Flow patterns around a complex building

The wind flow field around a complex building is calculated using a massively parallel computational fluid dynamics code. We model an onsite building because of its complex architectural features, which include a multilevel roof, an inner courtyard, and two alcoves on the northwest side.

Because local prevailing winds in the summer are from the southwest, flow fields for three wind directions are calculated: 200*, 225*, 250* measured clockwise from north. An open field lies to the southwest of the building, creating a relatively simple upwind fetch. However, there is a long row of Eucalyptus trees to the northeast. The row of trees is modeled with a drag term in the momentum equations.

Preliminary results from the model suggest that, in prevailing summer winds, the row of Eucalyptus trees appear to significantly affect the flow pattern. In addition to slowing the flow in the area around the canopy, a region of high wind speed forms between the southeast corner of the building and the trees. A recirculation zone forms in the lee of the building and drifts toward the trees as the wind angle becomes more westerly. A concentration of streamlines is exhibited at the tail of the recirculation zone. In the 200* case, the recirculation tail follows a line west and parallel to the tree line. However, when the winds are more westerly, the tail penetrates the line of trees.

Air movement in the courtyard is lid driven cavity-like with a secondary spiraling of the motion toward and exiting the east side of the courtyard. In the 200* and 225* cases, the spiraling motion is relatively strong compared to the 250* case where little spiraling motion is apparent. In all three cases, air exits the courtyard primarily near the northeast face. Trajectory analyses suggest that the probability upwind air will enter the courtyard is a function of the height above the ground and the wind direction. As the winds become more westerly, air movement in the alcoves on the northwest side of the building changes from a predominantly up-down circulation of air to a clockwise horizontal circulation.

A series of field experiments have been planned this summer to characterize the wind pattern around the building and to identify the interesting flow features that are calculated in the model results. In addition to the flow measurements, we also plan to conduct tracer releases at a location near the building and to measure the concentration patterns associated with these releases. The concentration patterns will be analyzed and compared with model results for this validation study.