Study of Near-building Airflow and Turbulent Eddies

A two part study of airflow about a single building was designed and executed by USARL personnel recently at White Sands Missile Range, NM. This study is a continuation of micrometeorological research that addresses airflow behavior within and above canopy domains (vegetative as well as urban). Based upon the guidance derived from a recent wind tunnel study completed by NOAA – ARL in the EPA Wind Tunnel Facility, five micro-meteorological masts were located with respect to the four side walls of a rectangular building and its roof top. The arrangement of the masts upwind, laterally, downwind and roof top was established to be optimum for our springtime southwesterly flow regime. In particular, the downwind mast in the lee of the building per the wind tunnel results was positioned to detect a reversal of flow in the cavity region.

During Phase I, two levels of Campbell station units were mounted at 10m and 2m on the ground based masts. Only one level was instrumented on the roof top mast. The Campbell units measured wind speed and direction, temperature, humidity, pressure and solar radiation every five seconds for a one minute averaged data set to characterize mean quantity conditions. The success of Phase I, encouraged the re-design and execution of Phase II with the same set up, but now with sonic anemometry on the same masts at the same locations. Each of the ground-based 10m masts were set up with three levels of sensors. The sonic anemometer-thermometers measured the u,v,w wind components and temperature (with the speed of sound) sampled at 20Hz. Two additional Campbell units were located just downwind of the corners of the building to detect horizontal eddy structure to compliment the five vertical arrays.

Several days of data were collected during windy springtime conditions at WSMR during both phases. Analysis of the wind data indicates that the placement of the masts spatially and the sensors vertically satisfied our criteria. In particular, when mean flow conditions were near perpendicular to the building’s west facing wall, the downwind sensors to the lee (east) of the building measured a reversal of flow occurring between the 10m level (westerly wind) and the 2m level (easterly wind) in the cavity region as reported by Snyder and Lawson and others. Acceleration of the flow was also noted above the roof top, channeling was detected adjacent to the building’s side walls, and a velocity deficit was present downwind in relation to the upwind reference measurements. As the wind directions changed during parts of some days, the cavity flow either shifted appropriately or disappeared.