Extended Abstract (564K)15.3
Large eddy simulations on the effects of surface geometry of building arrays on turbulent organized structures
Manabu Kanda, Tokyo Institute of Technology, Tokyo, Japan
Turbulent flow structures above different building arrays were investigated using a large eddy simulation model for city (LES-CITY). It was demonstrated that square and staggered building arrays produce contrastive turbulent behaviors that roughly corresponding to the conventional classification of D-type and K-type roughness, respectively. (1) The drag coefficients at the building heights for square arrays are insensitive to building area density, but those for staggered arrays are sensitive. (2) The relative contributions of ejections to sweeps at the building height for square arrays are sensitive to building area density and are nearly equal to or larger than 1.0 (ejection dominant), but those for staggered arrays are insensitive to building area density and are mostly smaller than 1.0 (sweep dominant). (3) Streaky patterns of longitudinal low speed regions (so called low speed streaks) exist in all simulated flows regardless of array type. The height variations of buildings with square arrays especially in denser areas drastically increase the drag coefficient and modify the turbulent flow structures compared to those of K-type roughness.
The mechanism of D- and K-type urban-like roughness flows and the difference from vegetation flows are discussed. Although urban-like roughness flows have mixing layer properties, especially in K-type arrays, it is concluded that the turbulent organized structures of urban-like roughness flows resemble those of flat-wall boundary layers.
Session 15, urban boundary layers (parallel with session 14)
Thursday, 26 August 2004, 1:45 PM-4:15 PM
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