricos (exterior, envelope e interior) e fisicos (calor, ar e umidade). Estes programas podem ser classificados em tres principais grupos: programas de simulacao de energia do edificio (BES), transferencia de calor, ar e umidade em componentes construtivos (BEHAM) e dinâmica de fluidos computacional (CFD). A falta de integracao entre esses programas constitui uma importante fonte de incerteza em simulacoes do desempenho higrotermico do edificio. Trabalhos recentes apresentaram mecanismos para a simulacao combinada de programas BES e BEHAM. Na simulacao combinada, os programas sao executados em paralelo, trocando informacoes durante o curso da simulacao, de forma a aprimorar a qualidade de ambas as simulacoes. O presente artigo apresenta a validacao inicial de simulacoes combinadas usando BES e BEHAM, utilizando os programas ESP-r e HAMFEM. A validacao e realizada atraves da comparacao com solucoes analiticas, comparacao com resultados de outros modelos e com resultados experimentais. Simulacoes combinadas usando BES e BEHAM demonstram grande melhoria na qualidade dos resultados, em particular com relacao ao calculo da umidade relativa no interior do edificio.ABSTRACTHeat, air and moisture (HAM) performance of buildings has been studied in the past using a variety of computer models, which are focused on specific geometrical and physical domains. These programs can be classified in three main types: building energy simulation (BES), building element heat, air and moisture simulation (BEHAM) and computational fluid dynamics (CFD). The lack of integration between these programs constitutes a major source of uncertainty in whole-building HAM simulations. This paper presents the initial validation of a generic framework for two-way coupling of two of these program types: BES and BEHAM. The BES program ESP-r and the BEHAM program HAMFEM are used to demonstrate the implementation of this generic framework. Validation is carried out through comparison with analytical solutions, inter-model comparison and experimental results, where the BES-BEHAM coupled simulations demonstrate major improvements in the accuracy of results when compared to stand-alone simulations, particularly concerning the prediction of moisture content in the indoor air.
Annotation The 2009 ASHRAE HandbookFundamentals covers basic principles and data used in the HVAC & R industry. Updated with research sponsored by ASHRAE and others, this volume includes 1,000 pages and 39 chapters covering general engineering information, basic materials, climate data, load and energy calculations, duct and pipe design, and sustainability, plus reference tables for abbreviations and symbols, I-P to SI conversions, and physical properties of materials. An accompanying CD-ROM (free with the bookalso sold separately) contains all the volume's chapters in both I-P and SI units.
This paper presents finite-volume-based scale-adaptive simulations of single paceline configurations up to eight cyclists for three different postures. In cycling, drag reduction by drafting in pacelines is a key strategy to limit energy expenditure. The drag reductions of individual cyclists and of the paceline as a whole are determined by several factors, including cycling posture. To the best of our knowledge, a systematic study on the effect of cyclist posture on the drag in single pacelines has not yet been published in the scientific literature. In this study, drag reduction and flow field data were computed while validation was performed by wind tunnel measurements. The three investigated postures concern a road race dropped posture with either a large or small sagittal torso angle and a time trial posture. For the considered pacelines in which all cyclists have the same posture, the drag of a cyclist could be reduced by changing either the posture, or the position, or both. Changing posture can yield a maximum drag reduction of about 15% for the leading cyclist. The position in the paceline with minimum drag was the one but last, independent of the investigated cycling postures. For the pacelines containing eight cyclists, maximum drag reductions up to 63% were found. The largest drag reduction was 68%, obtained by riding in penultimate position in an eight cyclist paceline in dropped position with a small sagittal torso angle.
Abstract Cycling races contain a multitude of motorcycles for various activities including television broadcasting. During parts of the race, these motorcycles can ride in close proximity of cyclists. Earlier studies focused on the impact of a nearby motorcycle on cyclist drag for in-line arrangements. It was shown that not only a motorcycle in front of a cyclist but also a motorcycle closely behind a cyclist can substantially reduce cyclist drag. However, there appears to be no information in the scientific literature about the impact of the motorcycle on cyclist drag for parallel and staggered arrangements. This paper presents wind tunnel measurements of cyclist drag for 32 different parallel and staggered cyclist-motorcycle arrangements. It is shown that the parallel arrangement leads to a drag increase for the cyclist, in the range of 5 to about 10% for a lateral distance of 2 to 1 m. The staggered arrangement can lead to either a drag increase or a drag decrease, where the latter is about 2% for most positions analyzed. For one of the parallel arrangements, computational fluid dynamics simulations were performed to provide insight into the reasons for the drag increase. A cyclist power model was used to convert the drag changes into potential time gains or losses. Compared to a lone cyclist riding at a speed of 46.8 km/h (13 m/s) on level road in calm weather, the time loss by a drag increase of 10%, 4% and − 2% was 2.16, 0.76 s and − 0.80 s per km, respectively. These time differences are large enough to influence the outcome of cycling races.
