Organized Motion in and above an Urbun Canopy.

概要

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To investigate turbulence characteristics and organized motion within and above the urban canopy, field observations were conducted in July 1991 and Nov. 1992 in Sapporo, Japan. The measurement heights were 5.4m, 10.3m, 18m, 35m and 45m aboveground; the canopy height was 7m. The profiles of σu, peaked slightly above the canopy, while σv, and σw had nearly uniform profiles. Vertical profiles of Reynolds stress peaked slightly at 1.5 times the canopy height and decreased slowly with height thereafter. A four-quadrant analysis showed that sweep and ejection motions caused the higher layer of Reynolds stress, during which high-velocity fluid from above moves downward toward the surface and low-velocity fluid from below moves upward. An ensemble-averaging technique was used to isolate typical features of the flow and temperature fields. A time-height cross section of velocity vectors and temperature contours showed details of the flow structures associated with temperature ramps. It has been noted that the organized motions play important roles in the transport of heat near the urban canopy, where the sweep motion causes negative temperature fluctuation and the ejection motions causes positive temperature fluctuation.
社団法人日本流体力学会の論文