An Experiment to Evaluate Models of Air Flow around a Building.

The goal of the experiment was to provide air-flow data around the exterior of a building, B170, that could be used to evaluate computational models under development.. A strategy was to first make an initial simulation to capture the important features of the flow pattern by using a simplified form of the building geometry and an idealized representation of the tree canopy around the building using a computational fluid dynamics (CFD) model, and to use these results to determine placement locations for the wind sensors. In another strategy to reduce the number of sensors required, the wind speed was normalized to wind speed observed at an upwind reference station. (The upwind fetch was an open stubble field.) This allowed measurements to be taken at different times with the same wind sensors. By using 8 sonic anemometers in a movable array, the normalization provided the equivalent of 54 sonic anemometers operating simultaneously at a fixed height of 2.6 m.

The upwind reference station was an energy budget system that measured wind speed and direction as well as the sensible heat flux to the ground surface. Because of normal variability in wind data, criteria were set up to determine which data would be rejected and the remainder used for model evaluation. The first criterion was that the wind data should be retained when the wind direction was approximately from SW; in practice all data was retained from the quadrant 195* to 285*. The second criterion was that with the above definition of "upwind", the wind data should be retained when the wind speed exceeded 2 m/s and the atmospheric stability conditions were neutral at the energy budget reference station. The data were acquired in one-second polls and was usually preprocessed into 10-minute averages and standard deviations. The 10-minute averages represent the most-probable atmospheric state of the winds at the measurement locations. The data loggers with 2 sonic anemometers each were normally able to operate in the averaging mode for 5-10 days without overwriting the memory buffers. But in a special "wind variability" study the sonic anemometers were operated continuously at one-second polls without preprocessing to average states. Quality assurance was provided by a quality control procedure of inspection of sonic anemometer performance in a slow-speed wind tunnel (1-2.5 m/s), and by the periodic quality control normalization of placing all sonic anemometers at the same height and approximate location as the upwind energy budget station over 3 to 5 days. Typical data were the mean normalized wind vectors for particular cases for fixed wind directions (averaged over 7.5 degrees), one-second (turbulence) wind data for a few cases, and the building horizontal and vertical projections. Data are available upon request. The data has been used in CFD model evaluations, for example, presented at this conference.

This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.