Characterizing Turbulent Wind Flow Near a Wind Barrier Using Sonic Anemometers

Army Research Laboratory

Thursday, October 01 2009

The resulting data analyses can be used to design and develop future computer models of microscale wind flows.

The Holloman High Speed Test Track (HHSTT) facility at Holloman Air Force Base (HAFB), NM, has a test section of 1.8 km that contains an artificial rain field generation capability over the track. The raindrops produced can be excessively deflected when the cross-track wind speed is greater than 1 m/s. To extend testing times to days when moderate wind conditions (1 to 5 m/s) are present, the HHSTT plans to construct a wind barrier for cross-track wind reduction. Before the construction of a complete wind barrier, an observational study was carried out to characterize the mean and turbulent wind fields using a small prototype section of the wind barrier.

Wind barriers are widely applied to modify the flow field and other meteorological factors in the nearby area. The shelter effect of a wind barrier has been recognized for many years. Wind breaks or shelterbelts using either tall vegetative stands or artificial materials have been widely applied in agriculture practices and wind erosion control. A prototype wind barrier with a length of 100 m and a height of 5 m was erected parallel to the track at a distance of 20 m from the west side of the track. An observational tower and tripod array were set up perpendicular to and across the barrier fence line and test track at the midpoint of the barrier. A 6-m reference tower was located 30 m to the west of the wind barrier, with two sonic anemometers located at 2-m and 6-m heights. Mounting booms were used to separate the anemometers to a distance of approximately 1.5 m from the center of the tower. Booms were mounted to point south, into the direction of the expected flow.

Five additional tripods, with eight additional sonic anemometers, were located to the east of the wind barrier using alternating anemometer arrangements; three tripods with two sonic anemometers were set up at distances of 5 m, 17 m, and 36 m from the barrier; and two tripods with one sonic anemometer were set up at distances of 10 m and 24 m from the barrier. Each of these tripods had a 2-m anemometer attached at the end of a 1-m boom extension, while the three tripods had an additional sensor at 4-m height. The sonic anemometers were oriented such that their V axis was parallel to the track and wind barrier for the convenience of instrumentation setup and data analysis. The sampling time for all instruments was synchronized with a sampling frequency of 20 Hz.

The data were collected on two laptop computers running the Linux operating system. The data were collected continuously over the observational period and were stored hourly for each instrument. Data files for each instrument were coded according to their instrument position relative to the tower plus the hour and date of collection for ease of use in post-test data processing.

The screen material for the wind break consists of a vinyl-coated polyester, which has 30% porosity. The material was tightly attached, using a series of metal clips, to an array of metal poles with additional metal strut reinforcements.