Measurement on the Wind Characteristics for a Turbulent Boundary Layer Flow over Mild Slope Embankment

紊流邊界層流越過緩坡度堤狀物之風場特性量測

蔡秉直(Ben-Jue Tsai) ； 蕭葆羲(Bao-Shi Shiau)

《海洋工程學刊》 10卷1期 (2010/06) Pp. 49-63

https://doi.org/10.6266/JCOE.2010.1001.03

摘要

In the present study, we reported the measured results of the wind speed and turbulence characteristics for the turbulent boundary layer flow over a two-dimensional embankment with mild slope angle of 3˚, 6˚, 9˚, 12˚, and 15°. The measured profiles of wind speed-up parameter, K(subscript L) at the top of the embankment show that speed-up becomes significantly in the region of Z/Z(subscript ref) ＜0.4 as the embankment slope angle increases. Here Z is the measured height, and Z(subscript ref) is the turbulent boundary layer thickness. At the heights above Z/Z(subscript ref) ＞0.4, the differences for the longitudinal turbulence intensity and Reynolds stress become smaller, and they approach to almost the same for embankment with various slope angles. As the wind speed-up parameter, K(subscript L) is scaled by the dimensionless measured height and embankment slope. It is transformed to a dimensionless parameter, S(subscript p). Analysis of the relation between S p and embankment slope angle θ (in radian), the log-log linear function is found and shown as: log[(Z/Z(subscript ref)/S(subscript p)] = -1.973log(θ)-0.204. At the beginning location of embankment top surface with the height Z/Z(subscript ref)= 0.15, it is evident that the lower frequencies power density increase as the flow passed from 0˚ (no embankment existed) changing to embankment slope angle 3˚. But as the embankment slope angle is increasing up to 15˚, the lower frequencies power density decrease, inversely.

關鍵字

紊流邊界層流 ； 堤 ； 紊流強度 ； 雷諾應力 ； 增速

並列摘要

In the present study, we reported the measured results of the wind speed and turbulence characteristics for the turbulent boundary layer flow over a two-dimensional embankment with mild slope angle of 3˚, 6˚, 9˚, 12˚, and 15°. The measured profiles of wind speed-up parameter, K(subscript L) at the top of the embankment show that speed-up becomes significantly in the region of Z/Z(subscript ref) ＜0.4 as the embankment slope angle increases. Here Z is the measured height, and Z(subscript ref) is the turbulent boundary layer thickness. At the heights above Z/Z(subscript ref) ＞0.4, the differences for the longitudinal turbulence intensity and Reynolds stress become smaller, and they approach to almost the same for embankment with various slope angles. As the wind speed-up parameter, K(subscript L) is scaled by the dimensionless measured height and embankment slope. It is transformed to a dimensionless parameter, S(subscript p). Analysis of the relation between S p and embankment slope angle θ (in radian), the log-log linear function is found and shown as: log[(Z/Z(subscript ref)/S(subscript p)] = -1.973log(θ)-0.204. At the beginning location of embankment top surface with the height Z/Z(subscript ref)= 0.15, it is evident that the lower frequencies power density increase as the flow passed from 0˚ (no embankment existed) changing to embankment slope angle 3˚. But as the embankment slope angle is increasing up to 15˚, the lower frequencies power density decrease, inversely.

並列關鍵字

turbulent boundary layer flow ； embankment ； turbulence intensity ； Reynolds stress ； speed-up