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Behavior of leakages exposed to dynamic wind loads. A numerical study using CDF on a single zone model

Dimitrios Kraniotis, Thomas Kringlebotn Thiis, Tormod Aurlien, 2011
leakage rate | air flow | air infiltration | crack | dynamic wind load | wind gust | computational fluid dynamics | shear-stress-transport | single zone model
Bibliographic info: 32nd AIVC Conference " Towards Optimal Airtightness Performance", Brussels, Belgium, 12-13 October 2011
Languages: English

Wind is a potential dominant factor regarding the air infiltration through building envelopes. Due to its dynamic characteristics, quite complex aerodynamic phenomena arise around a structure or through cracks and openings. Energy perfomance is influenced by the climate conditions and thus it should be much more researched. Despite the fact that steady state measurements of infiltration rates offer a simple and easy way of estimating an enclosure’s airtightness level, a supplement to those methods might be imposed. In this context, computational fluid dynamics could be a useful tool, generating interesting results and helping understand the role of flow mechanisms.

The current numerical study deals with the influence of wind gust on the infiltration rate of a bluff body (‘box’) on which cracks of varied size are located on different sides. Different internal volumes are also researched. On discussing the results, the dynamic leakage rates (infiltration and exfiltration) are under investigation, while the airflow patterns inside the ‘box’ are pointed out as well. Frequency characteristics of the wind gust and their correlation with the internal volume are also studied.

The results suggest that gust frequency is the dominant factor for air flows through cracks on the windward side, while the internal volume also plays an important role on the instantaneous leakage rates under unsteady wind conditions. The impact of the enclosure’s volume seems to be of importance for relatively small cracks. In addition, there is a difference among the leakage rates through the studied cracks and openings depending on their location or switching from a small to a big volume. Comparisons with the respective behavior of the cracks-openings under steady state enclosure’s pressurization at 50Pa are shown as well.

Since the studied enclosure represents a airtight single zone, where air flows only through the opening(s), a parallelism to the internal space of a high level airtight building arises. Taking into account the results of the current study, the influence of the frequency of the gust, the internal volume of a relatively airtight building and the location of the leakage area seem to be critical factors under climate conditions. Having ensured that leakages through the internal walls are very low, a further research should be proceed towards the importance of the location and airtightness of the internal walls. On the same mode internal volume’s control and exterior local climate might be also considered.

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