15.12
Turbulent Properties of Momentum Transfer Within the Urban Roughness Sublayer
Ehud Gavze, IIBR, Nes-Ziona, Israel; and E. Fattal and S. Pistinner
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E. Fattal, E. Gavze, S. Pistinner Israel Institute for Biological Research, P.O.B 19 Ness-Ziona, 74100, Israel
Turbulence measurements were conducted on two roofs and in the street between them, deep within an urban fetch of a city in Israel during the summer. Three pairs of ultrasonic anemometers were mounted at heights of 2 and 6 meters above the main roof top. The pairs were seven meters apart from each other, thus covering a third of the roof length. The roof height was roughly 10 meters above the street level, so that in terms of normalized heights the measurements were performed at 1.2 and 1.6. Another anemometer was mounted on an adjacent roof upwind at the same height above the roof level as the high downwind anemometers. Two more anemometers were mounted in the street at heights of 4 and 8 meters above street level. The sampling rates of each anemometer was 10Hz and data were collected on the same card to ensure synchronization.We find that the ratio of velocity fluctuations to momentum fluxes agree well with the predictions of similarity theory although it is unequivocally clear that such a similarity does not exist. Momentum fluxes, measured at two levels on the main roof, exhibit a well defined increase with height. A similar measurement with a single pair in an open area, roughly in the same time of year, revealed a similar structure of the momentum fluxes.
Session 15, Boundary Layers over Heterogeneous Surfaces
Friday, 19 July 2002, 8:30 AM-12:15 PM
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