Speaker
Description
The study deals with the wind flow measurements performed on campus of the University of Stavanger, using three commercial lidars. Two horizontally pointing, continuous-wave Doppler lidars are deployed at 16 m height, on the roof of Kjølv Egeland’s building at the northwest end of the campus, and a vertical continuous-wave profiler is installed at an elevation of 4 m on the roof of Ivar Langen’s building, further north on the campus. The installation of the lidars is temporary and mainly aimed at gaining experience in the use of the instruments and interpretation of the data they produce. However, their location introduces an opportunity to investigate the wind conditions at the university campus and in particular the influence of the urban setting on the wind flow.
All three lidars perform scans along a conical surface with an opening angle of 15°. 50 observation points distributed along a circle at a given distance are scanned within 1 second. The two horizontal lidars are set to measure the wind velocities at a single distance of 50 m, so that each observation point is revisited once every second. The vertical profiler records the data at 11 selected heights, distributed from z=10 m to z=300 m, with a sampling rate of about 0.05 Hz at each height. Reference data is acquired by 2-D sonic anemometers fixed to all three lidars.
The emphasis of the analysis is on the data gathered by the horizontal lidars, for which all 50 recordings of the radial wind speeds along the scanning circle are available, as needed to study complex flow conditions in an urban environment. The instruments are facing south-east (137° from N) and south-west (210° from N), respectively. The orientations were adopted by considering the prevailing wind directions as well as access to unobstructed views from the roof. With regards to the latter, the lidars are tilted upwards by approximately 5°.
The horizontal wind velocities in 50 observation points are reconstructed from the radial wind velocities, considering the angles between the beams and the lidar axis. The associated vertical mean wind profile over the extent of the scanning circle is calculated. Standard logarithmic and power laws are fitted to the mean profiles to get an estimate on site-specific parameters such as wind shear exponent and surface roughness. The time series in the mean wind direction are also analysed with respect to turbulence characteristics.
The mean wind speeds and the horizontal velocity time series derived from the lidar data are found to be consistent with the corresponding data from the sonic anemometers, with minor deviations associated with the different locations of the observation points.
Additionally, the mean wind profiles evaluated based on the data from the horizontal lidars are correlated with the simultaneous wind recordings by the wind profiler further north.
The study demonstrates the overall potential of remote wind sensing for wind monitoring in an urban environment. Since the flow around the buildings involves significant variability of the wind flow (veer, shear and significant fluctuations in the separated areas), “local” measurements over small observation volumes are essential to capture the flow field. In the present case, the wind velocities acquired in the 50 measurement points along the scanning circle are indeed found to capture the non-uniform flow in the monitored regions around the buildings in a realistic way. Together with the information from the vertically pointing wind profiler, the measurement data represents a valuable source of data for validation of the related numerical models for flow in an urban area.
| Conference Topic Areas | Track1: Wind Engineering and Industrial Aerodynamics |
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